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)

In primary rat hepatocytes, prolonged activation of the p42/44 mitogen-activated protein kinase (MAPK) pathway is associated with a decrease in DNA synthesis and increased expression of the cyclin-dependent kinase inhibitor (CKI) proteins p21Cip-1/WAF1 and p16INK4a. To evaluate the relative importance of these CKIs in mediating this response, we determined the impact of prolonged MAPK activation on DNA synthesis in primary cultures of hepatocytes derived from mice embryonically deleted (null) for either p21Cip-1/WAF1 or p16INK4a. When MAPK was activated in wild-type mouse hepatocytes for 24 h, via infection with a construct to express an inducible oestrogen receptor-Raf-1 fusion protein (DeltaRaf:ER), the expression of p21Cip-1/WAF1 and p16INK4a CKI proteins increased, cyclin-dependent kinase 2 (cdk2) and cdk4 activities decreased, and DNA synthesis decreased. Inhibition of RhoA GTPase function increased the basal expression of p21Cip-1/WAF1 and p27Kip-1 but not p16INK4a, and enhanced the ability of MAPK signalling to decrease DNA synthesis. Ablation of the expression of CCAATT enhancer-binding protein alpha (C/EBPalpha), but not of the expression of C/EBPbeta, decreased the ability of MAPK signalling to induce p21Cip-1/WAF1. When MAPK was activated in p16INK4a-null hepatocytes for 24 h, the expression of p21Cip-1/WAF1 increased, cdk2 and cdk4 activities decreased and DNA synthesis decreased. In contrast with these findings, prolonged activation of the MAPK pathway in hepatocytes from p21Cip-1/WAF1-null mice enhanced cdk2 and cdk4 activities and caused a large increase in DNA synthesis, despite elevated expression of p16INK4a. Inhibition of RhoA GTPase activity in p21Cip-1/WAF1-null cells partly blunted both the basal levels of DNA synthesis and the ability of prolonged MAPK signalling to increase DNA synthesis. Expression of anti-sense p21Cip-1/WAF1 in either wild-type or p16INK4a-null hepatocytes decreased the ability of prolonged MAPK signalling to increase the expression of p21Cip-1/WAF1, and permitted MAPK signalling to increase both cdk2 and cdk4 activities and DNA synthesis. These results argue that the ability of prolonged MAPK signalling to inhibit DNA synthesis in hepatocytes requires the expression of p21Cip-1/WAF1, and that the increased expression of p16INK4a has a smaller role in the ability of this stimulus to mediate growth arrest. Our results also suggest that RhoA function can modulate DNA synthesis in primary hepatocytes via the expression of p21Cip-1/WAF1 and p27Kip-1.
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PMID:Prolonged activation of the mitogen-activated protein kinase pathway promotes DNA synthesis in primary hepatocytes from p21Cip-1/WAF1-null mice, but not in hepatocytes from p16INK4a-null mice. 984 65

The tumour suppressor PTEN, also named MMAC1 or TEP1, is associated with a number of malignancies in human populations. This protein has a dual protein phosphatase activity, being also capable to dephosphorylate phosphatidylinositol 3,4,5 triphosphate. We have studied the mechanism of growth suppression attributable to PTEN. We observed that PTEN overexpression inhibits cell growth in a variety of normal and transformed, human and murine cells. Bromodeoxyuridine (BrdU) incorporation and TUNEL labelling experiments in transiently transfected cells demonstrate that this inhibition is due to a cell cycle arrest rather than induction of apoptosis. Given that PTEN is unable to cause cell growth arrest in retinoblastoma (Rb)-deficient cell lines, we have explored the possible requirement for pRb in the PTEN-induced inhibition of cell proliferation. We found that the co-expression of SV40 antigen, but not a mutant form (which binds exclusively to p53), and cyclin D1/cdk4 are able to overcome the PTEN-mediated growth suppression. In addition, the reintroduction of a functional pRb, but not its relatives p107 or p130, in Rb-deficient cells restores the sensitivity to PTEN-induced arrest. Finally, the hyperphosphorylation of transfected pRb is inhibited by PTEN co-expression and restored by PI-3K co-expression. Accordingly, PTEN gene is mostly expressed, in parallel to Akt, in mid-late G1 phase during cell cycle progression prior to pRb hyperphosphorylation. Finally, we have studied the signal transduction pathways modulated by PTEN expression. We found that PTEN-induced growth arrest can be rescued by the co-expression of active PI-3K and downstream effectors such as Akt or PDK1, and also certain small GTPases such as Rac1 and Cdc42, but not by active Ha-ras, raf or RhoA. Collectively, our data link the tumour suppressor activities of PTEN to the machinery controlling cell cycle through the modulation of signalling molecules whose final target is the functional inactivation of the retinoblastoma gene product.
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PMID:PTEN tumour suppressor is linked to the cell cycle control through the retinoblastoma protein. 1060 5

During cytokinesis of animal cells, the mitotic spindle plays at least two roles. Initially, the spindle positions the contractile ring. Subsequently, the central spindle, which is composed of microtubule bundles that form during anaphase, promotes a late step in cytokinesis. How the central spindle assembles and functions in cytokinesis is poorly understood. The cyk-4 gene has been identified by genetic analysis in Caenorhabditis elegans. Embryos from cyk-4(t1689ts) mutant hermaphrodites initiate, but fail to complete, cytokinesis. These embryos also fail to assemble the central spindle. We show that the cyk-4 gene encodes a GTPase activating protein (GAP) for Rho family GTPases. CYK-4 activates GTP hydrolysis by RhoA, Rac1, and Cdc42 in vitro. RNA-mediated interference of RhoA, Rac1, and Cdc42 indicates that only RhoA is essential for cytokinesis and, thus, RhoA is the likely target of CYK-4 GAP activity for cytokinesis. CYK-4 and a CYK-4:GFP fusion protein localize to the central spindle and persist at cell division remnants. CYK-4 localization is dependent on the kinesin-like protein ZEN-4/CeMKLP1 and vice versa. These data suggest that CYK-4 and ZEN-4/CeMKLP1 cooperate in central spindle assembly. Central spindle localization of CYK-4 could accelerate GTP hydrolysis by RhoA, thereby allowing contractile ring disassembly and completion of cytokinesis.
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PMID:CYK-4: A Rho family gtpase activating protein (GAP) required for central spindle formation and cytokinesis. 1087 Dec 80

We have investigated the role of Rho GTPase in cell growth by generating stable cells that express the wild-type RhoA (RhoA(wt)) under the control of an inducible promoter. Induction of RhoA(wt) had a biphasic effect on the actin cytoskeleton. At low levels of expression, RhoA(wt) stimulated the assembly of actin stress fibers without affecting cell growth. At high levels, there was a paradoxical disruption of the actin cytoskeleton accompanied by a growth arrest. Cell cycle analysis revealed a dual block at the G(1)/S and G(2)/M checkpoints. The G(1)/S arrest correlated with the accumulation of p21(Cip1), resulting in the inhibition of cdk2 activity, whereas the G(2)/M block correlated with the loss of microtubules. The cyclin B level and the cdc2 kinase activity, however, were increased, suggesting that the progression through mitosis rather than entry into the G(2)/M is defective when RhoA(wt) is overexpressed. Similar cell cycle defects and the loss of microtubules were observed after a cytochalasin D treatment, indicating that the ability of RhoA to regulate the integrity of actin cytoskeleton may be critical for the cell cycle transition through both the G(1)/S and M phase checkpoints.
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PMID:Overexpression of wild-type RhoA produces growth arrest by disrupting actin cytoskeleton and microtubules. 1107 94

Liver regeneration after partial hepatectomy (PH) involves several signaling mechanisms including activation of the small GTPases Ras and RhoA in response to mitogens leading to DNA synthesis and cell proliferation. Peroxisome proliferator-activated receptor-alpha (PPARalpha) regulates the expression of several key enzymes in isoprenoid synthesis, which are key events for membrane association of Ras and RhoA. Thus the role of PPARalpha in cell proliferation after PH was tested. After PH, an increase in PPARalpha DNA binding was observed in wild-type mice, correlating with an increase in the PPARalpha-regulated enzyme acyl-CoA oxidase. In addition, the PPARalpha-regulated genes farnesyl pyrophosphate synthase and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) synthase were significantly increased in wild-type mice. However, these increases were not observed in PPARalpha knockout (PPARalpha -/-) mice. The peak in DNA synthesis observed 42 h after PH was reduced by approximately 60% in PPARalpha -/- mice, despite increases in TNF-alpha and IL-1. Also, under these conditions, membrane association of Ras was high in wild-type mice after PH but was impaired in PPARalpha -/- mice. Accordingly, Ras was significantly elevated in the cytosol in PPARalpha -/- mice. This observation correlated with lower levels of active GTP-bound Ras after PH in PPARalpha -/- mice compared with wild-type mice. Similar observations were made for RhoA. Moreover, deletion of PPARalpha blunted the activation of cyclin-dependent kinase (cdk)2/cyclin E and cdk4/cyclin D complexes. Collectively, these results support the hypothesis that PPARalpha is necessary for cell cycle progression in regenerating mouse liver via mechanisms involving prenylation of small GTPases Ras and RhoA.
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PMID:Impaired Ras membrane association and activation in PPARalpha knockout mice after partial hepatectomy. 1238 8

Although RhoA plays an important role in cell proliferation and in Ras transformation in fibroblasts and mammary epithelial cells, its role in intestinal epithelial cells (IEC) is unknown. In a previous study (Ray RM, Zimmerman BJ, McCormack SA, Patel TB, and Johnson LR. Am J Physiol Cell Physiol 276: C684-C691, 1999), we showed that polyamine depletion [dl-alpha-difluoromethylornithine (DFMO) treatment] strongly inhibits the proliferation of IEC. In this report, we examined the effect of RhoA on IEC-6 cell proliferation and whether polyamine depletion inhibits cell proliferation in the presence of constitutively active RhoA. Constitutively active RhoA and vector-transfected IEC-6 cell lines were grown in the presence or absence of DFMO, which causes polyamine depletion by inhibiting ornithine decarboxylase, the first rate-limiting step in polyamine synthesis. Constitutively active RhoA significantly increased the rate of cell proliferation. These cells also lost contact inhibition and formed conspicuous foci when they were fully confluent. Decreased p21Waf1/Cip1 expression and increased cyclin-dependent kinase (Cdk2) mRNA levels and activity accompanied the increased proliferation. The inhibition of p21Waf1/Cip1 was independent of p53. There was no activation of the Ras-Raf-MEK-ERK pathway in the RhoA-transfected cell line. Polyamine depletion totally prevented the effect of activated RhoA on IEC-6 cell proliferation, focus formation, and Cdk2 expression. The stability of mRNA and protein for Cdk2 and p21Waf1/Cip1 in V14-RhoA cells was not significantly different from that of vector-transfected cells. In conclusion, RhoA activation decreased p21Waf1/Cip1 expression and increased basal and serum-induced ornithine decarboxylase activity, Cdk2 expression, Cdk2 protein, and Cdk2 activity, leading to the stimulation of IEC proliferation and transformation. Polyamine depletion totally prevented RhoA's effect on proliferation by decreasing Cdk2 expression and activity.
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PMID:RhoA stimulates IEC-6 cell proliferation by increasing polyamine-dependent Cdk2 activity. 1281 57

The ability of the transforming growth factor beta (TGF-beta) signaling pathways to inhibit proliferation of most cells while stimulating proliferation of others remains a conundrum. In this article, we report that the absence of RhoA and p160ROCK activity in fibroblastic NIH 3T3 cells and its presence in epithelial NMuMG cells can at least partially explain the difference in the TGF-beta growth response. Further, evidence is presented for TGF-beta-stimulated p160ROCK translocation to the nucleus and inhibitory phosphorylation of the cyclin-dependent kinase-activating phosphatase, Cdc25A. The resultant suppression of Cdk2 activity contributes to G1/S inhibition in NMuMG cells. These data provide evidence that signaling through RhoA and p160ROCK is important in TGF-beta inhibition of cell proliferation and links signaling components for epithelial transdifferentiation with regulation of cell-cycle progression.
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PMID:TGF-beta-induced RhoA and p160ROCK activation is involved in the inhibition of Cdc25A with resultant cell-cycle arrest. 1467 28

Nuclear p27kip1 is an established inhibitor of cyclin-dependent kinase-2, and it now appears that cytoplasmic p27kip1 inhibits the activation of RhoA. In this dual role, p27kip1 could coordinate cell cycle progression and cell migration.
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PMID:Stopping and going with p27kip1. 1506 85

Substantial evidence exists to support a role for RhoA signaling in adhesion and cytoskeletal reorganization, while relatively less is known about the participation of RhoA on cell survival. We provide evidence that RhoA functions as a differential modulator of apoptosis induced by anticancer agents. Specifically, both RhoA and caRhoA induce statistically significant resistance to statin, etoposide, 5-FU and taxol while increasing sensitivity to vincristine (all p<0.001). The IC50 values for statin, etoposide, 5-fluorouracil (5-FU) and taxol in caRhoA transfectant were 8.70+/-0.74, 4.08+/-0.12, 4.12+/-0.12 microg/ml and 3.84+/-0.16 ng/ml, respectively, whereas the respective IC50 values in the mock-transfected control were 3.40+/-0.21, 1.12+/-0.06, 1.21+/-0.06 microg/ml and 2.84+/-0.15 ng/ml. This represented a 2.6-, 3.5-, 3.2- and 1.4-fold resistance to statin, etoposide, 5-FU and taxol, respectively. In contrast, caRhoA increased sensitivity to vincristine, decreasing IC50 values from 4.61+/-0.46 to 3.73+/-0.44 ng/ml (p<0.001). Western blot analysis demonstrated that RhoA mediates induction of E2F-1, Cdk2 and PCNA, accompanying concurrent reduction in p21 and p27. However, cleavage assays of poly (ADP-ribose) polymerase, BID, caspase-8 and caspase-3 indicate that the cell growth modulation mediated by RhoA in response to these anticancer agents occurs through the inhibition of apoptosis. Taken together, these results indicate that RhoA differentially modulates cancer cell death depending on the anticancer agent.
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PMID:Differential effects of RhoA signaling on anticancer agent-induced cell death. 1564 15

Cleavage furrow formation marks the onset of cell division during early anaphase. The small GTPase RhoA and its regulators ECT2 and MgcRacGAP have been implicated in furrow ingression in mammalian cells, but the signaling upstream of these molecules remains unclear. We now show that the inhibition of cyclin-dependent kinase (Cdk)1 is sufficient to initiate cytokinesis. When mitotically synchronized cells were treated with the Cdk-specific inhibitor BMI-1026, the initiation of cytokinesis was induced precociously before chromosomal separation. Cytokinesis was also induced by the Cdk1-specific inhibitor purvalanol A but not by Cdk2/Cdk5- or Cdk4-specific inhibitors. Consistent with initiation of precocious cytokinesis by Cdk1 inhibition, introduction of anti-Cdk1 monoclonal antibody resulted in cells with aberrant nuclei. Depolymerization of mitotic spindles by nocodazole inhibited BMI-1026-induced precocious cytokinesis. However, in the presence of a low concentration of nocodazole, BMI-1026 induced excessive membrane blebbing, which appeared to be caused by formation of ectopic cleavage furrows. Depletion of ECT2 or MgcRacGAP by RNA interference abolished both of the phenotypes (precocious furrowing after nocodazole release and excessive blebbing in the presence of nocodazole). RNA interference of RhoA or expression of dominant-negative RhoA efficiently reduced both phenotypes. RhoA was localized at the cleavage furrow or at the necks of blebs. We propose that Cdk1 inactivation is sufficient to activate a signaling pathway leading to cytokinesis, which emanates from mitotic spindles and is regulated by ECT2, MgcRacGAP, and RhoA. Chemical induction of cytokinesis will be a valuable tool to study the initiation mechanism of cytokinesis.
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PMID:Inhibition of cyclin-dependent kinase 1 induces cytokinesis without chromosome segregation in an ECT2 and MgcRacGAP-dependent manner. 1611 7


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