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Query: UNIPROT:P04637 (p53)
 77,613 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We studied the molecular mechanism of successive multistep cervical carcinogenic progression with our previously established in vitro model system. This system was composed of primary human endocervical cells (HEN), two lines of HEN immortalized by HPV16 and their counterparts subsequently malignantly transformed by cigarette smoke condensate (CSC). The expression was examined of diverse cellular genes associated with oncogenesis and senescence, especially for cervical cancer. Consistent results were seen for the pairs of immortalized and malignantly transformed lines. Immortalization of HEN by HPV16 resulted in enhanced expression of H-ras, c-myc, B-myb, p53, p16INK4 and PCNA mRNA; enhanced expression of p16 and PCNA proteins; decreased expression of WAF1/p21/Cip1/Sid1 and fibronectin mRNA; and decreased p53 protein. On the other hand, the CSC-transformed counterparts of HPV16-immortalized cells had up-regulated levels of B-myb, p53 and WAF1 mRNA and p53 protein. Our results indicate that the differential activation or inactivation of multiple cellular genes is important for the immortalization, as well as the transformation, of human cervical cells. Further, we suggest that our in vitro model system is useful for investigating the molecular mechanism of multistep cervical carcinogenesis.
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PMID:Expression of cellular genes in HPV16-immortalized and cigarette smoke condensate-transformed human endocervical cells. 925 88

Inactivation of tumour suppressor gene function is a critical step in the development of human neoplasia. The Rb and CDKN2 tumour suppressor genes are inactivated in many tumour types, including the late stages of prostate cancer, and appear to function in the same suppressor pathway. p53, another major tumour suppressor is also mutated in a subset of advanced-stage prostate carcinomas. E-cadherin and other cell adhesion genes, which have been characterized as suppressors of the metastatic phenotype, are inactivated or downregulated during progression to advanced prostate cancer and have been associated with poor clinical outcome. The early genetic events involved a prostatic neoplasia are poorly understood, but loss of as yet undiscovered tumour suppressor genes may play a role in the initiation of this disease.
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PMID:Tumour suppressor genes in prostate cancer. 929 77

Recent data suggest that deletion of p16INK4 and mutation of TP53 are among the most common genetic events in the development of human cancer, since the codified proteins act as brakes of the abnormal cell cycle. As the molecular events leading to the development of pediatric bone sarcomas remain unclear, we analyzed 75 osteosarcoma and Ewing sarcoma samples from 43 pediatric patients to search for alterations at the TP53 or p16INK4 tumor suppressor genes. By means of PCR-DGGE (polymerase chain reaction and denaturing gradient gel electrophoresis) we detected TP53 point mutations in 18.6% of the tumor samples, but no constitutional mutations. In the analysis of p16INK4, 7% of the samples harbored deletions of the gene but no point mutations were detected by SSCP (single strand conformation polymorphism) analysis, just the polymorphism Ala-->Thr at codon 148. These data support the hypothesis that TP53 alterations may play a role in the development of pediatric bone tumors and that the primary mechanism of inactivation of p16INK4 seems to be homozygous deletion rather than point mutation.
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PMID:Analysis of the p16INK4 and TP53 tumor suppressor genes in bone sarcoma pediatric patients. 930 18

The familial melanoma gene (INK4a/MTS1/CDKN2) encodes potent tumor suppressor activity. Although mice null for the ink4a homolog develop a cancer-prone condition, a pathogenetic link to melanoma susceptibility has yet to be established. Here we report that mice with melanocyte-specific expression of activated H-rasG12V on an ink4a-deficient background develop spontaneous cutaneous melanomas after a short latency and with high penetrance. Consistent loss of the wild-type ink4a allele was observed in tumors arising in ink4a heterozygous transgenic mice. No homozygous deletion of the neighboring ink4b gene was detected. Moreover, as in human melanomas, the p53 gene remained in a wild-type configuration with no observed mutation or allelic loss. These results show that loss of ink4a and activation of Ras can cooperate to accelerate the development of melanoma and provide the first in vivo experimental evidence for a causal relationship between ink4a deficiency and the pathogenesis of melanoma. In addition, this mouse model affords a system in which to identify and analyze pathways involved in tumor progression against the backdrop of genetic alterations encountered in human melanomas.
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PMID:Cooperative effects of INK4a and ras in melanoma susceptibility in vivo. 935 52

Pancreatic cancer is the fifth leading cause of cancer death in the United States, and despite improvements in the results of surgical treatment for this disease, little impact has been made upon overall mortality. New advances in treatment will depend upon improved adjuvant therapy, early diagnosis, and a better understanding of tumor biology. This article summarizes the results of molecular genetic studies in pancreatic cancer and their potential clinical significance. Familial predisposition to pancreatic cancer, cytogenic studies, DNA ploidy analysis, and examination of specific oncogenes and tumor suppressor genes are reviewed. The most frequent mutations detected have been in the K-ras oncogene, which occur in 80% of pancreatic cancers. These mutations do not correlate with tumor stage or survival, but can be useful in differentiating pancreatic exocrine from endocrine tumors and chronic pancreatitis. Mutations in the p53 gene occur in approximately 50% of tumors, and appear to be an independent prognostic factor for patient survival. Mutations in the CDKN2 gene are frequently seen in sporadic pancreatic cancers, and have been implicated in cases of familial pancreatic cancer. The significance of mutations in APC, MCC, DCC, c-erbB-2, RB-1, and mismatch repair genes in the genesis of pancreatic cancer is less clear.
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PMID:The molecular genetics of pancreatic cancer. 936 57

The INK4a tumor suppressor locus encodes p16INK4a, an inhibitor of cyclin D-dependent kinases, and p19ARF, an alternative reading frame protein that also blocks cell proliferation. Surprisingly, mice lacking p19ARF but expressing functional p16INK4a develop tumors early in life. Their embryo fibroblasts (MEFs) do not senesce and are transformed by oncogenic Ha-ras alone. Conversion of ARF+/+ or ARF+/- MEF strains to continuously proliferating cell lines involves loss of either p19ARF or p53. p53-mediated checkpoint control is unperturbed in ARF-null fibroblast strains, whereas p53-negative cell lines are resistant to p19ARF-induced growth arrest. Therefore, INK4a encodes growth inhibitory proteins that act upstream of the retinoblastoma protein and p53. Mutations and deletions targeting this locus in cancer cells are unlikely to be functionally equivalent.
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PMID:Tumor suppression at the mouse INK4a locus mediated by the alternative reading frame product p19ARF. 939 58

There have been few reports on genetic alterations in thymomas. To investigate the expression of p16INK4A, RB, p53 and cyclin D1 in thymomas, we first examined 36 thymomas (non-invasive type, 16 cases; invasive type, 20 cases) and 3 thymic carcinomas, using immunohistochemistry. Abnormal expression of p16INK4A, RB, p53 and cyclin D1 was observed in 18, 8, 10 and 7 cases, respectively. Only a subgroup of invasive thymomas and thymic carcinomas showed an inverse correlation between p16INK4A and RB expression. Subsequently, we examined the 36 thymomas and 4 thymic carcinomas for mutations in p53 and CDKN2 genes, using PCR-SSCP and direct-sequencing analyses. No mutation of these genes was detected in the thymomas and thymic carcinomas examined. A polymorphism in the 3' untranslated region of exon 3 of CDKN2 was detected in 5 cases of thymoma. We searched for hypermethylation in the promoter region of CDKN2, observing it in 4 thymomas and 1 thymic carcinoma. Our data suggest that, unlike other more common cancers, alteration of the p53 gene may not play a significant role in the tumorigenesis of thymoma. However, inactivation of p16INK4A and RB may play a role in the progression of thymoma and thymic carcinoma.
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PMID:p16INK4, pRB, p53 and cyclin D1 expression and hypermethylation of CDKN2 gene in thymoma and thymic carcinoma. 939 39

To clarify the relative role of hepatitis C virus (HCV) and hepatitis B virus (HBV) in hepatocarcinogenesis in hepatitis B surface antigen (HBsAg)-negative hepatocellular carcinoma (HCC) in Taiwan, polymerase chain reaction (PCR) was used to detect the HCV-RNA and HBV-DNA sequences in the serum and liver tissues from 31 HBsAg-negative HCC patients. Twenty-one were positive for antibody to HCV (group 1) and 10 were negative (group 2). Hepatitis C virus-RNA was detected by PCR in the serum of 16 group 1 patients and in the liver tissue of 17; while HBV-DNA was found in the liver tissue of only four, and no HBV-DNA was found in the serum. Hepatitis C virus RNA was detected in the serum of one group 2 patient and in the liver tissue of another. In contrast, HBV viral DNA was found in the serum of four group 2 patients and in the liver tissues of five patients. This indicates that HCV plays an important role in hepatocarcinogenesis in HBsAg-negative patients in Taiwan, especially in those with antibody to HCV. In those without antibody to HCV, HBV might still be associated with the development of HCC in a significant proportion of such patients. In order to study the role of the p53 mutation in hepatocarcinogenesis, we investigated the status of the p53 mutation in 61 HCC samples from Taiwan. The exon 5 to 8 of the p53 gene in the tumour tissue of 61 HCC were amplified and sequenced. A total of 20 cases (32.8%) were found to have mutations: 36.6% (15/41) from the HBsAg-positive group and 25.0% (5/20) from the HBsAg-negative group. The corresponding normal liver showed no mutation. The mutation is widely distributed throughout the exon 5 to 8. Only four cases (6.6%), all positive for HBsAg, had a specific hotspot mutation at codon 249 with G to T transversion. These results show that scattered point mutations in p53 are not uncommon in HCC samples from Taiwan and may be important in the development of this cancer. However, the aflatoxin-related specific mutation seems much less related to the genesis of HCC in Taiwan. To study the role of telomerase activity in hepatocarcinogenesis, a total of 39 HCC tissues and the corresponding non-tumour liver tissues were analysed. The results showed that telomerase activity was detected in all the 39 tumour tissues, while it could be detected in six of the 39 non-tumour liver tissues. The high positive rate of telomerase activity in HCC samples suggests that telomerase activity is closely related to the development or progression of HCC. To determine whether exon 1 and exon 2 of the p16 gene are altered in HCC, thirty-four tumours from 30 HCC patients were examined by DNA sequencing analysis of PCR-amplified genomic DNA. Homozygous deletions of MTS1/p16/CDKN2 exon 1 were identified in 1/34 primary tumours (3%), no mutations or rearrangements were found in these specimens. These data suggest that alterations of MTS1/p16/CDKN2 gene are rarely found in HCC, and might play little role in the development of this cancer. To study the clonality of HCC, 18 patients with multiple HCC, most of them small in size, were analysed by DNA fingerprinting. In patients positive for hepatitis B surface antigen, the integration pattern of hepatitis B viral DNA in liver tissue was also analysed. The results by both methods showed that 8/9 hepatitis B surface antigen-positive patients were different in clonality. In the remaining nine patients negative for hepatitis B surface antigen, four had different band patterns in their tumours by DNA fingerprinting. This study indicated that polyclonality of multiple HCC was rather frequent and it highlighted the importance of eliminating the underlying cause of liver injury to improve the survival of these patients. Microsatellite markers were used to study the genetic changes of HCC. Thirty cases of HCC, most of them small in size, were studied. A total of 242 microsatellite markers mapping to 1-22 and X chromosomes was used. The results showed that the range of loss of het
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PMID:Molecular mechanism of hepatocarcinogenesis. 940 51

Members of the INK4 protein family specifically inhibit cyclin-dependent kinase 4 (cdk4) and cdk6-mediated phosphorylation of the retinoblastoma susceptibility gene product (Rb). p16INK4A, a prototypic INK4 protein, has been identified as a tumor suppressor in many human cancers. Inactivation of p16INK4A in tumors expressing wild-type Rb is thought to be required in order for many malignant cell types to enter S phase efficiently or to escape senescence. Here, we demonstrate another mechanism of tumor suppression by implicating p16INK4A in a G1 arrest checkpoint in response to DNA damage. Calu-1 non-small cell lung cancer cells, which retain Rb and lack p53, do not arrest in G1 following DNA damage. However, engineered expression of p16INK4A at levels compatible with cell proliferation restores a G1 arrest checkpoint in response to treatment with gamma-irradiation, topoisomerase I and II inhibitors, and cisplatin. A similar checkpoint can be demonstrated in p53-/- fibroblasts that express p16INK4A. DNA damage-induced G1 arrest, which requires the expression of pocket proteins such as Rb, can be abrogated by overexpression of cdk4, kinase-inactive cdk4 variants capable of sequestering p16INK4A, or a cdk4 variant incapable of binding p16INK4A. After exposure to DNA-damaging agents, there was no change either in overall levels of p16INK4A or in amounts of p16INK4A found in complex with cdks 4 and 6. Nonetheless, p16INK4A expression is required for the reduction in cdk4- and cdk6-mediated Rb kinase activity observed in response to DNA damage. During tumor progression, loss of p16INK4A expression may be necessary for cells with wild-type Rb to bypass this G1 arrest checkpoint and attain a fully transformed phenotype.
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PMID:p16INK4A participates in a G1 arrest checkpoint in response to DNA damage. 941 85

Elevation of p16, the CDKN2/p16 tumor suppressor gene (TSG) product, occurs at senescence in normal human uroepithelial cells (HUC). Immortal HUCs and bladder cancer cell lines show either alteration of p16 or pRb, the product of the retinoblastoma (RB) TSG. In addition, many human cancers show p16 or pRb alteration along with other genetic alterations that we associated with immortalization, including +20q and -3p. These observations led us to hypothesize that p16 elevation plays a critical role in senescence cell cycle arrest and that overcoming this block is an important step in tumorigenesis in vivo, as well as immortalization in vitro. Using a novel approach, we tested these hypotheses in the present study by examining p16 and pRb status in primary culture (P0) and after passage in vitro of transitional cell carcinoma (TCC) biopsies that represented both superficial bladder tumors and invasive bladder cancers. We demonstrated that all superficial TCCs showed elevated p16 after limited passage in vitro and then senesced, like normal HUCs. In contrast, all muscle invasive TCCs contained either a p16 or a pRb alteration at P0 and all spontaneously bypassed senescence (P = 0.001). Comparative genomic hybridization (CGH) was used to identify regions of chromosome loss or gain in all TCC samples. The application of a statistical model to the CGH data showed a high probability of elevated alteration rates of +20q11-q12 (0.99) and +8p22-pter (0.94) in the immortal muscle invasive TCCs, and of -9q (0.99) in the superficial TCCs. Three myoinvasive TCCs lost 3p13-p14. In this study, four of six myoinvasive TCCs also showed TP53 mutation that associated well with genome instability (P = 0.001), as previously hypothesized. Notably, TP53 mutation, which has been used as a marker of tumor progression in many human cancers, was less significant in associating with progression in this study (P = 0.04) than was p16 or pRb alteration (P = 0.001). Thus, these data support a new model in which overcoming senescence plays a critical role in human cancer pathogenesis and requires at least two genetic changes that occur in several combinations that can include either p16 or pRb loss and at least one additional alteration, such as +20q11-q12, -3p13-p14, or -8p21-pter.
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PMID:Overcoming cellular senescence in human cancer pathogenesis. 943 77


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