Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0019204 (hepatocellular carcinoma)
 71,386 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Mutations in the tumor suppressor p53 are a common event in hepatocellular carcinoma (HCC). Because HCCs typically occur in livers with chronic injury and impaired function, we have explored the role of wild-type p53 in regulating the growth and differentiation of Hep 3B hepatoma cells, a p53-negative line derived from a liver cancer. Stable Hep 3B cell lines were generated in which inducible p53 was introduced using either a temperature-sensitive mutant (p53val135) or a tamoxifen-regulated p53-estrogen receptor chimera (p53-mERtm-pBabepuro). In both cell lines, induction of transcriptionally active p53 was confirmed by assessing several p53 targets: Mdm2 protein, p21waf1 mRNA and protein, and the cyclin G promoter. Despite marked induction of p21waf1, cells with active p53 failed to undergo growth arrest, which is probably due to the presence of a non-functional retinoblastoma protein (pRb) in these cells. Apoptosis also was not observed, even after prolonged (48 h) serum starvation or exposure to cisplatinum. Lack of apoptosis was correlated with unchanged bax mRNA levels following p53 induction. Additionally, albumin mRNA levels remained unchanged, and there was no change in basal transactivation of a reporter containing the promoter of the haptoglobin gene, encoding an acute phase protein. This suggests that growth arrest may be required to promote liver-specific gene expression. Overall, our data demonstrate that introduction of transcriptionally active p53 does not alter the malignant, dedifferentiated phenotype of Hep 3B hepatoma cells. Hence, not all cancer cells are equally responsive to the re-activation of wild-type 53. The ability of a cancer cell to undergo p53-mediated phenotypic alterations may depend on the retention of functional downstream effector pathways.
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PMID:Resistance to p53-mediated growth arrest and apoptosis in Hep 3B hepatoma cells. 923 78

The REC2 recombinase is essential for recombinational repair following DNA damage as well as for successful meiosis and gene targeting in the corn smut Ustilago maydis. Here we report that overexpression of REC2 induced apoptotic cell death in human HuH-7, Hep G2, and Hep 3B hepatoma cells. Apoptosis was related to recombinase activity and was significantly increased by inhibition of retinoblastoma (Rb) expression with transforming growth factor-beta1. REC2-induced apoptosis was associated with a significantly reduced percentage of cells in the G1 phase of the cell cycle and a significant reduction in G2/M only in the Rb(-/-) Hep 3B cells. Overexpression of REC2 resulted in increased abundance of the hyperphosphorylated form of Rb. However, by immunoprecipitation REC2 was associated primarily with hypophosphorylated Rb, suggesting that REC2 may be involved in modulating the phosphorylation state of Rb. The A and B pocket domains with the spacer amino acid sequence and the carboxyl-terminal region of Rb were required for maximal binding to REC2. Overexpression of Rb significantly inhibited REC2-induced apoptosis even in the presence of transforming growth factor-beta1. Taken together, these data suggest a novel interaction of Rb with the recombinase REC2 and a role for this complex in bridging DNA recombination and apoptosis.
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PMID:A novel link between REC2, a DNA recombinase, the retinoblastoma protein, and apoptosis. 923 41

The retinoblastoma (RB) tumor suppressor is a nuclear phosphoprotein important for cell growth control and able to bind specifically to viral oncoproteins such as the SV40 large tumor antigen (T-ag). Human RB possesses a bipartite nuclear localization sequence (NLS) consisting of two clusters of basic amino acids within amino acids 860-877, also present in mouse and Xenopus homologs, which resembles that of nucleoplasmin. The T-ag NLS represents a different type of NLS, consisting of only one stretch of basic amino acids. To compare the nuclear import kinetics conferred by the bipartite NLS of RB to those conferred by the T-ag NLS, we used beta-galactosidase fusion proteins containing the NLSs of either RB or T-ag. The RB NLS was able to target beta-galactosidase to the nucleus both in vivo (in microinjected cells of the HTC rat hepatoma line) and in vitro (in mechanically perforated HTC cells). Mutational substitution of the proximal basic residues of the NLS abolished nuclear targeting activity, confirming its bipartite character. Nuclear accumulation of the RB fusion protein was half-maximal within about 8 min in vivo, maximal levels being between 3-4-fold those in the cytoplasm, which was less than 50% of the maximal levels attained by the T-ag fusion protein, while the initial rate of nuclear import of the RB protein was also less than half that of T-ag. Nuclear import conferred by both NLSs in vitro was dependent on cytosol and ATP and inhibited by the nonhydrolyzable GTP analog GTPgammaS. Using an ELISA-based binding assay, we determined that the RB bipartite NLS had severely reduced affinity, compared with the T-ag NLS, for the high affinity heterodimeric NLS-binding protein complex importin 58/97, this difference presumably representing the basis of the reduced maximal nuclear accumulation and import rate in vivo. The results support the hypothesis that the affinity of NLS recognition by NLS-binding proteins is critical in determining the kinetics of nuclear protein import.
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PMID:Kinetic characterization of the human retinoblastoma protein bipartite nuclear localization sequence (NLS) in vivo and in vitro. A comparison with the SV40 large T-antigen NLS. 926 57

The mammalian cell cycle is controlled by regulators of the G1 to S transition such as tumor suppressor proteins, p53 and retinoblastoma (RB); cyclin D1 and cyclin-dependent kinase 4; and inhibitor of cyclin dependent kinase, p16INK4A. Recently, aberrations of these cell cycle-related genes have been reported to contribute to the formation and development of cancer. In human hepatocellular carcinoma (HCC), high frequencies of aberration have been detected in the p53 and RB genes. Loss of heterozygosity (LOH) of chromosome 13q was detected in 35% of HCC and LOH on chromosome 17p was detected in 49%. Mutation of the p53 gene was also detected in 32%. The aberrations of these genes were observed more frequently in poorly differentiated and in advanced HCCs. On the other hand, genetic alterations of the cyclin D1 and p16INK4A genes were not so frequent, but appeared to be associated with the aggressive behavior of the tumor, which suggests that disruption of the cell cycle-related genes results in the progression of HCC. Further study with a substantial number of cases is required to determine the actual frequency of the aberrations of the G1 controlling genes in hepatocarcinogenesis.
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PMID:Alteration of cell cycle-related genes in hepatocarcinogenesis. 930 64

Carcinogenesis is a multistep process. Most hepatocellular carcinoma (HCC) is preceded by liver cirrhosis, but the genetic changes involved in cirrhosis are not known well. The present study was conducted to evaluate aberration of the retinoblastoma (RB) gene in HCC and adjacent non-tumorous liver using 22 patients with chronic liver damage accompanying HCC. The specimens obtained by microdissection from paraffin-embedded tissues were analyzed using an assay based on the polymerase chain reaction for highly polymorphic nucleotide sequences of microsatellites in the RB gene. Out of 22 cases, 15 showed constitutional heterozygosity for the microsatellite markers. In 11 (73.3%) of these 15 informative cases, the primary HCC foci showed loss of heterozygosity (LOH). In 8 of these 11 doubly informative (informative and LOH-positive in primary HCC) cases, LOH was found in 20 (64.5%) of 31 microdissected non-tumorous foci. All of the non-tumorous foci showing RB loss were cirrhotic lesions but there were no foci of chronic hepatitis. The remaining 4 cases without LOH in HCC foci showed no LOH in non-tumorous lesions. In our study, LOH of the RB gene was frequently observed in liver cirrhosis surrounding tumor.
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PMID:Loss of heterozygosity of the retinoblastoma gene in liver cirrhosis accompanying hepatocellular carcinoma. 934 98

Cytokines are growth inhibitory in a target cell specific manner. The signaling pathways that characterize each cell type play a crucial role in determining the responsiveness to cytokine triggering. Activin A has been shown to suppress the growth of primary hepatocytes. Similarly, the human HepG2 hepatoma cell line was growth arrested by activin A as judged by lack of cell proliferation and suppression of DNA synthesis. In HepG2 cells activin A further induced accumulation of retinoblastoma protein in the hypophosphorylated form known to prevent entrance into S phase. This finding implies the involvement of cyclin dependent kinases and CDK inhibitors. Examination of HepG2 cells following addition of activin A revealed reduced expression of CDK4 and conversely, an increase in the CKI p21(WAF1/Cip1). This accumulation of p21(WAF1/Cip1) protein was partly due to increased transcriptional activity. Functional inactivation of p53, using a miniprotein that oligomerizes with p53 and abrogates DNA binding, abolished the ability of activin A to induce transcriptional activation from the p21(WAF1/Cip1) promoter. Thus, activin A, like transforming growth factor beta, seems to suppress cell growth through the downstream target Rb. However, each of these cytokines seem to operate through a distinct pathway.
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PMID:Involvement of p21(WAF1/Cip1), CDK4 and Rb in activin A mediated signaling leading to hepatoma cell growth inhibition. 934 4

We demonstrated that introduction and expression of wild-type p53 gene in the human hepatocellular carcinoma cell line, Hep3B, resulted in up-regulation of both p21WAF1/CIP1 and bax gene expression and apoptosis. This cell line contains integrated hepatitis B virus sequences and lacks the expression of both p53 and retinoblastoma tumor suppressor genes because of deletions. Our results suggest that whereas an increased level of bax expression mediates apoptosis, an increased level of p21WAF1/CIP1 expression does not induce arrest of cell growth, presumably because of the deletion of the retinoblastoma gene. This study also confirms reported observations that p53 is a tumor suppressor gene, which induces apoptosis in malignant cells that lack normal p53 activity because of mutation, deletion, or inactivation of the gene by the presence of oncogenic viral proteins.
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PMID:Wild-type p53 induces apoptosis in Hep3B through up-regulation of bax expression. 935 71

In cycling cells, the retinoblastoma protein (pRb) is un- and/or hypo-phosphorylated in early G1 and becomes hyper-phosphorylated in late G1. The role of hypo-phosphorylation and identity of the relevant kinase(s) remains unknown. We show here that hypo-phosphorylated pRb associates with E2F in vivo and is therefore active. Increasing the intracellular concentration of the Cdk4/6 specific inhibitor p15(INK4b) by transforming growth factor beta treatment of keratinocytes results in G1 arrest and loss of hypo-phosphorylated pRb with an increase in unphosphorylated pRb. Conversely, p15(INK4b)-independent transforming growth factor beta-mediated G1 arrest of hepatocellular carcinoma cells results in loss of Cdk2 kinase activity with continued Cdk6 kinase activity and pRb remains only hypo-phosphorylated. Introduction of the Cdk4/6 inhibitor p16(INK4a) protein into cells by fusion to a protein transduction domain also prevents pRb hypo-phosphorylation with an increase in unphosphorylated pRb. We conclude that cyclin D:Cdk4/6 complexes hypo-phosphorylate pRb in early G1 allowing continued E2F binding.
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PMID:Hypo-phosphorylation of the retinoblastoma protein (pRb) by cyclin D:Cdk4/6 complexes results in active pRb. 938 Jun 98

Hepatitis B virus X protein (HBX) was studied for its capacity to form a specific complex with the retinoblastoma tumour suppressor protein (pRB), and for its effect on the expression of pRB. HBX was synthesized by in vitro transcription and translation in the presence of [35S]methionine. The synthesized HBX was assayed for its binding to a glutathione-S-transferase (GST)-pRB fusion protein bound to Sepharose beads. The in vivo binding was investigated by a co-immunoprecipitation and Western blot analysis of the cell extract from a CMV-HBX-transfected hepatoblastoma cell line, Hep G2 cells. These experiments demonstrated that HBX was unable to form a detectable complex with pRB. However, the level of pRB increased considerably in Hep G2 cells transfected with CMV-HBX clone. The alteration of pRB expression by HBX could be a mechanism, contributing to the development of hepatocellular carcinoma (HCC) in human.
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PMID:Effect of hepatitis B virus X protein on the expression of retinoblastoma gene product. 938 99

Glucocorticoids can induce a G1 arrest in the cell cycle progression of BDS1 rat hepatoma cells. In these cells, dexamethasone, a synthetic glucocorticoid, stimulated a rapid and selective increase in expression of the p21 cyclin-dependent kinase (CDK) inhibitor mRNA and protein and virtually abolished CDK2 phosphorylation of the retinoblastoma protein. Expression of the p27 CDK inhibitor, and other G1-acting cell cycle proteins, remained unaffected. Dexamethasone stimulated p21 promoter activity in a p53-independent manner that required functional glucocorticoid receptors. Transforming growth factor-beta, which also induced a G1 cell cycle arrest of the hepatoma cells, failed to elicit this response. Analysis of 5' deletions of the p21 promoter uncovered a glucocorticoid responsive region between nucleotides -1481 and -1184, which does not contain a canonical glucocorticoid response element but which can confer dexamethasone responsiveness to a heterologous promoter. Fine mapping of this region uncovered three distinct 50-60-base pair transcriptional elements that likely function as targets of glucocorticoid receptor signaling. Finally, ectopic expression of p21 had no effect on hepatoma cell growth in the absence of glucocorticoids but facilitated the ability of dexamethasone to inhibit cell proliferation. Thus, our results have established a direct transcriptional link between glucocorticoid receptor signaling and the regulated promoter activity of a CDK inhibitor gene that is involved in the cell cycle arrest of hepatoma cells.
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PMID:Glucocorticoids stimulate p21 gene expression by targeting multiple transcriptional elements within a steroid responsive region of the p21waf1/cip1 promoter in rat hepatoma cells. 944 36


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