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)

The role of the C-terminal domain of CTP: phosphocholine cytidylyltransferase (CT) was explored by the creation of a series of deletion mutations in rat liver cDNA, which were expressed in COS cells as a major protein component. Deletion of up to 55 amino acids from the C-terminus had no effect on the activity of the enzyme, its stimulation by lipid vesicles or on its intracellular distribution between soluble and membrane-bound forms. However, deletion of the C-terminal 139 amino acids resulted in a 90% decrease in activity, loss of response to lipid vesicles and a significant decrease in the fraction of membrane-bound enzyme. Identification of the domain that is phosphorylated in vivo was determined by analysis of 32P-labelled CT mutants and by chymotrypsin proteolysis of purified CT that was 32P-labelled in vivo. Phosphorylation was restricted to the C-terminal 52 amino acids (domain P) and occurred on multiple sites. CT phosphorylation in vitro was catalysed by casein kinase II, cell division control 2 kinase (cdc2 kinase), protein kinases C alpha and beta II, and glycogen synthase kinase-3 (GSK-3), but not by mitogen-activated kinase (MAP kinase). Casein kinase II phosphorylation was directed exclusively to Ser-362. The sites phosphorylated by cdc2 kinase and GSK-3 were restricted to several serines within three proline-rich motifs of domain P. Sites phosphorylated in vitro by protein kinase C, on the other hand, were distributed over the N-terminal catalytic as well as the C-terminal regulatory domain. The stoichiometry of phosphorylation catalysed by any of these kinases was less than 0.2 mol P/mol CT, and no effects on enzyme activity were detected. This study supports a tripartite structure for CT with an N-terminal catalytic domain and a C-terminal regulatory domain comprised of a membrane-binding domain (domain M) and a phosphorylation domain (domain P). It also identifies three kinases as potential regulators in vivo of CT, casein kinase II, cyclin-dependent kinase and GSK-3.
 ...
PMID:Functions of the C-terminal domain of CTP: phosphocholine cytidylyltransferase. Effects of C-terminal deletions on enzyme activity, intracellular localization and phosphorylation potential. 765 14

Transforming growth factor beta (TGF beta) is an important regulator of cellular proliferation. In normal ovarian epithelial cells, TGF beta acts to inhibit growth. However, in ovarian cancer cell lines, this effect is usually lost. Although the regulatory pathway of TGF beta remains unclear, TGF beta-treated cells arrest late in G1. This inhibition appears to involve blocking of the cyclin-dependent kinase phosphorylation of the retinoblastoma protein. Recently, a general inhibitor of cyclin-dependent kinases, CIP1/WAF1/p21, was identified. Expression of CIP1 is positively regulated by binding of wild-type p53 to a consensus response element upstream of the CIP1 gene. Overexpression of the CIP1 protein causes growth suppression, analogous to TGF beta and wild-type p53. We have examined the induction of CIP1 by TGF beta 1 in ovarian cancer cell lines that have been previously characterized for their proliferative response to TGF beta 1. OVCA420, a cell line that is dramatically growth inhibited by TGF beta 1, significantly induced CIP1 expression in response to TGF beta 1. CIP1 induction was accompanied by a decrease in cdk2 kinase activity and cdk2 protein levels. In three other cell lines that respond weakly to TGF beta 1, CIP1 expression was not induced. To determine if TGF beta 1 induction occurs via p53, regulation of p53 RNA and protein was examined. No differences in p53 transcription, steady-state protein level, de novo synthesis, phosphorylation, or subcellular accumulation were noted. Furthermore, TGF beta 1 could not induce transcription from a consensus p53 DNA binding site in the TGF beta 1-response cell line.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Transforming growth factor beta 1 can induce CIP1/WAF1 expression independent of the p53 pathway in ovarian cancer cells. 769 78

Progression through the cell cycle is catalyzed by cyclin-dependent kinases (CDKs) and is negatively controlled by CDK inhibitors (CDIs). We have isolated a new member of the p21CIP1/p27KIP1 CDI family and named it p57KIP2 to denote its apparent molecular mass and higher similarity to p27KIP1. Three distinct p57 cDNAs were cloned that differ at the start of their open reading frames and correspond to messages generated by the use of distinct splice acceptor sites. p57 is distinguished from p21 and p27 by its unique domain structure. Four distinct domains follow the heterogeneous amino-terminal region and include, in order, a p21/p27-related CDK inhibitory domain, a proline-rich (28% proline) domain, an acidic (36% glutamic or aspartic acid) domain, and a carboxy-terminal nuclear targeting domain that contains a putative CDK phosphorylation site and has sequence similarity to p27 but not to p21. Most of the acidic domain consists of a novel, tandemly repeated 4-amino acid motif. p57 is a potent inhibitor of G1- and S-phase CDKs (cyclin E-cdk2, cyclin D2-cdk4, and cyclin A-cdk2) and, to lesser extent, of the mitotic cyclin B-Cdc2. In mammalian cells, p57 localizes to the nucleus, associates with G1 CDK components, and its overexpression causes a complete cell cycle arrest in G1 phase. In contrast to the widespread expression of p21 and p27 in human tissues, p57 is expressed in a tissue-specific manner, as a 1.5-kb species in placenta and at lower levels in various other tissues and a 7-kb mRNA species observed in skeletal muscle and heart. The expression pattern and unique domain structure of p57 suggest that this CDI may play a specialized role in cell cycle control.
 ...
PMID:Cloning of p57KIP2, a cyclin-dependent kinase inhibitor with unique domain structure and tissue distribution. 772 83

It has been postulated that the product (pRB) of the retinoblastoma gene dissociates from the E2F-pRB complex upon phosphorylation by cyclin-dependent kinase(s) (cdk). However, there is no direct evident for the regulation of formation of the E2F-pRB complex via phosphorylation by purified cdk. Therefore, we investigated the regulation of formation of this complex by phosphorylation using pRB and purified cyclin A-cdk2, cyclin E-cdk2 or cyclin D1-cdk4. Purified pRB was incubated with nuclear extracts prepared from pRB-defective cells and then subjected to gel mobility shift assays. We confirmed that unphosphorylated pRB associated with various types of E2F but pRB has been phosphorylated by cyclin A-cdk2 did not. We found that E2F-pRB complexes were disrupted as a consequence of phosphorylation by cyclin A-cdk2, and the levels of the free forms of E2Fs increased. We also found that not only the E2F-pRB complexes but also the E2F-p107 complexes were disrupted upon phosphorylation by cyclin A-cdk2. Furthermore, E2F-pRB complexes were disrupted through phosphorylation by cyclin D1-cdk4 and cyclin E-cdk2, as well as by cyclin A-cdk2. These results clearly demonstrate that the phosphorylation of pRB and p107 by cdks regulates the formation of complexes between E2F and pRB or p107.
 ...
PMID:The interactions of E2F with pRB and with p107 are regulated via the phosphorylation of pRB and p107 by a cyclin-dependent kinase. 775 45

Neurofilament (NF) protein [high molecular mass (NF-H)] is extensively phosphorylated in vivo. The phosphorylation occurs mainly in its characteristic KSP (Lys-Ser-Pro) repeat motifs. There are two major types of KSP motifs in the NF-H tail domain: KSPXKX and KSPXXX. Recent studies by two different laboratories have demonstrated the presence of a cdc2-like kinase [cyclin-dependent kinase-5 (cdk5)] in nervous tissue that selectively phosphorylates KSPXKX and XS/TXK motifs in NF-H and lysine-rich histone (H1). This article describes the identification of phosphatases dephosphorylating three different substrates: histone (H1), NF-H in a NF preparation, and a bacterially expressed C-terminal tail domain of NF-H, each containing KSPXKX repeats phosphorylated in vitro by cdk5. Among various phosphatases identified, protein phosphatase (PP) 2A from rabbit skeletal muscle appeared to be the most effective phosphatase in in vitro assays. Three phosphatase activity peaks--P1, P2, and P3--were partially purified from frozen rat spinal cord by ion exchange and size exclusion column chromatography and then characterized on the basis of biochemical, pharmacological, and immunochemical studies. One of the three peaks was identified as PP2A, whereas the others were mixtures of both PP2A and PP1. These three peaks could dephosphorylate cdk5-phosphorylated 32P-histone (H1), 32P-NF-H in the NF preparation, and 32P-NF-H tail fusion protein. These studies suggest the involvement of PP2A or a PP2A-like activity in the regulation of the phosphorylation state of KSPXKX motifs in NF-H.
 ...
PMID:Neuronal cyclin-dependent kinase-5 phosphorylation sites in neurofilament protein (NF-H) are dephosphorylated by protein phosphatase 2A. 776 48

The mechanism of cell cycle withdrawal during terminal differentiation is poorly understood. We report here that the cyclin-dependent kinase (CDK) inhibitor p21Cip1/WAF1 is induced at early times of both keratinocyte and myoblast differentiation. p21Cip1/WAF1 induction is accompanied by a drastic inhibition of total Cdk2, as well as p21Cip1/WAF1-associated CDK kinase activities. p21Cip1/WAF1 has been implicated in p53-mediated G1 arrest and apoptosis. In keratinocyte differentiation, Cip1/WAF1 induction is observed even in cells derived from p53-null mice. Similarly, keratinocyte differentiation is associated with induction of Cip1/WAF1 promoter activity in both wild-type and p53-negative keratinocytes. Induction of the Cip1/WAF1 promoter upon differentiation is abolished by expression of an adenovirus E1A oncoprotein (d1922/947), which is unable to bind p105-Rb, p107, or cyclin A but which still binds the nuclear phosphoprotein p300. Overexpression of p300 can suppress the E1A effect, independent of its direct binding to E1A. Thus, terminal differentiation-induced growth arrest in both keratinocyte and myoblast systems is associated with induction of Cip1/WAF1 expression. During keratinocyte differentiation, Cip1/WAF1 induction does not require p53 but depends on the transcriptional modulator p300.
 ...
PMID:Involvement of the cell-cycle inhibitor Cip1/WAF1 and the E1A-associated p300 protein in terminal differentiation. 777 29

The terminal differentiation of C2C12 skeletal muscle cells involves the activation of unique sets of genes and an irreversible withdrawal from the cell cycle. This process is associated with a decrease in cdk2 activity in cell extracts. The decrease in cdk2 activity correlates with diminished levels of cdk2 and cyclin A and with a marked induction of the p21 cyclin-dependent kinase (cdk) inhibitor. The upregulation of p21 occurred at the levels of mRNA and protein, and p21 formed a complex with the cyclin kinases in myotubes. Further, the immunodepletion of p21 from myotube extracts neutralized the heat-stable cdk2 inhibitory activity that was induced upon myogenic differentiation. The levels of p21 mRNA, protein, and activity remained constant in myotubes when they were reexposed to mitogen-rich growth medium, indicating that permanent changes in the cell's genetic program contribute to its sustained expression following terminal differentiation. Indeed, 10T1/2 fibroblasts transformed with the myogenic factor MyoD, but not the parental multipotent cells, upregulated p21 transcript levels when induced to differentiate by serum withdrawal, demonstrating that the upregulation is an integral feature of myogenic commitment and differentiation. The functional consequences of this upregulation were indicated by ectopically expressing p21 in myoblasts; this was sufficient for cell cycle arrest in mitogen-rich growth medium. The induction and sustained expression of p21 appears to be a contributory mechanism by which myocytes irreversibly exit the cell cycle upon terminal differentiation.
 ...
PMID:MyoD-induced expression of p21 inhibits cyclin-dependent kinase activity upon myocyte terminal differentiation. 779 89

Transforming growth factor beta (TGF beta) acts on epithelial thyroid cells, negatively controlling their proliferation and functions. The effects of TGF beta on epithelial rat thyroid cells (FRTL-5) and on two TGF beta-resistant rat thyroid cell clones (FRTL-5H2 and FRTL-R) were investigated. FRTL-5H2 represents a rat thyroid cell clone overexpressing active erbB-2 oncogene, recently obtained after FRTL-5 cell infection with a retrovirus vector carrying the erbB-2 human oncogene (G. Mincione et al., Cancer Res., 53: 5548-5553, 1993). FRTL-R is a FRTL-5 subclone spontaneously isolated after long term in culture. FRTL-5H2 and FRTL-R cell clones were stimulated by TGF beta at the same concentration of 5 ng/ml that induced 70% inhibition of [3H]thymidine incorporation in control FRTL-5 thyroid cells. Nuclear events regulated by TGF beta, such as cyclin and cyclin-dependent kinase gene expression, were then analyzed. In FRTL-5 cells, TGF beta was found to reduce the expression of cdk2 and cyclin A genes; the same treatment did not modify nuclear gene expression in the resistant cell clones. TGF beta is known to reduce iodide uptake in thyroid cells; in both FRTL-5H2 and FRTL-R cells, TGF beta was found to inhibit the thyrotropin-induced iodide uptake. Thus, thyroid cell clones, resistant to the growth-inhibitory activity of TGF beta, were sensitive to TGF beta inhibition of iodide incorporation, suggesting that TGF beta activates divergent signaling pathways in these cells, separately controlling cell proliferation and differentiation parameters. Studies on TGF beta receptors showed similar amounts of TGF beta-binding species on FRTL-5 cells and TGF beta-resistant clones, while 125I-labeled TGF beta cross-linking experiments revealed differences; thus, the TGF beta-resistant cells showed a 40% decrease in the amount of labeled type II TGF beta receptor on the cell surface. However, this different pattern of TGF beta receptors cannot totally account for the shown TGF beta resistance to growth inhibition that might also be due to perturbation in signaling pathways.
 ...
PMID:Epithelial rat thyroid cell clones, escaping from transforming growth factor beta negative growth control, are still inhibited by this factor in the ability to trap iodide. 779 96

The orderly progression through the cell cycle is mediated by the sequential activation of several cyclin/cyclin-dependent kinase (cdk) complexes. These kinases phosphorylate a number of cellular substrates, among which is the product of the retinoblastoma gene, pRb. Phosphorylation of pRb in late G1 causes the release of the transcription factor E2F from pRb, resulting in the transcriptional activation of E2F-responsive genes. We show here that phosphorylation of the pRb-related p107 is also cell cycle regulated. p107 is first phosphorylated at 8 hr following serum stimulation of quiescent fibroblasts, which coincides with an increase in cyclin D1 protein levels. Consistent with this, we show that a cyclin D1/cdk4 complex, but not a cyclin E/cdk2 complex, can phosphorylate p107 in vivo. Furthermore, phosphorylation of p107 can be abolished by the overexpression of a dominant-negative form of cdk4. Phosphorylation of p107 results in the loss of the ability to associate with E2F-4, a transcription factor with growth-promoting and oncogenic activity. A p107-induced cell cycle block can be released by cyclin D1/cdk4 but not by cyclin E/cdk2. These data indicate that the activity of p107 is regulated by phosphorylation through D-type cyclins.
 ...
PMID:Regulation of the retinoblastoma protein-related p107 by G1 cyclin complexes. 779 74

In an attempt to define the basis for sphingolipid regulation of cell proliferation, we studied the effects of glucosylceramide (GlcCer) synthase inhibition by threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) on NIH 3T3 cells overexpressing insulin-like growth factor-1 (IGF-1) receptor. PDMP treatment resulted in a time-dependent decrease in GlcCer levels and an increase in cellular ceramide levels. PDMP abolished serum and IGF-1-stimulated cell proliferation, as measured by a reduction in [3H]thymidine incorporation, protein, and DNA levels. However it did not affect IGF-1-mediated early signaling events, including receptor tyrosine kinase, MAP kinase, and phosphatidylinositol 3-kinase activities. Two-color flow cytometry with propidium iodide and 5-bromo-2'-deoxyuridine monophosphate labeling revealed an arrest of the cell cycle at G1/S and G2/M transitions in an asynchronous population of cells. These changes were time dependent, with maximal effects seen by 12-24 h. Removal of PDMP from the cell medium resulted in reversal of the cell cycle changes, with cells re-entering the S phase. The cell cycle arrest at the G1/S and G2/M transitions was confirmed in cells synchronized by pretreatment with nocodazole, aphidicolin, or hydroxyurea, and released from blockade in the presence of PDMP. A decrease in the activities of two cyclin-dependent kinases, p34cdc2 kinase and cdk2 kinase, was observed with PDMP treatment. When cell ceramide levels were increased by N-acetylsphingosine, comparable changes in the cell cycle distribution were seen. However, sphingomyelinase treatment was without effect. Therefore, it appears that ceramide mediates in part the inhibitory effect of GlcCer synthase inhibition on IGF-1-induced cell proliferation in 3T3 cells. The rapid production of decreased cyclin-dependent kinase activities by PDMP suggests that one of the crucial sites of action of the inhibitor lies in this area.
 ...
PMID:Cell cycle arrest induced by an inhibitor of glucosylceramide synthase. Correlation with cyclin-dependent kinases. 785 61


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>