Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.22 (cdc2)
 8,319 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ceramide is an intracellular lipid mediator generated through the sphingomyelin cycle in response to several extracellular signals. Ceramide has been shown to induce growth inhibition, c-myc downmodulation and apoptosis. In this paper we examined the mechanism by which ceramide induces growth suppression and the role of the G1-CDK/pRb/E2F pathway in this process. The addition of exogenous, cell-permeable C2-ceramide to the Hs 27 human diploid fibroblast cell line resulted in a dose-dependent induction of the p21WAF1/CIP1/Sdi1 kinase inhibitor with reduction of cyclin-D1 associated kinase activity. Furthermore, significant dephosphorylation of pRb was observed, with increased association of pRb and the E2F transcription factor into a transcriptionally inactive complex. Ceramide was also capable of inhibiting the transcriptional activity of a CAT reporter vector driven by E2F binding sites containing c-myc promoter transfected into Hs 27 cells. The requirement of the pRb protein for ceramide-induced c-myc downregulation was supported by the failure of ceramide to inhibit promoter activity in HeLa cells, in which pRb function is abrogated by the presence of the E7 Papilloma virus oncoprotein, and in pRb-deleted SAOS2 AT cells. Ceramide-induced downregulation of the c-myc promoter was restored in SAOS2 #1 cells in which a functional Rb gene was reintroduced. Our studies demonstrate that pRb dephosphorylation, induced by ceramide, is at least partly necessary for c-myc downregulation, and therefore the CDK-Rb-E2F pathway appears to be a target for the ceramide-induced modulation of cell cycle regulated gene transcription.
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PMID:The growth arrest and downregulation of c-myc transcription induced by ceramide are related events dependent on p21 induction, Rb underphosphorylation and E2F sequestering. 1020 Apr 87

Ceramide acts as a mediator of apoptosis in various cell lines, but little is known regarding the molecular mechanism linked to the cell cycle. In the present study, we examined the expression of p27(kip1) and its relationship to apoptosis induced by ceramide. We demonstrated that treatment of HL-60 cells with C6-ceramide resulted in G1 phase elevation followed by apoptotic cleavage associated with increase in the level of cdk inhibitor p27(kip1). Ceramide inhibited the kinase activities of cdk2 and cdk4 within 24 h of treatment. Ceramide-induced inhibition of cdk2 and cdk4 kinase activities was accompanied by increase of p27(kip1) in the cdks complexes. In addition, we have shown that both the cell death and expression of p27(kip1) protein induced by ceramide were significantly decreased in HL-60 cells overexpressing bcl-2. Furthermore, ceramide induced a significant increase in Bax protein expression coincided with increase in p27(kip1) protein level. These findings indicate that p27(kip1) may play important roles in mediating ceramide-induced apoptosis and its expression can be regulated by Bax and Bcl-2.
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PMID:Involvement of p27(kip1) in ceramide-mediated apoptosis in HL-60 cells. 1076 21

Ceramide is known to induce pRb (retinoblastoma gene product) dephosphorylation through the activation of ceramide-activated protein phosphatase (CAPP) during G1 arrest, but other molecular mechanisms linked to regulation of pRb dephosphorylation during ceramide-induced G1 arrest are poorly understood. In this paper, we investigated whether p21, a cdk (cyclin-dependent kinase) inhibitor, is involved in the induction of pRb dephosphorylation during ceramide-induced G1 arrest. In SK-Hep-1 cells, the addition of ceramide resulted in pRb dephosphorylation and G1 arrest. The activity of cdk2 was inhibited in response to ceramide during this process. p21 protein and mRNA were remarkably induced, while the protein level of p53, known as a transcriptional activator of p21, was not elevated at the same condition. p21 induction was also observed in the Hep3B cells lacking a functional p53 after exposure to ceramide. Although p21 is induced in ceramide-treated Hep3B cells, Hep3B cells do not induce G1 arrest, because Hep3B cells are deficient in a functional pRb protein. To confirm that pRb is a critical target for the induction of G1 arrest by inhibiting cdk2 activity through p53-independent p21, pRb-expressing vector was transfected into Hep3B cells. After treatment with ceramide, pRb-expressing cells (pRb+/+), but not pRb-/- cells, were arrested in G1 phase. In pRb+/+ cells, ceramide-mediated G1 arrest was accompanied by the accumulation of hypophosphorylated pRb and p21 associated with cdk2. Together, these results suggest that p21, induced through p53-independent pathway, participates in the induction of pRb dephosphorylation by inhibiting cdk2 activity during ceramide-mediated G1 arrest in hepatocarcinoma cells.
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PMID:Induction of p53-independent p21 during ceramide-induced G1 arrest in human hepatocarcinoma cells. 1087 74

Cyclin-dependent kinases have been implicated in the inactivation of retinoblastoma (Rb) protein and cell cycle progression. Recent studies have demonstrated that the lipid molecule ceramide is able to induce Rb hypophosphorylation leading to growth arrest and cellular senescence. In this study, we examined the underlying mechanisms of Rb hypophosphorylation and cell cycle progression utilizing the antiproliferative molecule ceramide. C6-Ceramide induced a G0/G1 arrest of the cell cycle in WI38 human diploid fibroblasts. Employing immunoprecipitation kinase assays, we found that ceramide specifically inhibited cyclin-dependent kinase CDK2, with a mild effect on CDC2 and significantly less effect on CDK4. The effect of ceramide was specific such that C6-dihydroceramide was not effective. Ceramide did not directly inhibit CDK2 in vitro but caused activation of p21, a major class of CDK-inhibitory proteins, and led to a greater association of p21 to CDK2. Using purified protein phosphatases, we showed that ceramide activated both protein phosphatase 1 and protein phosphatase 2A activities specific for CDK2 in vitro. Further, calyculin A and okadaic acid, both potent protein phosphatase inhibitors, together almost completely reversed the effects of ceramide on CDK2 inhibition. Taken together, these results demonstrate a dual mechanism by which ceramide inhibits the cell cycle. Ceramide causes an increase in p21 association with CDK2 and through activation of protein phosphatases selectively regulates CDK2. These events may lead to activation of Rb protein and subsequent cell cycle arrest.
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PMID:Regulation of cyclin-dependent kinase 2 activity by ceramide. 1111 37

Human GLTP on chromosome 12 (locus 12q24.11) encodes a 24 kD amphitropic lipid transfer protein (GLTP) that mediates glycosphingolipid (GSL) intermembrane trafficking and regulates GSL homeostatic levels within cells. Herein, we provide evidence that GLTP overexpression inhibits the growth of human colon carcinoma cells (HT-29; HCT-116), but spares normal colonic cells (CCD-18Co). Mechanistic studies reveal that GLTP overexpression arrested the cell cycle at the G1/S checkpoint via upregulation of cyclin-dependent kinase inhibitor-1B (Kip1/p27) and cyclin-dependent kinase inhibitor 1A (Cip1/p21) at the protein and mRNA levels, and downregulation of cyclin-dependent kinase-2 (CDK2), cyclin-dependent kinase-4 (CDK4), cyclin E and cyclin D1 protein levels. Assessment of the biological fate of HCT-116 cells overexpressing GLTP indicated no increase in cell death suggesting induction of quiescence. However, HT-29 cells overexpressing GLTP underwent cell death by necroptosis as revealed by phosphorylation of human mixed lineage kinase domain-like protein (pMLKL) via receptor-interacting protein kinase-3 (RIPK-3), elevated cytosolic calcium, and plasma membrane permeabilization by pMLKL oligomerization. Overexpression of W96A-GLTP, an ablated GSL binding site mutant, failed to arrest the cell cycle or induce necroptosis. Sphingolipid assessment (ceramide, monohexosylceramide, sphingomyelin, ceramide-1-phosphate, sphingosine, and sphingosine-1-phosphate) of HT-29 cells overexpressing GLTP revealed large decreases (>5-fold) in sphingosine-1-phosphate with minimal change in 16:0-ceramide, tipping the 'sphingolipid rheostat' (S1P/16:0-Cer ratio) towards cell death. Depletion of RIPK-3 or MLKL abrogated necroptosis induced by GLTP overexpression. Our findings establish GLTP upregulation as a previously unknown suppressor of human colon carcinoma HT-29 cells via interference with cell cycle progression and induction of necroptosis.
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PMID:Upregulation of human glycolipid transfer protein (GLTP) induces necroptosis in colon carcinoma cells. 3047 25