Establishing a High Throughput Epidermal Spheroid Culture System to Model Keratinocyte Stem Cell Plasticity

Epithelial dysregulation is a node for a variety of human conditions and ailments, including chronic wounding, inflammation, and over 80% of all human cancers. As a lining tissue, the skin epithelium is often subject to injury and has evolutionarily adapted by acquiring the cellular plasticity necessary to repair damaged tissue. Over the years, several efforts have been made to study epithelial plasticity using in vitro and ex vivo cell-based models. However, these efforts have been limited in their capacity to recapitulate the various phases of epithelial cell plasticity. We describe here a protocol for generating 3D epidermal spheroids and epidermal spheroid-derived cells from primary neonatal human keratinocytes. This protocol outlines the capacity of epidermal spheroid cultures to functionally model distinct stages of keratinocyte generative plasticity and demonstrates that epidermal spheroid re-plating can enrich heterogenous normal human keratinocytes (NHKc) cultures for integrinα6^hi/EGFR^lo keratinocyte subpopulations with enhanced stem-like characteristics. Our report describes the development and maintenance of a high throughput system for the study of skin keratinocyte plasticity and epidermal regeneration.

HPV-inactive cell populations arise from HPV16-transformed human keratinocytes after p53 knockout

HPV-inactive head and neck and cervical cancers contain HPV DNA but do not express HPV E6/E7. HPV-positive primary head and neck tumors usually express E6/E7, however they may produce HPV-inactive metastases. These observations led to our hypothesis that HPV-inactive cancers begin as HPV-active lesions, losing dependence on E6/E7 expression during progression. Because HPV-inactive cervical cancers often have mutated p53, we investigated whether p53 loss may play a role in the genesis of HPV-inactive cancers. p53 knockout (p53-KO) by CRISPR-Cas9 resulted in a 5-fold reduction of E7 mRNA in differentiation-resistant HPV16 immortalized human keratinocytes (HKc/DR). E7 expression was restored by 5-Aza-2 deoxycytidine in p53 KO lines, suggesting a role of DNA methylation in this process. In-situ hybridization showed that p53 KO lines consist of mixed populations of E6/E7-positive and negative cells. Hence, loss of p53 predisposes HPV16 transformed cells to losing dependence on the continuous expression of HPV oncogenes for proliferation.

Self-assembling 3D spheroid cultures of human neonatal keratinocytes have enhanced regenerative properties

Relative to conventional two-dimensional (2-D) culture, three-dimensional (3-D) suspension culture of epithelial cells more closely mimics the in vivo cell microenvironment regarding cell architecture, cell to matrix interaction, and osmosis exchange. However, primary normal human keratinocytes (NHKc) rapidly undergo terminal differentiation and detachment-induced cell death (anoikis) upon disconnection from the basement membrane, thus greatly constraining their use in 3-D suspension culture models. Here, we examined the 3-D anchorage-free growth potential of NHKc isolated from neonatal skin explants of 59 different individuals. We found that 40% of all isolates naturally self-assembled into multicellular spheroids within 24 h in anchorage-free culture, while 60% did not. Placing a single spheroid back into 2-D monolayer culture yielded proliferating cells that expressed elevated levels of nuclear P63 and basal cytokeratin 14. These cells also displayed prolonged keratinocyte renewal and a gene expression profile corresponding to cellular heterogeneity, quiescence, and de-differentiation. Notably, spheroid-derived (SD) NHKc were enriched for a P63/K14 double-positive population that formed holoclonal colonies and reassembled into multicellular spheroids during 3-D suspension subculture. This study reveals marked phenotypic differences in neonatal keratinocyte suspension cultures isolated from different individuals and present a model system that can be readily employed to study epithelial cell behavior, along with a variety of dermatological diseases.

HPV16-transformed human keratinocytes depend on SIX1 expression for proliferation and HPV E6/E7 gene expression

The homeodomain transcription factor SIX1 plays a critical role in embryogenesis, is not expressed in normal adult tissue, but is expressed in many malignancies, including cervical cancer. SIX1 drives the progression of HPV16-immortalized human keratinocytes (HKc/HPV16) toward malignancy: HKc/HPV16 express high levels of SIX1 mRNA and protein; overexpression of SIX1 in HKc/HPV16 produces pre-malignant, differentiation-resistant lines (HKc/DR); SIX1 overexpression in HKc/DR induces tumorigenicity. In this paper, we explore the consequences of inhibition of SIX1 expression in premalignant HKc/DR. Only partial inhibition of SIX1 expression could be obtained in HKc/DR by RNA interference. Decreased SIX1 expression (up to 80%) in HKc/DR resulted in slower proliferation, decreased HPV16-E6/E7 mRNA levels, and increased p53 protein levels. Gene expression changes induced in HKc/DR by anti-SIX1 shRNA were indicative of mesenchymal-epithelial transition (MET) and changes in TGF-beta signaling. We conclude that HPV16-transformed cells depend on SIX1 for survival, HPV16 E6/E7 gene expression and epithelial-mesenchymal transition.

Abstract LB-329: Molecular mechanisms of loss of E7 expression in HPV16-transformed human keratinocytes

Human papillomavirus (HPV) causes about 5% of all human cancers. The HPV oncoproteins E6/E7 are responsible for the transforming potential of the virus. Although continuous expression of the HPV oncogenes was considered indispensable for HPV-induced carcinogenesis, we and others have demonstrated that in a subset of HPV positive head and neck and cervical cancers, the HPV oncogenes are not expressed (HPV-inactive cancers). Based upon the observation that primary HPV-positive tumors express E6/E7, while metastases tend to be HPV-inactive, we hypothesized that HPV-inactive cancers begin as HPV-active lesions and lose their dependence on continuous E6/E7 expression during progression. This may be due to genetic and/or epigenetic modifications caused by the genomic instability and the additional carcinogens to which the tumor is exposed. We observed that HPV-inactive cancers of the cervix often have mutated p53, while HPV-active cancers do not. Therefore, we proposed that HPV positive tumors may become inactive if p53 becomes mutated. The CRISPR-Cas9 system was used to knock out the p53 gene in differentiation resistant HPV16 immortalized human keratinocytes (HKc-DR). The DNA deletions within the p53 gene were confirmed by PCR and gel electrophoresis, and further validated by Sanger sequencing. Using qPCR, we found that HPV16 E7 expression was significantly lower (5-fold) in the p53 knock out (KO) lines than in the p53 wild type (WT) lines Reduced E7 expression in p53 KO lines was reversed by using the demethylating agent 5 Aza 2 deoxycytidine, suggesting that DNA methylation plays a role in this process. Also, we used in situ hybridization to detect HPV16 E7 mRNA in p53 WT and KO lines grown as spheroids on an agarose cushion. Interestingly, while all p53 WT lines have a uniform distribution of E7 signal, the p53 KO lines showed some spheroids that were completely lacking E7 mRNA, and some had a mixed population of E7-positive and E7-negative cells. These results indicate that the p53 KO lines are a heterogenous population with regard to HPV16 E7 expression. We concluded that p53 loss of function mutation may be an important factor in driving HPV16 transformed cells to lose dependence on continuous expression of the HPV oncogenes and become HPV-inactive. However, complete loss of p53 alone is not sufficient to suppress E7 expression entirely. We also determined that loss of E7 expression may be due, at least in part, to DNA methylation. We are currently examining HPV URR methylation in the p53 WT and KO lines, and isolating pure lines with complete loss of HPV16 E7 expression for further studies of the molecular mechanisms that may lead to the HPV-inactive phenotype.

Citation Format: Fadi F. Abboodi, Kim E. Creek, Lucia A. Pirisi. Molecular mechanisms of loss of E7 expression in HPV16-transformed human keratinocytes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr LB-329.

Identification and characterization of HPV-independent cervical cancers

BACKGROUND

Human papillomavirus (HPV) initiates cervical cancer, and continuous expression of HPV oncogenes E6 and E7 is thought to be necessary to maintain malignant growth. Current therapies target proliferating cells, rather than specific pathways, and most experimental therapies specifically target E6/E7. We investigated the presence and expression of HPV in cervical cancer, to correlate HPV oncogene expression with clinical and molecular features of these tumors that may be relevant to new targeted therapies.

RESULTS

While virtually all cervical cancers contained HPV DNA, and most expressed E6/E7 (HPV-active), a subset (8%) of HPV DNA-positive cervical cancers did not express HPV transcripts (HPV-inactive). HPV-inactive tumors occurred in older women (median 54 vs. 45 years, p = 0.02) and were associated with poorer survival (median 715 vs 3046 days, p = 0.0003). Gene expression profiles of HPV-active and -inactive tumors were distinct. HPV-active tumors expressed E2F target genes and increased AKT/MTOR signaling. HPV-inactive tumors had increased WNT/β-catenin and Sonic Hedgehog signaling. Substantial genome-wide differences in DNA methylation were observed. HPV-inactive tumors had a global decrease in DNA methylation; however, many promoter-associated CpGs were hypermethylated. Many inflammatory response genes showed promoter methylation and decreased expression. The somatic mutation landscapes were significantly different. HPV-active tumors carried few somatic mutations in driver genes, whereas HPV-inactive tumors were enriched for non-synonymous somatic mutations (p-value < 0.0000001) specifically targeting TP53, ARID, WNT, and PI3K pathways.

MATERIALS AND METHODS

The Cancer Genome Atlas (TCGA) cervical cancer data were analyzed.

CONCLUSIONS

Many of the gene expression changes and somatic mutations found in HPV-inactive tumors alter pathways for which targeted therapeutics are available. Treatment strategies focused on WNT, PI3K, or TP53 mutations may be effective against HPV-inactive tumors and could improve survival for these cervical cancer patients.

Abstract 3219: Targeting lipid metabolism and ER stress in renal cell carcinoma by englerin A

Renal cell carcinoma (RCC) is among the top ten most common forms of cancer and is the leading malignancy of the kidney. Clear cell renal carcinoma (cc-RCC), the most frequent type of RCC, is one of the most refractory cancers with an incidence that is on the rise. The two-year survival rate for patients with metastatic disease is under 20% despite approved targeted therapies. Hence, there is an urgent need to investigate novel agents. Screening of plant extracts in search of new anti-cancer agents resulted in the discovery of englerin A (EA), a guaiane sesquiterpene with potent cytotoxicity against RCC and a small subset of other cancers. Although a few cellular targets have been identified for EA, in most instances, modulation of these targets required concentrations of EA much higher than that required to kill tumor cells highly sensitive to EA. Hence, it is still not clear what mechanisms account for the cytotoxicity of EA in tumor cells highly sensitive to EA. Unlike any prior study, the current study used a systems biology approach to explore the mechanism(s) of action of EA. Metabolomics analyses were conducted after treatment of human RCC A498 cells with 100 nM EA for 24 and 48 h. Pathway analysis revealed that 88% of the metabolic disturbance associated with englerin A at 24 h was due to changes in lipid metabolism. In particular, among the top metabolites, several ceramides and glucosylceramides increased up to 18- and 178-fold, respectively. On the other hand, all sphingomyelins decreased up to 5.5-fold. Furthermore, EA induced depletion in phosphatidylcholine, phosphatidylglycerol, and phosphatidylethanolamine phospholipids. At 48 h of englerin A treatment, the main findings from pathway analysis were the accumulation of fatty acylcarnitine derivatives, purines, pyrimidines, and phosphatidyl serine phospholipids, as well as the depletion of reduced glutathione indicating dysfunctional mitochondria and oxidative stress. Moreover, microarray analyses determined that EA (100 nM) induced ER stress signaling and an acute inflammatory response including interferon signaling, likely due to the generation of ceramides which were toxic to both A498 and UO-31 renal cancer cells. Quantitative PCR and Western Blot analyses confirmed that EA induced both the unfolded protein and acute inflammatory response. Furthermore, fluorescence confocal microscopy revealed that EA at 25 nM disrupted the morphology of the ER confirming the deleterious effect of EA on the ER. Collectively, our findings suggest that cc-RCC is highly sensitive to disruptions in lipid metabolism and ER stress and that these vulnerabilities can be targeted for the treatment of cc-RCC and possibly other lipid storing cancers. Furthermore, our results also suggest that ceramides may be a mediator of some of the actions of EA. Lastly, the acute inflammatory response induced by EA may mediate anti-tumor immunity.

Note: This abstract was not presented at the meeting.

Citation Format: Ayse Batova, Diego Altomare, Kim E. Creek, Robert K. Naviaux, Lin Wang, Kefeng Li, Erica Green, Richard Williams, Jane C. Naviaux, Mitchell Diccianni, Alice L. Yu. Targeting lipid metabolism and ER stress in renal cell carcinoma by englerin A [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3219. doi:10.1158/1538-7445.AM2017-3219

Six1 promotes colorectal cancer growth and metastasis by stimulating angiogenesis and recruiting tumor-associated macrophages

The homeoprotein Six1 is overexpressed in many human cancers and is associated with increased tumor progression and metastasis. Recent studies have shown that Six1 is associated with poorer overall survival in advanced-stage colorectal cancer (CRC). In the current study, we explored the functional changes and molecular events associated with Six1 overexpression in a mouse model of CRC. An orthotopic model and a splenic injection metastasis model were used to investigate the role of Six1 in CRC tumor growth and metastasis using mouse colon adenocarcinoma MC38 cells overexpressing Six1. We found that overexpression of Six1 dramatically promotes CRC tumor growth and metastasis in vivo. Six1 overexpression in MC38 increased protein levels of aldehyde dehydrogenase-1 and expanded CD44+/CD166+ populations, indicating Six1 increased features of cancer stem cells. In addition, Six1 overexpression stimulated angiogenesis by upregulating the expression of vascular endothelial growth factor (VEGF). Six1-overexpressing tumor cells recruited tumor-associated macrophages (TAM) by increasing the expression of macrophage-specific colony stimulating factor, chemokine (C-C motif) ligand 2/5 and VEGF, further facilitating CRC tumor growth and metastasis. Furthermore, we determined that Six1 activated mitogen-activated protein kinase (MAPK) signaling in CRC cells. In summary, our studies strongly suggest that Six1 overexpression promotes CRC growth and metastasis and remodels tumor stroma by stimulating angiogenesis and recruiting TAM. MAPK activation may be a pivotal event in Six1-associated tumor progression, which may provide opportunities for pharmacologic intervention.

Englerin A induces an acute inflammatory response and reveals lipid metabolism and ER stress as targetable vulnerabilities in renal cell carcinoma

Renal cell carcinoma (RCC) is among the top ten most common forms of cancer and is the most common malignancy of the kidney. Clear cell renal carcinoma (cc-RCC), the most common type of RCC, is one of the most refractory cancers with an incidence that is on the rise. Screening of plant extracts in search of new anti-cancer agents resulted in the discovery of englerin A, a guaiane sesquiterpene with potent cytotoxicity against renal cancer cells and a small subset of other cancer cells. Though a few cellular targets have been identified for englerin A, it is still not clear what mechanisms account for the cytotoxicity of englerin A in RCC, which occurs at concentrations well below those used to engage the targets previously identified. Unlike any prior study, the current study used a systems biology approach to explore the mechanism(s) of action of englerin A. Metabolomics analyses indicated that englerin A profoundly altered lipid metabolism by 24 h in cc-RCC cell lines and generated significant levels of ceramides that were highly toxic to these cells. Microarray analyses determined that englerin A induced ER stress signaling and an acute inflammatory response, which was confirmed by quantitative PCR and Western Blot analyses. Additionally, fluorescence confocal microscopy revealed that englerin A at 25 nM disrupted the morphology of the ER confirming the deleterious effect of englerin A on the ER. Collectively, our findings suggest that cc-RCC is highly sensitive to disruptions in lipid metabolism and ER stress and that these vulnerabilities can be targeted for the treatment of cc-RCC and possibly other lipid storing cancers. Furthermore, our results suggest that ceramides may be a mediator of some of the actions of englerin A. Lastly, the acute inflammatory response induced by englerin A may mediate anti-tumor immunity.

Case-control study of candidate gene methylation and adenomatous polyp formation

PURPOSE

Colorectal cancer (CRC) is one of the most common and preventable forms of cancer but remains the second leading cause of cancer-related death. Colorectal adenomas are precursor lesions that develop in 70-90 % of CRC cases. Identification of peripheral biomarkers for adenomas would help to enhance screening efforts. This exploratory study examined the methylation status of 20 candidate markers in peripheral blood leukocytes and their association with adenoma formation.

METHODS

Patients recruited from a local endoscopy clinic provided informed consent and completed an interview to ascertain demographic, lifestyle, and adenoma risk factors. Cases were individuals with a histopathologically confirmed adenoma, and controls included patients with a normal colonoscopy or those with histopathological findings not requiring heightened surveillance (normal biopsy, hyperplastic polyp). Methylation-specific polymerase chain reaction was used to characterize candidate gene promoter methylation. Odds ratios (ORs) and 95 % confidence intervals (95% CIs) were calculated using unconditional multivariable logistic regression to test the hypothesis that candidate gene methylation differed between cases and controls, after adjustment for confounders.

RESULTS

Complete data were available for 107 participants; 36 % had adenomas (men 40 %, women 31 %). Hypomethylation of the MINT1 locus (OR 5.3, 95% CI 1.0-28.2) and the PER1 (OR 2.9, 95% CI 1.1-7.7) and PER3 (OR 11.6, 95% CI 1.6-78.5) clock gene promoters was more common among adenoma cases. While specificity was moderate to high for the three markers (71-97 %), sensitivity was relatively low (18-45 %).

CONCLUSION

Follow-up of these epigenetic markers is suggested to further evaluate their utility for adenoma screening or surveillance.

Human Papillomavirus Type 16 L2 DNA Methylation in Exfoliated Cervical Cells From College-Age Women

OBJECTIVES

The Carolina Women's Care Study (CWCS) at the University of South Carolina followed 467 young women with the goal of identifying biomarkers of human papillomavirus (HPV) persistence. In this study, we analyzed the methylation of HPV16 DNA.

METHODS

The aims of this study were to determine the methylation status of the HPV16 L2 gene in DNA isolated from exfoliated cervical cells collected longitudinally as part of the CWCS and to determine the prevalence of polymorphisms (single nucleotide polymorphisms [SNPs]) in folate metabolizing enzymes and DNA repair enzymes known to affect DNA methylation in blood-derived genomic DNA from CWCS participants. For methylation studies, DNA samples were bisulfite converted and amplified with the EpiTect Whole Bisulfitome kit. Polymerase chain reaction was performed for amplicons containing 5 CpG sites in L2. Pyrosequencing was carried out using EpigenDx and analyzed with PyroMark Software. Taqman genotyping assays were performed to determine selected SNP alleles in the CWCS cohort.

RESULTS AND CONCLUSIONS

Methylation data were obtained for 82 samples from 27 participants. Of these, 22 participants were positive for HPV16 for 3 or more visits (≥12 months). Methylation in L2 was detectable, but methylation levels varied and were not associated with HPV16 persistence. No linearity of methylation levels over time was observed in participants for whom longitudinal data could be analyzed. Analysis of 9 selected SNPs did not reveal an association with persistence. We conclude that at early stages of infection methylation of HPV16 L2 DNA in Pap test samples is not a predictive biomarker of HPV persistence.

Abstract 4048: Stem cell properties of normal human keratinocytes influence transformation responses to HPV16

Human papillomavirus (HPV) infection is the primary cause of cervical cancer. While HPV infection is very common, cervical cancer is a rare outcome. Why some women develop cervical cancer and others do not is not well understood, but likely involves host cell-specific factors and a woman's ability to get rid of HPV-infected cells. We have previously reported marked variability of epidermal growth factor receptor (EGFR) expression in normal human epidermal tissue from different individuals and demonstrated that increased immortalization by HPV16 E6 and E7 oncogenes correlated with lower basal levels of EGFR. We now report a significantly greater transformation response in stem cell-like keratinocytes after transfection with the full length HPV16 genome. Primary normal human keratinocyte strains (NHKc) from 59 individuals were cultured in 3-D anchorage-free suspension to assess spheroid forming ability and to determine resistance to anchorage-independent cell death. Only about 40% of NHKc strains survived and formed spheroids in 3-D culture and grew when plated back in monolayers as spheroid-derived NHKc (SD-NHKc). Fluorescence-activated cell sorting analysis found that SD-NHKc were enriched in cells expressing known keratinocyte stem cell markers: low levels of EGFR and high levels of integrin α6, while spheroid-non forming strains (SNF-NHKc) had dramatically reduced numbers of EGFRlo/ITGα6hi cells. Isolation and cultivation of EGFRlo/ITGα6hi keratinocytes isolated from primary monolayer NHKc cultures revealed this cell population to behave like SD-NHKc with respect to anchorage-independent survival, proliferative potential, cell morphology, and clonogenicity. Upon transfection with HPV16 DNA, most NHKc strains acquired anchorage-independence and exhibited increased expression of EGFR. Importantly, EGFRlo/ITGα6hi keratinocytes and SD-NHKc displayed exuberant growth responses after transfection with HPV16 DNA and significantly higher transformation efficiency by HPV16. In contrast, SNF-NHKc grew more sluggishly and were relatively resistant to HPV16-mediated immortalization. Our study indicates that stem cell-like keratinocytes are preferentially transformed by HPV16 DNA and that stemness is a phenotypic determinant of susceptibility to HPV16-mediated transformation in primary human keratinocytes.

Citation Format: Yvon Woappi, Kim E. Creek, Lucia Pirisi. Stem cell properties of normal human keratinocytes influence transformation responses to HPV16. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4048.

Abstract 2025: SIX1 overexpression extends the lifespan of normal human keratinocytes and promotes epithelial-mesenchymal transition

SIX1, a homeodomain-containing transcription factor, has a critical role in the expansion of progenitor cells during embryogenesis. The overexpression of SIX1 contributes to tumorigenesis, promoting malignant transformation and metastasis. Six1 promotes tumor progression by induction of epithelial-to-mesenchymal transition (EMT). In HPV16-transformed human keratinocytes (HKc), SIX1 overexpression produces EMT and a differentiation-resistant phenotype at early stages of in-vitro progression, and transforms cells to malignancy at late stages. We transfected normal HKc with a plasmid encoding human-SIX1 in order to determine to what extent SIX1 overexpression may induce growth, differentiation and EMT changes in normal cells. We also studied the effects of expressing the HRas-V12 oncogene while downregulating the p53 tumor suppressor gene in normal HKc expressing SIX1, in order to push these keratinocytes to a precancerous state. Normal HKc overexpressing SIX1 (HKc/SIX1) or a combination of SIX1, HRas-V12 and p53i (HKc/ALL3) grow continuously while their vector-transfected controls senesced. Continuous growth past the end of the normal lifespan was also observed in normal human fibroblasts overexpressing SIX1. HKc/SIX1 and HKc/ALL3 exhibit a spindle-shape and fibroblastic appearance rather than the cuboidal morphology of epithelial cells. They are also morphologically distinct from SIX1-overexpressing human fibroblasts. HKc /SIX1 and HKc/ALL3 grow best in KSFM supplemented with 10% FBS and 1mM CaCl2, while normal HKc grow best in KSFM with 0.1 mM CaCl2. RT-PCR confirmed that mRNA levels of SIX1 were significantly increased and p53 levels were significantly decreased, and that HRasV12 was expressed in HKc/ALL3. The growth rates of HKc/SIX1 and HKc/ALL3 are comparable to those of early-stage HPV16-immoratlized cells (HKc/HPV16). Invasion assays demonstrated that HKc/SIX1 are more invasive than normal HKc, and their invasiveness is comparable to that of HKc/HPV16. The invasiveness of HKc/ALL3 is greater than that of late-stage, differentiation-resistant HPV-immortalized cells (HKc/DR), which are about 2.5-fold more invasive than HKc/HPV16. In conclusion, SIX1 promotes continued proliferation and invasiveness, signs indicative of cellular transformation, even in the background of normal HKc. Currently, we are exploring the gene expression changes induced by SIX1 in normal cells. Additionally, we plan to investigate whether these cells express stem cell markers. The results of these studies suggest that SIX1 facilitates the establishment of primary human keratinocytes into immortal cell lines, or perhaps into stem-like cells with extended proliferation potential.

Citation Format: Maria Hosseinipour, Aspasia Amiridis, Diego Altomare, Kim E. Creek, Lucia Pirisi. SIX1 overexpression extends the lifespan of normal human keratinocytes and promotes epithelial-mesenchymal transition. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2025.

A healthy lifestyle index is associated with reduced risk of colorectal adenomatous polyps among non-users of non-steroidal anti-inflammatory drugs

In a Columbia, South Carolina-based case-control study, we developed a healthy lifestyle index from five modifiable lifestyle factors (smoking, alcohol intake, physical activity, diet, and body mass index), and examined the association between this lifestyle index and the risk of colorectal adenomatous polyps (adenoma). Participants were recruited from a local endoscopy center and completed questionnaires related to lifestyle behaviors prior to colonoscopy. We scored responses on each of five lifestyle factors as unhealthy (0 point) or healthy (1 point) based on current evidence and recommendations. We added the five scores to produce a combined lifestyle index for each participant ranging from 0 (least healthy) to 5 (healthiest), which was dichotomized into unhealthy (0-2) and healthy (3-5) lifestyle scores. We used logistic regression to calculate odds ratios (OR) and 95% confidence intervals (CI) for adenoma with adjustment for multiple covariates. We identified 47 adenoma cases and 91 controls. In the main analyses, there was a statistically nonsignificant inverse association between the dichotomous (OR 0.54; 95% CI 0.22, 1.29) and continuous (OR 0.75; 95% CI 0.51, 1.10) lifestyle index and adenoma. Odds of adenoma were significantly modified by the use of non-steroidal anti-inflammatory drugs (NSAIDs) (p(interaction) = 0.04). For participants who reported no use of NSAIDs, those in the healthy lifestyle category had a 72% lower odds of adenoma as compared to those in the unhealthy category (OR 0.28; 95% CI 0.08, 0.98), whereas a one-unit increase in the index significantly reduced odds of adenoma by 53% (OR 0.47; 95% CI 0.26, 0.88). Although these findings should be interpreted cautiously given our small sample size, our results suggest that higher scores from this index are associated with reduced odds of adenomas, especially in non-users of NSAIDs. Lifestyle interventions are required to test this approach as a strategy to prevent colorectal adenomatous polyps.

Prefrontal microRNA-221 Mediates Environmental Enrichment-Induced Increase of Locomotor Sensitivity to Nicotine

BACKGROUND

Environmental enrichment alters susceptibility in developing drug addiction. We have demonstrated that rats raised in an enriched condition are more sensitive than rats raised in an impoverished condition to nicotine-induced locomotor activity, and this is associated with alterations of phosphorylated extracellular signal-regulated kinase 1/2 within the prefrontal cortex. This study determined the impact of microRNA-221 in the prefrontal cortex on phosphorylated extracellular signal-regulated kinase 1/2 and the enriched environment-dependent behavioral changes in response to nicotine.

METHODS

A microRNA array was conducted to profile microRNA expression in the prefrontal cortex of enriched condition and impoverished condition rats in response to repeated nicotine (0.35 mg/kg, s.c.) administration. microRNA-221 in the prefrontal cortex, nucleus accumbens, and striatum was further verified by quantitative real-time PCR. Lentiviral-mediated overexpression of microRNA-221 in PC12 cells and the medial prefrontal cortex was performed to determine the effects of microRNA-221 on nicotine-mediated phosphorylated extracellular signal-regulated kinase 1/2, phosphorylated cAMP-response element-binding protein, and locomotor activity.

RESULTS

microRNA-221 was profoundly upregulated in the prefrontal cortex but not in nucleus accumbens and striatum of enriched condition rats relative to impoverished condition rats following repeated administration of nicotine. Overexpression of lentiviral-microRNA-221 attenuated nicotine-induced increase in phosphorylated extracellular signal-regulated kinase 1/2 in PC12 cells. Lentiviral-microRNA-221 overexpression in the medial prefrontal cortex further increased locomotor activity in impoverished condition but not in enriched condition rats in response to repeated nicotine administration. Accordingly, lentiviral-microRNA-221 attenuated nicotine-induced increases in phosphorylated extracellular signal-regulated kinase 1/2 and phosphorylated cAMP-response element-binding protein in the medial prefrontal cortex of impoverished condition but not enriched condition rats.

CONCLUSION

These findings suggest that environmental enrichment, via upregulation of prefrontal microRNA-221 expression, suppresses the nicotine-induced activation of extracellular signal-regulated kinase and cAMP-response element-binding protein, which provides a potential mechanism underlying enhanced locomotor sensitivity to nicotine.

Human papillomavirus status and gene expression profiles of oropharyngeal and oral cancers from European American and African American patients

BACKGROUND

Disparities in prevalence, human papillomavirus (HPV) status, and mortality rates for head and neck cancer have been described between African American and European American patients.

METHODS

We studied the HPV status and gene expression profiles in 56 oropharyngeal/oral cavity tumors and 9 normal tissue samples from European American and African American patients treated in South Carolina between 2010 and 2012.

RESULTS

Overall, 59% of tumors were HPV DNA-positive, but only 48% of those expressed E7 mRNA (HPV-active). The prevalence of HPV-active tumors was 10% in African American patients and 39% in European American patients. Tumors positive for HPV DNA but negative for HPV mRNA exhibited gene expression profiles distinct from those of both HPV-active and HPV-negative cancers, suggesting that HPV DNA-positive/RNA-negative tumors may constitute a unique group.

CONCLUSION

This study provides a direct assessment of differential expression patterns in HPV-related oropharyngeal cancer arising from African American and European American patients, for which there is a paucity of data. © 2015 Wiley Periodicals, Inc. Head Neck 00: 000-000, 2015.

Abstract 450: Head and neck cancer and HPV infection: A potential role for peritumoral neurogenesis in HPV-associated malignancy

Background: Head and neck cancers account for 5% of all cancer related deaths and present with complex molecular pathology and clinical features owing to their functional anatomical location. The molecular etiology of head and neck squamous cancer (HNSC) has gained extensive attention recently revealing key mutations, viral infection, and an emerging landscape of varying disease sub-types. While perineural invasion has long been associated with poor outcome in HNSC, the association of neurogenesis-related genes with cancer progression has only recently come into focus in HNSC. Using prospectively acquired patient samples and TCGA HNSC mutational analyses we further characterized the sequelae of molecular changes in neurogenesis-related genes and propose that these genes play a significant role in HNSC development.

Methods: All clinical specimens were collected under approval by Institutional Review Board. Prospectively collected samples were analyzed for HPV DNA by linear arrays (InnoLipa) and q-PCR for E7-RNA. Gene expression arrays were conducted to determine differences in HPV activity and neuronal associated gene ontologies (Agilent). Gene expression profiles were compared in oral HPV+ and HPV- cultured oral keratinocytes as well as the TCGA Kandoth & Tang datasets. Gene targets were validated by Immunohistochemistry and qPCR.

Results: Initial unsupervised hierarchical clustering analysis of our HNSC cohort revealed a separation of HPV+ HPV+E7-(HPV-inactive: HPVin), and HPV- tumors with changes in the expression of key neurogenesis-related genes. For example, POU4F1, NGFR, and GRIN2C were significantly up-regulated (P&lt;0.05) in HPV+ vs HPVin cancers. Additional analysis of TCGA data revealed divergence of the mutational spectra in HNSC with and without perineural invasion.

Conclusion: Our preliminary findings indicate the emerging importance of neurogenesis-related genes and perineural involvement in HNSC and support a divergence of HPV+, HPVin, and HPV- HNSC sub-types.

Citation Format: Christian A. Graves, Swati Tomar, Diego Altomare, James R. Wells, Kim E. Creek, Lucia Pirisi. Head and neck cancer and HPV infection: A potential role for peritumoral neurogenesis in HPV-associated malignancy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 450. doi:10.1158/1538-7445.AM2014-450

Disparity in the persistence of high-risk human papillomavirus genotypes between African American and European American women of college age

BACKGROUND

Cervical cancer incidence and mortality rates are higher in African Americans than in European Americans (white, non-Hispanic of European ancestry). The reasons for this disparity are not known.

METHODS

We recruited a population-based longitudinal cohort of 326 European American and 113 African American female college freshmen in Columbia, South Carolina, to compare clearance of high-risk human papillomavirus (HR-HPV) infection between ethnicities. HPV testing and typing from samples obtained for Papanicolaou testing occurred every 6 months.

RESULTS

African American participants had an increased risk of testing positive for HR-HPV, compared with European American participants, but the frequency of incident HPV infection was the same in African American and European American women. Thus, exposure to HPV could not explain the higher rate of HPV positivity among African American women. The time required for 50% of participants to clear HR-HPV infection was 601 days for African American women (n = 63) and 316 days for European American women (n = 178; odds ratio [OR], 1.61; 95% confidence interval [CI], 1.08-2.53). African American women were more likely than European American women to have an abnormal result of a Papanicolaou test (OR, 1.58; 95% CI, 1.05-2.39).

CONCLUSIONS

We propose that the longer time to clearance of HR-HPV among African American women leads to increased rates of abnormal results of Papanicolaou tests and contributes to the increased rates of cervical cancer observed in African American women.

Transcriptomes and shRNA suppressors in a TP53 allele-specific model of early-onset colon cancer in African Americans

African Americans are disproportionately affected by early-onset, high-grade malignancies. A fraction of this cancer health disparity can be explained by genetic differences between individuals of African or European descent. Here the wild-type Pro/Pro genotype at the TP53Pro72Arg (P72R) polymorphism (SNP: rs1042522) is more frequent in African Americans with cancer than in African Americans without cancer (51% vs. 37%), and is associated with a significant increase in the rates of cancer diagnosis in African Americans. To test the hypothesis that Tp53 allele-specific gene expression may contribute to African American cancer disparities, TP53 hemizygous knockout variants were generated and characterized in the RKO colon carcinoma cell line, which is wild type for TP53 and heterozygous at the TP53Pro72Arg locus. Transcriptome profiling, using RNAseq, in response to the DNA-damaging agent etoposide revealed a large number of Tp53-regulated transcripts, but also a subset of transcripts that were TP53Pro72Arg allele specific. In addition, a shRNA-library suppressor screen for Tp53 allele-specific escape from Tp53-induced arrest was performed. Several novel RNAi suppressors of Tp53 were identified, one of which, PRDM1β (BLIMP-1), was confirmed to be an Arg-specific transcript. Prdm1β silences target genes by recruiting H3K9 trimethyl (H3K9me3) repressive chromatin marks, and is necessary for stem cell differentiation. These results reveal a novel model for African American cancer disparity, in which the TP53 codon 72 allele influences lifetime cancer risk by driving damaged cells to differentiation through an epigenetic mechanism involving gene silencing.

IMPLICATIONS

TP53 P72R polymorphism significantly contributes to increased African American cancer disparity.

Six1 promotes epithelial-mesenchymal transition and malignant conversion in human papillomavirus type 16-immortalized human keratinocytes

Six1, a member of the Six family of homeodomain transcription factors, is overexpressed in various human cancers, and SIX1 overexpression is associated with tumor progression and metastasis. Six1 messenger RNA levels increase during in vitro progression of human papillomavirus type 16 (HPV16)-immortalized human keratinocytes (HKc/HPV16) toward a differentiation-resistant (HKc/DR) phenotype. In this study, we show that HKc/DR-overexpressing Six1 exhibited a more mesenchymal phenotype, as characterized by a fibroblastic appearance and increased invasion. We utilized Whole Human Genome Microarrays to explore the gene expression changes associated with Six1 overexpression in HKc/DR. We found that overexpression of Six1 downregulated epithelial-related genes and upregulated mesenchymal-related genes, which suggests that Six1 overexpression induces epithelial-mesenchymal transition (EMT). Pathway analysis of the microarray data showed alterations in the transforming growth factor-beta (TGF-β) pathway, including enhanced expression of the TGF-β receptor type II (TβRII), and activation of the mitogen-activated protein kinase (MAPK) pathway in HKc/DR-overexpressing Six1, suggesting that Smad-independent pathways of TGF-β signaling may be involved in Six1-mediated EMT. p38 MAPK activation was required for sustained Six1-induced EMT and TβRII overexpression. Finally, we determined that Six1 overexpression in HKc/DR resulted in malignant conversion and increased the cancer stem cell (CSC)-like population. Thus, Six1 overexpression promotes EMT, CSCs properties and malignant conversion in HKc/DR through MAPK activation, which supports the possible use of p38-TβRII inhibitors for the treatment of cancers overexpressing Six1.

Partial loss of Smad signaling during in vitro progression of HPV16-immortalized human keratinocytes

Background

Disruption of the transforming growth factor-beta (TGF-β) signaling pathway is observed in many cancers, including cervical cancer, resulting in TGF-β resistance. While normal human keratinocytes (HKc) and human papillomavirus type 16-immortalized HKc (HKc/HPV16) are sensitive to the growth inhibitory effects of TGF-β, HKc/HPV16 develop resistance to TGF-β1 as they progress in vitro to a differentiation resistant phenotype (HKc/DR). The loss of sensitivity to the antiproliferative effects of TGF-β1 in HKc/DR is due, at least partially, to decreased expression of the TGF-β receptor type I. In the present study, we explored in detail whether alterations in Smad protein levels, Smad phosphorylation, or nuclear localization of Smads in response to TGF-β could contribute to the development of TGF-β resistance during in vitro progression of HKc/HPV16, and whether TGF-β induction of a Smad-responsive reporter gene was altered in HKc/DR.

Methods

Western blot analysis was used to assess Smad protein levels. In order to study Smad nuclear localization we performed indirect immunofluorescence. In addition, we determined Smad-mediated TGF-β signaling using a luciferase reporter construct.

Results

We did not find a decrease in protein levels of Smad2, Smad3 or Smad4, or an increase in the inhibitory Smad7 that paralleled the loss of sensitivity to the growth inhibitory effects of TGF-β1 observed in HKc/DR. However, we found diminished Smad2 phosphorylation, and delayed nuclear Smad3 localization in response to TGF-β1 in HKc/DR, compared to normal HKc and TGF-β sensitive HKc/HPV16. In addition, we determined that TGF-β1 induction of a Smad responsive promoter is reduced by about 50% in HKc/DR, compared to HKc/HPV16.

Conclusions

These results demonstrate that alterations in Smad protein levels are not associated with the loss of response to the antiproliferative effects of TGF-β in HKc/DR, but that diminished and delayed Smad phosphorylation and nuclear localization, and decreased Smad signaling occur in response to TGF-β in HKc/DR.

HPV prevalence at enrollment and baseline results from the Carolina Women's Care Study, a longitudinal study of HPV persistence in women of college age

Background

Cervical cancer, a rare outcome of high-risk human papillomavirus (HPV) infection, disproportionately affects African American women, who are about twice more likely than European American women to die of the disease. Most cervical HPV infections clear in about one year. However, in some women HPV persists, posing a greater risk for cervical dysplasia and cancer. The Carolina Women’s Care Study (CWCS) was conducted to explore the biological, genetic, and lifestyle determinants of persistent HPV infection in college-aged European American and African American women. This paper presents the initial results of the CWCS, based upon data obtained at enrollment.

Methods

Freshman female students attending the University of South Carolina were enrolled in the CWCS and followed until graduation with biannual visits, including two Papanicolaou tests, cervical mucus collection, and a questionnaire assessing lifestyle factors. We recruited 467 women, 293 of whom completed four or more visits for a total of 2274 visits.

Results and conclusion

CWCS participants were 70% European American, 24% African American, 3% Latina/Hispanic, and 3% Asian. At enrollment, 32% tested positive for any HPV. HPV16 infection was the most common (18% of infections). Together, HPV16, 66, 51, 52, and 18 accounted for 58% of all HPV infections. Sixty-four percent of all HPV-positive samples contained more than one HPV type, with an average of 2.2 HPV types per HPV-positive participant. We found differences between African American and European American women in the prevalence of HPV infection (38.1% African American, 30.7% European American) and abnormal Papanicolaou test results (9.8% African-American, 5.8% European American). While these differences did not reach statistical significance at enrollment, as the longitudinal data of this cohort are analyzed, the sample size will allow us to confirm these results and compare the natural history of HPV infection in college-aged African American and European American women.

Abstract 4026: HPV16-positive and HPV16-negative head and neck squamous cell carcinomas display different patterns of expression of genes involved in the control of growth and EMT

Up to 60% of oropharyngeal cancers and 25% of head and neck squamous cell carcinomas (HNSCC) are high-risk human papillomavirus (HPV) positive, primarily HPV16. Differences in risk factors, age of presentation and clinical behavior of these tumors indicate that HPV+ and HPV- tumors develop with different molecular mechanisms and are biologically distinct. Based upon a gene expression profile comparison of HPV- and HPV+ HNSCC specimens, obtained from the Medical University of South Carolina ENT/Head and Neck Surgery clinic, we identified 384 candidate genes differentially expressed (125 genes up-regulated and 223 down-regulated) in HPV+ in comparison with HPV- tumors. GO analysis of the microarray data indicated that gene expression changes in HPV+ tumors affected primarily proliferation and cell cycle control, while HPV- tumors showed changes in genes involved in EMT, cell motility, and angiogenesis. We selected five genes (c-MET, TP53, TGF-beta2, BRCA1 and SIX1) for further analysis in a set of 44 tumor and four normal (tonsil and uvula) samples. Seventeen tumor samples were from African American (AA) patients, and 27 from European Americans (EA). The prevalence of HPV infection was 30% in samples from AA patients, and 65% in those from EA patients. Most HPV+ tumor samples (20 of 24) were positive for HPV16 and a subset of the HPV16+ tumor samples (55%) expressed HPV16 E7, as documented by real-time RT/PCR using tumor-derived RNA. The prevalence of active HPV infections (where E7 was expressed) was 17% in AA and 50% in EA patients. These tumor samples were utilized to explore the expression of the selected genes by real-time RT/PCR. Data were normalized to normal human keratinocytes based on three reference genes derived from a panel of seven candidate reference genes, using Normfinder, BestKeeper and GeNorm. Normalized relative quantities for each gene of interest were then calculated using qbasePLUS (Biogazelle.) c-MET was overexpressed, when compared to control tissue, in all tumor samples but levels of c-MET were the highest in HPV- EA samples, and comparatively lower in HPV+ samples. TP53 was overexpressed in HPV+ samples; TGF-beta2 and Six1 were clearly overexpressed in all tumor samples, compared to control tissue samples; and BRCA1 levels were higher in HPV+ samples, compared to HPV- samples and controls. These data are consistent with our microarray results that indicate that HPV- tumors exhibit gene expression profiles indicative of activation of EMT. We are investigating the molecular interactions that lead to overexpression of SIX1, c-MET and BRCA1 in these tumors, and the functional consequences of this overexpression in terms of cell growth and EMT.

Citation Format: Swati Tomar, Sangeeta Kowli, Diego Altomare, Christian Graves, Susannah Kassler, Natalie A. Sutkowski, Marion Boyd Gillespie, Saundra H. Glover, Kim E. Creek, Lucia A. Pirisi-Creek. HPV16-positive and HPV16-negative head and neck squamous cell carcinomas display different patterns of expression of genes involved in the control of growth and EMT. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4026. doi:10.1158/1538-7445.AM2013-4026

Abstract 3478: Gene expression profiles from exfoliated cervical cells identify potential biomarkers predictive of HPV16 clearance or persistence

Cervical cancer is the second most common cancer in women worldwide with about 500,000 new cases and 250,000 deaths annually. The incidence of cervical cancer has dramatically decreased in developed countries over the past fifty years, mainly due to effective Pap test screening and follow-up programs that allow for early detection and treatment. However, many abnormal cervical lesions detected by the Pap test would spontaneously regress if not treated; therefore current screening and follow-up protocols result in expensive and painful interventions that also may compromise future pregnancies. The etiologic agent of cervical cancer is sexually-transmitted, high-risk human papillomavirus (HR-HPV), with HPV16 being responsible for 50% of all cervical cancer. Most women will acquire HR-HPV at some point during their lifetime; however most of these infections clear within 9-18 months. Only women with persistent HR-HPV infection are truly at risk of developing cervical cancer. Biomarkers that would identify women at risk for persistent HR-HPV infection would allow physicians to follow these patients, sparing others unnecessary and costly follow-up. We have performed microarray gene expression profiling, using Agilent 4x44K human microarrays, on five HPV16 positive exfoliated cervical cell samples collected in RNAlater (Ambion) from women who cleared an HPV16 infection, and eight HPV16 positive cervical cell samples from women with persistent HPV16 infection, defined as being positive for HPV16 for at least one year. Data analysis was performed using limma/limmaGUI (Bioconductor), GeneSifter (Geospiza), and Cluster/Treeview (Eisen Lab) software. Using the nonparametric Wilcoxon rank-sum test and 0.01 and 2 as p-value and fold change cutoffs, respectively, we identified 391 differentially expressed genes in HPV16 persisters as compared to HPV16 clearers. In addition, we identified a molecular signature composed of 14 genes that separates the samples into their corresponding groups (persisters and clearers) when studied by both cluster analysis and correlation analysis. Expression of 4 immune-related genes (IL6, IL1A, IL1B and TNF-alpha) was also determined by quantitative real time PCR. Expression of all four genes was confirmed to be downregulated in HPV16 persisters as compared to HPV16 clearers. These 4 potential biomarker genes, and others to be validated, have potential clinical importance, since they can predict if HPV16 infections will be persistent or will be cleared. We are currently validating these initial results with a second, much larger validation set of exfoliated cervical cells collected from women that had persistent HPV16 infections or were able to clear the HPV16 infection. Supported by grant P20MD001770 from the NIH/NIMHD

Citation Format: Diego Altomare, Susannah Kassler, Carolyn Banister, Amy Messersmith, Saundra Glover, Lucia Pirisi-Creek, Kim E. Creek. Gene expression profiles from exfoliated cervical cells identify potential biomarkers predictive of HPV16 clearance or persistence. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3478. doi:10.1158/1538-7445.AM2013-3478

Abstract 4268: Resistance to growth inhibition by transforming growth factor-beta is associated with activation of the PI3K-Akt pathway in HPV16-immortalized human keratinocytes at late stages of in vitro progression

Transforming growth factor-beta (TGF-ß) plays a vital role in embryonic development, cell proliferation, inflammation and wound repair. The Smad proteins are the central mediators of TGF-ß signal transduction. However, recently several non-Smad pathways (ex., Erk, Jnk, p38 MAPK, PI3K-Akt) have been determined to play key roles in TGF-ß signaling. TGF-ß signaling is often disrupted in cancer, including cervical cancer. Human papillomavirus (HPV) is the main etiological agent in cervical cancer. HPV type 16 (HPV16)-immortalized human keratinocytes (HKc/HPV16) are initially very sensitive to growth inhibition by TGF-ß. However, HKc/HPV16 become increasingly resistant to TGF-ß during in vitro progression, and are completely resistant to TGF-ß-induced growth inhibition at late-stages of transformation, when they exhibit a differentiation resistant phenotype (HKc/DR). Although HKc/DR are completely resistant to the growth inhibitory effects of TGF-ß, some Smad signaling remains. A reporter construct containing tandem repeats of Smad binding elements was induced by TGF-ß in HKc/DR at about 50% of the level observed in HKc/HPV16. Furthermore, TGF-ß was capable of inducing epithelial-mesenchymal transition (EMT) in HKc/DR. To further explore TGF-ß signaling in HKc/HPV16 and HKc/DR, we used phospho specific antibody microarrays from Full Moon BioSystems. These arrays feature phospho and non-phospho pairs of specific antibodies pertinent to the TGF-ß pathway. Protein extracts from HKc/HPV16 and HKc/DR untreated or treated for 90 min with 40 pM TGF-ß were compared on the antibody microarrays. Activation of the Akt pathway by TGF-ß was observed in HKc/DR but not in HKc/HPV16. Similarly, PI3K and mTOR showed activation by TGF-ß in HKc/DR but not HKc/HPV16. We conclude that TGF-ß signals primarily through Smad-dependent pathways to inhibit cell proliferation in HKc/HPV16, but that non-canonical (non-smad) signaling through the PI3K-Akt-mTOR axis predominates in HKc/DR.

Citation Format: Rupa Velidandla, Gehana Vaswani, Sangeeta Kowli, Lucia Pirisi-Creek, Kim E. Creek. Resistance to growth inhibition by transforming growth factor-beta is associated with activation of the PI3K-Akt pathway in HPV16-immortalized human keratinocytes at late stages of in vitro progression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4268. doi:10.1158/1538-7445.AM2013-4268

The synthetic caged garcinia xanthone cluvenone induces cell stress and apoptosis and has immune modulatory activity

Several caged Garcinia xanthone natural products have potent bioactivity and a documented value in traditional Eastern medicine. Previous synthesis and structure activity relationship studies of these natural products resulted in the identification of the pharmacophore represented by the structure of cluvenone. In the current study, we examined the anticancer activity of cluvenone and conducted gene expression profiling and pathway analyses. Cluvenone was found to induce apoptosis in T-cell acute lymphoblastic leukemia cells (EC₅₀ = 0.25 μmol/L) and had potent growth-inhibitory activity against the NCI60 cell panel, including those that are multidrug-resistant, with a GI₅₀ range of 0.1 to 2.7 μmol/L. Importantly, cluvenone was approximately 5-fold more potent against a primary B-cell acute lymphoblastic leukemia compared with peripheral blood mononuclear cells from normal donors, suggesting that it has significant tumor selectivity. Comparison of cluvenone's growth-inhibitory profile to those in the National Cancer Institute database revealed that compounds with a similar profile to cluvenone were mechanistically unlike known agents, but were associated with cell stress and survival signaling. Gene expression profiling studies determined that cluvenone induced the activation of mitogen-activated protein kinase and NrF2 stress response pathways. Furthermore, cluvenone was found to induce intracellular reactive oxygen species formation. Lastly, the modulation in the expression of several genes associated with T cell and natural killer cell activation and function by cluvenone suggests a role as an immune-modulator. The current work highlights the potential of cluvenone as a chemotherapeutic agent and provides support for further investigation of these intriguing molecules with regard to mechanism and targets.

Mechanisms of decreased expression of transforming growth factor-beta receptor type I at late stages of HPV16-mediated transformation

Transforming growth factor-beta (TGF-beta) signaling is disrupted in many cancers, including cervical cancer, leading to TGF-beta resistance. Although initially sensitive, human papillomavirus type 16 (HPV16) immortalized human keratinocytes (HKc/HPV16) become increasingly resistant to the growth inhibitory effects of TGF-beta during in vitro progression to a differentiation resistant phenotype (HKc/DR). We have previously shown that loss of TGF-beta sensitivity in HKc/DR is attributed to decreased expression of TGF-beta receptor type I (TGF-beta RI), while the levels of TGF-beta receptor type II (TGF-beta RII) remain unchanged. The present study explored molecular mechanisms leading to reduced TGF-beta RI expression in HKc/DR. Using TGF-beta RI and TGF-beta RII promoter reporter constructs, we determined that acute expression of the HPV16 oncogenes E6 and E7 decreased the promoter activity of TGF-beta RI and TGF-beta RII by about 50%. However, promoter activity of TGF-beta RI is decreased to a greater extent than TGF-beta RII as HKc/HPV16 progress to HKc/DR. Reduced TGF-beta RI expression in HKc/DR was found not to be linked to mutations within the TGF-beta RI promoter or to promoter methylation. Electrophoretic mobility shift and supershift assays using probes encompassing Sp1 binding sites in the TGF-beta RI promoter found no changes between HKc/HPV16 and HKc/DR in binding of the transcription factors Sp1 or Sp3 to the probes. Also, Western blots determined that protein levels of Sp1 and Sp3 remain relatively unchanged between HKc/HPV16 and HKc/DR. Overall, these results demonstrate that mutations in or hypermethylation of the TGF-beta RI promoter, along with altered levels of Sp1 or Sp3, are not responsible for the reduced expression of TGF-beta RI we observe in HKc/DR. Rather the HPV16 oncogenes E6 and E7 themselves exhibit an inhibitory effect on TGF-beta receptor promoter activity.

Gene expression changes during HPV-mediated carcinogenesis: a comparison between an in vitro cell model and cervical cancer

We used oligonucleotide microarrays to investigate gene expression changes associated with multi-step human papillomavirus type 16 (HPV16)-mediated carcinogenesis in vitro. Gene expression profiles in 4 early passage HPV16-immortalized human keratinocyte (HKc) lines derived from different donors were compared with their corresponding 4 late-passage, differentiation-resistant cell lines, and to 4 pools of normal HKc, each composed of 3 individual HKc strains, on Agilent 22 k human oligonucleotide microarrays. The resulting data were analyzed using a modified T-test coded in R to obtain lists of differentially expressed genes. Gene expression changes identified in this model system were then compared with gene expression changes described in published studies of cervical intraepithelial neoplasia (CIN) and cervical cancer. Common genes in these lists were further studied by cluster analysis. Genes whose expression changed in the same direction as in CIN or cervical cancer (concordant) at late stages of HPV16-mediated transformation in vitro formed one major cluster, while those that changed in the opposite direction (discordant) formed a second major cluster. Further annotation found that many discordant expression changes involved gene products with an extracellular localization. Two novel genes were selected for further study: overexpression of SIX1 and GDF15, observed during in vitro progression in our model system, was confirmed in tissue arrays of cervical cancer. These microarray-based studies show that our in vitro model system reflects many cellular and molecular alterations characteristic of cervical cancer, and identified SIX1 and GDF15 as 2 novel potential biomarkers of cervical cancer progression.

NFI is an essential positive transcription factor for human papillomavirus type 16 early gene expression

Human papillomavirus type 16 (HPV16) is the primary etiologic agent for greater than 50% of all cervical carcinomas. Expression of the HPV16 E6 and E7 oncoproteins is under control of the upstream regulatory region (URR), which contains a myriad of transcription factor binding sites, including 7 half sites for NFI. These NFI binding sites were used as probes in electrophoretic mobility shift assays (EMSAs), and mutational analysis of individual and multiple NFI binding sites was performed in order to demonstrate the relative importance of particular NFI sites to URR activity. By using 5 NFI half sites as an enhancer, we were able to detect a 4-fold increase in URR activity. Our results define the role and relative contribution of NFI binding sites to the basal activity of the HPV16 promoter, and demonstrate that NFI binding sites can act independently to enhance HPV16 URR activity in immortalized keratinocytes.

Human retinoblastoma is not caused by known pRb-inactivating human DNA tumor viruses

Retinoblastomas occur as the consequence of inactivation of the tumor suppressor retinoblastoma protein (pRb), classically upon biallelic inactivation of the RB1 gene locus. Recently, human papillomavirus (HPV) genomic DNA has been detected in retinoblastomas. To investigate the possibility that oncoproteins encoded by pRb-inactivating DNA tumor viruses play a role in the pathogenesis of human retinoblastoma, 40 fresh-frozen tumors were analyzed for the presence of HPV, adenovirus (HAdV) and polyomavirus (BKV, JCV and SV40) genomic DNA sequences by real-time polymerase chain reaction (PCR). Tumors were screened for genetic and epigenetic alterations in all 27 exons of the RB1 gene locus and promoter by exonic copy number detection, sequencing and methylation-specific PCR of the promoter region. Retinoblastoma tumors from children with bilateral familial (n=1), bilateral nonfamilial (n=1) and unilateral nonfamilial (n=38) disease were analyzed. Inactivating modifications to the RB1 gene locus were identified on both the alleles in 27 tumors, one allele in 8, and neither allele in 5 cases. A median of over 107,000 tumor cells were analyzed for viral genomic DNA in each PCR reaction. All tumor samples were negative for 37 HPV types, 51 HAdV types, BKV and JCV genomic sequences. Very low copy number (0.2-260 copies per 100,000 tumor cells) SV40 genomic DNA detected in 8 of 39 samples was demonstrated to be consistent with an artifact of plasmid-derived SV40. In contrast to recent reports, we obtained substantial quantitative evidence indicating that neither HPV nor any other pRb-inactivating human DNA tumor viruses play a role in the development of retinoblastoma, regardless of RB1 genotype.

Role of micro-RNAs in regulation of lentiviral latency and persistence

Small interfering RNAs have been demonstrated to serve as a molecular defence against numerous retroviruses in plants and insects and, more recently, in primates. With the recent findings of micro-RNAs (miRNAs) that seem to play a pivotal role in the survival of the host, we have explored the role of miRNAs in lentiviral (LV) replication. We have previously hypothesized that, at least in the case of lentivirus infection, small interfering RNAs are involved in the inhibition of these types of viruses by the formation of intramolecular triplex formation (triplexes) between the polypurine tracks sequences of LV provirus and miRNAs and blocking the viral replication at the preintegration complex levels, placing these viruses into a suspended latency. Using several latently and chronically infected LV cell lines and human PBMCs from HIV-1-infected individuals, we show that perinuclear triplexes are formed in LV-infected cells. The number of triplexes decreased in cells with productive replication of LVs. Therefore, the degree of replication of HIV-1 and other LVs, both in the HIV-1 or other LV-infected cell lines and the HIV-1 infected PBMCs, inversely correlate with the number of cytoplasmic triplexes present in a particular cell. This correlation was further confirmed by the stimulation of PBMCs and LV-infected cell lines with appropriate mitogens. Treatment with Tagetin, a RNA polymerase III inhibitor, resulted in a significant decrease in triplexes and a dramatic increase in the LV replication. Our data suggest that triplex formation may be an important mechanism of LV latency mediated by endogenous miRNAs.

RNA degradation in human breast tissue after surgical removal: a time-course study

There is much interest in the study of human malignancy using gene expression profiling techniques. Expression profiles obtained from microarrays utilize RNA extracted from the tissue in question. Currently, cell cultures or fresh tissue processed "quickly" are used in these studies. To our knowledge, there are no published reports of a time-course of RNA degradation in surgically removed breast tissue. Such a time-course study is critically needed. We obtained normal breast tissue from breast reduction surgery. Portions of breast tissue kept at room temperature were sampled and placed into RNAlater to preserve RNA at different time-points from 10 min to 3 h after the surgical removal. We evaluated total RNA integrity from each specimen using agarose gel electrophoresis and real-time quantitative RT-PCR analysis of four genes. Electrophoresis showed good-quality, intact RNA at all time points up to 3 h. Quantitative RT-PCR showed no difference in amplified products among all samples. Our study showed that there was no loss of RNA integrity in normal breast tissue for up to 3 h after surgical removal.

NFI-Ski interactions mediate transforming growth factor beta modulation of human papillomavirus type 16 early gene expression

Human papillomaviruses (HPVs) are present in virtually all cervical cancers. An important step in the development of malignant disease, including cervical cancer, involves a loss of sensitivity to transforming growth factor beta (TGF-beta). HPV type 16 (HPV16) early gene expression, including that of the E6 and E7 oncoprotein genes, is under the control of the upstream regulatory region (URR), and E6 and E7 expression in HPV16-immortalized human epithelial cells is inhibited at the transcriptional level by TGF-beta. While the URR contains a myriad of transcription factor binding sites, including seven binding sites for nuclear factor I (NFI), the specific sequences within the URR or the transcription factors responsible for TGF-beta modulation of the URR remain unknown. To identify potential transcription factors and binding sites involved in TGF-beta modulation of the URR, we performed DNase I footprint analysis on the HPV16 URR using nuclear extracts from TGF-beta-sensitive HPV16-immortalized human keratinocytes (HKc/HPV16) treated with and without TGF-beta. Differentially protected regions were found to be located around NFI binding sites. Electrophoretic mobility shift assays, using the NFI binding sites as probes, showed decreased binding upon TGF-beta treatment. This decrease in binding was not due to reduced NFI protein or NFI mRNA levels. Mutational analysis of individual and multiple NFI binding sites in the URR defined their role in TGF-beta sensitivity of the promoter. Overexpression of the NFI family members in HKc/HPV16 decreased the ability of TGF-beta to inhibit the URR. Since the oncoprotein Ski has been shown to interact with and increase the transcriptional activity of NFI and since cellular Ski levels are decreased by TGF-beta treatment, we explored the possibility that Ski may provide a link between TGF-beta signaling and NFI activity. Anti-NFI antibodies coimmunoprecipitated endogenous Ski in nuclear extracts from HKc/HPV16, confirming that NFI and Ski interact in these cells. Ski levels dramatically decreased upon TGF-beta treatment of HKc/HPV16, and overexpression of Ski eliminated the ability of TGF-beta to inhibit the URR. Based on these studies, we propose that TGF-beta inhibition of HPV16 early gene expression is mediated by a decrease in Ski levels, which in turn dramatically reduces NFI activity.

Human papillomavirus type 16 E6 and E7 cooperate to increase epidermal growth factor receptor (EGFR) mRNA levels, overcoming mechanisms by which excessive EGFR signaling shortens the life span of normal human keratinocytes

Epidermal growth factor receptor (EGFR) levels are dramatically increased in human keratinocytes (HKc) immortalized with full-length human papillomavirus type 16 (HPV16) DNA (HKc/HPV16), but increases in EGFR levels actually precede immortalization. In some normal HKc strains, acute expression of HPV16 E6 (but not HPV16 E5, HPV16 E7, or HPV6 E6) from LXSN retroviral vectors produced an increase in EGFR mRNA levels detectable at 24 h and stable for up to 10 days after infection. However, about one-half of the individual normal HKc strains we analyzed proved unresponsive to E6 induction of EGFR mRNA despite the robust expression of E6 and degradation of p53. E6 responsiveness of normal HKc strains correlated inversely with initial EGFR levels: although HKc strains expressing relatively low basal EGFR levels grew poorly and tolerated the infection protocol with difficulty, they responded to E6 with an increase in EGFR mRNA and protein and with robust proliferation. However, those HKc strains expressing high basal EGFR levels grew well, but did not respond to E6 with increased EGFR levels or with proliferation. Immunostaining of paraffin-embedded foreskin tissue for the EGFR confirmed that there is an intrinsic interindividual variability of EGFR expression in HKC: These results prompted us to investigate the effects of overexpression of the EGFR in normal HKC: Infection of normal HKc with a LXSN retrovirus expressing the full-length human EGFR cDNA resulted in a dramatic reduction in growth rate and a shorter life span. Although acute expression (1-10 days after infection) of HPV16 E7 alone did not induce the EGFR, acute expression of E6 and E7 together increased EGFR levels in normal HKc unresponsive to E6 alone. Also, HKc infected with E7 alone expressed increased EGFR levels at early stages of extended life span (at passage 9 after infection), and HKc immortalized by HPV16 E7 alone expressed EGFR levels comparable with those of E6/E7-immortalized cells. These results support a key role of the EGFR in HPV16-mediated transformation of HKC: In addition, these data show that normal HKc do not tolerate excessive EGFR levels/signaling, and such intolerance must be overcome in order for HKc to become immortalized by HPV16. We conclude that both E6 and E7 contribute to increasing EGFR levels, but with different mechanisms: although E6 can increase EGFR levels, it cannot overcome the resistance of normal HKc to excessive EGFR signaling. On the other hand E7, which alone does not acutely increase EGFR mRNA or protein, allows for EGFR overexpression in normal HKC:

Genotyping single nucleotide polymorphisms using intact polymerase chain reaction products by electrospray quadrupole mass spectrometry

Both single nucleotide polymorphisms (SNPs) and mutations are commonly observed in the gene encoding the tumor suppressor protein, p53. SNPs occur at specific locations within genes whereas mutations may be distributed across large regions of genes. When determining nucleotide differences, mass spectrometry is the only method other than Sanger sequencing which offers direct structural information. Electrospray ionization (ESI) quadrupole mass spectrometry (MS) analysis of intact polymerase chain reaction (PCR) products was performed following a simple purification and on-line heating to limit ion adduction. The PCR products were amplified directly from genomic DNA rather than plasmids, as in our previous work. Two known polymorphisms of the p53 gene were genotyped. A cytosine (C) or guanine (G) transversion, designated C <--> G (G <--> C on the opposite strand), were each detected by a 40.0 Da change upon ESI quadrupole MS analysis. Using known PCR products as standards, the genotypes determined for 10 human samples corresponded with restriction fragment length polymorphism (RFLP) analysis. Cytosine/thymine (T) transitions, designated C <--> T (G <--> A on the opposite strand), were also genotyped by ESI-MS. This SNP is discriminated by a 15.0 Da change on one strand (C <--> T) and a 16.0 Da change on the other (G <--> A). Appropriate sample preparation and instrumental configuration (including heated sample inlet syringe and MS source), to limit adducts, are both vital for successful ESI quadrupole MS analysis of intact PCR products.

MS for identification of single nucleotide polymorphisms and MS/MS for discrimination of isomeric PCR products

ESI (electrospray ionization) MS and tandem mass spectrometry (MS/MS) were used for the analysis of single nucleotide polymorphisms (SNPs) and more complex genetic variations. Double-stranded (ds) PCR products were studied. PCR products of the proline [5'-x(G17)-x(C38)x-3'] and arginine variants [(5'-x(Gl7)-x(G38)x-3'] of the p53 gene are distinguished by an SNP (cytosine or guanine) and were discriminated using both quadrupole and quadrupole ion trap MS analysis. A 69 bp arginine mutant PCR product [5'-x(C17)-x(G38)x-3'] with a negating switch has the same mass as the proline variant but was readily distinguishable on ion trap MS/MS analysis; fragments containing the mutation site, but not the polymorphism, were identified. The 69 bp PCR products were restriction-enzyme-digested, to create 43 bp fragments. ESI quadrupole ion trap MS/MS analysis of the 43 bp product-ion spectra readily demonstrated both polymorphism and negating switch sites. MS and MS/MS are powerful and complementary techniques for analysis of DNA. MS can readily distinguish SNPs but MS/MS is required to differentiate isomeric PCR products (same nucleotide composition but different sequence).

Unique carboxyl-terminal sequences of wild type and alternatively spliced variant forms of transforming growth factor-alpha precursors mediate specific interactions with ErbB4 and ErbB2

We have previously reported that the human transforming growth factor-alpha (TGF-alpha) gene encodes three forms of TGF-alpha precursors, designated wild type (WT), variant I (VaI), and variant II (VaII), derived from alternative splicing. The two carboxyl-terminal valine residues of WT are replaced by 5 (GCRLY) or 4 (ATLG) amino acids in VaI or VaII, respectively. When overexpressed in Chinese hamster ovary (CHO) cells, VaI and ValI, but not WT, support autonomous growth. We detected tyrosine phosphorylation of ErbB2 in the absence of serum, in CHO cells expressing WT, VaI, or VaII, but not in mock transfectants. These observations prompted us to investigate possible interactions between the ErbBs and the TGF-alpha precursors in CHO cells. All TGF-alpha precursors were found to co-immunoprecipitate with the ErbBs, but with different specificity. WT co-immunoprecipitated with ErbB4, but not with ErbB1, ErbB2, or ErbB3. VaI and VaII co-immunoprecipitated with ErbB2, but not with ErbB1, ErbB3, or ErbB4. Confocal fluorescent microscopy analysis demonstrated that WT, VaI, and VaII all distribute equally to the cell surface while, as expected, a WT mutant lacking the two C-terminal valine residues does not. Point and deletion mutants involving the unique carboxyl-terminal residues of WT, VaI and VaII, indicated that the interactions between the three TGF-alpha precursors and the ErbBs were mediated by their carboxyl-terminal regions, which constitute distinct protein-binding motifs. A chimera of the intracellular domain of WT TGF-alpha linked to exogenous transmembrane and extracellular domains retained both the cell surface distribution and the specific interaction with ErbB4 of full-length WT, confirming that this interaction is mediated by the C-terminus of the TGF-alpha precursor. While interactions of WT and variant TGF-alpha with the ErbBs all result in ErbB2 activation, they produce different biological consequences, suggesting that the various TGF-alpha precursors differentially modulate ErbB signaling.

Retinoic acid resistance at late stages of human papillomavirus type 16-mediated transformation of human keratinocytes arises despite intact retinoid signaling and is due to a loss of sensitivity to transforming growth factor-beta

In our in vitro model of human cell carcinogenesis, normal human foreskin keratinocytes (HKc) transfected with human papillomavirus type 16 DNA (HKc/HPV16) progress toward malignancy through several phenotypically defined and reproducible "steps" that include immortalization, growth factor independence (HKc/GFI), differentiation resistance (HKc/DR), and ultimately malignant conversion. While HKc/HPV16 are very sensitive to growth inhibition by all-trans-retinoic acid (RA) at early passages, they lose their sensitivity to RA during progression in culture. However, gel mobility shift assays using the retinoid response elements DR1 and DR5 showed no changes in binding activity of nuclear extracts obtained from HKc/HPV16 at different stages of in vitro progression. Similarly, Western blot analyses for retinoic acid receptor gamma-1 and the retinoid X receptors failed to reveal any decreases in the levels of these retinoid receptors throughout progression. In addition, luciferase activity driven by the SV40 promoter with a DR5 enhancer element was activated following RA treatment of HKc/DR that were resistant to growth inhibition by RA. Since RA induces transforming growth factor-beta2 (TGF-beta2) in normal HKc and HKc/HPV16, we investigated whether this response changed during progression. Again, RA induced TGF-beta2 mRNA in early and late passage HKc/HPV16, HKc/GFI, and HKc/DR approximately to the same extent, confirming that the RA signaling pathways remained intact during in vitro progression despite the fact that the cells become resistant to growth inhibition by RA. We then investigated the sensitivity of HKc/HPV16 to growth inhibition by TGF-beta. While early passage HKc/HPV16 were as sensitive as normal HKc to growth inhibition by TGF-beta1 and TGF-beta2, the cells became increasingly resistant to both TGF-beta isotypes during in vitro progression. In addition, while both RA and TGF-beta produced a decrease in the levels of mRNA for the HPV16 oncogenes E6 and E7 in early passage HKc/HPV16, this effect was also lost at later stages of progression. Finally, blocking anti-TGF-beta antibodies partially prevented RA inhibition of growth and E6/E7 expression in early passage HKc/HPV16. Taken together, these data strongly suggest that inhibition of growth and HPV16 early gene expression in HKc/HPV16 by RA is mediated by TGF-beta and that a loss of RA sensitivity is linked to TGF-beta resistance rather than alterations in RA signaling.

Loss of transforming growth factor-beta (TGF-beta) receptor type I mediates TGF-beta resistance in human papillomavirus type 16-transformed human keratinocytes at late stages of in vitro progression

Human keratinocytes (HKc) immortalized by human papillomavirus type 16 DNA (HKc/HPV16) progress toward malignancy through growth factor-independent (HKc/GFI) and differentiation-resistant stages (HKc/DR). This progression is associated with a loss of sensitivity to growth inhibition by both all-trans-retinoic acid (RA) and transforming growth factor-beta (TGF-beta). In the accompanying article (Borger et al., 2000, Virology 270, 397-407), we demonstrate that RA resistance in HKc/HPV16 arises despite functional nuclear retinoid receptors and that TGF-beta mediates growth inhibition by RA. To investigate the basis for the loss of TGF-beta sensitivity during in vitro progression of HKc/HPV16, we explored the expression of TGF-beta receptors type I and type II in independently derived HKc/HPV16 lines and their corresponding HKc/GFI and HKc/DR derivatives. While TGF-beta receptor type II mRNA levels were unchanged during progression, mRNA levels for TGF-beta receptor type I decreased dramatically as the cells became TGF-beta resistant. At the HKc/DR stage, loss of TGF-beta receptor type I mRNA, compared to low-passage cells, ranged from 55 to 87% in four HKc/HPV16 lines examined. Immunohistochemistry, using anti-TGF-beta receptor type I antibodies, confirmed a loss of TGF-beta receptor type I expression in HKc/DR. Reintroduction of the TGF-beta-receptor type I into TGF-beta-resistant HKc/DR completely restored growth inhibition by TGF-beta. Southern blot analysis of DNA extracted from normal HKc, HKc/HPV16, and HKc/DR ruled out any gross changes in the TGF-beta receptor type I gene. The activity of the TGF-beta receptor type I promoter, cloned upstream of a luciferase reporter gene, was decreased in HKc/DR, to an extent comparable to the decrease in mRNA levels for the TGF-beta receptor type I. Thus, TGF-beta resistance at late stages of HPV16-mediated transformation of HKc is the result of a loss of expression of TGF-beta receptor type I.

Population-based, case-control study of HER2 genetic polymorphism and breast cancer risk

BACKGROUND

Alterations of the HER2 (also known as erbB-2 or neu) proto-oncogene have been implicated in the carcinogenesis and prognosis of breast cancer. A polymorphism at codon 655 (GTC/valine to ATC /isoleucine [Val(655)Ile]) in the transmembrane domain-coding region of this gene has been identified and may be associated with the risk of breast cancer. We evaluated this hypothesis in a subgroup of women who participated in a large-scale, population-based, case-control study of breast cancer in Shanghai, China.

METHODS

Genomic DNA from 339 patients with breast cancer and 361 healthy control subjects was examined for the Val(655)Ile polymorphism with a polymerase chain reaction-restriction fragment-length polymorphism-based assay. All study subjects completed a structured questionnaire during an in-person interview. All P values are from two-sided tests.

RESULTS

We found that 25.1% of the case patients and 21.7% of the control subjects were heterozygous for the Val allele and 3.2% of the case patients and 0. 3% of the control subjects were homozygous for this allele (P =.005). Compared with women with the Ile/Ile genotype, women who had the Ile/Val or Val/Val genotype had an elevated risk of breast cancer (odds ratio [OR] = 1.4; 95% confidence interval [CI] = 1.0-2.0; P =. 05) after adjustment for age, educational level, study period, history of breast fibroadenoma, leisure physical activity, and age at first live birth. The risk was elevated even more among women who were homozygous for the Val allele (OR = 14.1; 95% CI = 1.8-113.4). The association was more pronounced among younger women (</=45 years) than among older women (>45 years). The adjusted OR associated with the Val allele was 1.7 (95% CI = 1.1-2.6) for younger women and 1.0 (95% CI = 0.5-1.9) for older women.

CONCLUSIONS

Results of this study suggest that polymorphisms of the HER2 gene may be important susceptibility biomarkers for breast cancer risk, particularly among younger women.

Human keratinocytes and tumor-derived cell lines express alternatively spliced forms of transforming growth factor-alpha mRNA, encoding precursors lacking carboxyl-terminal valine residues

The human transforming growth factor-alpha (TGF-alpha) gene is thought to contain five introns and six exons, encoding a transmembrane precursor (proTGF-alpha) from which the mature polypeptide is released by proteolytic cleavage. We identified a novel 32-nucleotide exon (exon alpha) within intron 5 and an alternative splice acceptor site in exon 6, splitting exon 6 into two segments: 6A and 6B. Therefore, in addition to wild type (wt) proTGF-alpha mRNA, which skips exon alpha, two novel proTGF-alpha variants are produced: Variant I (VaI), skipping exons alpha and 6A, and Variant II (VaII) which includes exon alpha and skips exon 6A. The only significant difference between variant and wt proTGF-alpha proteins is that the two wt carboxyl-terminal valines are replaced in the variants by five or four other amino acids, respectively. Both variant TGF-alpha mRNAs were readily detected in human keratinocytes and tumor-derived cell lines. Their protein products were cleaved as efficiently as wt TGF-alpha in response to the calcium ionophore A23187. However, both variants (but not wt) reduced serum requirements for proliferation in CHO cells. In addition, VaII-expressing CHO cells (not VaI or wt) formed foci in monolayer cultures. These results suggest that variant TGF-alpha precursors induce autonomous growth.

Comparison of the metabolism of retinol delivered to human keratinocytes either bound to serum retinol-binding protein or added directly to the culture medium

Retinol (vitamin A) circulates in the blood bound to retinol-binding protein (RBP), which is thought to be responsible for the delivery of the vitamin to target cells, including the basal cells of the skin (keratinocytes). The process by which keratinocytes acquire retinol from RBP remains controversial. A mechanism for retinol delivery to keratinocytes involving cell surface RBP receptors has been proposed, while other studies support an RBP receptor-independent process. To further explore retinol uptake we have used a model system of human foreskin keratinocytes cultured in serum-free media to compare the metabolism of [3H]retinol delivered to the cells either bound to RBP or added directly to the culture medium. The majority of the cell-associated radioactivity found in keratinocytes incubated for 0.5 to 24 h with either free or RBP bound [3H]retinol was present as [3H]retinyl ester irrespective of the mode of delivery. In keratinocytes incubated for 24 h with [3H]retinol added directly to the culture medium or bound to RBP, [3H]retinyl ester comprised 76 and 80%, respectively, of the total cell-associated radioactivity. Also, the relative cellular levels of the different retinyl esters species synthesized by the keratinocytes were the same whether the [3H]-retinol was delivered free or bound to RBP. Finally, the kinetics of loss (turnover) of cell-associated [3H]-retinol and [3H]retinyl esters from keratinocytes pre-labeled with [3H]retinol delivered free or bound to RBP was the same. Overall, this study demonstrates that the rate and extent of retinol esterification by keratinocytes and the types of esters synthesized are the same whether the vitamin is delivered to the cells free or bound to RBP and argues against RBP receptor-mediated delivery of retinol to specific sites on the plasma membrane that influence overall retinol metabolism.

Glucocorticoids stimulate growth of human papillomavirus type 16 (HPV16)-immortalized human keratinocytes and support HPV16-mediated immortalization without affecting the levels of HPV16 E6/E7 mRNA

We investigated the effects of the glucocorticoids hydrocortisone and dexamethasone on human papillomavirus type 16 (HPV16)-mediated human cell carcinogenesis using normal human keratinocytes (HKc) and HKc immortalized by transfection with HPV16 DNA (HKc/HPV16). Normal HKc did not require glucocorticoids for proliferation. In contrast, growth of early passage HKc/HPV16 strictly required these hormones, although glucocorticoid dependence became less stringent during in vitro progression. Glucocorticoid dependence was acquired by HKc early after immortalization with HPV16 DNA, and glucocorticoids were required for efficient HKc immortalization. However, treatment of HKc/HPV16 with hydrocortisone or dexamethasone did not increase the steady-state levels of HPV16 E6/E7 mRNA or protein. Firefly luciferase activity expressed under the control of the HPV16 upstream regulatory region and P97 promoter increased by about fourfold following dexamethasone treatment of HeLa, but only twofold in HKc/HPV16, and less than twofold in SiHa. However, all of these cell lines expressed sufficient endogenous glucocorticoid receptors to allow for a dexamethasone response of the mouse mammary tumor virus promoter. These results indicate that mechanisms other than a direct influence by glucocorticoids on HPV16 early gene expression may contribute to the striking biological effects of these steroids on HPV16-mediated human cell carcinogenesis.

Evaluation of transdermal penetration enhancers using a novel skin alternative

A novel alternative to animal skin models was developed in order to aid in the screening of transdermal penetration enhancers. The skin alternative consists of a dermal layer containing human fibroblasts dispersed in a collagen matrix and an epidermal layer of differentiated and stratified human keratinocytes. Skin alternatives were placed in modified Franz diffusion cells (receptor volume 12 mL, donor area 3.14 cm2, n = 5) and enhancer solution (0.4 M in propylene glycol (PG)) was applied. Following 1 h of pretreatment, 10 microL of saturated hydrocortisone (HC) solution in PG was applied, and the cells were occluded with Parafilm. Samples were removed from the receptor compartment over 24 h, replaced with fresh receptor solution, and analyzed for steroid content using HPLC. Skin HC content was also determined. Receptor concentration at 24 h (Q24) for full-thickness skin alternative (control) was 28.6 +/- 13.7 microM and permeability (P) was 8.3 x 10(-4) +/- 5.5 x 10(-4) cm h-1. Azone (1) produced a Q24 of 105.0 +/- 36.1 microM and a P of 11.3 x 10(-4) +/- 1.8 x 10(-4) cm h-1, while the novel penetration enhancer 1-dodecyl-2-pyrrolidinone (2) produced a Q24 of 164.8 +/- 61.2 microM and a P of 33.3 x 10(-4) +/- 6.6 x 10(-4) cm h-1. Compound 3 produced the highest values for all permeability parameters tested with a P of 48.0 +/- 36.8 cm h-1 and a Q24 of 186.1 +/- 45.1 microM. When compared to the control, compound 1 gave an enhancement ratio (ER) of 3.7 for Q24 and 1.4 for P. Compound 2 gives an ER 5.8 for Q24 and 4.0 for P. These enhancement ratios are similar to those found using HC and human skin.

Uptake and metabolism of [3H]retinoic acid delivered to human foreskin keratinocytes either bound to serum albumin or added directly to the culture medium

Retinoic acid (RA), a potent modulator of cell proliferation and differentiation is present in plasma bound to serum albumin. The biologic significance or source of plasma RA is not clear. Although most cellular RA is believed to be made in situ via the oxidation of retinol, plasma RA could potentially provide target cells with a source of preformed RA. To investigate RA uptake, we have used a model system of human foreskin keratinocytes (HKc) cultured in serum-free media to compare the uptake and metabolism of [3H]RA added directly to the culture medium in ethanol to that delivered bound to bovine serum albumin (BSA). [3H]RA added directly to the culture medium was rapidly taken up by HKc during the first 10 min of incubation (25-35% of the applied RA), no further accumulation occurred between 10 min and 90 min, and then cell-associated radioactivity rapidly decreased to about 3-5% of the applied dose by 12 h. In contrast, when [3H]RA was delivered to HKc bound to BSA, total cell-associated radioactivity reached about 2.5% of the applied dose by 5 min, increased to 3-5% of the applied radioactivity by 1 h, and no further accumulation or loss occurred over the next 23 h. The uptake by HKc of [3H]RA delivered bound to BSA or added directly to the culture medium was not influenced by pre-treatment of the cells for 72 h with unlabeled RA or by excess unlabeled RA added at the time of uptake. Analysis of the cells and media by high-performance liquid chromatography for RA metabolites found that [3H]RA added directly to the medium is rapidly converted by HKc to polar compounds that are subsequently excreted back into the medium. Also, RA added directly to the medium was susceptible to degradation in the absence of cells. In marked contrast, [3H]RA added to the media bound to BSA was much less susceptible to degradation in the absence of cells, and few [3H]RA metabolites were found in the media even after exposure to HKc for 24 h. The binding of RA to albumin clearly protects RA from conversion to polar metabolites, and also provides for a controlled delivery of RA from the aqueous extracellular environment to the cell surface.

Progressive loss of sensitivity to growth control by retinoic acid and transforming growth factor-beta at late stages of human papillomavirus type 16-initiated transformation of human keratinocytes

Retinoids (vitamin A and its natural and synthetic derivatives) have shown potential as chemopreventive agents, and diets poor in vitamin A and/or its precursor beta-carotene have been linked to an increased risk of cancer at several sites including the cervix. Human papillomavirus (HPV) plays an important role in the etiology of cervical cancer. We have developed an in vitro model of cancer progression using human keratinocytes (HKc) immortalized by HPV16 DNA (HKc/HPV16). Although immortal, early passage HKc/HPV16, like normal HKc, require epidermal growth factor (EGF) and bovine pituitary extract (BPE) for proliferation and undergo terminal differentiation in response to serum and calcium. However, following prolonged culture, growth factor independent HKc/HPV16 lines that no longer require EGF and BPE can be selected (HKc/GFI). Further selection of HKc/GFI produces lines that are resistant to serum- and calcium- induced terminal differentiation (HKc/DR). HKc/DR, but not early passage HKc/HPV16, are susceptible to malignant conversion following transfection with viral Harvey ras or Herpes simplex virus type II DNA. We have investigated the sensitivity of low to high passage HKc/HPV16 and HKc/GFI to growth control by all-trans-retinoic acid (RA, an active metabolite of vitamin A). Early passage HKc/HPV16 are very sensitive to growth inhibition by RA, and in these cells RA decreases the expression of the HPV16 oncogenes E6 and E7. However, as the cells progress in culture they lose their sensitivity to RA. Growth inhibition by RA may be mediated through the cytokine transforming growth factor-beta (TGF-beta), a potent inhibitor of epithelial cell proliferation. RA treatment of HKc/HPV16 and HKc/GFI results in a dose-and time-dependent induction (maximal of 3-fold) in secreted levels of TGF-beta. Also, Northern blot analysis of mRNA isolated from HKc/HPV16 demonstrated that RA treatment induced TGF-beta 1 and TGF-beta 2 expression about 3- and 50-fold, respectively. We next studied the effect of TGF-beta 1 and TGF-beta 2 on the proliferation of early to late passage HKc/HPVa6, HKc/GFI and HKc/DR. While early passage HKc/HPV16 were as sensitive as normal HKc to growth inhibition by TGF-beta 1 and TGF-beta 2, the cells became increasingly resistant to TGF-beta during in vitro progression, with the proliferation of HKc/DR being virtually unaffected by TGF-beta 1 or TGF-beta 2 treatment. Overall, loss of growth inhibition by RA parallels loss of TGF-beta sensitivity.(ABSTRACT TRUNCATED AT 400 WORDS)