Novel mutations in the polyadenine tract of the transforming growth factor beta type II receptor gene are found in a subpopulation of human pancreatic adenocarcinomas

TGF-β signaling in health, disease, and therapeutics

Transforming growth factor (TGF)-β is a multifunctional cytokine expressed by almost every tissue and cell type. The signal transduction of TGF-β can stimulate diverse cellular responses and is particularly critical to embryonic development, wound healing, tissue homeostasis, and immune homeostasis in health. The dysfunction of TGF-β can play key roles in many diseases, and numerous targeted therapies have been developed to rectify its pathogenic activity. In the past decades, a large number of studies on TGF-β signaling have been carried out, covering a broad spectrum of topics in health, disease, and therapeutics. Thus, a comprehensive overview of TGF-β signaling is required for a general picture of the studies in this field. In this review, we retrace the research history of TGF-β and introduce the molecular mechanisms regarding its biosynthesis, activation, and signal transduction. We also provide deep insights into the functions of TGF-β signaling in physiological conditions as well as in pathological processes. TGF-β-targeting therapies which have brought fresh hope to the treatment of relevant diseases are highlighted. Through the summary of previous knowledge and recent updates, this review aims to provide a systematic understanding of TGF-β signaling and to attract more attention and interest to this research area.

Analysis of microsatellite instability in Korean patients with pancreatic cancer

BACKGROUND

Pancreatic cancer (PC) is a dangerous malignancy with a high mortality rate. Diagnosing PC at an early stage is difficult, and approximately 5% of the patients survive for 5 years. Microsatellite instability (MSI) plays an important role in colorectal cancer (CRC) for prognosis and immunotherapy. Evaluation of MSI status is important as it is recognized biomarker for the positive response of immune checkpoint blockade therapy in cancer. To our knowledge, there is no report yet on the prevalence of MSI in Korean PC patients. Studies have reported conflicting prevalence of MSI in PC.

METHODS

Therefore, to improve the likelihood of MSI identification in PC, we included 133 patients with PC; paired tumor and normal tissue DNA were isolated and MSI was analyzed using Promega panel and immunohistochemistry (IHC) was also performed.

RESULTS

Our results from the Promega panel indicated that one (0.7%) tumor was MSI-high (MSI-H), 13 (9.8%) were MSI-low (MSI-L), and 119 (89.5%) were microsatellite stable (MSS). IHC result also confirmed dMMR in only one sample.

CONCLUSIONS

The finding of low incidence of MSI-H observed by the Promega panel also matched IHC results, so this study suggested that in Korean PC patients, MSI prevalence is infrequent.

Early-onset pancreatic cancer: a review of molecular mechanisms, management, and survival

OBJECTIVES

Early-onset pancreatic cancer (EOPC) - defined as pancreatic cancer diagnosed before the age of 50 years - is associated with a poor prognosis as compared to later-onset pancreatic cancer (LOPC). Emerging evidence suggests that EOPC may exhibit a genetic signature and tumor biology that is distinct from that of LOPC. We review genetic mutations that are more prevalent in EOPC relative to LOPC and discuss the potential impact of these mutations on treatment and survival.

MATERIALS AND METHODS

Using PubMed and Medline, the following terms were searched and relevant citations assessed: "early onset pancreatic cancer," "late onset pancreatic cancer," "pancreatic cancer," "pancreatic cancer genes," and "pancreatic cancer targeted therapy."

RESULTS

Mutations in CDKN2, FOXC2, and SMAD4 are significantly more common in EOPC as compared to LOPC. In addition, limited data suggest that PI3KCA mutations are more frequently observed in EOPC as compared to LOPC. KRAS mutations are relatively rare in EOPC.

CONCLUSIONS

Genetic mutations associated with EOPC are distinct from those of LOPC. The preponderance of the evidence suggest that poor outcomes in EOPC are related both to advanced stage of presentation and unique tumor biology. The molecular and genetic features of EOPC warrant further investigation in order to optimize management.

Comprehensive characterisation of pancreatic ductal adenocarcinoma with microsatellite instability: histology, molecular pathology and clinical implications

OBJECTIVE

Recently, tumours with microsatellite instability (MSI)/defective DNA mismatch repair (dMMR) have gained considerable interest due to the success of immunotherapy in this molecular setting. Here, we aim to clarify clinical-pathological and/or molecular features of this tumour subgroup through a systematic review coupled with a comparative analysis with existing databases, also providing indications for a correct approach to the clinical identification of MSI/dMMR pancreatic ductal adenocarcinoma (PDAC).

DESIGN

PubMed, SCOPUS and Embase were searched for studies reporting data on MSI/dMMR in PDAC up to 30 November 2019. Histological and molecular data of MSI/dMMR PDAC were compared with non-MSI/dMMR PDAC and with PDAC reference cohorts (including SEER database and The Cancer Genome Atlas Research Network - TCGA project).

RESULTS

Overall, 34 studies with 8323 patients with PDAC were included in the systematic review. MSI/dMMR demonstrated a very low prevalence in PDAC (around 1%-2%). Compared with conventional PDAC, MSI/dMMR PDAC resulted strongly associated with medullary and mucinous/colloid histology (p<0.01) and with a KRAS/TP53 wild-type molecular background (p<0.01), with more common JAK genes mutations. Data on survival are still unclear.

CONCLUSION

PDAC showing typical medullary or mucinous/colloid histology should be routinely examined for MSI/dMMR status using specific tests (immunohistochemistry, followed by MSI-PCR in cases with doubtful results). Next-generation sequencing (NGS) should be adopted either where there is limited tissue or as part of NGS tumour profiling in the context of precision oncology, acknowledging that conventional histology of PDAC may rarely harbour MSI/dMMR.

Immune-Based Therapies and the Role of Microsatellite Instability in Pancreatic Cancer

Pancreatic cancer is one of the most aggressive malignancies with limited treatment options thus resulting in high morbidity and mortality. Among all cancers, with a five-year survival rates of only 2-9%, pancreatic cancer holds the worst prognostic outcome for patients. To improve the overall survival, an earlier diagnosis and stratification of cancer patients for personalized treatment options are urgent needs. A minority of pancreatic cancers belong to the spectrum of Lynch syndrome-associated cancers and are characterized by microsatellite instability (MSI). MSI is a consequence of defective mismatch repair protein functions and it has been well characterized in other gastrointestinal tumors such as colorectal and gastric cancer. In the latter, high levels of MSI are linked to a better prognosis and to an increased benefit to immune-based therapies. Therefore, the same therapies could offer an opportunity of treatment for pancreatic cancer patients with MSI. In this review, we summarize the current knowledge about immune-based therapies and MSI in pancreatic cancer.

Efficacy of EUS-guided FNB using a Franseen needle for tissue acquisition and microsatellite instability evaluation in unresectable pancreatic lesions

Background

The efficacy of immune checkpoint blockade in the treatment of microsatellite instability (MSI)-high tumors was recently reported. Therefore, the acquisition of histological specimens is desired in cases of unresectable solid pancreatic lesions (UR SPLs). This study investigated the efficacy of endoscopic ultrasound-guided fine-needle biopsy (EUS-FNB) using a Franseen needle for UR SPL tissue acquisition and MSI evaluation.

Methods

A total of 195 SPL patients who underwent EUS-guided fine-needle aspiration (EUS-FNA) or EUS-FNB (EUS-FNAB) between January 2017 and March 2020 were enrolled in this study. Among them, 89 SPL patients (FNB: 28, FNA: 61) underwent EUS-FNAB using a 22-G needle (UR SPLs: 58, FNB: 22, FNA: 36) (UR SPLs after starting MSI evaluation: 23, FNB: 9, FNA: 14).

Results

The puncture number was significantly lower with FNB than with FNA (median (range): 3 (2–5) vs 4 (1–8), P <  0.01, UR SPLs: 3 (2–5) vs 4 (1–8), P = 0.036). Histological specimen acquisition was more commonly achieved with FNB than with FNA (92.9% (26/28) vs 68.9% (42/61), P = 0.015, UR SPLs: 100% (22/22) vs 72.2% (26/36), P <  0.01). The histological specimen required for MSI evaluation was acquired more often with FNB than with FNA (88.9% (8/9) vs 35.7% (5/14), P = 0.03).

Conclusions

EUS-FNB using a Franseen needle is efficient for histological specimen acquisition and sampling the required amount of specimen for MSI evaluation in UR SPL patients.

Frequency of mismatch repair deficiency in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has an ominous prognosis and there are only few treatment options. It is therefore crucial to investigate possible predictive markers that may improve the treatment of this disease. Mismatch repair (MMR) deficiency (d-MMR), meaning MMR protein loss (l-MMR) and/or microsatellite instability (MSI), is predictive of response to immunotherapy, but its frequency has to our knowledge not been elucidated in Scandinavian PDACs. Our aims were to examine the frequency of d-MMR in a Danish cohort of PDACs. We constructed multi-punch tissue microarrays (TMAs) using primary tumor tissue. Immunohistochemistry (IHC) for the DNA MMR proteins MLH1, MSH2, MSH6 and PMS2 was performed, and their expression was evaluated using a scoring system from 0 to 4. If the overall score was between 0-2 or if IHC was inconclusive for technical reasons, IHC on whole-tissue sections and MSI using PCR was performed. A final score of 0, 1-2 or 3-4 defined the tumor as l-MMR, MMR reduced (r-MMR) or MMR proficient. In total, 4/164 (2.4 %), 2/164 (1.2 %) and 3/164 (1.8 %) were l-MMR, r-MMR, or inconclusive based on IHC. MSI testing of these specimens showed that two of the four l-MMR tumors were MSI-high, while the remaining cases were microsatellite stable (MSS). In conclusion, in this study of Danish PDACss, d-MMR was found in a small proportion of the tumors. For these patients, individualized treatment using immunotherapy could be considered.

Circulating Tumor DNA-Based Detection of Microsatellite Instability and Response to Immunotherapy in Pancreatic Cancer

Pancreatic cancer is an aggressive malignancy with poor survival. Research has indicated the association of few genetic aberrations with pancreatic cancer. The data regarding the prevalence of microsatellite instability in pancreatic cancer is diverse and controversial. However, it could be an actionable target in pancreatic cancer especially due to availability of immune checkpoint inhibitors which has demonstrated promising results in different types of cancers. We present a case of pancreatic cancer whose microsatellite instability status was identified on liquid biopsy (circulating tumor DNA testing). Our patient showed a dramatic ongoing durable response to immunotherapy. We were able to do serial monitoring with liquid biopsy that showed clinical utility and validity.

Pancreatic ductal adenocarcinoma harboring microsatellite instability / DNA mismatch repair deficiency. Towards personalized medicine

Pancreatic cancer is a major cause of cancer-associated mortality, with a dismal overall prognosis that has remained almost unchanged for many decades. Pancreatic cancer has few prevalent genetic mutations. Available data on dMMR pancreatic cancer is limited and heterogeneous with regard to its prevalence and prognostic implications. Discordant results are mainly due to differences in detection methods and sample sizes. Interest in dMMR is growing since initial reports on immune checkpoint inhibition therapy for pancreatic cancer has shown it to be effective, generating impressive and durable responses. However, it has been accompanied by several questions regarding the appropriate screening, detection tools, patient selection, timing and modality of testing. Herein, we provide an extensive literature review and outline recommendations for testing.

The analysis of microsatellite instability in extracolonic gastrointestinal malignancy

Microsatellite instability (MSI) is a genetic feature of sporadic and familial cancers of multiple sites and is related to defective mismatch repair (MMR) protein function. Lynch syndrome (LS) is a familial form of MMR deficiency that may present with a spectrum of MSI positive cancers including gastrointestinal (GI) malignancies. The incidence of high level MSI (MSI-H) in colorectal carcinoma is well defined in both familial and sporadic cases and these tumours portend a better overall prognosis in colorectal carcinoma (CRC). There are certain morphological features that suggest MSI-H CRC and international guidelines have been established for the evaluation of MSI in CRC. The prevalence and morphological features of extracolonic GI MSI-H tumours are less well documented. Furthermore, it is unclear whether the guidelines for the assessment of MSI in CRC are appropriate for application to extracolonic GI malignancies. This review aims to summarise the recent literature on MSI in extracolonic LS-related GI tract malignancies with special attention to the assessment of the MMR system by evaluation of specific microsatellite markers and/or immunohistochemical evaluation of MMR protein expression. The reported prevalence of sporadic and LS-related MSI-H tumours along with their associated unique morphological patterns and related prognostic or therapeutic implications will be discussed.

Epigenetic targeting in pancreatic cancer

The prognosis of pancreatic cancer patients is very poor, with a 5-year survival of less than 6%. Therefore, there is an urgent need for new therapeutic options in pancreatic cancer. In the past years it became evident that deregulation of epigenetic mechanisms plays an important role in pancreatic carcinogenesis. This review focuses on the exploitation of drugs that alter histone modifications, DNA methylation and microRNA expression as options for the treatment of pancreatic cancer.

Simulation-based analyses reveal stable microsatellite sequences in human pancreatic cancer

Genomic analysis using tissue samples is an essential approach in cancer genetics. However, technical and biological limits exist in this approach. Microsatellite instability (MSI) is frequently observed in human tumors. MSI assays are now prevalent and regarded as commonplace. However, several technical problems have been left unsolved in the conventional assay technique. Indeed, the reported frequencies of MSI differ widely in each malignancy. An example is pancreatic cancer. Using a unique fluorescent technique, we found that MSI is extremely infrequent in this malignancy, despite the relatively high frequencies in some reports. In a series of simulations, we have demonstrated that the extremely low frequency was derived neither from less sensitive assays nor from a scarcity of cancer cells in tissue samples. Furthermore, analyzing laser-capture microdissection (LCM)-processed cell populations of a microsatellite-unstable colorectal cancer cell line, HCT116, we have shown that MSI can be detected only when comparing two cell populations that have grown independently to a sufficiently large size. When MSI is not detected in analyses using tissue samples, LCM is not advisable. We therefore did not extend our study to LCM of tissue specimens. We conclude that microsatellite sequence alterations are not detectable in human pancreatic cancer.

Role of Radiation-induced TGF-beta Signaling in Cancer Therapy

TGF-β signaling regulates several different biological processes involving cell-growth, differentiation, apoptosis, motility, angiogenesis, epithelial mesenchymal transition and extracellular matrix production that affects embryonic development and pathogenesis of various diseases, including cancer, its effects depending on the cellular context and physiological environment. Growth suppression mediated by TGF-β signaling often associated with inhibition of c-myc, cdks and induction of p15, p27, Bax and p21. Despite its growth inhibitory effect, in certain conditions TGF-β may act as a promoter of cell proliferation and invasion. Loss of responsiveness to growth suppression by TGF-β due to mutation or loss of TGF-beta type II receptor (TβRII) and Smad4 in several different cancer cells are reported. In addition, TGF-β binding to its receptor activates many non-canonical signaling pathways. Radiation induced TGF-β is primarily involved in normal tissue injury and fibrosis. Seminal studies from our group have used radio-adjuvant therapies, involving classical components of the pathway such as TβRII and SMAD4 to overcome the growth promoting effects of TGF-β. The main impediment in the radiation-induced TGF-β signaling is the induction of SMAD7 that blocks TGF-β signaling in a negative feedback manner. It is well demonstrated from our studies that the use of neutralizing antibodies against TGF- β can render a robust radio-resistant effect. Thus, understanding the functional interactions of TGF-β signaling components of the pathway with other molecules may help tailor appropriate adjuvant radio-therapeutic strategies for treatment of solid tumors.

TGFbeta modulates PTEN expression independently of SMAD signaling for growth proliferation in colon cancer cells

Signaling pathways enabling transforming growth factor-beta (TGFbeta)'s conversion from a tumor suppressor to a tumor promoter are not well characterized. TGFbeta utilizes intracellular SMADs to mediate growth suppression; however, TGFbeta-induced proliferative pathways may become more apparent when SMAD signaling is abrogated. Here, we determined regulation of the tumor suppressor PTEN by TGFbeta utilizing SMAD4-null colon cancer cells. TGFbeta downregulated PTEN mRNA and simultaneously induced growth proliferation. TGFbeta also induced both SMAD2 and SMAD3 nuclear translocation, but only triggered SMAD2-specific transcriptional activity in the absence of SMAD4. Interference of SMAD2 with DN-SMAD2 enhanced TGFbeta-induced cell proliferation, but downregulation of PTEN expression by TGFbeta was unaffected. TGFbeta increased PI3K tyrosine phosphorylation, and inhibition of PI3K pharmacologically or by DN-p85 transfection reversed both TGFbeta-induced PTEN suppression and TGFbeta-induced cell proliferation. Thus, TGFbeta activates PI3K to downregulate PTEN for enhancement of cell proliferation that is independent of SMAD proteins.

Smad4-dependent TGF-beta signaling suppresses RON receptor tyrosine kinase-dependent motility and invasion of pancreatic cancer cells

Transforming growth factorbeta (TGF-beta) signals through Smad-dependent and Smad-independent pathways. However, Smad signaling is altered by allelic deletion or intragenic mutation of the Smad4 gene in more than half of pancreatic ductal adenocarcinomas. We show here that loss of Smad4-dependent signaling leads to aberrant expression of RON, a phosphotyrosine kinase receptor, and that signaling by RON cooperates with Smad4-independent TGF-beta signaling to promote cell motility and invasion. Restoring Smad4 expression in a pancreatic ductal adenocarcinoma cell line that is deficient in Smad4 repressed RON expression. Conversely, small interference RNA knock down of Smad4 or blocking TGF-beta signaling with a TGF-beta type I receptor kinase inhibitor in Smad4-intact cell lines induced RON expression. TGF-beta-induced motility and invasion were inhibited in cells that express Smad4 and that have low levels of RON compared with isogenically matched cells that were deficient in Smad4. Furthermore, knocking down RON expression in Smad4-deficient cells suppressed TGF-beta-mediated motility and invasion. We further determined that Smad4-dependent signaling regulated RON expression at the transcriptional level by real-time reverse transcription PCR and RON promoter luciferase reporter assays. Functional inactivation by site-directed mutations of two Smad binding sites on the RON promoter inhibited TGF-beta-mediated repression of RON promoter activity. These studies indicate that loss of Smad4 contributes to aberrant RON expression and that cross-talk of Smad4-independent TGF-beta signaling and the RON pathway promotes an invasive phenotype.

Signal transduction pathway through activin receptors as a therapeutic target of musculoskeletal diseases and cancer

Activin, myostatin and other members of the TGF-beta superfamily signal through a combination of type II and type I receptors, both of which are transmembrane serine/threonine kinases. Activin type II receptors, ActRIIA and ActRIIB, are primary ligand binding receptors for activins, nodal, myostatin and GDF11. ActRIIs also bind a subset of bone morphogenetic proteins (BMPs). Type I receptors that form complexes with ActRIIs are dependent on ligands. In the case of activins and nodal, activin receptor-like kinases 4 and 7 (ALK4 and ALK7) are the authentic type I receptors. Myostatin and GDF11 utilize ALK5, although ALK4 could also be activated by these growth factors. ALK4, 5 and 7 are structurally and functionally similar and activate receptor-regulated Smads for TGF-beta, Smad2 and 3. BMPs signal through a combination of three type II receptors, BMPRII, ActRIIA, and ActRIIB and four type I receptors, ALK1, 2, 3, and 6. BMPs activate BMP-specific Smads, Smad1, 5 and 8. Smad proteins undergo multimerization with co-mediator Smad, Smad4, and translocated into the nucleus to regulate the transcription of target genes in cooperation with nuclear cofactors. The signal transduction pathway through activin type II receptors, ActRIIA and ActRIIB, with type I receptors is involved in various human diseases. In this review, we discuss the role of signaling through activin receptors as therapeutic targets of intractable neuromuscular diseases, endocrine disorders and cancers.

Smad4 is dispensable for normal pancreas development yet critical in progression and tumor biology of pancreas cancer

SMAD4 is inactivated in the majority of pancreatic ductal adenocarcinomas (PDAC) with concurrent mutational inactivation of the INK4A/ARF tumor suppressor locus and activation of the KRAS oncogene. Here, using genetically engineered mice, we determined the impact of SMAD4 deficiency on the development of the pancreas and on the initiation and/or progression of PDAC-alone or in combination with PDAC--relevant mutations. Selective SMAD4 deletion in the pancreatic epithelium had no discernable impact on pancreatic development or physiology. However, when combined with the activated KRAS(G12D) allele, SMAD4 deficiency enabled rapid progression of KRAS(G12D)-initiated neoplasms. While KRAS(G12D) alone elicited premalignant pancreatic intraepithelial neoplasia (PanIN) that progressed slowly to carcinoma, the combination of KRAS(G12D) and SMAD4 deficiency resulted in the rapid development of tumors resembling intraductal papillary mucinous neoplasia (IPMN), a precursor to PDAC in humans. SMAD4 deficiency also accelerated PDAC development of KRAS(G12D) INK4A/ARF heterozygous mice and altered the tumor phenotype; while tumors with intact SMAD4 frequently exhibited epithelial-to-mesenchymal transition (EMT), PDAC null for SMAD4 retained a differentiated histopathology with increased expression of epithelial markers. SMAD4 status in PDAC cell lines was associated with differential responses to transforming growth factor-beta (TGF-beta) in vitro with a subset of SMAD4 wild-type lines showing prominent TGF-beta-induced proliferation and migration. These results provide genetic confirmation that SMAD4 is a PDAC tumor suppressor, functioning to block the progression of KRAS(G12D)-initiated neoplasms, whereas in a subset of advanced tumors, intact SMAD4 facilitates EMT and TGF-beta-dependent growth.

Truncating mutations in the ACVR2 gene attenuates activin signaling in prostate cancer cells

Activins are classified as members of the TGFbeta superfamily of signaling molecules and both activin and TGFbeta ligands signal through structurally and functionally related serine/threonine kinase receptors. Defects in these signaling pathways have been associated with the initiation and progression of the cancer phenotype. Inactivating mutations in the TGFbeta type II receptor gene, TGFbetaR2, have been identified in a variety of tumors and cell lines, particularly those with microsatellite instability (MSI). More recently, mutations in the activin type II receptor gene, ACVR2, were identified in colon and pancreatic cell lines and tumors with MSI. Because prostate tumors appear to have a high incidence of MSI, we analyzed prostate cancer cell lines, with and without MSI, for ACVR2 and TGFbetaR2 mutations. Our analysis of 6 prostate cell lines revealed mutations in the ACVR2 gene in 22Rv-1, LAPC-4, DU145, and LNCaP cells and mutations in the TGFbetaR2 gene in 22Rv-1 and LAPC-4. PC3 and H660 cells were wild-type for ACVR2 and TFGbetaR2. All of the ACVR2 mutations were truncating mutations, and using an activin response assay, we demonstrate that truncating mutations of the ACVR2 gene result in a significant reduction in activin mediated cell signaling. Inactivation of ACVR2 is a common event in prostate cancer cells suggesting it may play an important role in the development of prostate cancer.

Defective DNA mismatch repair in long-term (> or =3 years) survivors with pancreatic cancer

BACKGROUND/AIMS

Defective DNA mismatch repair (MMR) in pancreatic cancer, reported in up to 13% of sporadic pancreatic cancers, may predict a good prognosis. To determine if long-term survival in pancreatic cancer could be attributed to defective DNA MMR, we ascertained its prevalence in 35 pancreatic cancer patients who survived > or =3 years after surgery.

METHODS

We performed immunohistochemistry (IHC) for MMR proteins hMLH1, hMSH2, and hMSH6 in all 35 tumors and microsatellite instability (MSI) studies in 34/35 tumors using 10 microsatellite markers in paired normal and tumor DNA. Defective DNA MMR was defined as absence of protein expression on IHC and/or MSI in > or =30% of markers studied.

RESULTS

On IHC, 3/35 (8.6%) tumors had defective DNA MMR. All 3 had absent expression of a DNA MMR protein (hMLH1 in 2 and hMSH2) and 2/3 also had MSI; the third could not be tested. Definitely 2, and probably all 3 patients had hereditary nonpolyposis colon cancer as determined by clinical and genetic profiles.

CONCLUSION

Defective DNA MMR is uncommon in long-term survivors of pancreatic cancer and does not account for the survival benefit in those with sporadic pancreatic cancer.

Trichostatin A induces transforming growth factor beta type II receptor promoter activity and acetylation of Sp1 by recruitment of PCAF/p300 to a Sp1.NF-Y complex

Transforming growth factor beta type II receptor (TbetaRII) is a tumor suppressor gene that can be transcriptionally silenced by histone deacetylases (HDACs) in cancer cells. In this report, we demonstrated the mechanism by which trichostatin A (TSA), an inhibitor of HDAC, induces the expression of TbetaRII in human pancreatic cancer cell lines by modulating the transcriptional components that bind a specific DNA region of the TbetaRII promoter. This region of the TbetaRII promoter possesses Sp1 and NF-Y binding sites in close proximity (located at -102 and -83, respectively). Treatment of cells with TSA activates the TbetaRII promoter in a time-dependent manner through the recruitment of p300 and PCAF into a Sp1.NF-Y.HDAC complex that binds this DNA element. The recruitment of p300 and PCAF into the complex is associated with a concomitant acetylation of Sp1 and an overall decrease in the amount of HDAC associated with the complex. Transient overexpression of p300 or PCAF potentiated TSA-induced TbetaRII promoter activity. The effect of PCAF was dependent on its histone acetyltransferase activity, whereas that of p300 was independent. Stable transfection of PCAF caused an increase in TbetaRII mRNA expression, the association of PCAF with TbetaRII promoter, and the acetylation of Sp1. Taken together, these results showed that TSA treatment of pancreatic cancer cells leads to transcriptional activation of the TbetaRII promoter through modulation of the components of a Sp1.NF-Y.p300.PCAF.HDAC-1 multiprotein complex. Moreover, the interaction of NF-Y with the Sp1-associated complex may further explain why this specific Sp1 site mediates transcriptional responsiveness to TSA.

Uterine sarcomas express KIT protein but lack mutation(s) in exon 11 or 17 of c-KIT

OBJECTIVE

Several tumors express the protein product of the protooncogene c-KIT. Some of these respond to imatinib mesylate, a tyrosine kinase inhibitor. The tumors that respond frequently have mutation(s) in exon 11 of c-KIT that encodes for the regulatory juxtamembrane helix. Some tumors that express KIT protein have mutation(s) in exon 17 of c-KIT; however, these do not respond to imatinib mesylate. This investigation was performed to determine the expression of KIT protein and mutational status of exons 11 and 17 of c-KIT in uterine sarcomas.

METHODS

Twenty-five uterine sarcomas treated from 1990 to 2002 were evaluated. These included 14 malignant mullerian mixed tumors (MMMT), 7 leiomyosarcomas (LMS), 2 endometrial stromal sarcomas (ESS), and 2 high-grade heterologous sarcomas (HGHS). Formalin-fixed, paraffin-embedded tissue sections were immunostained with anti-KIT antibody (Santa Cruz Biotechnology, Santa Cruz, CA) with a semiquantitative assessment. Normal myometrium when present in the section was used as an internal negative control. Areas of tumor were microdissected followed by DNA extraction, polymerase chain reaction (PCR) amplification of exons 11 and 17, single-strand conformational polymorphism (SSCP), and DNA sequencing to detect the presence of mutation(s).

RESULTS

All 25 tumors expressed KIT protein at varying levels as assessed by immunohistochemistry. The staining was diffuse and of moderate to strong intensity in 22 tumors. In three tumors (one of each type except MMMT) the staining intensity was weak. In MMMT the epithelial and sarcomatous foci stained similarly. No mutation(s) in exons 11 or 17 of c-KIT were identified in 24/25 tumors. One LMS had deletion of both exons 11 and 17.

CONCLUSIONS

Although uterine sarcomas express KIT protein, they lack KIT-activating mutation(s) in exon 11 or 17 of c-KIT. Therefore, these tumors are unlikely to respond to imatinib mesylate.

Rap1 reverses transcriptional repression of TGF-beta type II receptor by a mechanism involving AP-1 in the human pancreatic cancer cell line, UK Pan-1

The TGF-beta signaling pathway has potent anti-mitogenic effects in epithelial cells and loss of negative growth regulation is often associated with increased tumorigenicity. The human pancreatic ductal adenocarcinoma cell line, UK Pan-1, which expresses DPC4, is not highly responsive to TGF-beta due to transcriptional repression of TGF-beta type II receptor (RII). Here, we show that UK Pan-1 cells transfected with a plasmid to overexpress rap1 protein (UK/rap1) causes an increase in RII transcription and restores sensitivity to TGF-beta growth inhibition. The overexpression of rap1 was associated with diminished ras signaling as measured by ras binding domain (RBD)-binding assays. Electrophoretic mobility shift assays (EMSA) analysis revealed increased binding of nuclear proteins to a previously identified positive regulatory element (PRE1) of the RII promoter in rap1 transfected cells. Competition with an oligo containing the AP-1 consensus site was able to inhibit this binding of nuclear proteins to the PRE1 region. Further EMSA analysis using antibodies to various AP-1 components revealed that junB antibodies partially depleted the increase in binding to the PRE1 seen in UK/rap1 cells while antibodies to other AP-1 constituents such as c-jun, c-fos, and ATF-1 had no effect on binding. Consistent with this data, transient transfection of UK Pan-1 cells with junB resulted in greater RII transcription (twofold) as measured by RII-luciferase assay. Mutation of the AP-1 site inhibited junB-mediated or rap1-mediated increases in RII promoter activity. These data suggest that rap1 signaling may mediate an increase in RII transcription via increased binding of nuclear factors including junB to the PRE1 region of the RII promoter.

Absence of mutations in the transforming growth factor-beta inducible early gene 1, TIEG1, in pancreatic cancer

Pancreatic cancers frequently have defects in components of the transforming growth factor-beta (TGF-beta) signaling pathway. TIEG1 (TGF-beta inducible early gene) is a recently characterized transcription factor regulated by TGF-beta that induces apoptosis when overexpressed in pancreatic adenocarcinoma cell lines. Alterations on chromosome 8q, where TIEG1 is located, are also relatively frequent in pancreatic cancers. To determine if TIEG1 may be involved in the tumorigenesis of pancreatic cancer, we performed mutational screening of this gene in 22 pancreatic cancer cell lines. No sequence alterations were observed. Reverse transcription-polymerase chain reaction analysis was also performed to rule out the possibility that the expression of the gene is altered by genetic events other than mutation. Likewise, no alterations in expression were found. Thus, an essential role of TIEG1 in pancreatic cancer can be excluded.

RhoB, not RhoA, represses the transcription of the transforming growth factor beta type II receptor by a mechanism involving activator protein 1

The transforming growth factor-beta (TGF-beta) type I (T beta R-I) and type II (T beta R-II) receptors are responsible for transducing TGF-beta signals. We have previously shown that inhibition of farnesyltransferase activity results in an increase in T beta R-II expression, leading to enhanced TGF-beta binding, signaling, and inhibition of tumor cell growth, suggesting that a farnesylated protein(s) exerts a repressive effect on T beta R-II expression. Likely candidates are farnesylated proteins such as Ras and RhoB, which are both farnesylated and involved in cell growth control. Neither a dominant negative Ha-Ras, constitutively activated Ha-Ras, or a pharmacological inhibitor of MEK1 affected T beta R-II transcription. However, ectopic expression of RhoB, but not the closely related family member RhoA, resulted in a 5-fold decrease of T beta R-II promoter activity. Furthermore, ectopic expression of RhoB, but not RhoA, resulted in a significant decrease of T beta R-II protein expression and resistance of tumor cells to TGF-beta-mediated cell growth inhibition. Deletion analysis of the T beta R-II promoter identified a RhoB-responsive region, and mutational analysis of this region revealed that a site for the transcription factor activator protein 1 (AP1) is critical for RhoB-mediated repression of T beta R-II transcription. Electrophoretic mobility shift assays clearly showed that the binding of AP1 to its DNA-binding site is strongly inhibited by RhoB. Consequently, transcription assays using an AP1 reporter showed that AP1-mediated transcription is down-regulated by RhoB. Altogether, these results identify a mechanism by which RhoB antagonizes TGF-beta action through transcriptional down-regulation of AP1 in T beta R-II promoter.

Restoration of transforming growth factor-beta signaling enhances radiosensitivity by altering the Bcl-2/Bax ratio in the p53 mutant pancreatic cancer cell line MIA PaCa-2

In this study, we investigated whether lack of transforming growth factor beta (TGF-beta) type II receptor (RII) expression and loss of TGF-beta signaling played a role in radiation resistance of pancreatic cancer cells MIA PaCa-2 that possess a mutated p53 gene. Transfection of this cell line with a RII cDNA led to a stimulation of the transcriptional activity of p3TP-Lux, a TGF-beta-responsive reporter construct. The RII transfectants (MIA PaCa-2/RII) showed a significant increase in sensitivity to radiation when compared with MIA PaCa-2/vector cells. The increase in sensitivity to radiation was reversed by neutralizing antibodies to TGF-beta, indicating that these changes were dependent on TGF-beta signaling. Compared with MIA PaCa-2/vector cells, MIA PaCa-2/RII cells showed a greater than 3-fold increase in apoptosis after radiation. Enhanced radiation sensitivity of MIA PaCa-2/RII cells was associated with an induction of Bax mRNA and protein that was followed by a release of cytochrome c and activation of caspase-3 and poly(ADP-ribose) polymerase cleavage after radiation exposure. Overexpression of Bcl-x(L) or treatment with antisense oligodeoxynucleotides targeted against Bax significantly inhibited radiation-induced apoptosis in MIA PaCa-2/RII but not in MIA PaCa-2/Vector cells, suggesting that Bax induction is necessary for radiation-induced TGF-beta signaling-mediated apoptosis. Thus, restoration of TGF-beta signaling sensitized these cells to ionizing radiation, although these cells possess a mutated p53 gene. In addition, disruption of RII function by dominant negative mutant of RII inhibited the radiation-induced TGF-beta signaling and apoptosis in primary cultures of mouse embryonic fibroblasts. Together, these observations imply that RII is an important component of radiation-induced TGF-beta signaling, and loss of function of RII may enhance resistance to radiation-induced apoptosis.

Early growth response-1 gene: potential radiation response gene marker in prostate cancer

This study was undertaken to determine whether the transcription factor EGR-1 expression: (1) in the primary tumor, correlates with radiation response in terms of complete local tumor control with no evidence of disease or recurrence and no evidence of metastasis; (2) in the postirradiated biopsies correlates with residual tumor; and (3) correlates with the expression of Egr-1 target genes such as TP53, pRB, and Bax. The authors analyzed: (1) 25 pretreated surgically resected paraffin-embedded primary adenocarcinomas of the prostate for the presence of EGR-1 expression and mutation, and correlated this with clinical endpoints such as serum prostate-specific antigen levels and current clinical status; (2) 27 postirradiated biopsies of prostate for the presence of EGR-1 expression, and correlated these findings to the residual tumor status; and (3) 12 prospective prostate tumor specimens for EGR-1 expression and its target genes. EGR-1 expression was determined by immunohistochemistry and mutations were screened in two regions of the Egr-1 gene (trinucleotide AGC repeats in transactivation domain [TD] and poly A tract in 3'UTR) by polymerase chain reaction-single strand conformational polymorphism analysis. Of 25 patients, 18 patients showed expression of EGR-1. EGR-1 overexpression correlated with treatment failure. No correlation with EGR-1 overexpression and its target genes was found, which may indirectly suggest that overexpressed EGR-1 may lack transactivation function. In summary, EGR-1 overexpression in the mutant form may provide an indication of clinical failure (local recurrence or metastasis).

Combined copy status of 18q21 genes in colorectal cancer shows frequent retention of SMAD7

Deletions of chromosome band 18q21 appear with very high frequency in a variety of carcinomas, especially in colorectal cancer. Potent tumor suppressor genes located in this region encode transforming growth factor beta (TGF-beta) signal transducers SMAD2 and SMAD4, and inactivation of either one leads to impaired TGF-beta-mediated cell growth/apoptosis. Following the assignment of SMAD7 to 18q21, we first refined the SMAD7 gene position within this region by genetically mapping SMAD7 between SMAD2 and SMAD4. Further, to compare the respective frequencies of genetic alterations of these three SMAD genes in colorectal cancer, we undertook a large-scale evaluation of the copy status of each of these genes on DNA samples from colorectal tumor biopsy material. Among a subset of 233 DNA samples for which data were available for all four genes, SMAD4, SMAD2, and the nearby gene DCC showed high deletion rates (66%, 64%, and 59%, respectively), whereas SMAD7 was deleted in only 48% of the tumors. Unexpectedly, we found some gene duplications; SMAD7 appears to be more frequently amplified (10%) than the three other genes (4-7%). Compiled data for SMAD genes in each tumor show that the most common combination (26% of all the tumors) consists of the simultaneous deletions of SMAD2 and SMAD4 associated with normal diploidy or even duplication of SMAD7. Since SMAD7 normally counteracts SMAD2 and SMAD4 in TGF-beta signaling, we hypothesize that the tumor might not benefit from simultaneous SMAD7 inactivation, thereby exerting selective pressure to retain or even to duplicate the SMAD7 gene.

Adenovirus-mediated gene transfer of dominant-negative Smad4 blocks TGF-beta signaling in pancreatic acinar cells

Transforming growth factor-beta (TGF-beta) is a potent inhibitor of pancreatic acinar cell growth. Smad4 is a central mediator in the TGF-beta signaling pathway. To study the effect of Smad4 on pancreatic growth, cell cycle protein expression, and the expression of a TGF-beta-responsive promoter in vitro, we constructed an adenovirus containing dominant-negative COOH terminal truncated Smad4 (AddnSmad4) downstream of the rat elastase promoter. Acinar cells expressed dominant-negative Smad4 within 8 h after infection, and expression persisted for 72 h. Mouse pancreatic acini were infected with either AddnSmad4 or control adenovirus expressing green fluorescent protein, and TGF-beta was added 8 h after infection. Acinar cells were then incubated for 1, 2, or 3 days, and [(3)H]thymidine incorporation was determined. AddnSmad4 significantly reduced TGF-beta inhibition of [(3)H]thymidine incorporation, with maximal effects on day 3. AddnSmad4 also completely blocked TGF-beta-mediated growth inhibition in the presence of basic fibroblast growth factor. We next examined the effects of AddnSmad4 on TGF-beta-induced expression of the cell cycle regulatory proteins p21(Cip1) and p27(Kip1). TGF-beta induced upregulation of p21(Cip1), which was completely blocked by AddnSmad4. AddnSmad4 also inhibited TGF-beta-induced expression of the TGF-beta-responsive luciferase reporter 3TP-Lux. These results show that Smad4 is essential in TGF-beta-mediated signaling in pancreatic acinar cells.

The role of genetic factors in the etiology of pancreatic adenocarcinoma: an update

Pancreatic cancer is a disease with a very poor prognosis and its etiology is still largely elusive. The only consistent environmental risk factor is cigarette smoking. A previous history of pancreatitis or diabetes mellitus is also considered to be a risk factor. Epidemiological studies have confirmed that relatives of those with pancreatic cancer have an increased risk of this malignancy, and it has been evaluated that 3-5% of all pancreatic cancer cases are caused by genetic predisposition to the disease. Usually this occurs in the setting of a known inherited cancer syndrome caused by mutations in genes such as BRCA1/2 and CDKN2A. Whether or not a true site-specific pancreatic adenocarcinoma syndrome exists is not known. The real challenge for the management of high risk patients is to develop new screening methods than can identify pre-neoplastic or early neoplastic lesions in a timely manner.

Role of TGFbeta signaling in skin carcinogenesis

The TGFbeta signaling pathway is one of the most important mechanisms in the maintenance of epithelial homeostasis. Alterations leading to either the repression or enhancement of this pathway have been shown to affect cancer development. Although TGFbeta inhibits growth of normal epithelial cells, it is paradoxically overexpressed in many epithelial cancers. It has been postulated that TGFbeta acts as a tumor suppressor at the early stages of carcinogenesis, but overexpression of TGFbeta at late stages of carcinogenesis may be a critical factor for tumor invasion and metastasis. The detailed mechanisms regulating this functional switch of TGFbeta remain to be elucidated. The relevance of the TGFbeta signaling pathway to the development of primary epithelial tumors in man has been further substantiated by the discovery of mutations in TGFbeta receptors and in the downstream signaling mediators, the Smads. The epidermis is one of the major targeting tissues for TGFbeta signaling. Chemical carcinogenesis studies have revealed a paradoxical effect of TGFbeta on skin carcinogenesis: inhibition of papilloma formation but promotion of malignant conversion. In addition, deletion of the TGFbeta type II receptor accelerates skin carcinogenesis. This review focuses on our current understanding of the role of TGFbeta signaling in skin carcinogenesis.

Aberrant cell cycle progression contributes to the early-stage accelerated carcinogenesis in transgenic epidermis expressing the dominant negative TGFbetaRII

Mutations in the transforming growth factor beta type II receptor (TGFbetaRII) have been found in various malignant tumors, suggesting that loss of TGFbeta signaling plays a causal role in late-stage cancer development. To test whether loss of TGFbetaRII is involved in early-stage carcinogenesis, we have generated transgenic mice expressing a dominant negative TGFbetaRII (deltabetaRII) in the epidermis. These mice exhibited an increased susceptibility to chemical carcinogenesis protocols at both early and late stages. In the current study, parameters for cell cycle progression and chromosome instability were analysed in deltabetaRII tumors. DeltabetaRII papillomas showed an increased S phase in flow cytometry. Bromodeoxyuridine (BrdU) labeling and mitotic indices in deltabetaRII papillomas also showed a threefold increase compared to papillomas developing in non-transgenic mice. When papillomas further progressed to squamous cell carcinomas (SCC), both control and deltabetaRII SCC showed similar BrdU labeling indices and percentages of S phase cells. However, deltabetaRII SCC cells showed a sixfold increase in the G2/M population. Mitotic indices in deltabetaRII SCC also showed a threefold increase compared to non-transgenic SCC. Consistent with a perturbed cell cycle, deltabetaRII papillomas and SCC showed reduced expression of the TGFbeta target genes p15 (INK4b), p21 (WAF-1) and p27 (Kip1), inhibitors of cyclin-dependent kinases (cdks). However, most deltabetaRII papilloma cells exhibited normal centrosome numbers, and deltabetaRII SCC exhibited a similar extent of centrosome abnormalities compared to control SCC (35-40% cells). Most of deltabetaRII SCC exhibited diploid chromosome profiles. These data indicate that inactivation of TGFbetaRII accelerates skin tumorigenesis at early stages by the acceleration of loss of cell cycle control, but not by increased chromosome instability.

Characterization of a newly established human pancreatic carcinoma cell line, UK Pan-1

BACKGROUND

A highly tumorigenic cell line designated as UK Pan-1 was established in a surgically removed human pancreatic adenocarcinoma and characterized as having many of the genotypic and phenotypic alterations commonly found in pancreatic tumors.

METHODS

The cell line was characterized by its morphology, growth rate in monolayer culture and soft agar, tumorigenicity in nude mice, and chromosomal analysis. Furthermore, the status of p53, Ki-ras mutation and transforming growth factor (TGF)-/receptor expression were determined. The characteristics of UK Pan-1 were compared with those of other commonly used pancreatic carcinoma cell lines.

RESULTS

Quiescent UK Pan-1 cells could be stimulated to proliferate in growth factor free nutrient media, indicating a growth factor independent phenotype. UK Pan- 1 cells grew in soft agar and rapidly formed tumors in nude mice. This cell line possesses a mutation at codon 12 of the c-Ki-ras-2 gene that is commonly found in pancreatic carcinoma. Fluorescence in situ hybridization showed that two alleles of p53 tumor suppressor gene were present in UK Pan-1. However, sequencing analysis revealed a mutation in one allele at exon 8, codon 273 (G to A; Arg to His). Additional growth assays indicated that the cell line was insensitive to negative growth regulation induced by exogenous TGF-beta. Molecular analysis of the TGF-beta signaling pathway showed that UK Pan-1 did not express appreciable levels of the TGF-beta receptor type I, II, or III mRNAs, but did express DPC4 mRNA. Karyotype analysis revealed an 18q21 deletion indicating a possible loss of heterozygosity for DPC4, as well as other chromosomal deletions and rearrangements.

CONCLUSIONS

This study indicates that UK Pan-1 is a highly tumorigenic cell line possessing a molecularly complex pattern of mutations that may be used as a model to further the understanding of the mechanisms responsible for the development of pancreatic carcinoma.

TIEG proteins join the Smads as TGF-beta-regulated transcription factors that control pancreatic cell growth

The control of epithelial cell proliferation, differentiation, and apoptosis requires a balance between signaling and transcriptional regulation. Recent developments in pancreatic cell research have revealed that transforming growth factor-beta (TGF-beta) signaling is important for the regulation of each of these phenomena. More importantly, perturbations in this pathway are associated with pancreatic cancer. A chief example of these alterations is the mutation in the TGF-beta-regulated transcription factor Smad4/DPC4 that is found in a large percentage of pancreatic tumors. Surprisingly, studies on transcription factors have remained an underrepresented area of pancreatic research. However, the discovery of Smad4/DPC4 as a transcription factor fueled further studies aimed at characterizing transcription factors involved in normal and neoplastic pancreatic cell growth. Our laboratory recently described the existence of a novel family of zinc finger transcription factors, TGF-beta-inducible early-response gene (TIEG)1 and TIEG2, from the exocrine pancreas that, similarly to Smads, participate in the TGF-beta response and inhibit epithelial cell proliferation. This review therefore focuses on describing the structure and function of these two families of transcription factor proteins that are becoming key players in the regulation of pancreatic cell growth.

Transforming growth factor-beta and breast cancer: Transforming growth factor-beta/SMAD signaling defects and cancer

Transforming growth factor-beta (TGF-beta) is a tumor suppressor, the function of which is compromised in many types of human cancer, including breast cancer. The tumor suppressive effects of TGF-beta are caused by potent inhibition of cell proliferation due to cell cycle arrest in the G1 phase. Such antiproliferative responses are mediated by a signaling system that includes two types of cell surface receptors and intracellular signal transducers, the SMAD proteins. Different molecular mechanisms can lead to loss of antiproliferative TGF-beta responses in tumor cells, including mutations in components of the signaling system and inhibition of the SMAD signaling pathway by aberrant activities of various regulatory molecules. Some of these mechanisms will be discussed, with emphasis on their potential involvement in breast tumorigenesis.

The TGF-beta signaling inhibitor Smad7 enhances tumorigenicity in pancreatic cancer

Transforming growth factor-beta (TGF-beta) signaling is dependent on the heterodimerization of the type II TGF-beta receptor (TbetaRII) with the type I TGF-beta receptor (TbetaRI). Activated TbetaRI then mediates TGF-beta signals by inducing the phosphorylation of Smad2 and/or Smad3, which separately hetetorodimerize with Smad4 and translocate to the nucleus. Phosphorylation of Smad2/Smad3 by activated TbetaRI is inhibited by two newly discovered members of the Smad family, Smad6 and Smad7. We now report that Smad7 mRNA levels are increased in human pancreatic cancer by comparison with the normal pancreas, and that by in situ hybridization, Smad7 is over-expressed in the cancer cells within the tumor mass. Stable transfection of COLO-357 human pancreatic cancer cells with a full-length Smad7 construct leads to complete loss of the growth inhibitory response to TGF-beta1, without altering TGF-beta1-mediated induction of PAI-I. Furthermore, Smad7 transfected COLO-357 cells display enhanced anchorage-independent growth and accelerated growth in nude mice. These findings point to a previously unrecognized mechanism for selective suppression of TGF-beta-mediated growth inhibition in cancer cells that allows for continued activation of the PAI-I promoter by TGF-beta1, which may act to enhance the tumorigenicity of certain cancer cells.

Molecular genetics and related developments in pancreatic cancer

Cancer of the pancreas is a genetic disease. The most common genetic alterations identified to date in pancreatic cancer are activation of the K-ras oncogene (approximately 90%) and inactivation of the p16 (approximately 95%), p53 (50% to 75%), DPC4 (55%), and BRCA2 (7%) tumor suppressor genes. An understanding of the molecular genetics of carcinoma of the pancreas is important because it may help explain the aggregation of pancreatic cancer in families and may lead to the development of novel tests to detect early cancers. For example, the aggregation of pancreatic cancer in some families has been shown to result from inherited mutations in cancer-causing genes, and genetic alterations shed from pancreatic cancers have been detected in stool specimens. In addition, we believe that an improved knowledge of the molecular genetics of pancreatic cancer will lead to the development of a new generation of rational and more effective treatments.