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

In the cell cycle the transition from G2 phase to cell division (M) is strictly controlled by protein phosphorylation-dephosphorylation reactions effected by several protein kinases and phosphatases. Although much indirect and direct evidence point to a key role of protein phosphatase 2A (PP2A) at the G2/M transition, the control of the enzyme activity prior to and after the transition are not fully clarified. Using synchronized HeLa cells we determined the PP2A activity (i.e. the increment sensitive to inhibition by 2nM okadaic acid) in immunoprecipitates obtained with antibodies raised against a conserved peptide sequence (residues 169-182, Ab(169/182)) of the PP2A catalytic subunit (PP2A C). Two different substrates were offered: the phospho-peptide KR(p)TIRR and histone H1 phosphorylated by means of the cyclin-dependent protein kinase p34(cdc2). The results indicate that in HeLa cells the specific activity of PP2A towards both substrates goes through a minimum in late G2 phase and stays low until metaphase. Treatment of G2 cells with TPA (10(-7) M) caused a reactivation of the downregulated PP2A activity within 20 min, i.e. the same time frame within which TPA was shown earlier to block HeLa cells at the transition from G2 to mitosis [Kinzel et al., 1988. Cancer Res. 48, 1759-1762]. Activation of PP2A was also induced by TPA in mitotic cells. The low activity of PP2A in mitotic cells was accompanied by a strong reaction of mitotic PP2A C with anti-P-Tyr antibodies in Western blots, which was reversed by treatment of mitotic cells with TPA. The results suggest that the activity of cellular PP2A requires downregulation for the transition from G2 phase to mitosis. Unscheduled reactivation of PP2A induced by TPA in late G2 phase appears to inhibit the progress into mitosis.
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PMID:Downregulation of protein phosphatase 2A activity in HeLa cells at the G2-mitosis transition and unscheduled reactivation induced by 12-O-tetradecanoyl phorbol-13-acetate (TPA). 1618 Mar 10

PKC-delta is a serine/threonine kinase that mediates diverse signal transduction pathways. We previously demonstrated that overexpression of PKC-delta slowed the G1 progression of Caco-2 colon cancer cells, accelerated apoptosis, and induced cellular differentiation. In this study, we further characterized the PKC-delta dependent signaling pathways involved in these tumor suppressor actions in Caco-2 cells overexpressing PKC-delta using a Zn2+ inducible expression vector. Consistent with a G1 arrest, increased expression of PKC-delta caused rapid and significant downregulation of cyclin D1 and cyclin E proteins (50% decreases, P<0.05), while mRNA levels remained unchanged. The PKC agonist, phorbol 12-myristate 13-acetate (TPA, 100 nM, 4 h), induced two-fold higher protein and mRNA levels of p21(Waf1), a cyclin-dependent kinase (cdk) inhibitor in PKC-delta transfectants compared with empty vector (EV) transfected cells, whereas the PKC-delta specific inhibitor rottlerin (3 microM) or knockdown of this isoenzyme with specific siRNA oligonucleotides blocked p21(Waf1) expression. Concomitantly, compared to EV control cells, PKC-delta upregulation decreased cyclin D1 and cyclin E proteins co-immunoprecipitating with cdk6 and cdk2, respectively. In addition, overexpression of PKC-delta increased binding of cdk inhibitor p27(Kip1) to cdk4. These alterations in cyclin-cdks and their inhibitors are predicted to decrease G1 cyclin kinase activity. As an independent confirmation of the direct role PKC-delta plays in cell growth and cell cycle regulation, we knocked down PKC-delta using specific siRNA oligonucleotides. PKC-delta specific siRNA oligonucleotides, but not irrelevant control oligonucleotides, inhibited PKC-delta protein by more than 80% in Caco-2 cells. Moreover, PKC-delta knockdown enhanced cell proliferation ( approximately 1.4-2-fold, P<0.05) and concomitantly increased cyclin D1 and cyclin E expression ( approximately 1.7-fold, P<0.05). This was a specific effect, as nontargeted PKC-zeta was not changed by PKC-delta siRNA oligonucleotides. Consistent with accelerated apoptosis in PKC-delta transfectants, compared to EV cells, PKC-delta upregulation increased proapoptotic regulator Bax two-fold at mRNA and protein levels, while antiapoptotic Bcl-2 protein was decreased by 50% at a post-transcriptional level. PKC-delta specific siRNA oligonucleotides inhibited Bax protein expression by more than 50%, indicating that PKC-delta regulates apoptosis through Bax. Taken together, these results elucidate two critical mechanisms regulated by PKC-delta that inhibit cell cycle progression and enhance apoptosis in colon cancer cells. We postulate these antiproliferative pathways mediate an important tumor suppressor function for PKC-delta in colonic carcinogenesis.
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PMID:Protein kinase C delta inhibits Caco-2 cell proliferation by selective changes in cell cycle and cell death regulators. 1643 69

TPA is a potent regulator of cell growth, including cell proliferation and differentiation. In this study, we determined the effect of silibinin on TPA-induced growth arrest in breast cancer cells. Silibinin increased growth arrest of the G2/M phase in a dose-dependent fashion. Silibinin decreased the basal level of cyclin B1 and cdc2 expression, which is involved in S phase and G2/M transition. In addition, TPA-induced G2/M phase arrest was increased by silibinin. Under the same conditions, TPA-induced down-regulation of cyclin B1 and cdc2 was decreased by silibinin. In contrast, TPA-induced p21 expression was further increased by silibinin. To determine the regulatory mechanism of TPA-induced growth arrest, we pretreated cells with various inhibitors, such as UO126, SB203580, and LY294002. Interestingly, TPA-induced growth arrest was significantly increased by LY294002, but not by UO126 and SB203580. In addition, TPA-induced down-regulation of cyclin B1 was inhibited by LY294002; however, the basal level of p21 was increased by TPA and TPA-induced p21 expression was further increased by LY294002. Finally, adenoviral constitutively active-Akt (Ad-CA-Akt) overexpression regulated the up-regulation of cyclin B1 and the down-regulation of p21. Therefore, we have demonstrated that silibinin has an additive effect on TPA-induced growth arrest through the PI-3-kinase/Akt-dependent pathway.
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PMID:12-O-Tetradecanoyl phorbol-13-acetate (TPA)-induced growth arrest is increased by silibinin by the down-regulation of cyclin B1 and cdc2 and the up-regulation of p21 expression in MDA-MB231 human breast cancer cells. 2055 89

Genome variability and changes in immune homeostasis, induced in man in the course of long-term industrial contact with ionizing radiation (IR) sources were studied by using unique biomaterials stored in the Radiobiological Repository for Human Tissues at the Southern Urals Biophysics Institute, FMBA. The biomaterials, peripheral blood samples and blood DNA were obtained from the "Mayak" PA employers occupationally exposed to prolonged external gamma-radiation and/or internal alpha-radiation from incorporated 239Pu in a wide range of accumulated doses. A significant increase in the polymorphism of microsatellite-associated peripheral blood DNA repeats was revealed in a group of persons with accumulated doses of external gamma-radiation above 2.0 Gy, as well as in the descendants of parents with preconceptive doses of higher than 2.0 Gy. In persons whose parents had a preconceptive dose above 2.0 Gy, an increase in the gene p53 mutation rate was observed, and descendants of persons with dose of 3.0 Gy and higher showed mtDNA heteroplasmy, regardless of the sex of an exposed parent. Changes in the expression of membrane markers for the effector and regulatory T-lymphocytes depending on radiation type and dose load were determined. The growth factor level variations (TGF-beta1, EGF, HGF, FGF) in peripheral blood serum in persons exposed to radiation from gamma- or alpha-sources, allow us to consider them as biomarkers of radiation-induced disturbances in immune homeostasis. The concentration changes of TGF-beta1, apoptosis proteins (p53, TPA-cyk, sAPO-1/Fas), and the adhesion molecule sCD27 in the case of cardiovascular diseases in the serum of both irradiated and non-irradiated "Mayak" PA employers point to the information value of these immune response characteristics as specific biomarkers of cardiac disorders. It is proposed that the revealed changes in immune homeostasis and in the variability of somatic cell genome may provoke development of tumors and cardiovascular diseases in man in delayed periods after prolonged exposure to IR.
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PMID:[Delayed and transgenerational molecular and genetic effects of prolonged influence of ionizing radiation in nuclear plant workers]. 2152 Jun 13

CDK4 is crucial for G1-to-S transition of cell cycle. It is well established that ubiquitin-mediated degradations of CDK inhibitors and cyclins are pivotal for the timely and unidirectional progression of cell cycle. However, how CDK4 itself is modulated by ubiquitin-mediated degradation has been elusive. Here we report that the steady-state level of CDK4 is controlled by PAQR4, a member of the progestin and adipoQ receptor family, and SKP2, an E3 ubiquitin ligase. Knockdown of PAQR4 leads to reduction of cell proliferation, accompanied by reduced protein level of CDK4. PAQR4 reduces polyubiquitination and degradation of CDK4. PAQR4 interacts with the C-terminal lobe of CDK4. On the other hand, SKP2 also interacts with the C-terminal lobe of CDK4 and enhances polyubiquitination and degradation of CDK4. Importantly, PAQR4 and SKP2 bind to the same region in CDK4, and PAQR4 competes with SKP2 for the binding, thereby abrogating SKP2-mediated ubiquitination of CDK4. Using a two-stage DMBA/TPA-induced skin cancer model, we find that PAQR4-deleted mice are resistant to chemical carcinogen-induced tumor formation. Collectively, our findings reveal that the steady-state level of CDK4 is controlled by the antagonistic actions between PAQR4 and SKP2, contributing to modulation of cell proliferation and tumorigenesis.
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PMID:The steady-state level of CDK4 protein is regulated by antagonistic actions between PAQR4 and SKP2 and involved in tumorigenesis. 2899 27


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