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)

Cyclins play a fundamental role in regulating cell cycle events in all eukaryotic cells. The human cyclin A gene was identified as the site of integration of hepatitis B virus in a hepatocarcinoma cell line; in addition, cyclin A is associated with the E2F transcription factor in a complex which is dissociated by the E1A oncogene product. Such findings suggest that cyclin A is a target for oncogenic signals. We have now found that DNA synthesis and entry into mitosis are inhibited in human cells microinjected with anti-cyclin A antibodies at distinct times. Cyclin A binds both cdk2 and cdc2, giving two distinct cyclin A kinase activities, one appearing in S phase, the other in G2. These results suggest that cyclin A defines novel control points of the human cell cycle.
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PMID:Cyclin A is required at two points in the human cell cycle. 131 67

The subcellular distribution and regulation of MAP kinase isoforms in chicken hepatoma DU249 cells was investigated with antibodies directed against peptides patterned after sequences in the mitogen-activated protein (MAP) kinases, sea star p44mpk, and rat p44erk1. MonoQ chromatography of cytosol from these cells afforded the resolution of at least four peaks of myelin basic protein (MBP) phosphotransferase activity, but only one of these (peak II) was stimulated in extracts from phorbol ester-treated cells. A 40- to 41-kDa (p41) doublet on Western blots detected with three different MAP kinase antibodies was coincident with peak II, and it probably corresponded to the avian homolog of p42mapk/erk2. Immunofluorescent studies with DU249 cells and chicken embryo fibroblasts revealed that most of the cross-reactive protein with at least two different MAP kinase antibodies was distributed in the nucleus. Subcellular fractionation studies confirmed a predominantly nuclear localization for p41 MAP kinase. Nocodazole arrest of DU249 cells was exploited for the detection of an M-phase-activated MBP kinase that was resolved from p41 MAP kinase by phenyl-Superose chromatography. Western blotting analysis with antibodies for the cdc2-encoded protein kinase and p13suc1-agarose binding studies allowed positive identification of this MBP kinase as p34cdc2.
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PMID:Immunological characterization of avian MAP kinases: evidence for nuclear localization. 132 21

Cyclin proteins form complexes with members of the p34cdc2 kinase family and they are essential components of the cell cycle regulatory machinery. They are thought to determine the timing of activation, the subcellular distribution, and/or the substrate specificity of cdc2-related kinases, but their precise mode of action remains to be elucidated. Here we report the cloning and sequencing of avian cyclin B2. Based on the use of monospecific antibodies raised against bacterially expressed protein, we also describe the subcellular distribution of cyclin B2 in chick embryo fibroblasts and in DU249 hepatoma cells. By indirect immunofluorescence microscopy we show that cyclin B2 is cytoplasmic during interphase of the cell cycle, but undergoes an abrupt translocation to the cell nucleus at the onset of mitotic prophase. Finally, we have examined the phenotypic consequences of expressing wild-type and mutated versions of avian cyclin B2 in HeLa cells. We found that expression of cyclin B2 carrying a mutation at arginine 32 (to serine) caused HeLa cells to arrest in a pseudomitotic state. Many of the arrested cells displayed multiple mitotic spindles, suggesting that the centrosome cycle had continued in spite of the cell cycle arrest.
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PMID:Cyclin B2 undergoes cell cycle-dependent nuclear translocation and, when expressed as a non-destructible mutant, causes mitotic arrest in HeLa cells. 153 84

This study characterizes the insulin-activated serine/threonine protein kinases in H4 hepatoma cells active on a 37-residue synthetic peptide (called the SKAIPS peptide) corresponding to a putative autoinhibitory domain in the carboxyl-terminal tail of the p70 S6 kinase as well as on recombinant p70 S6 kinase. Three peaks of insulin-stimulated protein kinase active on both these substrates are identified as two (possibly three) isoforms of the 40-45-kDa erk/microtubule-associated protein (MAP)-2 kinase family and a 150-kDa form of cdc2. Although distinguishable in their substrate specificity, these protein kinases together with the p54 MAP-2 kinase share a major common specificity determinant reflected in the SKAIPS peptide: the requirement for a proline residue immediately carboxyl-terminal to the site of Ser/Thr phosphorylation. In addition, however, at least one peak of insulin-stimulated protein kinase active on recombinant p70, but not on the SKAIPS peptide, is present although not yet identified. MFP/cdc2 phosphorylates both rat liver p70 S6 kinase and recombinant p70 S6 kinase exclusively at a set of Ser/Thr residues within the putative autoinhibitory (SKAIPS peptide) domain. erk/MAP kinase does not phosphorylate rat liver p70 S6 kinase, but readily phosphorylates recombinant p70 S6 kinase at sites both within and in addition to those encompassed by the SKAIPS peptide sequences. Although the tryptic 32P-peptides bearing the cdc2 and erk/MAP kinase phosphorylation sites co-migrate with a subset of the sites phosphorylated in situ in insulin-stimulated cells, phosphorylation of the p70 S6 kinase by these proline-directed protein kinases in vitro does not reproducibly activate p70 S6 kinase activity. Thus, one or more erk/MAP kinases and cdc2 are likely to participate in the insulin-induced phosphorylation of the p70 S6 kinase. In addition to these kinases, however, phosphorylation of the p70 S6 kinase by other as yet unidentified protein kinases is necessary to recapitulate the multisite phosphorylation required for activation of the p70 S6 kinase.
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PMID:An array of insulin-activated, proline-directed serine/threonine protein kinases phosphorylate the p70 S6 kinase. 173 88

Control over the nuclear transport of transcription factors (TFs) represents a level of gene regulation integral to cellular processes such as differentiation, transformation and signal transduction. The Saccharomyces cerevisiae TF SWI5 is excluded from the nucleus in a cell cycle-dependent fashion, mediated by phosphorylation by the cyclin-dependent kinase (cdk) CDC28. Nuclear entry occurs in G1. beta-galactosidase fusion proteins carrying SWI5 amino acids 633-682, including the nuclear localization sequence (NLS: Lys-Lys-Tyr-Glu-Asn-Val-Val-Ile-Lys-Arg-Ser-Pro-Arg-Lys-Arg-Gly-Arg-Pro- Arg-Lys655) were analyzed for subcellular localization in appropriate temperature-sensitive yeast strains blocked in G1 or G2/M using indirect immunofluorescence, and for nuclear import kinetics in living rat hepatoma or Vero African green monkey kidney cells microinjected with fluorescently labeled bacterially expressed protein and quantitative confocal laser microscopy. Cell cycle-dependent nuclear localization in yeast was both NLS and cdk site-dependent, whereby mutation of the cdk site serines (Ser646 and Ser664) to alanine resulted in constitutive nuclear localization. In mammalian cells, the SWI5 fusion proteins were similarly transported to the nucleus in an NLS-dependent fashion, while the mutation to Ala of the cdk site serines increased the maximal level of nuclear accumulation from about 1- to over 8-fold. We suggest that phosphorylation at the cdk sites inhibits nuclear transport of SWI5, consistent with our previous observations for the inhibition of SV40 large tumor antigen nuclear transport by phosphorylation by the cdk cdc2. The results indicate for the first time that a yeast NLS and, fascinatingly, its regulatory mechanisms are functional in higher eukaryotes, implying the universal nature of regulatory signals for protein transport to the nucleus.
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PMID:Cyclin-dependent kinase site-regulated signal-dependent nuclear localization of the SW15 yeast transcription factor in mammalian cells. 761 96

The regulation of nuclear protein transport by phosphorylation plays a central role in gene expression in eukaryotic cells. We previously showed that nuclear import of SV40 large tumor antigen (T-ag) fusion proteins is regulated by the CcN motif, comprising phosphorylation sites for casein kinase II and the cyclin-dependent kinase cdc2, together with the nuclear localization signal. Regulation of nuclear uptake by CcN motif kinase sites also holds true for the yeast transcription factor SWI5 and the Xenopus nuclear phosphoprotein nucleoplasmin. To test directly whether a kinase site other than those of the CcN motif could regulate nuclear import of T-ag, the CcN motif casein kinase II site, which markedly increases the rate of T-ag nuclear import, was replaced by a consensus site for the cAMP-dependent protein kinase (PK-A) using site-directed mutagenesis. The resultant fusion protein could be specifically phosphorylated by PK-A in vitro and in cell extracts. Nuclear import of the fluorescently labeled protein was analyzed in the HTC rat hepatoma cell line both in vivo (microinjected cells) and in vitro (mechanically perforated cells) in the presence and the absence of cAMP and/or PK-A catalytic subunit using confocal laser scanning microscopy. In vitro PK-A-prephosphorylated protein was also tested. All results indicated that the rate of nuclear import was increased by phosphorylation at the PK-A site (2-5-fold), demonstrating that kinases other than those of the CcN motif can regulate nuclear import in response to stimulatory signals. The phosphorylation-regulated nuclear localization signal derived here represents an important first step toward developing a signal conferring inducible nuclear targeting of molecules of interest.
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PMID:A consensus cAMP-dependent protein kinase (PK-A) site in place of the CcN motif casein kinase II site simian virus 40 large T-antigen confers PK-A-mediated regulation of nuclear import. 862 46

A protein kinase inhibitor K252a suppressed the growth of HuH7 hepatoma cells and the hyperphosphorylation of retinoblastoma protein (pRb) at late G1 phase of cell cycle. However, K252a treatment did not alter the levels of cyclin D1, cyclin E, cyclin A and Cdk2 protein bound to cyclin E or cyclin A. Therefore, the K252a inhibition of pRb phosphorylation is considered to be brought about probably by inhibiting the action of Cdk-cyclin complex rather than by changing its cellular level. These results also suggest that K252a is a useful tool for investigating the mechanism of phosphorylation of pRb mediated by Cdk-cyclin.
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PMID:K252a inhibits the phosphorylation of pRb without changing the levels of G1 cyclins and Cdk2 protein in human hepatoma cells. 869 9

In the present study, we describe that ginsenoside-Rg1 (G-Rg1) stimulates the proliferation of cultured human hepatoma SK-HEP-1 cells. The incorporation of [3H] thymidine into DNA was increased in the cells in response to G-Rg1. The stimulatory effect of G-Rg1 on DNA synthesis in SK-HEP-1 cells require newly synthesized proteins, since cycloheximide blocked the DNA synthetic activity stimulated with G-Rg1. Thus, we examined whether G-Rg1 induces the intracellular protein levels of regulatory proteins for cell cycle progression using immunoblottings. The results from immunoblottings showed that G-Rg1 induced the levels of cyclin E and cdk2 proteins in the cells. Furthermore, the results from immuno-complex kinase assays for cyclin E-dependent kinase showed that G-Rg1 up-regulates the kinase activity in a dose-dependent manner. These results suggest that G-Rg1 stimulates cell-growth of SK-HEP-1 cells by inducing the intracellular levels of cyclin E/cdk2 complex, which in turn up-regulates cyclin E-dependent kinase activity.
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PMID:Ginsenoside-Rg1 positively regulates cyclin E-dependent kinase activity in human hepatoma SK-HEP-1 cells. 882 5

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

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


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