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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)

The poly(A) tail found on almost all eukaryotic messenger RNAs is important in enhancing translation initiation and determining mRNA stability. Control of poly(A)-tail synthesis thus has the potential to be a key regulatory step in gene expression and is indeed known to be important during early development in many organisms. To study a possible basis for such regulation, we examined phosphorylation of poly(A) polymerase (PAP) by p34(cdc2)/cyclin B (maturation/mitosis-promoting factor, MPF). We show here that PAP can be phosphorylated in vivo and in vitro by MPF. Consistent with this, PAP becomes hyperphosphorylated both during meiotic maturation of Xenopus laevis oocytes and in HeLa cells arrested at M phase, times in the cell-cycle when MPF is known to be active. We show further that hyperphosphorylation by MPF dramatically reduces the activity of purified PAP, and that PAP isolated from mitotic HeLa cells is similarly inhibited by hyperphosphorylation. This repression probably contributes to the well established reductions in poly(A)+ RNA and/or protein synthesis known to occur in M-phase cells.
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PMID:Cell-cycle related regulation of poly(A) polymerase by phosphorylation. 891 82

We showed previously that p34(cdc2)/cyclin B (MPF) hyperphosphorylates poly(A) polymerase (PAP) during M-phase of the cell cycle, causing repression of its enzymatic activity. Mutation of three cyclin-dependent kinase (cdk) consensus sites in the PAP C-terminal regulatory domain prevented complete phosphorylation and MPF-mediated repression. Here we show that PAP also contains four nearby non-consensus cdk sites that are phosphorylated by MPF. Remarkably, full phosphorylation of all these cdk sites was required for repression of PAP activity, and partial phosphorylation had no detectable effect. The consensus sites were phosphorylated in vitro at a 10-fold lower concentration of MPF than the non-consensus sites. Consistent with this, during meiotic maturation of Xenopus oocytes, consensus sites were phosphorylated prior to the non-consensus sites at metaphase of meiosis I, and remained so throughout maturation, while the non-consensus sites did not become fully phosphorylated until after 12 h of metaphase II arrest. We propose that PAP's multiple cdk sites, and their differential sensitivity to MPF, provide a mechanism to link repression specifically to late M-phase. We discuss the possibility that this reflects a general means to control the timing of cdk-dependent regulatory events during the cell cycle.
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PMID:Inhibition of poly(A) polymerase requires p34cdc2/cyclin B phosphorylation of multiple consensus and non-consensus sites. 946 83

Vertebrate poly(A) polymerase (PAP) contains a catalytic domain and a C-terminal Ser-Thr-rich regulatory region. Consensus and nonconsensus cyclin-dependent kinase (cdk) sites are conserved in the Ser-Thr-rich region in vertebrate PAPs. PAP is phosphorylated by cdc2-cyclin B on these sites in vitro and in vivo and is inactivated by hyperphosphorylation in M-phase cells, when cdc2-cyclin B is active. In the experiments described here, we undertook a genetic approach in chicken DT40 cells to study the function of PAP phosphorylation. We found that PAP is highly conserved in chicken and is essential in DT40 cells. While cells could tolerate reduced levels of PAP, even modest overexpression of either wild-type PAP or a mutant PAP with two consensus cdk sites mutated (cdk- PAP) was highly deleterious and at a minimum resulted in reduced growth rates. Importantly, cells that expressed cdk- PAP had a significantly lower growth rate than did cells that expressed similar levels of wild-type PAP, which was reflected in increased accumulation of cells in the G0-G1 phase of the cell cycle. We propose that the lower growth rate is due to the failure of hyperphosphorylation and thus M-phase inactivation of cdk- PAP.
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PMID:Deregulation of poly(A) polymerase interferes with cell growth. 971 May 85

We have previously shown that poly(A) polymerase (PAP) is negatively regulated by cyclin B-cdc2 kinase hyperphosphorylation in the M phase of the cell cycle. Here we show that cyclin B(1) binds PAP directly, and we demonstrate further that this interaction is mediated by a stretch of amino acids in PAP with homology to the cyclin recognition motif (CRM), a sequence previously shown in several cell cycle regulators to target specifically G(1)-phase-type cyclins. We find that PAP interacts with not only G(1)- but also G(2)-type cyclins via the CRM and is a substrate for phosphorylation by both types of cyclin-cdk pairs. PAP's CRM shows novel, concentration-dependent effects when introduced as an 8-mer peptide into binding and kinase assays. While higher concentrations of PAP's CRM block PAP-cyclin binding and phosphorylation, lower concentrations induce dramatic stimulation of both activities. Our data not only support the notion that PAP is directly regulated by cyclin-dependent kinases throughout the cell cycle but also introduce a novel type of CRM that functionally interacts with both G(1)- and G(2)-type cyclins in an unexpected way.
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PMID:Poly(A) polymerase phosphorylation is dependent on novel interactions with cyclins. 1086 87

The HIV-1 encoded accessory protein, viral protein R (Vpr) is responsible for several biological effects in HIV-1-infected cells including nuclear transport of the preintegration complex, activation of long terminal repeat (LTR)-mediated transcription, and the induction of cell-cycle arrest and apoptosis. Vpr's ability to arrest cells at the G2 phase of the cell cycle is due to the inactivation of p34(cdc2) cyclin B complex, resulting in hypophosphorylation of substrates involved in cell-cycle progression from G2 to mitosis (M). Poly(A) polymerase (PAP), the enzyme responsible for poly(A) addition to primary transcripts, contains multiple consensus phosphorylation sites for p34(cdc2) cyclin B kinase that regulates its catalytic activity. We investigated the effects of Vpr on the activity of PAP in Jurkat cells using a superinfection system. Superinfection of cells using Vpr+ vesicular stomatitis virus G protein (VSV-G)-pseudotyped virus caused a complete dephosphorylation of PAP. Cotransfection studies in 293T cells and Xenopus oocyte RNA injection experiments mirrored these effects. Vpr's dramatic effect on PAP dephosphorylation was reflected in enhanced polyadenylation activity in PAP activity assays. HIV-1 Vpr appears to enhance processes that are coupled to transcription such as polyadenylation and could ultimately prove to optimize HIV-1 replication and contribute to HIV-1 pathogenesis. (C)2002 Elsevier Science.
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PMID:Hypophosphorylation of poly(A) polymerase and increased polyadenylation activity are associated with human immunodeficiency virus type 1 Vpr expression. 1187 34

The present study was conducted to investigate the relation between in vitro developmental competence and the expression of a panel of developmentally important genes in germinal vesicle (GV) stage oocytes. One-month-old prepubertal and adult sheep oocytes were used as models of low and high quality gametes, respectively. Cumulus-oocyte complexes (COCs) derived from lambs and ewes were in vitro matured and fertilized, and their cleavage rate at 22, 26, and 32 hr post fertilization and the blastocyst yield were observed to assess their developmental potential. In parallel, the relative abundance (RA) of 11 genes was analyzed by semi-quantitative Reverse Transcription Polymerase Chain Reaction (RT-PCR) assay in the two groups of oocytes. We observed similar maturation and fertilization rates in the two groups, but a significant lower rate of cleaved prepubertal oocytes (P < 0.05), a general delay in the timing of their first division (P < 0.01), and a lower blastocysts production (P < 0.05). The analysis of gene expression evidenced no difference in the RA of four transcripts [superoxide dismutase (SOD), ubiquitin, beta-actin, cyclin B] in the two classes of oocytes, but a statistically lower RA of seven messenger RNAs (mRNA) [Na(+)K(+)ATPase, p34(cdc2), Glucose-transporter I (Glut-1), Activin, Zona Occludens Protein 2 (PanZO2), Poli(A)Polymerase (PAP), E-Cadherin (E-Cad)] in the prepubertal oocytes compared to the adult ones. The present data show for the first time in the ovine species that the lower developmental competence is associated with deficiencies in the mRNAs storage during the oocyte growth.
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PMID:Relations between relative mRNA abundance and developmental competence of ovine oocytes. 1694 75

Elongation of the poly(A) tails of specific mRNAs in the cytoplasm is a crucial regulatory step in oogenesis and early development of many animal species. The best studied example is the regulation of translation by cytoplasmic polyadenylation elements (CPEs) in the 3' untranslated region of mRNAs involved in Xenopus oocyte maturation. In this review we discuss the mechanism of translational control by the CPE binding protein (CPEB) in Xenopus oocytes as follows: 1. The cytoplasmic polyadenylation machinery such as CPEB, the subunits of cleavage and polyadenylation specificity factor (CPSF), symplekin, Gld-2 and poly(A) polymerase (PAP). 2. The signal transduction that leads to the activation of CPE-mediated polyadenylation during oocyte maturation, including the potential roles of kinases such as MAPK, Aurora A, CamKII, cdk1/Ringo and cdk1/cyclin B. 3. The role of deadenylation and translational repression, including the potential involvement of PARN, CCR4/NOT, maskin, pumilio, Xp54 (Ddx6, Rck), other P-body components and isoforms of the cap binding initiation factor eIF4E. Finally we discuss some of the remaining questions regarding the mechanisms of translational regulation by cytoplasmic polyadenylation and give our view on where our knowledge is likely to be expanded in the near future.
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PMID:Translational control by cytoplasmic polyadenylation in Xenopus oocytes. 1831 45