Loss of one p53 allele results in four-fold reduction of p53 mRNA and protein: a basis for p53 haplo-insufficiency

Autophagy suppression in DNA damaged cells occurs through a newly identified p53-proteasome-LC3 axis

Macroautophagy is thought to have a critical role in shaping and refining cellular proteostasis in eukaryotic cells recovering from DNA damage. Here, we report a mechanism by which autophagy is suppressed in cells exposed to bacterial toxin-, chemical-, or radiation-mediated sources of genotoxicity. Autophagy suppression is directly linked to cellular responses to DNA damage, and specifically the stabilization of the tumor suppressor p53, which is both required and sufficient for regulating the ubiquitination and proteasome-dependent reduction in cellular pools of microtubule-associated protein 1 light chain 3 (LC3A/B), a key precursor of autophagosome biogenesis and maturation, in both epithelial cells and an ex vivo organoid model. Our data indicate that suppression of autophagy, through a newly identified p53-proteasome-LC3 axis, is a conserved cellular response to multiple sources of genotoxicity. Such a mechanism could potentially be important for realigning proteostasis in cells undergoing DNA damage repair.

Single loss of a Trp53 allele triggers an increased oxidative, DNA damage and cytokine inflammatory responses through deregulation of IκBα expression

Dose of Trp53, the main keeper of genome stability, influences tumorigenesis; however, the causes underlying and driving tumorigenesis over time by the loss of a single p53 allele are still poorly characterized. Here, we found that single p53 allele loss specifically impacted the oxidative, DNA damage and inflammatory status of hematopoietic lineages. In particular, single Trp53 allele loss in mice triggered oxidative stress in peripheral blood granulocytes and spleenocytes, whereas lack of two Trp53 alleles produced enhanced oxidative stress in thymus cells, resulting in a higher incidence of lymphomas in the Trp53 knockout (KO) mice compared with hemizygous (HEM). In addition, single or complete loss of Trp53 alleles, as well as p53 downregulation, led to a differential increase in basal, LPS- and UVB-induced expression of a plethora of pro-inflammatory cytokine, such as interleukin-12 (Il-12a), TNFα (Tnfa) and interleukin (Il-23a) in bone marrow-derived macrophage cells (BMDMs) compared to WT cells. Interestingly, p53-dependent increased inflammatory gene expression correlated with deregulated expression of the NF-κB pathway inhibitor IκBα. Chromatin immunoprecipitation data revealed decreased p65 binding to Nfkbia in the absence of p53 and p53 binding to Nfkbia promoter, uncovering a novel crosstalk mechanism between p53 and NF-κB transcription factors. Overall, our data suggest that single Trp53 allele loss can drive a sustained inflammatory, DNA damage and oxidative stress response that, over time, facilitate and support carcinogenesis.

The impact of p53 function on the metabolic activation of the carcinogenic air pollutant 3-nitrobenzanthrone and its metabolites 3-aminobenzanthrone and N-hydroxy-3-aminobenzanthrone in human cells

The tumour suppressor p53, encoded by TP53, is a key player in a wide network of signalling pathways. We investigated its role in the bioactivation of the environmental carcinogen 3-nitrobenzanthrone (3-NBA)found in diesel exhaust and its metabolites 3-aminobenzanthrone (3-ABA) and N-hydroxy-3-aminobenzanthrone (N-OH-3-ABA) in a panel of isogenic human colorectal HCT116 cells differing only with respect to their TP53 status [i.e. TP53(+/+), TP53(+/-), TP53(-/-), TP53(R248W/+) or TP53(R248W/-)]. As a measure of metabolic competence, DNA adduct formation was determined using 32P-postlabelling. Wild-type (WT) p53 did not affect the bioactivation of 3-NBA; no difference in DNA adduct formation was observed in TP53(+/+), TP53(+/-) and TP53(-/-) cells. Bioactivation of both metabolites 3-ABA and N-OH-3-ABA on the other hand was WT-TP53 dependent. Lower 3-ABA- and N-OH-3-ABA-DNA adduct levels were found in TP53(+/-) and TP53(-/-) cells compared to TP53(+/+) cells, and p53's impact was attributed to differences in cytochrome P450 (CYP) 1A1 expression for 3-ABA whereas for N-OH-3-ABA, an impact of this tumour suppressor on sulphotransferase (SULT) 1A1/3 expression was detected. Mutant R248W-p53 protein function was similar to or exceeded the ability of WT-p53 in activating 3-NBA and its metabolites, measured as DNA adducts. However, identification of the xenobiotic-metabolising enzyme(s) (XMEs), through which mutant-p53 regulates these responses, proved difficult to decipher. For example, although both mutant cell lines exhibited higher CYP1A1 induction after 3-NBA treatment compared to TP53(+/+) cells, 3-NBA-derived DNA adduct levels were only higher in TP53(R248W/-) cells but not in TP53(R248W/+) cells. Our results show that p53's influence on carcinogen activation depends on the agent studied and thereby on the XMEs that mediate the bioactivation of that particular compound. The phenomenon of p53 regulating CYP1A1 expression in human cells is consistent with other recent findings; however, this is the first study highlighting the impact of p53 on sulphotransferase-mediated (i.e. SULT1A1) carcinogen metabolism in human cells.

A novel mouse model of rhabdomyosarcoma underscores the dichotomy of MDM2-ALT1 function in vivo

Alternative splicing of the oncogene murine double minute 2 (MDM2) is induced in response to genotoxic stress. MDM2-ALT1, the major splice variant generated, is known to activate the p53 pathway and impede full-length MDM2's negative regulation of p53. Despite this perceptible tumor-suppressive role, MDM2-ALT1 is also associated with several cancers. Furthermore, expression of MDM2-ALT1 has been observed in aggressive metastatic disease in pediatric rhabdomyosarcoma (RMS), irrespective of histological subtype. Therefore, we generated a transgenic MDM2-ALT1 mouse model that would allow us to investigate the effects of this splice variant on the progression of tumorigenesis. Here we show that when MDM2-ALT1 is ubiquitously expressed in p53 null mice it leads to increased incidence of spindle cell sarcomas, including RMS. Our data provide evidence that constitutive MDM2-ALT1 expression is itself an oncogenic lesion that aggravates the tumorigenesis induced by p53 loss. On the contrary, when MDM2-ALT1 is expressed solely in B-cells in the presence of homozygous wild-type p53 it leads to significantly increased lymphomagenesis (56%) when compared with control mice (27%). However, this phenotype is observable only at later stages in life (⩾18 months). Moreover, flow cytometric analyses for B-cell markers revealed an MDM2-ALT1-associated decrease in the B-cell population of the spleens of these animals. Our data suggest that the B-cell loss is p53 dependent and is a response mounted to persistent MDM2-ALT1 expression in a wild-type p53 background. Overall, our findings highlight the importance of an MDM2 splice variant as a critical modifier of both p53-dependent and -independent tumorigenesis, underscoring the complexity of MDM2 posttranscriptional regulation in cancer. Furthermore, MDM2-ALT1-expressing p53 null mice represent a novel mouse model of fusion-negative RMS.

Loss of LZAP inactivates p53 and regulates sensitivity of cells to DNA damage in a p53-dependent manner

Chemotherapy and radiation, the two most common cancer therapies, exert their anticancer effects by causing damage to cellular DNA. However, systemic treatment damages DNA not only in cancer, but also in healthy cells, resulting in the progression of serious side effects and limiting efficacy of the treatment. Interestingly, in response to DNA damage, p53 seems to play an opposite role in normal and in the majority of cancer cells—wild-type p53 mediates apoptosis in healthy tissues, attributing to the side effects, whereas mutant p53 often is responsible for acquired cancer resistance to the treatment. Here, we show that leucine zipper-containing ARF-binding protein (LZAP) binds and stabilizes p53. LZAP depletion eliminates p53 protein independently of its mutation status, subsequently protecting wild-type p53 cells from DNA damage-induced cell death, while rendering cells expressing mutant p53 more sensitive to the treatment. In human non-small-cell lung cancer, LZAP levels correlated with p53 levels, suggesting that loss of LZAP may represent a novel mechanism of p53 inactivation in human cancer. Our studies establish LZAP as a p53 regulator and p53-dependent determinative of cell fate in response to DNA damaging treatment.

Clinicopathological and prognostic significance of survivin expression in renal cancer patients: a meta-analysis

BACKGROUND

Survivin has been reported to play a role in the diagnosis and prognosis of renal cell carcinoma (RCC); however, published data on this subject are conflicting.

AIM

To conduct a meta-analysis to evaluate the impact of survivin as a prognostic marker and its association with clinicopathological variables in patients with RCC.

METHOD

Comprehensive searches of electronic databases (PubMed, ISI Web of Knowledge Embase, Google Scholar Web and the Cochrane Library) were updated to June 2016 to retrieve eligible studies. The association strength was measured with relative risks (RRs) and pooled HRs with 95% CIs, which were extracted and pooled to determine the association between survivin expression and patient survival and clinicopathological features.

RESULTS

Ten studies with 1063 cases of RCC were included. Positive survivin expression in RCC was associated with the TNM stage (pooled RR 1.49; 95% CI 1.07 to 2.07) or Fuhrman grade (pooled RR 1.63; 95% CI 1.15 to 2.32) in patients. The correlation between survivin expression and gender was not significant (pooled RR 0.97; 95% CI 0.83 to 1.15). In addition, a considerable association was found between survivin expression and overall survival for patients with RCC (pooled HR 1.94; 95% CI 1.24 to 3.05 (multivariate model) and 5.41; 95% CI 4.08 to 7.17 (univariate model)).

CONCLUSIONS

Our results indicate that survivin is of prognostic significance in patients with RCC.

A complex three-way translocation with deletion of the TP53 gene in a blast crisis chronic myeloid leukemia patient

Chronic myeloid leukemia (CML) is characterized by the Philadelphia (Ph) chromosome created by the reciprocal translocation t(9;22) (q34;q11), resulting in the chimeric BCR-ABL oncogene. Variant Ph' chromosome translocations involving additional chromosomes are seen in 5-10% of CML cases. In the present study, a novel case of Ph' chromosome-positive CML is reported, with a three-way translocation involving chromosomal regions, 9q34, 22q11.2 and 17p11.2, with additional secondary changes. The three-way translocation has resulted in a deletion of the TP53 gene located on the chromosome 17p13.1 locus. Deletion of the TP53 gene may be a major contributing factor in the development of resistance to imatinib and blast crisis.

Carcinogenic polycyclic aromatic hydrocarbons induce CYP1A1 in human cells via a p53-dependent mechanism

The tumour suppressor gene TP53 is mutated in more than 50 % of human tumours, making it one of the most important cancer genes. We have investigated the role of TP53 in cytochrome P450 (CYP)-mediated metabolic activation of three polycyclic aromatic hydrocarbons (PAHs) in a panel of isogenic colorectal HCT116 cells with differing TP53 status. Cells that were TP53(+/+), TP53(+/−), TP53(−/−), TP53(R248W/+) or TP53(R248W/−) were treated with benzo[a]pyrene (BaP), dibenz[a,h]anthracene and dibenzo[a,l]pyrene, and the formation of DNA adducts was measured by ³²P-postlabelling analysis. Each PAH formed significantly higher DNA adduct levels in TP53(+/+) cells than in the other cell lines. There were also significantly lower levels of PAH metabolites in the culture media of these other cell lines. Bypass of the need for metabolic activation by treating cells with the corresponding reactive PAH-diol-epoxide metabolites resulted in similar adduct levels in all cell lines, which confirms that the influence of p53 is on the metabolism of the parent PAHs. Western blotting showed that CYP1A1 protein expression was induced to much greater extent in TP53(+/+) cells than in the other cell lines. CYP1A1 is inducible via the aryl hydrocarbon receptor (AHR), but we did not find that expression of AHR was dependent on p53; rather, we found that BaP-induced CYP1A1 expression was regulated through p53 binding to a p53 response element in the CYP1A1 promoter region, thereby enhancing its transcription. This study demonstrates a new pathway for CYP1A1 induction by environmental PAHs and reveals an emerging role for p53 in xenobiotic metabolism.

Expression of vimentin and survivin in clear cell renal cell carcinoma and correlation with p53

PURPOSE

This study focuses on investigating the expression correlation of vimentin, survivin and p53 in clear cell renal cell carcinoma (ccRCC) and the clinical significance.

METHODS

The mRNA and protein expression levels of the vimentin, survivin and p53 were determined in ccRCC and adjacent normal renal tissues, using quantitative real-time-polymerase chain reaction (qRT-PCR) and Western blot. We detected the expression and localization of vimentin, survivin and p53 protein in ccRCC by immunohistochemistrical SP method and analyzed the relationships among clinical pathologic parameters and patient prognosis.

RESULTS

The expression of vimentin and survivin was significantly increased in ccRCC compared with adjacent normal renal tissues, which were positively correlated with the pathological grade and clinical stage (P < 0.05). p53 was highly expressed in ccRCC compared with normal tissues (P < 0.05), which was not positively correlated with the pathological grade and clinical stage (P > 0.05). Furthermore, univariate and multivariate analysis showed that high expression levels of vimentin and survivin were independent prognostic indicators for ccRCC. The levels of vimentin and survivin were positively correlated in ccRCC (r = 0.428, P < 0.01).

CONCLUSIONS

Reliable basis about biological behavior and prognosis judgments of ccRCC can be provided by combining detection of vimentin and survivin. Foundation and new ideas for gene therapy of ccRCC may be provided by further studying the relationship among vimentin, survivin and p53 in ccRCC.

Clinical significance of different types of p53 gene alteration in surgically treated prostate cancer

Despite a multitude of p53 immunohistochemistry (IHC) studies, data on the combined effect of nuclear p53 protein accumulation and TP53 genomic inactivation are lacking for prostate cancer. A tissue microarray including 11,152 prostate cancer samples was analyzed by p53 IHC and fluorescence in situ hybridization. Nuclear p53 accumulation was found in 10.1% of patients including 1.4% with high-level and 8.7% with low-level immunostaining. TP53 sequencing revealed that 17 of 22 (77%) cases with high-level p53 immunostaining, but only 3% (1 of 31) low-level p53 cases carried putative dominant-negative mutations. TP53 deletions occurred in 14.8% of cancers. Both deletions and protein accumulation were linked to unfavorable tumor phenotype and prostate specific antigen (PSA) recurrence (p<0.0001 each). The combination of both methods revealed subgroups with remarkable differences in their clinical course. Tumors with either TP53 deletion (14%) or low-level p53 positivity (8.7%) had identical risks of PSA recurrence, which were markedly higher than in cancers without p53 alterations (p<0.0001). Tumors with both p53 deletion and low-level p53 positivity (1.5%) had a worse prognosis than patients with only one of these alterations (p<0.0001). Tumors with strong p53 immunostaining or homozygous inactivation through deletion of one allele and disrupting translocation involving the second allele had the worst outcome, independent from clinical and pathological parameters. These data demonstrate a differential clinical impact of various TP53 alterations in prostate cancer. Strong p53 immunostaining-most likely accompanying dominant negative or oncogenic p53 mutation-has independent prognostic relevance and may thus represent a clinical useful molecular feature of prostate cancer.

SIRT1 inhibition restores apoptotic sensitivity in p53-mutated human keratinocytes

Mutations to the p53 gene are common in UV-exposed keratinocytes and contribute to apoptotic resistance in skin cancer. P53-dependent activity is modulated, in part, by a complex, self-limiting feedback loop imposed by miR-34a-mediated regulation of the lysine deacetylase, SIRT1. Expression of numerous microRNAs is dysregulated in squamous and basal cell carcinomas; however the contribution of specific microRNAs to the pathogenesis of skin cancer remains untested. Through use of RNAi, miRNA target site blocking oligonucleotides and small molecule inhibitors, this study explored the influence of p53 mutational status, SIRT1 activity and miR-34a levels on apoptotic sensitivity in primary (NHEK) and p53-mutated (HaCaT) keratinocyte cell lines. SIRT1 and p53 are overexpressed in p53-mutated keratinocytes, whilst miR-34a levels are 90% less in HaCaT cells. HaCaTs have impaired responses to p53/SIRT1/miR-34a axis manipulation which enhanced survival during exposure to the chemotherapeutic agent, camptothecin. Inhibition of SIRT1 activity in this cell line increased p53 acetylation and doubled camptothecin-induced cell death. Our results demonstrate that p53 mutations increase apoptotic resistance in keratinocytes by interfering with miR-34a-mediated regulation of SIRT1 expression. Thus, SIRT1 inhibitors may have a therapeutic potential for overcoming apoptotic resistance during skin cancer treatment.

Integral analysis of p53 and its value as prognostic factor in sporadic colon cancer

BACKGROUND

p53 (encoded by TP53) is involved in DNA damage repair, cell cycle regulation, apoptosis, aging and cellular senescence. TP53 is mutated in around 50% of human cancers. Nevertheless, the consequences of p53 inactivation in colon cancer outcome remain unclear. Recently, a new role of p53 together with CSNK1A1 in colon cancer invasiveness has been described in mice.

METHODS

By combining data on different levels of p53 inactivation, we aimed to predict p53 functionality and to determine its effects on colon cancer outcome. Moreover, survival effects of CSNK1A1 together with p53 were also studied.Eighty-three formalin fixed paraffin embedded colon tumors were enriched for tumor cells using flow sorting, the extracted DNA was used in a custom SNP array to determine chr17p13-11 allelic state; p53 immunostaining, TP53 exons 5, 6, 7 and 8 mutations were determined in combination with mRNA expression analysis on frozen tissue.

RESULTS

Patients with a predicted functional p53 had a better prognosis than patients with non functional p53 (Log Rank p=0.009). Expression of CSNK1A1 modified p53 survival effects. Patients with low CSNK1A1 expression and non-functional p53 had a very poor survival both in the univariate (Log Rank p<0.001) and in the multivariate survival analysis (HR=4.74 95% CI 1.45 - 15.3 p=0.009).

CONCLUSION

The combination of mutational, genomic, protein and downstream transcriptional activity data predicted p53 functionality which is shown to have a prognostic effect on colon cancer patients. This effect was specifically modified by CSKN1A1 expression.

The molecular mechanism and potential role of heat shock-induced p53 protein accumulation

Workers who are exposed to extreme heat or work in hot environments may be at risk of heat stress. Exposure to extreme heat can result in occupational illnesses and injuries. On the other hand, local and regional heat therapy has been used for the treatment of some cancers, such as liver cancer, lung cancer, and kidney cancer. Although heat stress has been shown to induce the accumulation of p53 protein, a key regulator of cell cycle, apoptosis, DNA repair, and autophagy, how it regulates p53 protein accumulation and what the p53 targets are remain unclear. Here, we show that, among various genotoxic stresses, including ionizing radiation (IR) and ultraviolet (UV) radiation, heat stress contributes significantly to increase p53 protein levels in normal liver cells and liver cancer cells. Heat stress did not increase p53 mRNA expression as well as p53 promoter activity. However, heat stress enhanced the half-life of p53 protein. Moreover, heat stress increased the expression of puma and light chain 3 (LC-3), which are associated with the apoptotic and autophagic function of p53, respectively, whereas it did not change the expression of the cell cycle regulators p21, 14-3-3δ, and GADD45α, suggesting that heat-triggered alteration of p53 selectively modulates the downstream targets of p53. Our study provides a novel mechanism by which heat shock stimulates p53 protein accumulation, which is different from common DNA damages, such as IR and UV, and also provides new molecular basis for heat injuries or heat therapy.

microRNA-16 represses colorectal cancer cell growth in vitro by regulating the p53/survivin signaling pathway

Dysregulated expression of microRNAs (miRNA) is a hallmark of cancer. miR-16 has been reported to be downregulated and to act as a tumor suppressor in different cancer types. In the present study, we sought to investigate the possible roles and mechanisms of miR-16 and its relationship with p53 and survivin in CRC cells. We showed that miR-16 was downregulated in 67% of CRC tissues and was correlated with the degree of histological differentiation. Experiments in vitro showed that overexpression of miR-16 inhibited the proliferation and induced apoptosis of CRC cells through the intrinsic apoptosis pathway. We further showed that miR-16 repressed survivin expression at both the mRNA and protein levels and the survivin gene was a direct target of miR-16. In addition, miR-16 reduced p53 expression and p53 increased miR-16 levels, with downregulation of miR-16 targets survivin, cyclin D1 and CDK6. Our findings suggest that miR-16 represses colorectal cancer cell growth in vitro by regulating the p53/survivin signaling pathway. Our findings provide further evidence for the involvement of dysregulated miRNAs in CRC, and miR-16 could serve as a molecular target for CRC therapy.

The emergence of protein complexes: quaternary structure, dynamics and allostery. Colworth Medal Lecture

All proteins require physical interactions with other proteins in order to perform their functions. Most of them oligomerize into homomers, and a vast majority of these homomers interact with other proteins, at least part of the time, forming transient or obligate heteromers. In the present paper, we review the structural, biophysical and evolutionary aspects of these protein interactions. We discuss how protein function and stability benefit from oligomerization, as well as evolutionary pathways by which oligomers emerge, mostly from the perspective of homomers. Finally, we emphasize the specificities of heteromeric complexes and their structure and evolution. We also discuss two analytical approaches increasingly being used to study protein structures as well as their interactions. First, we review the use of the biological networks and graph theory for analysis of protein interactions and structure. Secondly, we discuss recent advances in techniques for detecting correlated mutations, with the emphasis on their role in identifying pathways of allosteric communication.

TUMOR SUPPRESSOR PATHWAYS AND CELLULAR ORIGINS OF BREAST CANCER: NEW COMPLEXITIES AND NEW HOPES

Heritable breast cancer syndromes have identified the recognition and processing of DNA double strand breaks as a fundamental vulnerability in the breast epithelium. The role of homology-directed DNA repair is particularly prominent, indicating that this repair pathway is rate-limiting. Although the activities of the tumor suppressor genes underlying heritable breast cancer act in a common pathway of DNA double strand break repair, the specific lesions result in surprisingly different patterns of biomarkers in the breast cancers, suggesting that they arise from different cell types that include the luminal, basal and progenitor cells within the breast epithelium. Therefore, each cell type appears to have distinct underlying vulnerabilities in repair of DNA double strand breaks. While the heterogeneity of targets poses a challenge to develop specific therapies, these pathways also render tumor cells sensitive to drugs targeting double strand break repair pathways offering new options for therapies. As double strand break repair is a common pathway underlying breast cancer risk, therapies that enhance the proficiency of this pathway offer a strategy for chemoprevention.

A deacetylase-deficient SIRT1 variant opposes full-length SIRT1 in regulating tumor suppressor p53 and governs expression of cancer-related genes

SIRT1 is an NAD-dependent deacetylase and epigenetic regulator essential for normal mammalian development and homeostasis. Here we describe a human SIRT1 splice variant, designated SIRT1-Δ2/9, in which the deacetylase coding sequence is lost due to splicing between exons 2 and 9. This work aimed to determine if SIRT1-Δ2/9 is a novel functional product of the SIRT1 gene. Endogenous SIRT1-Δ2/9 protein was identified in human cell lysate by immunoblotting and splice variant-specific RNA interference (RNAi). SIRT1-Δ2/9 mRNA is bound by CUGBP2, which downregulates its translation. Using pulldown assays, we demonstrate that SIRT1-Δ2/9 binds p53 protein. SIRT1-Δ2/9 maintains basal p53 protein levels and supports p53 function in response to DNA damage, as evidenced by RNAi-mediated depletion of SIRT1-Δ2/9 prior to damage. In turn, basal p53 downregulates SIRT1-Δ2/9 RNA levels, while stress-activated p53 eliminates SIRT1-Δ2/9. Loss of wild-type (wt) p53 has been correlated with overexpression of SIRT1-Δ2/9 in a range of human cancers. Exogenous SIRT1-Δ2/9 protein associates with specific promoters in chromatin and can regulate cancer-related gene expression, as evidenced by chromatin immunoprecipitation analysis and RNAi/genomic array data. SIRT1 is of major therapeutic importance, and potential therapeutic drugs are screened against SIRT1 deacetylase activity. Our discovery of SIRT1-Δ2/9 identifies a new, deacetylase-independent therapeutic target for SIRT1-related diseases, including cancer.

A continuum model for tumour suppression

This year, 2011, marks the forty-year anniversary of the statistical analysis of retinoblastoma that provided the first evidence that tumorigenesis can be initiated by as few as two mutations. This work provided the foundation for the two-hit hypothesis that explained the role of recessive tumour suppressor genes (TSGs) in dominantly inherited cancer susceptibility syndromes. However, four decades later, it is now known that even partial inactivation of tumour suppressors can critically contribute to tumorigenesis. Here we analyse this evidence and propose a continuum model of TSG function to explain the full range of TSG mutations found in cancer.

Toward a pathway-centered approach for the treatment of adrenocortical carcinoma

PURPOSE OF REVIEW

Adrenocortical carcinoma is an aggressive, lethal malignancy of the adrenal cortex. The rarity of the disease has stymied therapeutic development. Recent work toward understanding the molecular pathogenesis of the disease has identified several potential new diagnostic and therapeutic targets.

RECENT FINDINGS

The molecular characterization of adrenocortical carcinoma has identified dysregulation of the Gap 2/mitosis transition and the insulin-like growth factor 1 receptor signaling cascade as two major pathways for therapeutic development. These studies have also highlighted an unappreciated heterogeneity of the disease at the gene level that nevertheless seems to converge onto common cellular pathways. Additionally, the characterization of Wnt signaling through β-catenin in adrenal development, the demonstration of the involvement of BMP signaling in adrenocortical carcinoma growth regulation, and the discovery that ERCC1 expression levels can predict therapeutic response to platinum are just a few of the recent advances that promise to shed light on adrenocortical carcinoma biology.

SUMMARY

Short-term, therapeutic development should target the Gap 2/mitosis transition and the downstream signaling of the insulin-like growth factor 1 receptor receptor. Long-term, additional characterization of patient samples, particularly at the sequence level, is required to fully understand adrenocortical carcinoma biology and apply that knowledge to clinical practice.

Reduction of Pten dose leads to neoplastic development in multiple organs of Pten (shRNA) mice

To address the impact of partial reduction of Pten on tumor initiation, we generated PtenshRNA mice, in which PTEN expression was reduced below normal levels in various tissues. PtenshRNA mice frequently developed lymphoid and prostatic hyperplasia, splenomegaly, and sebaceous adenomas. Our observations support the notion that partial reduction of the dose of Pten with shRNA is sufficient to induce neoplastic disease in multiple organ systems.

Haplo-insufficiency: a driving force in cancer

It was originally proposed that tumour suppressor genes (TSGs) act in a recessive manner. Instead, numerous TSGs, including p53 and PTEN, exhibit haplo-insufficiency as a consequence of the dose-dependency of TSG function. Due to the challenges of identifying haplo-insufficient TSGs by human genetics analysis alone, mouse models play a pivotal role in firmly establishing the haplo-insufficiency of a gene, as in the recent identification of DOK2 as a haplo-insufficient lung TSG. In many cases, TSGs exhibit conditional or compound haplo-insufficiency, in which loss of one TSG allele is functionally important only in certain settings or after compound loss of other genes. The 5q deletion syndrome (5q(-) ) is a paradigm of compound haplo-insufficiency and demonstrates the importance of combinatorial interactions to elicit specific phenotypes. These concepts must be integrated into basic science studies to avoid delay in the identification of important TSGs. In the clinical realm, the challenges for molecular pathologists are the development of quantitative measures that can accurately and systematically ascertain the status of haplo-insufficient genes in tumour biopsies, and the use of this information to accurately predict prognosis and response to therapy.

SIRT1 undergoes alternative splicing in a novel auto-regulatory loop with p53

BACKGROUND

The NAD-dependent deacetylase SIRT1 is a nutrient-sensitive coordinator of stress-tolerance, multiple homeostatic processes and healthspan, while p53 is a stress-responsive transcription factor and our paramount tumour suppressor. Thus, SIRT1-mediated inhibition of p53 has been identified as a key node in the common biology of cancer, metabolism, development and ageing. However, precisely how SIRT1 integrates such diverse processes remains to be elucidated.

METHODOLOGY/PRINCIPAL FINDINGS

Here we report that SIRT1 is alternatively spliced in mammals, generating a novel SIRT1 isoform: SIRT1-ΔExon8. We show that SIRT1-ΔExon8 is expressed widely throughout normal human and mouse tissues, suggesting evolutionary conservation and critical function. Further studies demonstrate that the SIRT1-ΔExon8 isoform retains minimal deacetylase activity and exhibits distinct stress sensitivity, RNA/protein stability, and protein-protein interactions compared to classical SIRT1-Full-Length (SIRT1-FL). We also identify an auto-regulatory loop whereby SIRT1-ΔExon8 can regulate p53, while in reciprocal p53 can influence SIRT1 splice variation.

CONCLUSIONS/SIGNIFICANCE

We characterize the first alternative isoform of SIRT1 and demonstrate its evolutionary conservation in mammalian tissues. The results also reveal a new level of inter-dependency between p53 and SIRT1, two master regulators of multiple phenomena. Thus, previously-attributed SIRT1 functions may in fact be distributed between SIRT1 isoforms, with important implications for SIRT1 functional studies and the current search for SIRT1-activating therapeutics to combat age-related decline.

A new stochastic and state space model of human colon cancer incorporating multiple pathways

Background and Purpose

Studies by molecular biologists and geneticists have shown that tumors of human colon cancer are developed from colon stem cells through two mechanisms: The chromosomal instability and the micro-satellite instability. The purpose of this paper is therefore to develop a new stochastic and state space model for carcinogenesis of human colon cancer incorporating these biological mechanisms.

Results

Based on recent biological studies, in this paper we have developed a state space model for human colon cancer. In this state space model, the stochastic system is represented by a stochastic model, involving 2 different pathways-the chromosomal instability pathway and the micro-satellite instability pathway; the observation, cancer incidence data, is represented by a statistical model. Based on this model we have developed a generalized Bayesian approach to estimate the parameters through the posterior modes of the parameters via Gibbs sampling procedures. We have applied this model to fit and analyze the SEER data of human colon cancers from NCI/NIH.

Conclusions

Our results indicate that the model not only provides a logical avenue to incorporate biological information but also fits the data much better than other models including the 4-stage single pathway model. This model not only would provide more insights into human colon cancer but also would provide useful guidance for its prevention and control and for prediction of future cancer cases.

Reviewers

This article was reviewed by M.P. Little and M. Kimmel

Regulation of tumor suppressor p53 at the RNA level

p53 is a key tumor suppressor that triggers cell cycle arrest, senescence, or apoptosis in response to cellular stress. Frequent p53 mutation in human tumors allows survival, sustained growth, and tumor progression. p53 is expressed at low levels under normal conditions, due to rapid protein turnover. Stress signaling induces p53 protein stabilization through phosphorylation and other post-translational modifications. However, recent studies have demonstrated critical regulation of p53 at the mRNA level, mediated via both the 5'UTR and the 3'UTR and affecting both the stability and the translation efficiency of the p53 mRNA. Both proteins and microRNAs have been implicated in such regulation. The p53 target gene Wig-1 encodes a zinc finger protein that binds to double-stranded RNA and enhances p53 mRNA stability by binding to the 3'UTR in a positive feedback loop. Here, we shall summarize current knowledge about regulation of the p53 mRNA and discuss possible implications for cancer therapy.

The Arf-inducing transcription factor Dmp1 encodes a transcriptional activator of amphiregulin, thrombospondin-1, JunB and Egr1

Dmp1 (Dmtf1) encodes a Myb-like transcription factor implicated in tumor suppression through direct activation of the Arf-p53 pathway. The human DMP1 gene is frequently deleted in non-small cell lung cancers, especially those that retain wild-type INK4a/ARF and/or p53. To identify novel genes that are regulated by Dmp1, transcriptional profiles of lung tissue from Dmp1-null and wild-type mice were generated using the GeneChip Microarray. Comparative analysis of gene expression changes between the two groups resulted in identification of numerous genes that may be regulated by Dmp1. Notably, amphiregulin (Areg), thrombospondin-1 (Tsp-1), JunB, Egr1, adrenomedullin (Adm), Bcl-3 and methyl-CpG binding domain protein 1 (Mbd1) were downregulated in the lungs from Dmp1-null mice while Gas1 and Ect2 genes were upregulated. These target genes were chosen for further analyses since they are involved in cell proliferation, transcription, angiogenesis/metastasis, apoptosis, or DNA methylation, and thus could account for the tumor suppressor phenotype of Dmp1. Dmp1 directly bound to the genomic loci of Areg, Tsp-1, JunB and Egr1. Significant upregulation or downregulation of the novel Dmp1 target genes was observed upon transient expression of Dmp1 in alveolar epithelial cells, an effect which was nullified by the inhibition of de novo mRNA synthesis. Interestingly, these genes and their protein products were significantly downregulated or upregulated in the lungs from Dmp1-heterozygous mice as well. Identification of novel Dmp1 target genes not only provides insights into the effects of Dmp1 on global gene expression, but also sheds light on the mechanism of haploid insufficiency of Dmp1 in tumor suppression.

Pathways contributing to development of spontaneous mammary tumors in BALB/c-Trp53+/- mice

Mutation and loss of function in p53 are common features among human breast cancers. Here we use BALB/c-Trp53+/- mice as a model to examine the sequence of events leading to mammary tumors. Mammary gland proliferation rates were similar in both BALB/c-Trp53+/- mice and wild-type controls. In addition, sporadic mammary hyperplasias were rare in BALB/c-Trp53+/- mice and not detectably different from those of wild-type controls. Among the 28 mammary tumors collected from BALB/c-Trp53+/- mice, loss of heterozygosity for Trp53 was detected in more than 90% of invasive mammary tumors. Transplantation of Trp53+/- ductal hyperplasias also indicated an association between loss of the wild-type allele of Trp53 and progression to invasive carcinomas. Therefore, loss of p53 function seems to be a rate-limiting step in progression. Moreover, expression of biomarkers such as estrogen receptor alpha, progesterone receptor, Her2/Neu, and activated Notch1 varied among mammary tumors, suggesting that multiple oncogenic lesions collaborate with loss of p53 function. Expression of biomarkers was retained when tumor fragments were transplanted to syngeneic hosts. Tumors expressing solely luminal or basal keratins were also observed (27 and 11%, respectively), but the largest class of tumors expressed both luminal and basal keratins (62%). Overall, this panel of transplantable tumors provides a resource for detailed evaluation of the cell lineages undergoing transformation and preclinical testing of therapeutic agents targeting a variety of oncogenic pathways including cancer stem cells.

The p53 target Wig-1 regulates p53 mRNA stability through an AU-rich element

The p53 target gene Wig-1 encodes a double-stranded-RNA-binding zinc finger protein. We show here that Wig-1 binds to p53 mRNA and stabilizes it through an AU-rich element (ARE) in the 3' UTR of the p53 mRNA. This effect is mirrored by enhanced p53 protein levels in both unstressed cells and cells exposed to p53-activating stress agents. Thus, the p53 target Wig-1 is a previously undescribed ARE-regulating protein that acts as a positive feedback regulator of p53, with implications both for the steady-state levels of p53 and for the p53 stress response. Our data reveal a previously undescribed link between the tumor suppressor p53 and posttranscriptional gene regulation via AREs in mRNA.

Gene and microRNA expression in p53-deficient day 8.5 mouse embryos

BACKGROUND

Neural tube defects (NTDs) are one of the most common human birth defects, with a prevalence of approximately 1 in 1000 live births in the United States. In animal studies, deletion of p53 leads to a significant increase in embryos that exhibit exencephaly. Whereas several studies have closely investigated the morphologic changes of p53-deficient embryos, no study has reported the molecular-level alteration in p53-deficient embryos. Here we attempt to identify genes and microRNAs (miRNAs) modified by deletion of p53 in day 8.5 mouse embryos.

METHODS

Mouse embryos from p53 heterozygous crosses were collected, genotyped, and embryos of similar genotype (+/+; +/-; -/-) were pooled. RNA from the pooled samples was isolated to determine mRNA and miRNA expression levels using Whole Genome Bioarrays and Low Density Arrays, respectively.

RESULTS

In p53 -/- embryos, 388 genes showed statistically significant alteration in gene expression of more than twofold compared to p53 +/+ embryos. Expression of p53 and well known p53 target genes, such as p21 and cyclin G1, were significantly down-regulated in p53 -/- embryos. In contrast, expression of other p53 target genes, such as Mdm2, Noxa, and Puma, were unchanged. We also identified six genes (Csk, Itga3, Jarid2, Prkaca, Rarg, and Sall4), known to cause NTDs when deleted, that are also down-regulated in p53 -/- embryos. Finally, five miRNAs (mir-1, mir-30e-3p, mir-142-3p, mir-301, and mir-331) also showed statistically significant alterations in expression levels in p53 -/- embryos compared to p53 +/+ embryos. Combined analysis of the experimental data using stepwise regression model and two publicly available algorithms identified putative target genes of these miRNAs.

CONCLUSIONS

Our data have identified genes and miRNAs that may be involved in the mechanisms underlining NTDs and begin to define the developmental role of p53 in the etiology of NTDs.

CPEB regulation of human cellular senescence, energy metabolism, and p53 mRNA translation

Cytoplasmic polyadenylation element-binding protein (CPEB) stimulates polyadenylation and translation in germ cells and neurons. Here, we show that CPEB-regulated translation is essential for the senescence of human diploid fibroblasts. Knockdown of CPEB causes skin and lung cells to bypass the M1 crisis stage of senescence; reintroduction of CPEB into the knockdown cells restores a senescence-like phenotype. Knockdown cells that have bypassed senescence undergo little telomere erosion. Surprisingly, knockdown of exogenous CPEB that induced a senescence-like phenotype results in the resumption of cell growth. CPEB knockdown cells have fewer mitochondria than wild-type cells and resemble transformed cells by having reduced respiration and reactive oxygen species (ROS), normal ATP levels, and enhanced rates of glycolysis. p53 mRNA contains cytoplasmic polyadenylation elements in its 3' untranslated region (UTR), which promote polyadenylation. In CPEB knockdown cells, p53 mRNA has an abnormally short poly(A) tail and a reduced translational efficiency, resulting in an approximately 50% decrease in p53 protein levels. An shRNA-directed reduction in p53 protein by about 50% also results in extended cellular life span, reduced respiration and ROS, and increased glycolysis. Together, these results suggest that CPEB controls senescence and bioenergetics in human cells at least in part by modulating p53 mRNA polyadenylation-induced translation.

MDM2 SNP309 is associated with high grade node positive breast tumours and is in linkage disequilibrium with a novel MDM2 intron 1 polymorphism

INTRODUCTION

A functional polymorphism within MDM2, SNP309 T>G, has been linked to early onset cancer. This study examined clinical associations of breast cancer with SNP309 in a Scottish Caucasian population and investigated additional MDM2 intron 1 polymorphisms.

METHODS

Intron 1 of MDM2 was PCR amplified and directly sequenced from 299 breast cancer patients and 275 cancer free controls and compared with clinical and pathological parameters.

RESULTS

SNP309 was observed, for the control and breast cancer cohorts respectively, at frequencies of: T/T = 44.7% and 39.5%; G/T = 42.2% and 47.2%; G/G = 13.1% and 13.4%, indicating that SNP309 is not a predisposing factor for breast cancer. The 309G/G genotype was associated with high grade tumours (OR = 1.64, 95%CI = 1.06-2.53, p = 0.025) and greater nodal involvement (OR = 2.51, 95%CI = 1.26-4.98, p = 0.009). SNP309 was not associated with an earlier age of cancer diagnosis. No association was observed between genotype and age of breast cancer diagnosis when patients were stratified by menopausal status and estrogen receptor status. Three additional low frequency SNPs were identified: 344T>A, 285G>C and 443G>T, the latter two novel. SNP285 was in complete linkage disequilibrium with SNP309 (D' = 1.0) with the minor alleles being in phase with each other. Moreover, the 285C/C, 309G/G double homozygous genotype was only observed in the breast cancer cohort.

CONCLUSION

SNP309G/G is associated with poor prognostic breast cancer features in the Scottish population. Additionally, a novel SNP, SNP285, that is in linkage disequilibrium with SNP309, may also have a role in breast tumorigenesis.

Estrogen and progesterone induce persistent increases in p53-dependent apoptosis and suppress mammary tumors in BALB/c-Trp53+/- mice

Introduction

Treatment with estrogen and progesterone (E+P) mimics the protective effect of parity on mammary tumors in rodents and depends upon the activity of p53. The following experiments tested whether exogenous E+P primes p53 to be more responsive to DNA damage and whether these pathways confer resistance to mammary tumors in a mouse model of Li-Fraumeni syndrome.

Methods

Mice that differ in p53 status (Trp53^+/+, Trp53^+/-, Trp53^-/-) were treated with E+P for 14 days and then were tested for p53-dependent responses to ionizing radiation. Responses were also examined in parous and age-matched virgins. The effects of hormonal exposures on tumor incidence were examined in BALB/c-Trp53^+/- mammary tissues.

Results

Nuclear accumulation of p53 and apoptotic responses were increased similarly in the mammary epithelium from E+P-treated and parous mice compared with placebo and age-matched virgins. This effect was sustained for at least 7 weeks after E+P treatment and did not depend on the continued presence of ovarian hormones. Hormone stimulation also enhanced apoptotic responses to ionizing radiation in BALB/c-Trp53^+/- mice but these responses were intermediate compared with Trp53^+/+ and Trp^-/- tissues, indicating haploinsufficiency. The appearance of spontaneous mammary tumors was delayed by parity in BALB/c-Trp53^+/- mice. The majority of tumors lacked estrogen receptor (ER), but ER⁺ tumors were observed in both nulliparous and parous mice. However, apoptotic responses to ionizing radiation and tumor incidence did not differ among outgrowths of epithelial transplants from E+P-treated donors and nulliparous donors.

Conclusion

Therefore, E+P and parity confer a sustained increase in p53-mediated apoptosis within the mammary epithelium and suppress mammary tumorigenesis, but this effect was not retained in epithelial outgrowths.

Tumor suppressor and hepatocellular carcinoma

A few signaling pathways are driving the growth of hepatocellular carcinoma. Each of these pathways possesses negative regulators. These enzymes, which normally suppress unchecked cell proliferation, are circumvented in the oncogenic process, either the over-activity of oncogenes is sufficient to annihilate the activity of tumor suppressors or tumor suppressors have been rendered ineffective. The loss of several key tumor suppressors has been described in hepatocellular carcinoma. Here, we systematically review the evidence implicating tumor suppressors in the development of hepatocellular carcinoma.

Clinical significance of loss of heterozygosity for M6P/IGF2R in patients with primary hepatocellular carcinoma

AIM: To investigate the relationship between loss of heterozygosity (LOH) for mannose 6-phosphate/insulin-like growth factor 2 receptor (M6P/IGF2R) and the outcomes for primary HCC patients treated with partial hepatectomy.

METHODS: The LOH for M6P/IGF2R in primary HCC patients was assessed using six different gene-specific nucleotide polymorphisms. The patients studied were enrolled to undergo partial hepatectomy.

RESULTS: M6P/IGF2R was found to be polymorphic in 73.3% (22/30) of the patients, and of these patients, 50.0% (11/22) had tumors showing LOH in M6P/IGF2R. Loss of heterozygosity in M6P/IGF2R was associated with significant reductions in the two year overall survival rate (24.9% vs 65.5%; P = 0.04) and the disease-free survival rate (17.8% vs 59.3%; P = 0.03).

CONCLUSION: These results show M6P/IGF2R LOH predicts poor clinical outcomes in surgically resected primary HCC patients.

Aberrant p53 protein expression and function in a panel of hematopoietic cell lines with different p53 mutations

The p53 gene is one of the most important genes involved in carcinogenesis and its role in part has been clarified by research using cell lines. To know the comprehensive characteristics of 22 hematopoietic cell lines (T, 13 and non-T, nine lines), the relationship between p53 mutational status, its altered functioning, and its mRNA and protein levels were examined. p53 mutations were less frequent in T-cell lines (38% vs. 78%) with mainly single nucleotide substitutions generating missense codons. Of 22 different p53 mutations, 12 (54.5%) resulted in mutated proteins, with the mutations clustering mainly in the sequence-specific DNA-binding site region located from amino acid residues 102 to 292. p53 mRNA and protein assays determined that wild-type cell lines expressed constant levels of both mRNA and protein, but mutated cell lines demonstrated two expression patterns: protein over-expression with reduced mRNA levels, because of missense mutations; and protein under-expression with little mRNA expression, because of other mutations. The resistance to Nutlin (MDM2 inhibitor)-induced apoptosis was associated with p53 mutations independently of MDM2 expression levels. This clarification of the unique associations in cell lines useful for bio-medical studies will contribute to a better understanding of p53-associated carcinogenesis.

An adamantyl-substituted retinoid-derived molecule that inhibits cancer cell growth and angiogenesis by inducing apoptosis and binds to small heterodimer partner nuclear receptor: effects of modifying its carboxylate group on apoptosis, proliferation, and protein-tyrosine phosphatase activity

Apoptotic and antiproliferative activities of small heterodimer partner (SHP) nuclear receptor ligand (E)-4-[3'-(1-adamantyl)-4'-hydroxyphenyl]-3-chlorocinnamic acid (3-Cl-AHPC), which was derived from 6-[3'-(1-adamantyl)-4'-hydroxyphenyl]-2-naphthalenecarboxylic acid (AHPN), and several carboxyl isosteric or hydrogen bond-accepting analogues were examined. 3-Cl-AHPC continued to be the most effective apoptotic agent, whereas tetrazole, thiazolidine-2,4-dione, methyldinitrile, hydroxamic acid, boronic acid, 2-oxoaldehyde, and ethyl phosphonic acid hydrogen bond-acceptor analogues were inactive or less efficient inducers of KG-1 acute myeloid leukemia and MDA-MB-231 breast, H292 lung, and DU-145 prostate cancer cell apoptosis. Similarly, 3-Cl-AHPC was the most potent inhibitor of cell proliferation. 4-[3'-(1-adamantyl)-4'-hydroxyphenyl]-3-chlorophenyltetrazole, (2E)-5-{2-[3'-(1-adamantyl)-2-chloro-4'-hydroxy-4-biphenyl]ethenyl}-1H-tetrazole, 5-{4-[3'-(1-adamantyl)-4'-hydroxyphenyl]-3-chlorobenzylidene}thiazolidine-2,4-dione, and (3E)-4-[3'-(1-adamantyl)-2-chloro-4'-hydroxy-4-biphenyl]-2-oxobut-3-enal were very modest inhibitors of KG-1 proliferation. The other analogues were minimal inhibitors. Fragment-based QSAR analyses relating the polar termini with cancer cell growth inhibition revealed that length and van der Waals electrostatic surface potential were the most influential features on activity. 3-Cl-AHPC and the 3-chlorophenyltetrazole and 3-chlorobenzylidenethiazolidine-2,4-dione analogues were also able to inhibit SHP-2 protein-tyrosine phosphatase, which is elevated in some leukemias. 3-Cl-AHPC at 1.0 microM induced human microvascular endothelial cell apoptosis but did not inhibit cell migration or tube formation.

Stochastic model of transcription factor-regulated gene expression

We consider a stochastic model of transcription factor (TF)-regulated gene expression. The model describes two genes, gene A and gene B, which synthesize the TFs and the target gene proteins, respectively. We show through analytic calculations that the TF fluctuations have a significant effect on the distribution of the target gene protein levels when the mean TF level falls in the highest sensitive region of the dose-response curve. We further study the effect of reducing the copy number of gene A from two to one. The enhanced TF fluctuations yield results different from those in the deterministic case. The probability that the target gene protein level exceeds a threshold value is calculated with the knowledge of the probability density functions associated with the TF and target gene protein levels. Numerical simulation results for a more detailed stochastic model are shown to be in agreement with those obtained through analytic calculations. The relevance of these results in the context of the genetic disorder haploinsufficiency is pointed out. Some experimental observations on the haploinsufficiency of the tumour suppressor gene, Nkx 3.1, are explained with the help of the stochastic model of TF-regulated gene expression.