Genetic Modifiers of the p53 Pathway

Genetic variability profiling of the p53 signaling pathway in chronic lymphocytic leukemia. Individual and combined analysis of TP53, MDM2 and NQO1 gene variants

TP53 gene disruption, including 17p13 deletion [del(17p)] and/or TP53 mutations, is a negative prognostic biomarker in chronic lymphocytic leukemia (CLL) associated with disease progression, treatment failure and shorter survival. Germline variants in p53 signaling pathway genes could also lead to p53 dysfunction, but their involvement in CLL has not been thoroughly evaluated. The aim of this study was to determine the association of TP53, MDM2 and NQO1 gene variability with clinical and genetic data of CLL patients. Individual genotype and haplotype data of CLL patients were compared with clinical prognostic factors, cytogenetic and molecular cytogenetic findings as well as IGHV and TP53 mutational status. The study included 116 CLL patients and 161 healthy blood donors. TP53 (rs1042522, rs59758982, rs1625895), NQO1 (rs1800566) and MDM2 (rs2279744, rs150550023) variants were genotyped using different PCR approaches. Analysis of genotype frequencies revealed no association with the risk of CLL. TP53 rs1042522, rs1625895 and MDM2 rs2279744 variants were significantly associated with abnormal karyotype and the presence of del(17p). Similarly, these two TP53 variants were associated with TP53 disruption. Moreover, TP53 C-A-nondel and G-A-del haplotypes (rs1042522-rs1625895-rs59758982) were associated with an increased likelihood of carrying del(17p) and TP53 disruptions. MDM2 T-nondel haplotype (rs2279744-rs150550023) was found to be a low risk factor for del(17p) (OR = 0.32; CI: 0.12-0.82; p = 0.02) and TP53 disruptions (OR = 0.41; CI: 0.18-0.95; p = 0.04). Our findings suggest that TP53 and MDM2 variants may modulate the risk to have chromosome alterations and TP53 disruptions, particularly del(17p). To our knowledge this is the first study of several germline variants in p53 pathway genes in Argentine patients with CLL.

TP53 Gene Polymorphism at Codon 72 as a Response Predictor for Neoadjuvant Chemotherapy

Introduction

Breast cancer is the most prevalent cancer in women worldwide, and neoadjuvant chemotherapy is a favored method for achieving pathologic complete response (pCR). The TP53 gene is involved in inducing the response to chemotherapy drugs.

Objectives

The present study sought to correlate polymorphism variants at codon 72 with pCR to neoadjuvant chemotherapy.

Casuistry and Methods

The study was conducted in the state of Sergipe, in northeastern Brazil. A total of 206 patients with a histopathological diagnosis of breast cancer who underwent neoadjuvant chemotherapy from 2019 to 2022 were included. DNA samples were collected for the evaluation of TP53 polymorphism at codon 72. A prospective evaluation of the cases was conducted to verify the surgical pathologic response after chemotherapy; the Response Evaluation Criteria in Solid Tumors (RECIST) were used. The study was approved by the University of São Paulo Ethics and Research Committee.

Results

Of the 168 patients, 44.6% were Arg72Arg, 17.3% were Pro72Pro, and 38.0% were Arg72Pro; pCR was achieved in 21.4% of the patients; 10.1% had progressive disease, 13.7% had stable disease, and 54.2% had a partial pathologic response. The only predictor of pCR in multivariate regression was immunohistochemistry (p < 0.001). In the multivariate analysis, Arg72Pro and Pro72Pro increased the odds of the patient evolving with stable disease. This study was innovative in demonstrating a predictor of stable disease in response to neoadjuvant chemotherapy.

Conclusion

TP53 polymorphism at codon 72 is not a predictor of pCR, but it can be a predictor of stable disease.

The evaluation of the possibility of Li-Fraumeni syndrome in cancer patients in East Azarbaijan Province of Iran

INTRODUCTION

In 1969, Li-Fraumeni syndrome (LFS), which is a rare cancer predisposition syndrome, was reported for the first time. The main problem in LFS is the mutation in the TP53 gene, which is a crucial tumor suppressor gene in the cell cycle. A hereditary syndrome is inherited in an autosomal dominant pattern. There is a significant correlation between this syndrome and various cancers such as sarcoma, breast cancer, brain tumors, and different other types of malignancies. This study aimed to identify the possibility of LFS in cancer patients in the East Azarbaijan, Iran.

METHODS

In this experimental study, 45 children with cancer in the Northwest of Iran were investigated for LFS. DNA was extracted from the whole blood cells using the salting-out method. The region within the exons 5-8 of the TP53 gene has been replicated via Polymerase Chain Reaction (PCR) method. The PCR products were sent for Sanger sequencing, and finally, the data were analyzed by Chromas software.

RESULTS

In the studied probands, in 12 (26.67%) cases, polymorphisms in Exon 6 and Introns 6 and Intron 7 were identified, and no mutation was observed in exons 5-8 of the TP53 gene.

CONCLUSION

Our results show that there were no mutations in exons 5-8 of the TP53 gene as an indication of LFS possibility in these families. Further studies are needed to be done in a bigger population, and Next-Generation Sequencing (NGS) needs to be done to evaluate the whole genome of these patients to complete our data.

The African-centric P47S Variant of TP53 Confers Immune Dysregulation and Impaired Response to Immune Checkpoint Inhibition

The tumor suppressor TP53 is the most frequently mutated gene in cancer and is mutationally inactivated in 50% of sporadic tumors. Inactivating mutations in TP53 also occur in Li Fraumeni syndrome (LFS). In addition to germline mutations in TP53 in LFS that completely inactivate this protein, there are many more germline mutant forms of TP53 in human populations that partially inactivate this protein: we call these partially inactivating mutations "hypomorphs." One of these hypomorphs is a SNP that exists in 6%-10% of Africans and 1%-2% of African Americans, which changes proline at amino acid 47 to serine (Pro47Ser; P47S). We previously showed that the P47S variant of p53 is intrinsically impaired for tumor suppressor function, and that this SNP is associated with increased cancer risk in mice and humans. Here we show that this SNP also influences the tumor microenvironment, and the immune microenvironment profile in P47S mice is more protumorigenic. At basal levels, P47S mice show impaired memory T-cell formation and function, along with increased anti-inflammatory (so-called "M2") macrophages. We show that in tumor-bearing P47S mice, there is an increase in immunosuppressive myeloid-derived suppressor cells and decreased numbers of activated dendritic cells, macrophages, and B cells, along with evidence for increased T-cell exhaustion in the tumor microenvironment. Finally, we show that P47S mice demonstrate an incomplete response to anti-PD-L1 therapy. Our combined data suggest that the African-centric P47S variant leads to both intrinsic and extrinsic defects in tumor suppression.

Significance

Findings presented here show that the P47S variant of TP53 influences the immune microenvironment, and the immune response to cancer. This is the first time that a naturally occurring genetic variant of TP53 has been shown to negatively impact the immune microenvironment and the response to immunotherapy.

The role of BMI1 in endometrial cancer and other cancers

Endometrial cancer (EC) is the third leading gynecological malignancy, and its treatment remains challenging. B cell-specific Moloney murine leukemia virus integration site-1 (BMI1) is one of the core members of the polycomb group (PcG) family, which plays a promoting role in the occurrence and development of various tumors. Notably, BMI1 has been found to be frequently upregulated in endometrial cancer (EC) and promote the occurrence of EC through promoting epithelial-mesenchymal transition (EMT) and AKT/PI3K pathways. This review summarizes the structure and upstream regulatory mechanisms of BMI1 and its role in EC. In addition, we focused on the role of BMI1 in chemoradiotherapy resistance and summarized the current drugs that target BMI1.

Association between TP53 Arg72Pro variant and recurrent pregnancy loss in the Greek population

OBJECTIVES

The present case-control study investigates whether TP53 Arg72Pro variant (rs1042522) serves as a risk factor for recurrent pregnancy loss (RPL) in Greek women.

METHODS

The study group consisted of 100 patients with at least two miscarriages of unexplained etiology, before the 24th week of gestation. The control group included 106 women with no pregnancy loss history. DNA was extracted and genotyped using specific primers for PCR amplification of the Arg72 and Pro72 alleles. Sanger sequencing was used for the discrimination between heterozygotes and homozygotes for Arg72Pro variant.

RESULTS

This is the first study demonstrating the statistically significant higher frequency of TP53 Arg72Pro variant in Greek RPL women compared to controls (38% vs. 6.6%; OR=8.6682, 95% CI: 3.6446-20.6160; p<0.0001). GC genotype (Arg/Pro) and CC genotype (Pro/Pro) were statistically more common in RPL patients than in controls (16% vs. 1.9%; p=0.0027, and 22 vs. 4.7%; p=0.0008, respectively). C allele frequency was statistically significant higher in RPL group than in controls (30.0 vs. 5.7%; p<0.0001). According to the inheritance mode analysis, the model that best fit the data was the dominant model (OR=8.67, 95% CI=3.64-20.62; p<0.0001).

CONCLUSIONS

The is the first study disclosing strong evidence that TP53 rs1042522 is significantly associated with a higher risk for recurrent pregnancy loss in Greek women following a dominant model, thus, serving as a genetic marker for identifying women at increased risk of recurrent miscarriages.

Targeted Next-Generation Sequencing of Thymic Epithelial Tumours Revealed Pathogenic Variants in KIT, ERBB2, KRAS, and TP53 in 30% of Thymic Carcinomas

Simple Summary

The biology of thymic epithelial tumours (TETs), including thymomas and thymic carcinomas, and particularly the extent of molecular dysregulation, is poorly understood. Through next-generation sequencing of 15 genes implicated in common solid tumours in 53 TETs, we found a larger number of single nucleotide variants (SNVs) in thymic carcinomas than thymomas. About 30% of thymic carcinomas had at least one somatic pathogenic gene variant in TP53, ERBB2, KIT, or KRAS, whereas variants of uncertain clinical significance in KIT, ERBB2, and FOXL2 were found exclusively in thymomas. The presence of somatic pathogenic variants was non-significantly associated with shorter disease-free survival in thymic carcinoma patients. No somatic pathogenic or likely pathogenic SNV was found in thymomas. Importantly, we also evaluated germline SNVs, adding to the number of known genetic alterations in TETs and thereby enhancing our molecular understanding of these neoplasms.

Abstract

A better understanding of the molecular pathogenesis of thymic epithelial tumours (TETs) could revolutionise their treatment. We evaluated thymomas and thymic carcinomas by next-generation sequencing (NGS) of somatic or germline single nucleotide variants (SNVs) in genes commonly mutated in solid tumours. In total, 19 thymomas and 34 thymic carcinomas were analysed for nonsynonymous SNVs in 15 genes by targeted NGS (reference genome: hg19/GRCh37). Ten SNVs in TP53 (G154V, R158P, L194H, R267fs, R273C, R306 *, Q317 *), ERBB2 (V773M), KIT (L576P), and KRAS (Q61L) considered somatic and pathogenic/likely pathogenic were detected in 10 of 34 (29.4%) thymic carcinomas. No somatic SNVs confirmed as pathogenic/likely pathogenic were found in thymomas. Rare SNVs of uncertain or unknown functional and clinical significance, to our knowledge not reported previously in TETs, were found in ERBB2 (S703R), KIT (I690V), and FOXL2 (P157S) in 3 of 19 (16%) thymomas. The most frequent germline SNVs were TP53 P72R (94% TETs), ERBB2 I655V (40% TETs), and KIT M541L (9% TETs). No significant difference in median disease-free survival (DFS) was found between thymic carcinoma patients with and without pathogenic SNVs (p = 0.190); however, a trend toward a longer DFS was observed in the latter (16.0 vs. 30.0 months, respectively). In summary, NGS analysis of TETs revealed several SNVs in genes related to the p53, AKT, MAPK, and K-Ras signalling pathways. Thymic carcinomas showed greater genetic dysregulation than thymomas. The germline and rare SNVs of uncertain clinical significance reported in this study add to the number of known genetic alterations in TETs, thus extending our molecular understanding of these neoplasms. Druggable KIT alterations in thymic carcinomas have potential as therapeutic targets.

Association of TP53 gene polymorphisms with the risk of acute lymphoblastic leukemia in Moroccan children

BACKGROUND

TP53 gene plays a pivotal role in maintaining genetic stability and prevention of malignancies. Alterations of this gene are implicated in more than half of human cancers. To the best of our knowledge, this study is the first to explore TP53 polymorphisms in Moroccan childhood acute lymphoblastic leukemia (ALL).

METHODS AND RESULTS

DNA samples of 45 ALL children were obtained from peripheral blood. A total of 333 healthy Moroccans were used as controls. Polymerase chain reaction and Sanger sequencing were performed to analyze TP53 hotspot exons in cases. We identified a significant protective effect of the TP53-Arg variant at rs1042522 [OR 0.4593 (0.249-0.8472), p = 0.0127] and the Pro/Arg genotype [OR 0.0350 (0.0047-0.2583), p = 0.0010]. Additionally, we found a novel association between the C-allele of Arg213Arg 1800372 [OR 2.7736 (1.3821-5.5664), p = 0.0041] and the risk of childhood ALL. Importantly, TC/CC genotypes of this polymorphism were revealed to enhance the risk of ALL among females [OR 9.0 (3.1555-25.6693), p < 0.0001]. Arg213Arg was also noticed to be associated with the hemoglobin count of patients at diagnosis by linear regression (p = 0.0318). The analysis of penetrance showed a significant association of the CG/GG genotypes at rs1042522 and TC/CC genotypes at rs1800372 to childhood ALL via dominant model [OR 0.2090 (0.09074-0.4814), p = 0.0002 and OR 3.4205 (1.6084-7.2742), p = 0.0014 for rs1042522 and rs1800372 respectively]. No association was found between TP53 polymorphisms and patients survival.

CONCLUSION

Altogether, our findings indicated that TP53 polymorphisms are significantly involved in the genetic susceptibility to childhood ALL in Morocco.

Association of TP53 and CDKN2A Mutation Profile with Tumor Mutation Burden in Head and Neck Cancer

PURPOSE

Head and neck squamous cell carcinoma (HNSCC) is a frequently devastating cancer that affects more than a half million people annually worldwide. Although some cases arise from infection with human papillomavirus (HPV), HPV-negative HNSCC is more common, and associated with worse outcome. Advanced HPV-negative HNSCC may be treated with surgery, chemoradiation, targeted therapy, or immune checkpoint inhibition (ICI). There is considerable need for predictive biomarkers for these treatments. Defects in DNA repair capacity and loss of cell-cycle checkpoints sensitize tumors to cytotoxic therapies, and can contribute to phenotypes such as elevated tumor mutation burden (TMB), associated with response to ICI. Mutation of the tumor suppressors and checkpoint mediators TP53 and CDKN2A is common in HPV-negative HNSCC.

EXPERIMENTAL DESIGN

To gain insight into the relation of the interaction of TP53 and CDKN2A mutations with TMB in HNSCC, we have analyzed genomic data from 1,669 HPV-negative HNSCC tumors with multiple criteria proposed for assessing the damaging effect of TP53 mutations.

RESULTS

Data analysis established the TP53 and CDKN2A mutation profiles in specific anatomic subsites and suggested that specific categories of TP53 mutations are more likely to associate with CDKN2A mutation or high TMB based on tumor subsite. Intriguingly, the pattern of hotspot mutations in TP53 differed depending on the presence or absence of a cooccurring CDKN2A mutation.

CONCLUSIONS

These data emphasize the role of tumor subsite in evaluation of mutational profiles in HNSCC, and link defects in TP53 and CDKN2A to elevated TMB levels in some tumor subgroups.

The Role of the CREB Protein Family Members and the Related Transcription Factors in Radioresistance Mechanisms

In the framework of space flight, the risk of radiation carcinogenesis is considered a "red" risk due to the high likelihood of occurrence as well as the high potential impact on the quality of life in terms of disease-free survival after space missions. The cyclic AMP response element-binding protein (CREB) is overexpressed both in haematological malignancies and solid tumours and its expression and function are modulated following irradiation. The CREB protein is a transcription factor and member of the CREB/activating transcription factor (ATF) family. As such, it has an essential role in a wide range of cell processes, including cell survival, proliferation, and differentiation. Among the CREB-related nuclear transcription factors, NF-κB and p53 have a relevant role in cell response to ionising radiation. Their expression and function can decide the fate of the cell by choosing between death or survival. The aim of this review was to define the role of the CREB/ATF family members and the related transcription factors in the response to ionising radiation of human haematological malignancies and solid tumours.

miR-138-5p induces aggressive traits by targeting Trp53 expression in murine melanoma cells, and correlates with poor prognosis of melanoma patients

Deregulation of miRNAs contributes to the development of distinct cancer types, including melanoma, an aggressive form of skin cancer characterized by high metastatic potential and poor prognosis. The expression of a set of 580 miRNAs was investigated in a model of murine melanoma progression, comprising non-metastatic (4C11-) and metastatic melanoma (4C11+) cells. A significant increase in miR-138-5p expression was found in the metastatic 4C11+ melanoma cells compared to 4C11-, which prompted us to investigate its role in melanoma aggressiveness. Functional assays, including anoikis resistance, colony formation, collective migration, serum-deprived growth capacity, as well as in vivo tumor growth and experimental metastasis were performed in 4C11- cells stably overexpressing miR-138-5p. miR-138-5p induced an aggressive phenotype in mouse melanoma cell lines leading to increased proliferation, migration and cell viability under stress conditions. Moreover, by overexpressing miR-138-5p, low-growing and non-metastatic 4C11- cells became highly proliferative and metastatic in vivo, similar to the metastatic 4C11+ cells. Luciferase reporter analysis identified the tumor suppressor Trp53 as a direct target of miR-138-5p. Using data sets from independent melanoma cohorts, miR-138-5p and P53 expression were also found deregulated in human melanoma samples, with their levels negatively and positively correlated with prognosis, respectively. Our data shows that the overexpression of miR-138-5p contributes to melanoma metastasis through the direct suppression of Trp53.

MiR-3614-5p Is a Potential Novel Biomarker for Colorectal Cancer

MiR-3614-5p has been found in a variety of cancers including colorectal cancer. However, the association of miR-3614-5p with colorectal cancer is still unclear. Based on the Cancer Genome Atlas (TCGA) database, the relationship between miR-3614-5p and colorectal cancer can be proved. Wilcoxon rank-sum test was used to compare the miR-3614-5p expression in colorectal cancer tissues and under normal conditions, respectively. The logistic regression method was further employed to analyze the relationship between miR-3614-5p and clinicopathological characteristics. Also, the correlation between miR-3614-5p and survival rate was evaluated by Kaplan-Meier and Cox regression analysis. Besides, gene set enrichment analysis (GSEA) was used to investigate the biological functions of miR-3614-5p. The decrease of miR-3614-5p expression of colorectal cancer was significantly correlated with N stage (OR) = 0.7 for N1&N2 vs. N0), M stage (OR = 0.5 for M1 vs. M0), pathologic stage (OR = 0.7 for Stage III & Stage IV vs. Stage I & Stage II), neoplasm type (OR = 0.5 for rectum adenocarcinoma vs. colon adenocarcinoma), and lymphatic invasion (OR = 0.6 for YES vs. NO) (all p-values < 0.05). Kaplan-Meier survival analysis showed that colorectal cancer with low miR-3614-5p has a poorer prognosis than that of high miR-3614-5p (p = 0.005). According to univariate analysis, low miR-3614-5p was associated with poor overall survival (OS) [hazard ratio (HR) = 0.599; 95% confidence interval (CI): 0.418-0.857; p = 0.005]. In multivariate analysis, miR-3614-5p was closely related to OS (HR = 0.630; 95% CI: 0.405-0.978, p = 0.021). GSEA showed that the high expression phenotype of miR-3614-5p differentially enriches the P53 pathway. Meanwhile, the high expression phenotype of miR-3614-5p enhanced NK T cell activation, negative T cell selection, response to interleukin 2, and response to tumor cells. MiR-3614-5p is a possible prognostic marker of low survival rate for patients with colorectal cancer. Moreover, the P53 pathway and P38MAPK pathway may be the key pathways regulated by miR-3614-5p in colorectal cancer.

Mechanisms of TP53 Pathway Inactivation in Embryonic and Somatic Cells-Relevance for Understanding (Germ Cell) Tumorigenesis

The P53 pathway is the most important cellular pathway to maintain genomic and cellular integrity, both in embryonic and non-embryonic cells. Stress signals induce its activation, initiating autophagy or cell cycle arrest to enable DNA repair. The persistence of these signals causes either senescence or apoptosis. Over 50% of all solid tumors harbor mutations in TP53 that inactivate the pathway. The remaining cancers are suggested to harbor mutations in genes that regulate the P53 pathway such as its inhibitors Mouse Double Minute 2 and 4 (MDM2 and MDM4, respectively). Many reviews have already been dedicated to P53, MDM2, and MDM4, while this review additionally focuses on the other factors that can deregulate P53 signaling. We discuss that P14^ARF (ARF) functions as a negative regulator of MDM2, explaining the frequent loss of ARF detected in cancers. The long non-coding RNA Antisense Non-coding RNA in the INK4 Locus (ANRIL) is encoded on the same locus as ARF, inhibiting ARF expression, thus contributing to the process of tumorigenesis. Mutations in tripartite motif (TRIM) proteins deregulate P53 signaling through their ubiquitin ligase activity. Several microRNAs (miRNAs) inactivate the P53 pathway through inhibition of translation. CCCTC-binding factor (CTCF) maintains an open chromatin structure at the TP53 locus, explaining its inactivation of CTCF during tumorigenesis. P21, a downstream effector of P53, has been found to be deregulated in different tumor types. This review provides a comprehensive overview of these factors that are known to deregulate the P53 pathway in both somatic and embryonic cells, as well as their malignant counterparts (i.e., somatic and germ cell tumors). It provides insights into which aspects still need to be unraveled to grasp their contribution to tumorigenesis, putatively leading to novel targets for effective cancer therapies.

Associations of MDM2 and MDM4 Polymorphisms with Early-Stage Breast Cancer

Breast cancer is one of the most common cancers worldwide. Single nucleotide polymorphisms (SNPs) in MDM2 and MDM4 have been associated with various cancers. However, the influence on clinical characteristics of breast cancer has not been sufficiently investigated yet. Thus, this study aimed to investigate the relationship between SNPs in MDM2 (rs2279744, rs937283, rs937282) and MDM4 (rs1380576, rs4245739) and I-II stage breast cancer. For analysis, the genomic DNA was extracted from 100 unrelated women peripheral blood. Polymorphisms were analyzed with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. The study showed that MDM2 rs937283 and rs937282 were significantly associated with estrogen receptor status and human epidermal growth factor receptor 2 (HER2) status. SNPs rs1380576 and rs4245739, located in MDM4, were significantly associated with status of estrogen and progesterone receptors. Our findings suggest that rs937283 AG, rs937282 CG, rs1380576 CC, and rs4245739 AA genotypes were linked to hormonal receptor positive breast cancer and may be useful genetic markers for disease assessment.

Cancer and Tumour Suppressor p53 Encounters at the Juncture of Sex Disparity

There are many differences in cancer manifestation between men and women. New understanding of the origin of these point to fundamental distinctions in the genetic code and its demise. Tumour suppressor protein p53 is the chief operating officer of cancer defence and critically acts to safeguard against sustained DNA damaged. P53 cannot be ignored in cancer sex disparity. In this review we discuss the greater prevalence and associated death rates for non-reproductive cancers in males. The major tumour suppressor protein p53, encoded in the TP53 gene is our chosen context. It is fitting to ask why somatic TP53 mutation incidence is estimated to be disproportionately higher among males in the population for these types of cancers compared with females? We scrutinised the literature for evidence of predisposing genetic and epigenetic alterations that may explain this sex bias. Our second approach was to explore whether redox activity, either externally imposed or inherent to males and females, may define distinct risks that could contribute to the clear cancer sex disparities.

Long noncoding RNA MEG3 blocks telomerase activity in human liver cancer stem cells epigenetically

BACKGROUND

MEG3 downregulated the expression in several tumors and inhibits human tumorigenesis. But so far, the mechanism of MEG3 in tumorigenesis is still unclear.

METHODS

In gene infection, cellular and molecular technologies and tumorigenesis test in vitro and in vivo were performed, respectively.

RESULTS

Our results indicate that MEG3 enhances the P53 expression by triggering the loading of P300 and RNA polymerase II onto its promoter regions dependent on HP1α. Moreover, MEG3 increases the methylation modification of histone H3 at the 27th lysine via P53. Furthermore, MEG3 inhibits the expression of TERT by increasing the H3K27me3 in TERT promoter regions, thereby inhibiting the activity of telomerase by reducing the binding of TERT to TERC. Furthermore, MEG3 also increases the expression of TERRA; therefore, the interaction between TERC and TERT was competitively attenuated by increasing the interaction between TERRA and TERT, which inhibits the activity of telomerase in hLCSCs. Strikingly, MEG3 reduces the length of telomere by blocking the formation of complex maintaining telomere length (POT1-Exo1-TRF2-SNM1B) and decreasing the binding of the complex to telomere by increasing the interplay between P53 and HULC. Ultimately, MEG3 inhibits the growth of hLCSCs by reducing the activity of telomerase and attenuating telomeric repeat binding factor 2(TRF2).

CONCLUSIONS

Our results demonstrates MEG3 inhibits the occurrence of human liver cancer by blocking telomere, and these findings provide an important insight into the prevention and treatment of human liver cancer.

Survival of Lung Cancer Patients Dependent on the LOH Status for DMP1, ARF, and p53

Lung cancer is the leading cause of cancer deaths in the world, and accounts for more solid tumor deaths than any other carcinomas. The prognostic values of DMP1, ARF, and p53-loss are unknown in lung cancer. We have conducted survival analyses of non-small cell lung cancer (NSCLC) patients from the University of Minnesota VA hospital and those from the Wake Forest University Hospital. Loss of Heterozygosity (LOH) for hDMP1 was found in 26 of 70 cases (37.1%), that of the ARF/INK4a locus was found in 33 of 70 (47.1%), and that of the p53 locus in 43 cases (61.4%) in the University of Minnesota samples. LOH for hDMP1 was associated with favorable prognosis while that of p53 predicted worse prognosis. The survival was much shorter for ARF-loss than INK4a-loss, emphasizing the importance of ARF in human NSCLC. The adverse effect of p53 LOH on NSCLC patients' survival was neutralized by simultaneous loss of the hDMP1 locus in NSCLC and breast cancer, suggesting the possible therapy of epithelial cancers with metastatic ability.

Common genetic variants in the TP53 pathway and their impact on cancer

The TP53 gene is well known to be the most frequently mutated gene in human cancer. In addition to mutations, there are > 20 different coding region single-nucleotide polymorphisms (SNPs) in the TP53 gene, as well as SNPs in MDM2, the negative regulator of p53. Several of these SNPs are known to alter p53 pathway function. This makes p53 rather unique among cancer-critical genes, e.g. the coding regions of other cancer-critical genes like Ha-Ras, RB, and PI3KCA do not have non-synonymous coding region SNPs that alter their function in cancer. The next frontier in p53 biology will consist of probing which of these coding region SNPs are moderately or strongly pathogenic and whether they influence cancer risk and the efficacy of cancer therapy. The challenge after that will consist of determining whether we can tailor chemotherapy to correct the defects for each of these variants. Here we review the SNPs in TP53 and MDM2 that show the most significant impact on cancer and other diseases. We also propose avenues for how this information can be used to better inform personalized medicine approaches to cancer and other diseases.

Tumor suppressor p53 and metabolism

p53 plays a key role in tumor suppression. The tumor suppressive function of p53 has long been attributed to its ability to induce apoptosis, cell cycle arrest, and senescence in cells. However, recent studies suggest that other functions of p53 also contribute to its role as a tumor suppressor, such as its function in metabolic regulation. p53 regulates various metabolic pathways to maintain the metabolic homeostasis of cells and adapt cells to stress. In addition, recent studies have also shown that gain-of-function (GOF) mutant p53 proteins drive metabolic reprogramming in cancer cells, contributing to cancer progression. Further understanding of p53 and its GOF mutants in metabolism will provide new opportunities for cancer therapy.

Loss of TRP53 (p53) accelerates tumorigenesis and changes the tumor spectrum of SJL/J mice

Known as the guardian of the genome, transformation-related protein 53 (TRP53) is a well -known tumor suppressor. Here, we describe a novel TRP53 deficient mouse model on a tumor prone background—SJL/J mice. The absence of TRP53 (TRP53 nullizygosity) leads to a shift in the tumor spectrum from a non-Hodgkin’s-like disease to thymic lymphomas and testicular teratomas at a very rapid tumor onset averaging ~12 weeks of age. In haplotype studies, comparing tumor prone versus tumor resistant Trp53 null mouse strains, we found that other tumor suppressor, DNA repair and/or immune system genes modulate tumor incidence in TRP53 null strains, suggesting that even a strong tumor suppressor such as TRP53 is modulated by genetic background. Due to their rapid development of tumors, the SJL/J TRP53 null mice generated here can be used as an efficient chemotherapy or immunotherapy screening mouse model.

Evaluation of TP53 Codon 72, P21 Codon 31, and MDM2 SNP309 Polymorphisms in Iranian Patients with Acute Lymphocytic Leukemia

BACKGROUND

The tumor suppressing protein p53 and its downstream effector p21 play important roles in cell cycle regulation. Deficiency or deactivation of these proteins as a result of gene alterations has been indicated in several cancers. Such genetic variations could be considered as susceptibility indicators in acute lymphocytic leukemia (ALL). Therefore, we investigated the associations between ALL risk and TP53 codon 72, p21 codon 31, and MDM2 SNP309 polymorphisms in an Iranian population.

METHODS

Polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) was used to determine the MDM2 T309G (rs2279744), TP53 codon Arg72Pro (rs1042522), and p21 Ser31Arg (rs1801270) single nucleotide polymorphisms (SNPs). This study was performed in 115 ALL patients and 115 healthy controls in Khuzestan province in southwest Iran.

RESULTS

In the control group and ALL patients, p21 Ser/Arg, and MDM2 TG and GG genotypes were associated with significant 1.81-fold (95% confidence interval CI= 1.008-3.267; P < 0.05), 11.07-fold (95% CI= 5.10-24.05; P < 0.0001), and 19.41-fold (95% CI= 8.56-43.99; P < 0.0001) increased risks for ALL, respectively. The TP53 72 Arg allele was significantly more prevalent in ALL patients (56.96%) than in control subjects (47.39%), and was significantly associated with ALL (OR= 1.47; 95% CI = 1.017-2.121, P < 0.05).

CONCLUSION

The MDM2T309G and the p21 Ser31Arg SNPs indicate a significantly increased risk for developing ALL in Khuzestan province.

Clonal Selection of a Novel Deleterious TP53 Somatic Mutation Discovered in ctDNA of a KIT/PDGFRA Wild-Type Gastrointestinal Stromal Tumor Resistant to Imatinib

The standard of care for the first-line treatment of advanced gastrointestinal stromal tumor (GIST) is represented by imatinib, which is given daily at a standard dosage until tumor progression. Resistance to imatinib commonly occurs through the clonal selection of genetic mutations in the tumor DNA, and an increase in imatinib dosage was demonstrated to be efficacious to overcome imatinib resistance. Wild-type GISTs, which do not display KIT or platelet-derived growth factor receptor alpha (PDGFRA) mutations, are usually primarily insensitive to imatinib and tend to rapidly relapse in course of treatment. Here we report the case of a 53-year-old male patient with gastric GIST who primarily did not respond to imatinib and that, despite the administration of an increased imatinib dose, led to patient death. By using a deep next-generation sequencing barcode-aware approach, we analyzed a panel of actionable cancer-related genes in the patient cfDNA to investigate somatic changes responsible for imatinib resistance. We identified, in two serial circulating tumor DNA (ctDNA) samples, a sharp increase in the allele frequency of a never described TP53 mutation (c.560-7_560-2delCTCTTAinsT) located in a splice acceptor site and responsible for a protein loss of function. The same TP53 mutation was retrospectively identified in the primary tumor by digital droplet PCR at a subclonal frequency (0.1%). The mutation was detected at a very high allelic frequency (99%) in the metastatic hepatic lesion, suggesting a rapid clonal selection of the mutation during tumor progression. Imatinib plasma concentration at steady state was above the threshold of 760 ng/ml reported in the literature for the minimum efficacious concentration. The de novo TP53 (c.560-7_560-2delCTCTTAinsT) mutation was in silico predicted to be associated with an aberrant RNA splicing and with an aggressive phenotype which might have contributed to a rapid disease spread despite the administration of an increased imatinib dosage. This result underlies the need of a better investigation upon the role of TP53 in the pathogenesis of GISTs and sustains the use of next-generation sequencing (NGS) in cfDNA for the identification of novel genetic markers in wild-type GISTs.

African-centric TP53 variant increases iron accumulation and bacterial pathogenesis but improves response to malaria toxin

A variant at amino acid 47 in human TP53 exists predominantly in individuals of African descent. P47S human and mouse cells show increased cancer risk due to defective ferroptosis. Here, we show that this ferroptotic defect causes iron accumulation in P47S macrophages. This high iron content alters macrophage cytokine profiles, leads to higher arginase level and activity, and decreased nitric oxide synthase activity. This leads to more productive intracellular bacterial infections but is protective against malarial toxin hemozoin. Proteomics of macrophages reveal decreased liver X receptor (LXR) activation, inflammation and antibacterial defense in P47S macrophages. Both iron chelators and LXR agonists improve the response of P47S mice to bacterial infection. African Americans with elevated saturated transferrin and serum ferritin show higher prevalence of the P47S variant (OR = 1.68 (95%CI 1.07–2.65) p = 0.023), suggestive of its role in iron accumulation in humans. This altered macrophage phenotype may confer an advantage in malaria-endemic sub-Saharan Africa.

A polymorphism in human TP53 (P47S) that predominantly exists in individuals of African descent affects ferroptosis. Here, the authors show that this results in iron accumulation in macrophages leading to more productive infection by intracellular bacteria but improved anti-inflammatory response to the malarial toxin hemozoin.

BMP9 mediates the anticancer activity of evodiamine through HIF‑1α/p53 in human colon cancer cells

Colon cancer is one of the most common malignancies. Although there has been great development in treatment regimens over the last few decades, its prognosis remains poor. There is still a clinical need to find new drugs for colon cancer. Evodiamine (Evo) is a quinolone alkaloid extracted from the traditional herbal medicine plant Evodia rutaecarpa. In the present study, CCK-8, flow cytometry, reverse transcription quantitative polymerase chain reaction, western blot analysis and a xenograft tumor model were used to evaluate the anti-cancer activity of Evo in human colon cancer cells and determine the possible mechanism underlying this process. It was revealed that Evo exhibited prominent anti-proliferation and apoptosis-inducing effects in HCT116 cells. Bone morphogenetic protein 9 (BMP9) was notably upregulated by Evo in HCT116 cells. Exogenous BMP9 potentiated the anti-cancer activity of Evo, and BMP9 silencing reduced this effect. In addition, HIF-1α was also upregulated by Evo. The anticancer activity of Evo was enhanced by HIF-1α, but was reduced by HIF-1α silencing. BMP9 potentiated the effect of Evo on the upregulation of HIF-1α, and enhanced the antitumor effect of Evo in colon cancer, which was clearly reduced by HIF-1α silencing. In HCT116 cells, Evo increased the phosphorylation of p53, which was enhanced by BMP9 but reduced by BMP9 silencing. Furthermore, the effect of Evo on p53 was potentiated by HIF-1α and reduced by HIF-1α silencing. The present findings therefore strongly indicated that the anticancer activity of Evo may be partly mediated by BMP9 upregulation, which can activate p53 through upregulation of HIF-1α, at least in human colon cancer.

Mapping actionable pathways and mutations in brain tumours using targeted RNA next generation sequencing

Many biology-based precision drugs are available that neutralize aberrant molecular pathways in cancer. Molecular heterogeneity and the lack of reliable companion diagnostic biomarkers for many drugs makes targeted treatment of cancer inaccurate for many individuals. Identifying actionable hyperactive biological pathways in individual cancers may improve this situation.

To achieve this we applied a novel targeted RNA next generation sequencing (t/RNA-NGS) technique to surgically obtained glioma tissues. The test combines mutation detection with analysis of biological pathway activities that are involved in tumour behavior in many cancer types (e.g. tyrosine kinase signaling, angiogenesis signaling, immune response, metabolism), via quantitative measurement of transcript levels and splice variants of hundreds of genes. We here present proof of concept that the technique, which uses molecular inversion probes, generates a histology-independent molecular diagnosis and identifies classifiers that are strongly associated with conventional histopathology diagnoses and even with patient prognosis. The test not only confirmed known glioma-associated molecular aberrations but also identified aberrant expression levels of actionable genes and mutations that have so far been considered not to be associated with glioma, opening up the possibility of drug repurposing for individual patients. Its cost-effectiveness makes t/RNA-NGS to an attractive instrument to aid oncologists in therapy decision making.

[Update on Li-Fraumeni syndrome]

The Li-Fraumeni syndrome (LFS, online Mendelian inheritance in man, OMIM #151623) is considered to be one of the currently known most aggressive cancer predisposition syndromes. The heterogeneous spectrum of tumors is dominated by bone and soft tissue sarcomas, various brain tumors, premenopausal breast cancer and adrenocortical carcinoma (ACC). Even in childhood the cancer risk is very strongly increased and it is not uncommon for people with LFS to develop synchronous and metachronous tumors. Typical histopathological findings and molecular genetic signatures can help towards the diagnosis. Inheritance is autosomal dominant and the penetrance appears to be more variable than previously thought. The prevalence of LFS is approximately 1:5000 with a high interregional variance. The LFS is caused by germline mutations in the TP53 gene coding for the protein p53, an essential cellular transcription factor that initiates antitumor responses to cellular stress, such as DNA damage. In people with LFS, due to the loss of functional p53, the protective mechanism of the cells is weakened resulting in a significantly increased cancer risk. In order to improve the survival of people with LFS, structured tumor early recognition and surveillance strategies are recommended; however, national and international longitudinal observational studies are needed to evaluate the cost-effort-benefit balance. For this reason, the authors have established the LFS cancer predisposition registry in which all patients with LFS and other syndromes predisposing to cancer can be registered. Detailed information can be found at www.cancer-predisposition.org .

Single-Nucleotide Polymorphism 309T>G in the MDM2 Promoter Determines Functional Outcome After Stroke

Background and Purpose- The E3 ubiquitin ligase MDM2 (murine double minute 2) is the main negative regulator of the p53 protein-a key player in neuronal apoptosis after ischemia. A functional single-nucleotide polymorphism in the human MDM2 gene promoter (rs2279744) regulates MDM2 protein expression. We investigated whether the MDM2 SNP309, by controlling p53-mediated apoptosis, determines functional outcome after stroke. Methods- Primary cortical neurons were subjected to oxygen and glucose deprivation. Mice were subjected to ischemic (transient middle cerebral artery occlusion) or hemorrhagic (collagenase injection) stroke models. Protein and mRNA levels of MDM2 and p53 were measured in both neuronal and brain extracts. The interaction of MDM2 with p53 was disrupted by neuronal treatment with nutlin-3a. siRNA was used to knockdown MDM2 expression. We analyzed the link between the MDM2 SNP309 and functional outcome, measured by the modified Rankin Scale scores, in 2 independent hospital-based stroke cohorts: ischemic stroke cohort (408 patients) and intracerebral hemorrhage cohort (128 patients). Results- Experimental stroke and oxygen and glucose deprivation induced the expression of MDM2 in the brain and neurons, respectively. Moreover, oxygen and glucose deprivation promoted MDM2 binding with p53 in neurons. Disruption of the MDM2-p53 interaction with nutlin-3a, or MDM2 knockdown by siRNA, triggered p53 accumulation, which increased neuronal susceptibility to oxygen and glucose deprivation-induced apoptosis. Finally, we showed that patients harboring the G allele in the MDM2 promoter had higher MDM2 protein levels and showed better functional outcome after stroke than those harboring the T/T genotype. The T/T genotype was also associated with large infarct volume in ischemic stroke and increased lesion volume in patients with intracerebral hemorrhage. Conclusions- Our results reveal a novel role for the MDM2-p53 interaction in neuronal apoptosis after ischemia and show that the MDM2 SNP309 determines the functional outcome of patients after stroke.

SNPing away at mutant p53 activities

This Outlook by Ortiz and Lozano discusses the study by Basu et al. in this issue of Genes & Development. They describe SNPs in the p53 pathway that alter p53 transcriptional activity and are associated with cancer risk and show evidence for SNPs that influence the gain-of-function (GOF) activities of mutant p53.

A delicate balance in the levels of proteins that regulate the p53 tumor suppressor pathway exists such that subtle changes alter p53 tumor suppressor activity and cancer risk. Many single-nucleotide polymorphisms (SNPs) in the p53 pathway alter p53 transcriptional activity and are associated with cancer risk. In addition, some SNPs influence the gain-of-function (GOF) activities of mutant p53 through unknown mechanisms. In this issue of Genes & Development, Basu and colleagues (pp. 230–243) provide direct evidence that the presence of an R72 polymorphism enhances the GOF invasive and metastatic properties of mutant p53 by regulating interactions with PGC-1α, an important regulator of mitochondrial biogenesis and oxidative phosphorylation. The study culminates with evidence that R72 is associated with worse outcomes in human breast cancer.

Elevated telomere dysfunction in cells containing the African-centric Pro47Ser cancer-risk variant of TP53

Subtelomeric transcription and chromatin can have a significant impact on telomere repeat maintenance and chromosome stability. We have previously found that tumor suppressor protein p53 (TP53) can bind to retrotransposon-like elements in a majority of human subtelomeres to regulate TERRA transcription and telomeric histone acetylation in response to DNA damage. TP53 also prevents the accumulation of γH2AX DNA-damage signaling at telomeres. We now show that the inherited TP53 polymorphism Pro47Ser (hereafter S47), which is enriched in populations of African descent, is associated with elevated marks of telomere dysfunction. We found that human and mouse cells carrying the S47 variant show increased γH2AX DNA-damage signals at telomeres, as well as reduced TERRA transcription and subtelomeric histone acetylation in response to DNA damage stress. Cell-lines containing inducible genes for P47 or S47 versions of p53, as well mouse embryo fibroblasts (MEFs) reconstituted with human p53, showed elevated telomere-induced DNA damage foci and metaphase telomere signal loss in cells with S47. Human lymphoblastoid cell lines (LCLs) derived from individuals homozygous for S47, show increased accumulation of subtelomeric γH2AX and unstable telomere repeats in response to DNA damage relative to age matched LCLs homozygous for P47. Furthermore, LCLs with S47 had reduced replicative lifespan. These studies indicate that the naturally occurring S47 variant of p53 can affect telomeric chromatin, telomere repeat stability, and replicative capacity. We discuss the potential evolutionary significance of the S47 variant to African populations with respect to telomere regulation and the implications for inherited health disparities.

Tumor cells containing the African-Centric S47 variant of TP53 show increased Warburg metabolism

Mutations in the TP53 tumor suppressor gene remain a hallmark of human cancer. In addition to mutation of TP53, single nucleotide polymorphisms (SNPs) in this gene can have a profound impact on p53 function, and can affect cancer risk as well as other p53 functions. Wild type (WT) p53 contains a proline at amino acid 47, but approximately 1% of African-Americans express a p53 allele with a serine at amino acid 47 (Pro47Ser, hereafter S47). In a mouse model for this variant, mice expressing S47 are predisposed to spontaneous cancers. The S47 variant also is associated with increased pre-menopausal breast cancer risk in African American women. We recently reported that S47 tumor cells are resistant to the majority of cytotoxic chemotherapeutic agents, but show increased sensitivity to a subset of anti-cancer agents, compared to tumors with WT p53. In this work, we report on another potentially promising therapeutic vulnerability of S47 tumors. We find that S47 tumors show decreased mitochondrial metabolism, along with increased dependency on glycolysis. S47 tumor cells also show increased sensitivity to the glycolytic poison 2-deoxy-glucose. We propose that the altered metabolism in S47 tumor cells may be yet another potentially-actionable therapeutic vulnerability to exploit in cancer-prone individuals with this genotype.

Oncogenic Metabolism Acts as a Prerequisite Step for Induction of Cancer Metastasis and Cancer Stem Cell Phenotype

Metastasis is a major obstacle to the efficient and successful treatment of cancer. Initiation of metastasis requires epithelial-mesenchymal transition (EMT) that is regulated by several transcription factors, including Snail and ZEB1/2. EMT is closely linked to the acquisition of cancer stem cell (CSC) properties and chemoresistance, which contribute to tumor malignancy. Tumor suppressor p53 inhibits EMT and metastasis by negatively regulating several EMT-inducing transcription factors and regulatory molecules; thus, its inhibition is crucial in EMT, invasion, metastasis, and stemness. Metabolic alterations are another hallmark of cancer. Most cancer cells are more dependent on glycolysis than on mitochondrial oxidative phosphorylation for their energy production, even in the presence of oxygen. Cancer cells enhance other oncogenic metabolic pathways, such as glutamine metabolism, pentose phosphate pathway, and the synthesis of fatty acids and cholesterol. Metabolic reprogramming in cancer is regulated by the activation of oncogenes or loss of tumor suppressors that contribute to tumor progression. Oncogenic metabolism has been recently linked closely with the induction of EMT or CSC phenotypes by the induction of several metabolic enzyme genes. In addition, several transcription factors and molecules involved in EMT or CSCs, including Snail, Dlx-2, HIF-1α, STAT3, TGF-β, Wnt, and Akt, regulate oncogenic metabolism. Moreover, p53 induces metabolic change by directly regulating several metabolic enzymes. The collective data indicate the importance of oncogenic metabolism in the regulation of EMT, cell invasion and metastasis, and adoption of the CSC phenotype, which all contribute to malignant transformation and tumor development. In this review, we highlight the oncogenic metabolism as a key regulator of EMT and CSC, which is related with tumor progression involving metastasis and chemoresistance. Targeting oncometabolism might be a promising strategy for the development of effective anticancer therapy.

Tumor suppression by the EGR1, DMP1, ARF, p53, and PTEN Network

Recent studies have indicated that EGR1 is a direct regulator of tumor suppressors including TGFβ1, PTEN, and p53. The Myb-like transcription factor Dmp1 is a physiological regulator of the Arf-p53 pathway through transactivation of the Arf promoter and physical interaction of p53. The Dmp1 promoter has binding sites for Egr proteins, and Egr1 is a target for Dmp1. Crosstalks between p53 and PTEN have been reported. The Egr1-Dmp1-Arf-p53-Pten pathway displays multiple modes of interaction with each other, suggesting the existence of a functional network of tumor suppressors that maintain normal cell growth and prevent the emergence of incipient cancer cells.

TP53 codon 72 Polymorphism and bladder cancer risk: a meta-analysis and emphasis on the role of tumor or smoking status

Background: Various studies had explored the relationship between TP53 codon 72 polymorphisms and the risk of bladder cancer (BC). However, their results remained inconsistent and the definite role of smoking or tumor status associated with this polymorphism in BC cases was seldom involved. Hence, this meta-analysis was to disclose such associations. Methods: Systematical and comprehensive retrieval of online databases PubMed, PMC, EMBASE and Web of Science were conducted to obtain eligible studies, up to May 30th, 2018. Pooled odds ratios (ORs) with 95% confidence intervals (CI) were utilized to assess the associations between TP53 codon 72 polymorphisms and BC susceptibilities under five genetic comparison models. Results: Ultimately, this meta-analysis enrolled 22 applicable studies with 3,791 BC cases and 4,917 controls. Our results suggested that the variant genotypes were associated with BC risk in Asian subgroup (allele model: OR=1.19, 95% CI=1.04-1.34; dominant model: OR=1.27, 95% CI=1.06-1.52; homozygote model: OR=1.36, 95% CI=1.03-1.80), while negative outcomes were presented in Caucasians. In the relationship between TP53 codon 72 polymorphisms and BC tumor stage in Asian group, positive results were presented in allele model: OR=1.68, 95% CI=1.04-2.72; dominant model: OR=2.46, 95% CI=1.08-5.61; heterozygous model: OR=2.32, 95% CI=1.04-5.14; homozygote model: OR=2.66, 95% CI=1.04-6.81. However, no evidence was revealed between this polymorphism and BC tumor grade. Besides, significant associations were displayed between TP53 codon 72 polymorphism and smoking status (allele model: OR=1.40, 95% CI=1.06-1.84; dominant model OR=1.72, 95% CI=1.18-2.50; heterozygous model: OR=1.77, 95% CI=1.19-2.64). Conclusion: Taken together, our results shed light on that TP53 codon 72 polymorphism was significantly associated with the susceptibility to BC in Asians. In addition, positive associations were also revealed between this polymorphism and tumor stage/smoking status in BC cases.

The transcription-independent mitochondrial cell death pathway is defective in non-transformed cells containing the Pro47Ser variant of p53

Approximately half of all human cancers contain mutations in the TP53 tumor suppressor. In addition to mutations, there are single nucleotide polymorphisms (SNPs) in TP53 that can dampen p53 function, and can increase cancer risk and decrease the efficacy of cancer therapy. Approximately 6% of Africans and 1% of African-Americans express a p53 allele with a serine instead of proline at position 47 (Pro47Ser, or S47). The S47 variant is associated with increased breast cancer risk in pre-menopausal African Americans, and in a mouse model for the S47 variant, mice are predisposed to spontaneous cancers. We recently showed that the S47 variant is impaired for p53-mediated apoptosis in response to radiation and some genotoxic agents, particularly cisplatin. Here we identify the mechanism for impaired apoptosis of S47 in response to cisplatin. We show that following cisplatin treatment, the S47 variant shows normal stabilization and serine 15 phosphorylation, but reduced ability to bind to the peptidyl prolyl isomerase PIN1, which controls the mitochondrial localization of p53. This is accompanied by impaired mitochondrial localization of S47, along with decreased induction of cleaved caspase-3. Interestingly, we show that this defect occurs only for cisplatin and not for camptothecin. These findings show that normal tissues may respond differently to genotoxic stress depending upon this TP53 genotype. These data suggest that toxicity to cisplatin may be decreased in S47 individuals, and that this compound may be a superior treatment option for these individuals.

Aberrant Expression of p14ARF in Human Cancers: A New Biomarker?

The ARF and INK4a genes are located on the CDKN2a locus, both showing tumor suppressive activity. ARF has been shown to monitor potentially harmful oncogenic signalings, making early stage cancer cells undergo senescence or programmed cell death to prevent cancer. Conversely, INK4a detects both aging and incipient cancer cell signals, and thus these two gene functions are different. The efficiency of detection of oncogenic signals is more efficient for the for the former than the latter in the mouse system. Both ARF and INK4a genes are inactivated by gene deletion, promoter methylation, frame shift, aberrant splicing although point mutations for the coding region affect only the latter. Recent studies show the splicing alterations that affect only ARF or both ARF and INK4a genes suggesting that ARF is inactivated in human tumors more frequently than what was previously thought. The ARF gene is activated by E2Fs and Dmp1 transcription factors while it is repressed by Bmi1, Tbx2/3, Twist1, and Pokemon nuclear proteins. It is also regulated at protein levels by Arf ubiquitin ligase named ULF, MKRN1, and Siva1. The prognostic value of ARF overexpression is controversial since it is induced in early stage cancer cells to eliminate pre-malignant cells (better prognosis); however, it may also indicate that the tumor cells have mutant p53 associated with worse prognosis. The ARF tumor suppressive protein can be used as a biomarker to detect early stage cancer cells as well as advanced stage tumors with p53 inactivation.

A polymorphism in the tumor suppressor p53 affects aging and longevity in mouse models

Tumor suppressor p53 prevents early death due to cancer development. However, the role of p53 in aging process and longevity has not been well-established. In humans, single nucleotide polymorphism (SNP) with either arginine (R72) or proline (P72) at codon 72 influences p53 activity; the P72 allele has a weaker p53 activity and function in tumor suppression. Here, employing a mouse model with knock-in of human TP53 gene carrying codon 72 SNP, we found that despite increased cancer risk, P72 mice that escape tumor development display a longer lifespan than R72 mice. Further, P72 mice have a delayed development of aging-associated phenotypes compared with R72 mice. Mechanistically, P72 mice can better retain the self-renewal function of stem/progenitor cells compared with R72 mice during aging. This study provides direct genetic evidence demonstrating that p53 codon 72 SNP directly impacts aging and longevity, which supports a role of p53 in regulation of longevity.

How long most animals live depends on the balance between the biological processes that allow them to regenerate their tissues when damaged and those that prevent them from developing cancer. Regeneration relies mostly on cells, in particular stem cells, dividing to make new cells, while cancer occurs when cell division becomes uncontrolled.

Tumor suppressor genes protect against cancer. One such gene encodes a protein called p53 that eliminates damaged cells before they can become cancerous. The p53 protein is also believed to be involved in regulating how quickly an animal ages and how long it lives, but this second role has not yet been clearly established.

Previous studies using different strategies to change the activity of p53 in several mouse models have led to inconsistent results. However, the mouse models used in these earlier studies did not reflect how p53 works under normal conditions.

Zhao et al. have now used mice in which the mouse gene for p53 was replaced with one of two versions of the equivalent human gene to study its impact on lifespan and the aging process. The two versions of p53 only differ slightly; a single building block of the protein, the amino acid at position 72, is a proline in one version but an arginine in the other. This difference makes one version of p53 weaker than the other; in other words, it is less able to eliminate damaged cells. Zhao et al. revealed that the mice with the weaker p53 lived for longer and appeared to age more slowly too. Further experiments showed that the stem cells in the mice with a weaker p53 were able to keep dividing and create new cells for longer. This is important because a decline in this activity – which is known as self-renewal – is a hallmark of aging.

Together these findings show that a small yet common change in p53 impacts both aging and lifespan, possibly by altering how stem cells are regulated. Further work is now needed to better understand why the different versions of p53 have different effects on stem cells.

Mutant p53 controls tumor metabolism and metastasis by regulating PGC-1α

Basu et al. show that mutant p53 enhances migration and metastasis of tumors through the ability to bind and regulate PGC-1α and that this regulation is markedly impacted by the codon 72 polymorphism.

Mutant forms of p53 protein often possess protumorigenic functions, conferring increased survival and migration to tumor cells via their “gain-of-function” activity. Whether and how a common polymorphism in TP53 at amino acid 72 (Pro72Arg; referred to here as P72 and R72) impacts this gain of function has not been determined. We show that mutant p53 enhances migration and metastasis of tumors through the ability to bind and regulate PGC-1α and that this regulation is markedly impacted by the codon 72 polymorphism. Tumor cells with the R72 variant of mutant p53 show increased PGC-1α function along with greatly increased mitochondrial function and metastatic capability. Breast cancers containing mutant p53 and the R72 variant show poorer prognosis compared with P72. The combined results reveal PGC-1α as a novel “gain-of-function” partner of mutant p53 and indicate that the codon 72 polymorphism influences the impact of mutant p53 on metabolism and metastasis.

Aberrant expression of p16INK4a in human cancers - a new biomarker?

The ARF and INK4a genes are located in the same CDKN2a locus, both showing its tumor suppressive activity. ARF has been shown to detect potentially harmful oncogenic signals, making incipient cancer cells undergo senescence or apoptosis. INK4a, on the other hand, responds to signals from aging in a variety of tissues including islets of Langerhans, neuronal cells, and cancer stem cells in general. It also detects oncogenic signals from incipient cancer cells to induce them senescent to prevent neoplastic transformation. Both of these genes are inactivated by gene deletion, promoter methylation, frame shift, and aberrant splicing although mutations changing the amino acid sequences affect only the latter. Recent studies indicated that polycomb gene products EZH2 and BMI1 repressed p16^INK4a expression in primary cells, but not in cells deficient for pRB protein function. It was also reported that that p14^ARF inhibits the stability of the p16^INK4a protein in human cancer cell lines and mouse embryonic fibroblasts through its interaction with regenerating islet-derived protein 3γ. Overexpression of INK4a is associated with better prognosis of cancer when it is associated with human papilloma virus infection. However, it has a worse prognostic value in other tumors since it is an indicator of pRB loss. The p16^INK4a tumor suppressive protein can thus be used as a biomarker to detect early stage cancer cells as well as advanced tumor cells with pRB inactivation since it is not expressed in normal cells.

Pathways from senescence to melanoma: focus on MITF sumoylation

Cutaneous melanoma is a deadly skin cancer that originates from melanocytes. The development of cutaneous melanoma involves a complex interaction between environmental factors, mainly ultraviolet radiation from sunlight, and genetic alterations. Melanoma can also occur from a pre-existing nevus, a benign lesion formed from melanocytes harboring oncogenic mutations that trigger proliferative arrest and senescence entry. Senescence is a potent barrier against tumor progression. As such, the acquisition of mutations that suppress senescence and promote cell division is mandatory for cancer development. This topic appears central to melanoma development because, in humans, several somatic and germline mutations are related to the control of cellular senescence and proliferative activity. Consequently, primary melanoma can be viewed as a paradigm of senescence evasion. In support of this notion, a sumoylation-defective germline mutation in microphthalmia-associated transcription factor (MITF), a master regulator of melanocyte homeostasis, is associated with the development of melanoma. Interestingly, this MITF variant has also been recently reported to negatively impact the program of senescence. This article reviews the genetic alterations that have been shown to be involved in melanoma and that alter the process of senescence to favor melanoma development. Then, the transcription factor MITF and its sumoylation-defective mutant are described. How sumoylation misregulation can change MITF activity and impact the process of senescence is discussed. Finally, the contribution of such information to the development of anti-malignant melanoma strategies is evaluated.

Mechanistic roles of microRNAs in hepatocarcinogenesis: A study of thioacetamide with multiple doses and time-points of rats

Environmental chemicals exposure is one of the primary factors for liver toxicity and hepatocarcinoma. Thioacetamide (TAA) is a well-known hepatotoxicant and could be a liver carcinogen in humans. The discovery of early and sensitive microRNA (miRNA) biomarkers in liver injury and tumor progression could improve cancer diagnosis, prognosis, and management. To study this, we performed next generation sequencing of the livers of Sprague-Dawley rats treated with TAA at three doses (4.5, 15 and 45 mg/kg) and four time points (3-, 7-, 14- and 28-days). Overall, 330 unique differentially expressed miRNAs (DEMs) were identified in the entire TAA-treatment course. Of these, 129 DEMs were found significantly enriched for the “liver cancer” annotation. These results were further complemented by pathway analysis (Molecular Mechanisms of Cancer, p53-, TGF-β-, MAPK- and Wnt-signaling). Two miRNAs (rno-miR-34a-5p and rno-miR-455-3p) out of 48 overlapping DEMs were identified to be early and sensitive biomarkers for TAA-induced hepatocarcinogenicity. We have shown significant regulatory associations between DEMs and TAA-induced liver carcinogenesis at an earlier stage than histopathological features. Most importantly, miR-34a-5p is the most suitable early and sensitive biomarker for TAA-induced hepatocarcinogenesis due to its consistent elevation during the entire treatment course.

A functionally significant SNP in TP53 and breast cancer risk in African-American women

A coding region polymorphism exists in the TP53 gene (Pro47Ser; rs1800371) in individuals of African descent, which reduces p53 tumor suppressor function in a mouse model. It has been unclear whether this functionally significant polymorphism alters cancer risk in humans. This analysis included 6907 women with breast cancer and 7644 controls from the AMBER, ROOT, and AABC consortia. We used multivariable logistic regression to estimate associations between the TP53 Pro47Ser allele and overall breast cancer risk. Because polymorphisms in TP53 tend to be associated with cancer risk in pre-menopausal women, we also limited our analyses to this population in the AMBER and ROOT consortia, where menopausal status was known, and conducted a fixed effects meta-analysis. In an analysis of all women in the AMBER, ROOT, and AABC consortia, we found no evidence for association of the Pro47Ser variant with breast cancer risk. However, when we restricted our analysis to only pre-menopausal women from the AMBER and ROOT consortia, there was a per allele odds ratio of 1.72 (95% confidence interval 1.08-2.76; p-value = 0.023). Although the Pro47Ser variant was not associated with overall breast cancer risk, it may increase risk among pre-menopausal women of African ancestry. Following up on more studies in human populations may better elucidate the role of this variant in breast cancer etiology. However, because of the low frequency of the polymorphism in women of African ancestry, its impact at a population level may be minimal.

Signalling pathways in UHRF1-dependent regulation of tumor suppressor genes in cancer

Epigenetic silencing of tumor suppressor genes (TSGs) through DNA methylation and histone changes is a main hallmark of cancer. Ubiquitin-like with PHD and RING Finger domains 1 (UHRF1) is a potent oncogene overexpressed in various solid and haematological tumors and its high expression levels are associated with decreased expression of several TSGs including p16^INK4A, BRCA1, PPARG and KiSS1. Using its several functional domains, UHRF1 creates a strong coordinated dialogue between DNA methylation and histone post-translation modification changes causing the epigenetic silencing of TSGs which allows cancer cells to escape apoptosis. To ensure the silencing of TSGs during cell division, UHRF1 recruits several enzymes including histone deacetylase 1 (HDAC1), DNA methyltransferase 1 (DNMT1) and histone lysine methyltransferases G9a and Suv39H1 to the right place at the right moment. Several in vitro and in vivo works have reported the direct implication of the epigenetic player UHRF1 in tumorigenesis through the repression of TSGs expression and suggested UHRF1 as a promising target for cancer treatment. This review describes the molecular mechanisms underlying UHRF1 regulation in cancer and discusses its importance as a therapeutic target to induce the reactivation of TSGs and subsequent apoptosis.

p53 Proteoforms and Intrinsic Disorder: An Illustration of the Protein Structure-Function Continuum Concept

Although it is one of the most studied proteins, p53 continues to be an enigma. This protein has numerous biological functions, possesses intrinsically disordered regions crucial for its functionality, can form both homo-tetramers and isoform-based hetero-tetramers, and is able to interact with many binding partners. It contains numerous posttranslational modifications, has several isoforms generated by alternative splicing, alternative promoter usage or alternative initiation of translation, and is commonly mutated in different cancers. Therefore, p53 serves as an important illustration of the protein structure–function continuum concept, where the generation of multiple proteoforms by various mechanisms defines the ability of this protein to have a multitude of structurally and functionally different states. Considering p53 in the light of a proteoform-based structure–function continuum represents a non-canonical and conceptually new contemplation of structure, regulation, and functionality of this important protein.

The African-specific S47 polymorphism of p53 alters chemosensitivity

The TP53 protein is known to affect the sensitivity of tumor cells to cell death by DNA damaging agents. We recently reported that human and mouse cells containing an African-specific coding region variant of p53, Pro47Ser (hereafter S47), are impaired in the transactivation of a small subset of p53 target genes including GLS2 and SCO2, and are markedly resistant to cisplatin. Further, mice containing this variant are markedly predisposed to cancer. Together these findings suggested that cancer-affected humans with the S47 variant might not be effectively treated with cisplatin. To more directly test this premise, we created transformed derivatives of mouse embryo fibroblasts (MEFs) containing wild type p53 (WT) and the S47 variant and analyzed them for chemosensitivity. We find that transformation with E1A and Ras actually reverses the chemosensitivity/transcriptional differences between WT p53 and S47. Specifically, E1A/Ras-transformed S47 cells show increased sensitivity to cisplatin and paclitaxel, and comparable transactivation of GLS2 and SCO2, compared to cells with WT p53. These data suggest that the functional differences between WT p53 and S47 in primary cells may not hold true for transformed cells. They also offer hope that cisplatin and paclitaxel may be effective chemotherapeutic drugs for S47 individuals with cancer.