p53: tumor suppression through control of the cell cycle

Targeting the p53 signaling pathway in cancers: Molecular mechanisms and clinical studies

Tumor suppressor p53 can transcriptionally activate downstream genes in response to stress, and then regulate the cell cycle, DNA repair, metabolism, angiogenesis, apoptosis, and other biological responses. p53 has seven functional domains and 12 splice isoforms, and different domains and subtypes play different roles. The activation and inactivation of p53 are finely regulated and are associated with phosphorylation/acetylation modification and ubiquitination modification, respectively. Abnormal activation of p53 is closely related to the occurrence and development of cancer. While targeted therapy of the p53 signaling pathway is still in its early stages and only a few drugs or treatments have entered clinical trials, the development of new drugs and ongoing clinical trials are expected to lead to the widespread use of p53 signaling-targeted therapy in cancer treatment in the future. TRIAP1 is a novel p53 downstream inhibitor of apoptosis. TRIAP1 is the homolog of yeast mitochondrial intermembrane protein MDM35, which can play a tumor-promoting role by blocking the mitochondria-dependent apoptosis pathway. This work provides a systematic overview of recent basic research and clinical progress in the p53 signaling pathway and proposes that TRIAP1 is an important therapeutic target downstream of p53 signaling.

HuR posttranscriptionally regulates WEE1: implications for the DNA damage response in pancreatic cancer cells

HuR (ELAV1), an RNA-binding protein abundant in cancer cells, primarily resides in the nucleus, but under specific stress (e.g., gemcitabine), HuR translocates to the cytoplasm in which it tightly modulates the expression of mRNA survival cargo. Here, we demonstrate for the first time that stressing pancreatic ductal adenocarcinoma (PDA) cells by treatment with DNA-damaging anticancer agents (mitomycin C, oxaliplatin, cisplatin, carboplatin, and a PARP inhibitor) results in HuR's translocation from the nucleus to the cytoplasm. Importantly, silencing HuR in PDA cells sensitized the cells to these agents, whereas overexpressing HuR caused resistance. HuR's role in the efficacy of DNA-damaging agents in PDA cells was, in part, attributed to the acute upregulation of WEE1 by HuR. WEE1, a mitotic inhibitor kinase, regulates the DNA damage repair pathway, and therapeutic inhibition of WEE1 in combination with chemotherapy is currently in early phase trials for the treatment of cancer. We validate WEE1 as a HuR target in vitro and in vivo by demonstrating (i) direct binding of HuR to WEE1's mRNA (a discrete 56-bp region residing in the 3' untranslated region) and (ii) HuR siRNA silencing and overexpression directly affects the protein levels of WEE1, especially after DNA damage. HuR's positive regulation of WEE1 increases γ-H2AX levels, induces Cdk1 phosphorylation, and promotes cell-cycle arrest at the G2-M transition. We describe a novel mechanism that PDA cells use to protect against DNA damage in which HuR posttranscriptionally regulates the expression and downstream function of WEE1 upon exposure to DNA-damaging agents.

Precursor lesions for sporadic pancreatic cancer: PanIN, IPMN, and MCN

Pancreatic cancer is still a dismal disease. The high mortality rate is mainly caused by the lack of highly sensitive and specific diagnostic tools, and most of the patients are diagnosed in an advanced and incurable stage. Knowledge about precursor lesions for pancreatic cancer has grown significantly over the last decade, and nowadays we know that mainly three lesions (PanIN, and IPMN, MCN) are responsible for the development of pancreatic cancer. The early detection of these lesions is still challenging but provides the chance to cure patients before they might get an invasive pancreatic carcinoma. This paper focuses on PanIN, IPMN, and MCN lesions and reviews the current level of knowledge and clinical measures.

Immunocytochemical assessment of p53 protein to detect malignancy in increased cell-yield brush cytology from the biliopancreatic tree

BACKGROUND

Malignancies arising from the biliopancreatic tree are often diagnostic challenges for the gastroenterologist and the pathologist, especially when strictures without masses are present.

AIM

To evaluate the diagnostic yield of p53 immunocytology for the detection of malignancies in material obtained by biliopancreatic tree brushing by means of an increased cell-yield procedure.

PATIENTS AND METHODS

Cytologic specimens obtained from biliary and pancreatic tree brushing in 24 patients with biliary strictures suspected for malignancy were assessed by conventional Papanicolau staining and p53 immunocytochemistry.

RESULTS

Papanicolau staining detected 67% and p53 87% of the malignancies in the study group. p53 immunocytology displayed excellent sensitivity, specificity, and diagnostic accuracy.

CONCLUSIONS

p53 immunocytology may represent a useful diagnostic tool in the detection of malignancies from biliary and pancreatic tree brushing, especially when using an increasing cell-yield procedure.

Pancreatic intraepithelial neoplasia and pancreatic tumorigenesis: of mice and men

CONTEXT

Pancreatic cancer has a poor prognosis with a 5-year survival of less than 5%. Early detection is at present the only way to improve this outlook. This review focuses on the recent advances in our understanding of pancreatic carcinogenesis, the scientific evidence for a multistaged tumor progression, and the role genetically engineered mouse models can play in recapitulating the natural course and biology of human disease.

OBJECTIVES

To illustrate the stepwise tumor progression of pancreatic cancer and genetic alterations within the different stages of progression and to review the findings made with genetically engineered mouse models concerning pancreatic carcinogenesis.

DATA SOURCES

A review of recent literature on pancreatic tumorigenesis and genetically engineered mouse models.

CONCLUSIONS

Pancreatic cancer develops through stepwise tumor progression in which preinvasive stages, called pancreatic intraepithelial neoplasia, precede invasive pancreatic cancer. Genetic alterations in oncogenes and tumor suppressor genes underlying pancreatic cancer are also found in pancreatic intraepithelial neoplasia. These mutations accumulate during progression through the consecutive stages of pancreatic intraepithelial neoplasia lesions. Also in genetically engineered mouse models of pancreatic ductal adenocarcinoma, tumorigenesis occurs through stepwise progression via consecutive mouse pancreatic intraepithelial neoplasia, and these models provide important tools for clinical applications. Nevertheless differences between mice and men still remain.

Morphogenesis of pancreatic cancer: role of pancreatic intraepithelial neoplasia (PanINs)

INTRODUCTION

Pancreatic ductal adenocarcinoma (i.e., pancreatic cancer) is an almost universally lethal disease. The identification of precursor lesions of pancreatic cancer provides an opportunity for early detection and potential therapeutic intervention before the development of invasive cancer.

DISCUSSION

It is now established that pancreatic cancers do not arise de novo but rather exhibit a sequential histological and genetic progression of precursor lesions culminating in frank, invasive neoplasia. Pancreatic intraepithelial neoplasia (PanIN) is the most common non-invasive precursor lesion of pancreatic cancer. The development of a consensus nomenclature scheme for PanINs has facilitated research into pancreatic cancer precursors and enabled standardization of results across institutions.

CONCLUSION

PanINs harbor many of the molecular alterations observed in invasive pancreatic cancer, confirming their status as true non-invasive precursor lesions. Recently developed genetically engineered mouse models of pancreatic cancer also demonstrate the stepwise PanIN progression model, underscoring the commonalities in pancreatic neoplasia between mouse and man.

Pathology of dysplasia and cancer in inflammatory bowel disease

Morphologic identification of dysplasia in mucosal biopsies is the best and most reliable marker of an increased risk for malignancy in patients who have inflammatory bowel disease, and it forms the basis of the recommended endoscopic surveillance strategies that are in practice for patients who have this illness. In ulcerative colitis (UC) and Crohn's disease (CD), dysplasia is defined as unequivocal neoplastic epithelium that is confined to the basement membrane, without invasion into the lamina propria. Unfortunately, unlike in UC, only a few studies have evaluated the pathologic features and biologic characteristics of dysplasia and carcinoma in CD specifically. As a result, this article focuses mainly on the pathologic features, adjunctive diagnostic methods, and differential diagnosis of dysplasia in UC.

p53, DCC and thymidylate synthase as predictors of survival after resection of hepatic metastases from colorectal cancer

BACKGROUND

Hepatic metastasis from colorectal cancer is a common problem. Hepatic resection offers the only chance of cure. Prognosis of patients following hepatic resection is currently based on clinicopathological factors (of both the primary cancer and the hepatic metastasis), which do not accurately predict the subsequent behaviour of the tumour. The aim of this study was to evaluate three molecular genetic markers - p53, DCC (deleted in colonic cancer) and thymidylate synthase - in both the primary colorectal tumour and the resected hepatic metastases, and to determine their correlation, if any, with survival in patients with resected hepatic metastases from colorectal cancer.

METHODS

Sixty-three patients with hepatic metastases and 40 corresponding colorectal primary tumours were studied using immunohistochemical staining for p53, DCC and thymidylate synthase, as well as p53 gene mutations using polymerase chain reaction-single-stranded conformational polymorphism (PCR-SSCP) analysis. The results were correlated with survival.

RESULTS

There was no correlation between p53, DCC or thymidylate synthase immunohistochemical staining, or between p53 PCR-SSCP analysis, and survival for either hepatic metastases or the colorectal primary tumour.

CONCLUSION

Prediction of prognosis in patients having resection of hepatic metastases from colorectal cancer continues to be problematic. Other genetic markers or combination of markers need to be evaluated.

Temperature-sensitive ovarian carcinoma cell line (OvBH-1)

OvBH-1 cells from a patient with ovarian clear cell carcinoma were established and their biochemical status was analyzed. Cells grown at 37 degrees C exhibited normal cell cycle distribution, whereas the cells shifted to 31 degrees C were arrested in the G(2) / M phase of the cell cycle. Immunochemical analysis using anti-p53 antibodies (DO-1, PAb240, PAb421, and PAb1620) revealed that only the DO-1 antibody reacted with p53 with a high and similar percentage at both temperatures. PAb240 reacted with a low percentage of cells at 37 degrees C and no reaction was observed at 31 degrees C. PAb421 antibody stained a significantly lower percentage of cells at 37 degrees C than at 31 degrees C. Cells were not stained with PAb1620 antibody and were negative for antibodies against p21(WAF1) and MDM2 proteins independently of the temperature. Sequencing of all coding exons of the p53 gene demonstrated only a neutral genetic polymorphism, i.e. a G-to-A substitution (GAG to GAA) at nucleotide position 13 432. Thus, the observed temperature sensitivity of OvBH-1 cells cannot be ascribed to a p53 primary structure mutation. Based upon immunochemical analyses, we consider, however, that p53 in nuclei of OvBH-1 cells is in a highly unstable conformation. Furthermore, the N-terminal portion of the p53 protein at Ser20 has not been modified, and Lys373 and / or Ser378 of the C-terminus is acetylated and / or phosphorylated. The nuclear location signal of p53 is preserved. Induction of MDM2 protein is uncoupled from the cell regulatory machinery and the induction of p21(WAF1) by p53 is impaired in OvBH-1 cells.

Molecular biology of pancreatic cancer; oncogenes, tumour suppressor genes, growth factors, and their receptors from a clinical perspective

Pancreatic cancer represents the fourth leading cause of cancer death in men and the fifth in women. Prognosis remains dismal, mainly because the diagnosis is made late in the clinical course of the disease. The need to improve the diagnosis, detection, and treatment of pancreatic cancer is great. It is in this type of cancer, in which the mortality is so great and the clinical detection so difficult that the recent advances of molecular biology may have a significant impact. Genetic alterations can be detected at different levels. These alterations include oncogene mutations (most commonly, K-ras mutations, which occur in 75% to more than 95% of pancreatic cancer tissues), tumour suppressor genes alterations (mainly, p53, p16, DCC, etc.), overexpression of growth factors (such as EGF, TGF alpha, TGF beta 1-3, aFGF, bTGF, etc.) and their receptors (i.e., EGF receptor, TGF beta receptor I-III, etc.). Insights into the molecular genetics of pancreatic carcinogenesis are beginning to form a genetic model for pancreatic cancer and its precursors. These improvements in our understanding of the molecular biology of pancreatic cancer are not simply of research interest, but may have clinical implications, such as risk assessment, early diagnosis, treatment, and prognosis evaluation.

Diagnostic p53 immunostaining of endobiliary brush cytology: preoperative cytology compared with the surgical specimen

BACKGROUND

Endobiliary brush cytology is important in the distinction of malignant and benign causes of extrahepatic bile duct obstruction. The additional diagnostic value of p53 immunostaining on these cytology specimens was assessed.

METHODS

All patients with extrahepatic bile duct obstruction who underwent endoscopic retrograde cholangiopancreatography (ERCP) with endobiliary brush cytology and subsequent surgery at the Academic Medical Center in Amsterdam during a 3-year period were studied. p53 Immunocytology was compared with the corresponding conventional light microscopic cytology and p53 immunostaining of the subsequent surgical specimen.

RESULTS

Fifty-three patients with the following diagnoses were included: pancreatic carcinoma (23), bile duct carcinoma (15), ampullary carcinoma (5), lymph node metastases (2), carcinoma of unknown origin (4), chronic pancreatitis (3), and primary sclerosing cholangitis (1). Fifty-one percent of the carcinomas showed positive p53 immunostaining; all four surgical specimens without carcinoma were negative. The sensitivities of conventional light microscopic cytology, p53 immunocytology, and both tests combined were 29%, 24%, and 43%, respectively. These sensitivities were higher in cases of bile duct carcinoma (46%, 40%, and 66%) compared with cases of pancreatic carcinoma (13%, 9%, and 22%). Specificities of both tests were 100%.

CONCLUSIONS

p53 Immunostaining on endobiliary brush cytology may be helpful in the diagnosis of malignant extrahepatic bile duct stenosis, especially in patients with bile duct carcinoma. Cancer (Cancer Cytopathol)

p53 alterations in atypical alveolar hyperplasia of the human lung

Atypical alveolar hyperplasia (AAH) is a potential precursor lesion from which lung adenocarcinomas arise and may be a good target for studying the early events of lung tumorigenesis. We have previously shown that AAHs are neoplastic epithelial proliferations that often harbor activating mutations of the K-ras oncogene. In the current study, we examined a spectrum of AAHs to determine the frequency and timing of p53 alterations in lung tumorigenesis. We analyzed 37 AAHs and their paired overt lung neoplasms for p53 protein accumulation using the monoclonal antibody DO7. DNA sequence analysis of the p53 gene was performed on those cases demonstrating p53 protein accumulation. AAHs were classified as low-grade, high-grade, or AAH-like carcinoma based on cytoarchitectural features. Accumulation of the p53 protein was found in none (0%) of 20 low-grade AAHs, in 1 (9%) of 11 high-grade AAHs, and in three (50%) of six AAH-like carcinomas. There was a statistically significant trend toward p53 accumulation with increasing grade of the AAHs. A missense mutation in exon 7 of the p53 gene was found in 1 AAH-like carcinoma, whereas mutations in exons 5 through 8 could not be detected in the other three AAHs with p53 protein accumulation. Three of the paired overt carcinomas harbored p53 mutations that were not present in the AAHs. Alterations of p53 do not appear to be common events in AAHs, especially when these lesions exhibit low-grade cytoarchitectural features. Alterations of p53, however, are more frequent at the level of AAH-like carcinoma and may be associated with the transition from a benign to a malignant proliferation of pneumocytes.

Clinical and pathological associations with p53 tumour-suppressor gene mutations and expression of p21WAF1/Cip1 in colorectal carcinoma

Inactivation of the p53 tumour-suppressor gene is common in a wide variety of human neoplasms. In the majority of cases, single point mutations in the protein-encoding sequence of p53 lead to positive immunohistochemistry (IHC) for the p53 protein, and are accompanied by loss of the wild-type allele. Recently, the WAF1/Cip1 gene was identified as one of the genes induced by wild-type p53, and increased expression of p21WAF1/Cip1 has been found to reflect the status of the p53 tumour-suppressor pathway. We investigated the inactivation of p53 in a relatively small, but well-characterised, group of 46 colorectal carcinomas that were previously studied for allelic alterations, ras oncogene mutations and DNA aneuploidy. Alterations in p53 were identified by IHC, loss of 17p and DNA sequence analysis of exons 5-8, whereas p21WAF1/Cip1 protein expression was determined by IHC. p53 mutations were identified in 19 of the 46 tumours (41%), whereas positive IHC for p53 was found in 21 of the 46 tumours (46%). Positive IHC for p21WAF1/Cip1 was detected in 16 of 42 cases (38%). We found no relationship between p21WAF1/Cip1 staining and p53 protein expression or p53 mutational status. Inactivating mutations in the p53 gene correlated with LOH at 17p but not with LOH at 5q or 18q, Dukes' stage, tumour grade or DNA ploidy. There was a higher survival rate independent of Dukes' stage in the group with no alterations in p53 compared with those with evidence of dysfunction of p53, but the difference was not statistically significant. We conclude that inactivation of p53 and altered expression of p21WAF1/Cip1 are common in colorectal carcinoma but do not correlate with each other or with the clinical or pathological parameters investigated.

Alterations of the p15, p16,and p18 genes in osteosarcoma

Activation of cyclin-dependent kinases (CDKs) by interaction with cyclins regulates progression through cell cycle checkpoints. This process is counterbalanced by CDK inhibitors (CDKIs), which can inhibit progression through the cell cycle. Because CDKI expression acts to inhibit cellular proliferation, CDKIs may have a role as tumor suppressors. One class of CDKIs, characterized by the presence of ankyrin repeats, has at least four members (p15INK4B), p16INK4, p18, and p19). Two of these, p15INK4B, p16INK4, have been mapped to chromosome 9p21, a region of frequent loss in a wide variety of cancers. Alterations of p16INK4 have been detected in various tumors and cell lines. We analyzed p15INK4B, p16INK4, and p18 alterations in 52 osteosarcomas (including 11 explants), and 23 other various sarcomas. Single-stranded conformation polymorphism analysis [polymerase chain reaction (PCR-SSCP)] of the coding regions of these CDKI genes detected a missense mutation of p16INK4 exon 1 in one soft tissue sarcoma. Southern blotting detected complete deletion of p15INK4B and p16INK4 genes in osteosarcomas from 2 patients and a soft tissue sarcoma from another individual. Loss of heterozygosity (LOH) at chromosome 9p21 was observed with a microsatellite probe closely linked to the INK4 genes in the latter case. Deletions of both p15INK4B and p16INK4 genes were detected in five of eight osteosarcoma cell lines. By contrast, no alterations of p18 were detected in any sample. Together these data suggest that alterations of the p15INK4B and p16INK4 genes, but not p18, may occur in approximately 5% of sarcomas. However, deletions of the p15INK4B and P16INK4 genes are frequent in osteosarcoma cell lines and probably have a role in tumor cell growth in culture. Notably, all seven detectable deletions involved both p15INK4B and p16INK4 genes, suggesting that both contribute individual tumor suppressor activity.

Molecular genetics of exocrine pancreatic neoplasms

Molecular genetic studies of pancreatic ductal adenocarcinoma have revealed the common co-existence of K-ras, p53, and MTS1 mutations. The finding of K-ras mutations in epithelial lesions of ducts suggests them as a precursor intraepithelial neoplasm. The clinical importance of this line of work can only be anticipated at present, and a fuller understanding of genetic alterations in these neoplasms is necessary.