Microinjection technique used to study functional interaction between p53 and hepatitis B virus X gene in apoptosis

Microinjection of expression vectors into cultured cells has been utilized to study functional interaction of p53 and the hepatitis B virus HBx gene in apoptosis. This approach allows us to determine protein-protein interactions in primary cultured human cells at a single cell level, including fibroblasts, mammary epithelial cells, renal epithelial cells, and hepatocytes. In principle, this approach can be used to study functional interaction of p53 and any gene that is either pro- or anti-apoptotic. The use of primary cultured human cells minimizes ambiguous results associated with immortalized or tumorigenic cell lines. Moreover, it is an easy and effective way to introduce genes of interests into primary human cells with defined genetic defects, thereby facilitating the delineation of genetic pathways.     

Expression of the p53 Gene and Activation of p53-Dependent Transcription in Melanoma Cell Lines

Malignant melanoma has poor prognosis because of its high metastatic potential and resistance to chemotherapy. A possible approach to more effective therapy is induction of p53-dependent apoptosis. This approach is promising, since the wild-type _p53 is expressed in most melanomas. An attempt was made to estimate the functional activity of p53 in several malignant melanoma cell lines. Most lines were characterized by a high protein level and nuclear localization of p53. All cell lines expressing the wild-type p53 showed stabilization of p53, its translocation into the nucleus, and activation of several target genes in response to DNA-damaging agents, suggesting that p53 was functionally active. A high-molecular-weight protein localized in the cytoplasm and mimicking a p53 epitope was found in several cell lines. It was shown that the DO-1 epitope is not derived from p53, ruling out cytoplasmic retention of p53 in melanoma cell lines. A mechanism of camptothecin-induced stabilization of p53 by decreasing the level of the HDM2 mRNA was described for melanoma cells but not for normal melanocytes, suggesting a differential effect of camptothecin on tumor-derived and primary cells.__________Translated from Molekulyarnaya Biologiya, Vol. 39, No. 3, 2005, pp. 445–456.Original Russian Text Copyright © 2005 by Razorenova, Agapova, Chumakov.     

Defective apoptosis and B-cell lymphomas in mice with p53 point mutation at Ser 23

Phosphorylation of the p53 tumor suppressor at Ser20 (murine Ser23) has been proposed to be critical for disrupting p53 interaction with its negative regulator, MDM2, and allowing p53 stabilization. To determine the importance of Ser23 for the function of p53 in vivo, we generated a mouse in which the endogenous p53 locus was targeted to replace Ser23 with alanine. We show that, in mouse embryonic fibroblasts generated from Ser23 mutant mice, Ser23 mutation did not dramatically reduce IR-induced p53 protein stabilization or p53-dependent cell cycle arrest. However, in Ser23 mutant thymocytes and in the developing cerebellum, p53 stabilization following IR was decreased and resistance to apoptosis was observed. Homozygous Ser23 mutant animals had a reduced lifespan, but did not develop thymic lymphomas or sarcomas that are characteristic of p53-/- mice. Instead, Ser23 mutant animals died between 1 and 2 years with tumors that were most commonly of B-cell lineage. These data support an important role for Ser20/23 phosphorylation in p53 stabilization, apoptosis and tumor suppression.     

Palmdelphin,a novel target of p53 with Ser46 phosphorylation,controls cell death in response to DNA damage

The tumor suppressor gene p53 regulates apoptosis in response to DNA damage. Promoter selectivity of p53 depends on mainly its phosphorylation. Particularly, the phosphorylation at serine-46 of p53 is indispensable in promoting pro-apoptotic genes that are, however, poorly determined. In the current study, we identified palmdelphin as a pro-apoptotic gene induced by p53 in a phosphorylated serine-46-specific manner. Upregulation of palmdelphin was observed in wild-type p53-transfected cells, but not in serine-46-mutated cells. Expression of palmdelphin was induced by p53 in response to DNA damage. In turn, palmdelphin induced apoptosis. Intriguingly, downregulation of palmdelphin resulted in necroptosis-like cell death via ATP depletion. Upon DNA damage, palmdelphin dominantly accumulated in the nucleus to induce apoptosis. These findings define palmdelphin as a target of serine-46-phosphorylated p53 that controls cell death in response to DNA damage.     

等Tm检测探针寡核苷酸芯片在p53突变热点检测中的应用

用等长探针检测基因的点突变,不同GC含量探针的碱基错分辨率很难均一。尝试利用探针近似等Tm的原则设计、制备了检测抑癌基因p53外显子7中密码子245、248、249单碱基突变及缺失的寡核苷酸芯片。实验得到较好的碱基错配分辨率,检测不同位点的碱基错配分辨率较为一致,芯片检测结果与测序结果一致。实验结果为制备检测p53常见热点突变的寡核酸芯片奠定了基础。     

Clinical implication of p53 mutation in lung cancer

Lung cancer development involves multiple genetic abnormalities leading to malignant transformation of the bronchial epithelial cells, followed by invasion and metastasis. One of the most common changes is mutation of the p53 tumor suppressor gene. The frequency of p53 alterations in lung cancer is highest in small cell and squamous cell carcinomas. A genetic “signature” of the type of p53 mutations has been associated with carcinogens in cigarette smoke. The majority of clinical studies suggest that lung cancers with p53 alterations carry a worse prognosis, and may be relatively more resistant to chemotherapy and radiation. An understanding of the role of p53 in human lung cancer may lead to more rational targeted approaches for treating this disease. P53 gene replacement is currently under clinical investigation but clearly more effective means of gene deliver to the tumor cells are required. Novel approaches to lung cancer therapy are needed to improve the observed poor patient survival despite current therapies.     

Polymorphism analyses of hepatitis B virus X gene in hepatocellular carcinoma patients from southern China

Chronic hepatitis B virus(HBV)infection is one of the major causes of hepatocellularcarcinoma(HCC),and the HBV X(HBx)gene plays a critical role in the molecular pathogenesis ofHBV-related HCC.We have investigated whether there are particular HBx gene mutations associated withHCC in patients from southern China.The HBx gene was examined in 51 paraffin-embedded tumor tissuesamples from patients with HCC and 25 serum samples from the HBV carrier by nested polymerase chainreaction(PCR),single-stranded conformational polymorphism and heteroduplex analysis.The HBx geneswith potentially important mutations from tumor tissue samples were cloned,sequenced and aligned withthe published HBx gene sequence.HBV genotypes in tumor tissue samples were analyzed by nested PCR.Analyses of HBx gene polymorphism showed that 31.3% of HBx gene fragments in tumor tissue sampleshad a special pattern.A common deletion at nt 382-400 of the HBx gene accompanied by 29 point mutationswas detected in four randomly selected tumor tissue samples with this pattern which caused a frame-shiftin the HBx open reading frame with a new stop codon at nt 1818,resulting in an HBx polypeptide chaintruncated at the C end in these cases.Among the four randomly selected samples,three were HBV genotypeB,and one was not detected by our present assay.In another tumor tissue sample,amplification of thefull-length HBx gene yielded a shorter fragment.Sequencing of this fragment revealed a 264 bp deletionbetween nt 1577 and 1840 of the HBV gene.These results suggest that HBx gene mutation occurs frequentlyin HCC samples,and the deletion at nt 382-400 of the HBx gene might play a role in carcinogenesis of HCCin southern China.     

p63 is a suppressor of tumorigenesis and metastasis interacting with mutant p53

p53 mutations, occurring in two-thirds of all human cancers, confer a gain of function phenotype, including the ability to form metastasis, the determining feature in the prognosis of most human cancer. This effect seems mediated at least partially by its ability to physically interact with p63, thus affecting a cell invasion pathway, and accordingly, p63 is deregulated in human cancers. In addition, p63, as an 'epithelial organizer', directly impinges on epidermal mesenchimal transition, stemness, senescence, cell death and cell cycle arrest, all determinant in cancer, and thus p63 affects chemosensitivity and chemoresistance. This demonstrates an important role for p63 in cancer development and its progression, and the aim of this review is to set this new evidence that links p63 to metastasis within the context of the long conserved other functions of p63.     

促凋亡基因p53AIP1的研究进展

p53AIPl基因是近年发现的促凋亡基因,在p53依赖性的凋亡通路中起重要作用。p53AIPl介导线粒体凋亡途径,其表达依赖于p53蛋白的Ser^46的磷酸化。p53AIPl可直接促进凋亡,其促凋亡作用可能强于p53本身,并对p53抗性的肿瘤细胞也有作用。因此,对p53AIPl的深入研究可能会为对p53基因治疗有抗性的肿瘤患者带来新的希望。     

A case report of hepatocellular carcinoma and focal nodular hyperplasia with a myelolipoma in two chimpanzees and a review of spontaneous hepatobiliary tumors in non-human primates

Spontaneous hepatobiliary tumors in non-human primates are uncommon. Here we report a case of hepatic carcinoma and a case of hepatic focal nodular hyperplasia (FNH) and myelolipoma in two captive chimpanzees. A 16-year-old male chimpanzee (4X0392) died after an 8-month history of hepatic amyloidosis and low-grade anemia. Necropsy findings included a hepatic neoplasm with highly pleomorphic hepatocytes arranged into irregular thickened trabeculae. The diagnosis was high-grade hepatocellular carcinoma. A second male chimpanzee (4X0080), 23 years of age, died suddenly of heart failure secondary to cardiomyopathy. An incidental finding at necropsy was a liver mass characterized by multinodularity, prominent fibrous septa, and biliary hyperplasia. These features were consistent with FNH. While 4X0392 had no history of experimental viral exposure, 4X0080 was vaccinated with inactivated hepatitis B virus, an attenuated hepatitis A virus, and was experimentally infected with hepatitis C virus and human immunodeficiency virus. A survey of the literature revealed 68 reported cases of hepatobiliary tumors in non-human primates, including 12 hepatocellular adenomas, eight cholangiocellular adenomas/cystadenomas, 22 hepatocellular carcinomas, seven cholangiocarcinomas, and seven gallbladder adenocarcinomas. The majority of reported cases have been in prosimians and Old World monkeys. Hepatic neoplasia is rare in chimpanzees. Only four hepatic neoplasms have been reported in chimpanzees, three of which were associated with viral hepatitis. FNH has not been previously described in any non-human primate.     

Comparison of genome-scale DNA methylation profiles in hepatocellular carcinoma by viral status

Hepatocellular carcinoma (HCC) incidence has steadily increased in the US over the past 30 years. Our understanding of epigenetic regulation in HCC is still limited, especially the impact of hepatitis B virus (HBV) or hepatitis C virus (HCV) infection on aberrant DNA methylation. We performed genome-wide DNA methylation profiling in 33 fresh frozen tumor samples, including 10 HBV-HCC, 13 HCV-HCC, and 10 non-infected (NIV-HCC) using the Illumina HumanMethylation450 BeadChip. Gene expression profiling was also performed using the Illumina whole-genome DASL HT Assay. Biological influences and gene networks of the differentially-methylated (DM) CpG loci were predicted using the Ingenuity Pathway Analysis. Genome-wide methylation analysis identified 7, 26, and 98 DM loci between HBV-HCC vs. HCV-HCC, HBV-HCC vs. NIV-HCC, and HCV-HCC vs. NIV-HCC, respectively, at P < 5 × 10^?5 for each. Overall, the DM loci were highly enriched for enhancers (48%), promoters (37%), or CpG islands and surrounding regions (37%). Most DM loci were hypermethylated in HCV-HCC compared to HBV-HCC or NIV-HCC. The DM loci were associated with a variety of biological functions including Cell Morphology (HBV-HCC vs. NIV-HCC), Cell Death/ Survival (HBV-HCC vs. NIV-HCC), or Cellular Growth and Proliferation (HCV-HCC vs. NIV-HCC). A subset of the DM loci were correlated (either positively or negatively) with their gene expression or associated with alcohol consumption, BMI, cirrhosis, diabetes, and cigarette smoking. Our findings of differential methylation by viral infection lend insights into the potential effects of viral infection on the epigenetic regulation and further the development and progression of HCC.     

HBV DNA can bind to P53 protein and influence p53 transactivation in hepatoma cells

Hepatitis B virus (HBV) may contribute to hepatocarcinogenesis by blocking p53 function. A p53 response element-like binding sequences, TGCCT?TGCCT, was found in HBV genome. To clarify whether HBV DNA can, like some other DNA viruses, bind to P53 protein and form a DNA-protein complex, we used a series of plasmids encoding full-length or mutant HBV or p53 fragments to determine the binding ability of HBV DNA after cotransfected into cells by electrophoretic mobility shift (and supershift) assay. We found that HBV DNA could bind to P53 protein and form DNA-protein complexes in human hepatoma cell lines. Cotransfection with p53 and HBV DNA increased the replication of HBV, CAT activity, tumor cell apoptosis, and cytoplasmic P53 accumulation in the hepatoma cells. In conclusions, our observations suggest that the interaction of HBV and p53 at the levels of protein-protein and DNA-protein, which resulted in inactivation of p53 transactivation.     

Expression and clinicopathological significance of lipin-1 in human breast cancer and its association with p53 tumor suppressor gene

Breast cancer (BC) is an important cause of female cancer-related death. It has recently been demonstrated that metabolic disorders including lipid metabolism are a hallmark of cancer cells. Lipin-1 is an enzyme that displays phosphatidate phosphatase activity and regulates the rate-limiting step in the pathway of triglycerides and phospholipids synthesis. The objective of this study was to evaluate lipin-1 expression, its prognostic significance, and its correlation with p53 tumor suppressor in patients with BC. In this study, 55 pairs of fresh samples of BC and adjacent noncancerous tissue were used to analyze lipin-1, using quantitative real-time polymerase chain reaction and immunohistochemistry (IHC) staining. The expression of other clinicopathological variables and p53 was also examined using IHC technique. The cell migration was studied in MCF-7 and MDA-MB231 cells following the inhibition of lipin-1 by propranolol. Our results show that the relative expression of lipin-1 messenger RNA was significantly higher in BC tissues compared with the adjacent normal tissue and its inhibition reduced cell migration in cancer cells. This upregulation was negatively correlated with histological grade of tumor and p53 status (p = .001 and p = .034) respectively and positively correlated with the tumor size (p = .006). Our results also seem to indicate that the high lipin-1 expression is related to a good prognosis in patients with BC. The expression of lipin-1 may be considered as a novel independent prognostic factor. The inhibition of lipin-1 may also have therapeutic significance for patients with BC. The correlation between lipin-1 and p53 confirms the role of p53 in the regulation of lipid metabolism in cancer cells.