Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.11.1 (protein kinase)
 81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The differential activation of cyclin and cyclin-dependent kinase genes by the adenovirus E1A gene product (E1A) or serum factors was studied with a rat 3Y1 derivative cell line, g12-21, in which the E1A12S cDNA can be expressed in response to dexamethasone (dex). The induction of DNA synthesis in quiescent g12-21 cells occurred within 12 h after serum stimulation, while it occurred within 8 h after treatment with dex. The expression of cyclin D1 and E genes in the serum-stimulated cells was induced in mid G1 and mid to late G1, respectively, while that of the cyclin D1 gene was not induced and the induction of the cyclin E gene was shifted to the G1/S boundary in the dex-treated cells. The cdk2 gene was induced in late G1 and cdc2 and cyclin A genes at the G1/S boundary in both serum-stimulated and dex-treated cells. These results suggest that E1A skips cell cycle events which normally occur in early to mid G1 and may directly activate late-response genes. Analysis of the transcription factor E2F complexes formed in the promoter regions of cdc2 and dihydrofolate reductase genes showed that the amount of complexes formed is maximal at the G1/S boundary, but decreases in S phase when these genes are transcribed extensively.
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PMID:Differential activation of cyclin and cyclin-dependent kinase genes by adenovirus E1A12S cDNA product. 837 70

The mammalian transcription factor E2F binds to several cellular proteins including Rb, p107, cyclin A, cyclin E, and p33cdk2 protein kinase in a stage-specific manner during cell cycle. Its recognition sequence, TTTCGCGC, is present in two of the human adenovirus early promoters and in several promoters of cellular genes whose products are implicated in the control of cell proliferation. These observations suggest that E2F may play an important role in cell-cycle regulation and prompted us to ask whether E2F-like activities are present in yeast. We found that the E2F motif can function as an activating sequence in Schizosaccharomyces pombe when cloned upstream of a reporter gene. Consistent with this, the expression of adenovirus E2 promoter in S. pombe was dependent on both E2F motifs of this promoter. A protein, spE2F, that binds to the E2F site was partially purified from S. pombe using DNA-affinity chromatography. The binding specificity of this protein was compared to that of human E2F using a number of mutant E2F sites as competitors. These studies showed that spE2F recognizes a sequence closely related to the E2F site. Ultraviolet cross-linking and Southwestern blot studies indicated that the molecular size of spE2F is 30 kDa. Previous studies have shown that a cis-acting element, ACGCGTNA, also called MluI cell cycle box, or MCB, is critical for the regulated expression of cell cycle related genes both in fission and budding yeast. In S. pombe, the cdc10 gene product binds to this element and controls the cell cycle related genes. Electrophoretic mobility shift assays and molecular size determination studies indicated that spE2F is different from that encoded by cdc10. Thus, our studies suggest that spE2F is a novel transcription factor. We discuss these results in light of recent observations about the periodically expressed genes involved in the cell cycle progression in yeast.
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PMID:E2F site activates transcription in fission yeast Schizosaccharomyces pombe and binds to a 30-kDa transcription factor. 837 97

The human embryonal carcinoma (EC) cell line NEC14 can be induced to differentiate morphologically by the addition of 10(-2) M N,N'-hexamethylene-bis-acetamide (HMBA). The N-myc gene is expressed at a high level in the undifferentiated cells, but the level decreased steeply after 12-24 h HMBA treatment, returning to its original level after 48 h. The alteration in the N-myc level was well correlated with the formation of complexes with the E2F motif in the N-myc promoter region, and no complex was formed with cell extracts prepared from cells treated with HMBA for 12-24 h. The absence of E2F complexes during this period was caused by an inhibitor generated by a phosphatase reaction. Treatment of the 12-h extract with a cyclic AMP-dependent protein kinase resulted in the formation of E2F complexes, and treatment of the undifferentiated (0 h) and 48-h extracts with a calf intestinal phosphatase abolished complex formation completely. An inhibitor generated by the 0-h extract after treatment with a phosphatase inhibited E2F complex formation by the untreated 0-h extract in the presence of phosphatase inhibitors, okadaic acid and sodium vanadate. One of the two E2F complexes in the undifferentiated cells contained cyclin A, but the complex with similar mobility, formed after the transient decrease in the N-myc level, did not.
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PMID:Protein phosphorylation required for the formation of E2F complexes regulates N-myc transcription during differentiation of human embryonal carcinoma cells. 838 53

During studies of the activation and inactivation of the cyclin B-p34cdc2 protein kinase (MPF) in cell-free extracts of Xenopus oocytes and eggs, we found that a bacterially expressed fusion protein between the Escherichia coli maltose-binding protein and the Xenopus c-mos protein kinase (malE-mos) activated a 42 kDa MAP kinase. The activation of MAP kinase on addition of malE-mos was consistent, whereas the activation of MPF was variable and failed to occur in some oocyte extracts in which cyclin A or okadaic acid activated both MPF and MAP kinase. In cases when MPF activation was transient, MAP kinase activity declined after MPF activity was lost, and MAP kinase, but not MPF, could be maintained at a high level by the presence of malE-mos. When intact oocytes were treated with progesterone, however, the activation of MPF and MAP kinase occurred simultaneously, in contrast to the behaviour of extracts. These observations suggest that one role of c-mos may be to maintain high MAP kinase activity in meiosis. They also imply that the activation of MPF and MAP kinase in vivo are synchronous events that normally rely on an agent that has still to be identified.
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PMID:The c-mos proto-oncogene protein kinase turns on and maintains the activity of MAP kinase, but not MPF, in cell-free extracts of Xenopus oocytes and eggs. 838 16

We have examined the roles of type-1 (PP-1) and type-2A (PP-2A) protein-serine/threonine phosphatases in the mechanism of activation of p34cdc2/cyclin B protein kinase in Xenopus egg extracts. p34cdc2/cyclin B is prematurely activated in the extracts by inhibition of PP-2A by okadaic acid but not by specific inhibition of PP-1 by inhibitor-2. Activation of the kinase can be blocked by addition of the purified catalytic subunit of PP-2A at a twofold excess over the activity in the extract. The catalytic subunit of PP-1 can also block kinase activation, but very high levels of activity are required. Activation of p34cdc2/cyclin B protein kinase requires dephosphorylation of p34cdc2 on Tyr15. This reaction is catalysed by cdc25-C phosphatase that is itself activated by phosphorylation. We show that, in interphase extracts, inhibition of PP-2A by okadaic acid completely blocks cdc25-C dephosphorylation, whereas inhibition of PP-1 by specific inhibitors has no effect. This indicates that a type-2A protein phosphatase negatively regulates p34cdc2/cyclin B protein kinase activation primarily by maintaining cdc25-C phosphatase in a dephosphorylated, low activity state. In extracts containing active p34cdc2/cyclin B protein kinase, dephosphorylation of cdc25-C is inhibited, whereas the activity of PP-2A (and PP-1) towards other substrates is unaffected. We propose that this specific inhibition of cdc25-C dephosphorylation is part of a positive feedback loop that also involves direct phosphorylation and activation of cdc25-C by p34cdc2/cyclin B. Dephosphorylation of cdc25-C is also inhibited when cyclin A-dependent protein kinase is active, and this may explain the potentiation of p34cdc2/cyclin B protein kinase activation by cyclin A. In extracts supplemented with nuclei, the block on p34cdc2/cyclin B activation by unreplicated DNA is abolished when PP-2A is inhibited or when stably phosphorylated cdc25-C is added, but not when PP-1 is specifically inhibited. This suggests that unreplicated DNA inhibits p34cdc2/cyclin B activation by maintaining cdc25-C in a low activity, dephosphorylated state, probably by keeping the activity of a type-2A protein phosphatase towards cdc25-C at a high level.
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PMID:Dephosphorylation of cdc25-C by a type-2A protein phosphatase: specific regulation during the cell cycle in Xenopus egg extracts. 838 19

Several signaling molecules have been identified which act as inhibitors of epithelial cell growth. The mechanisms for this negative growth regulation are still poorly understood. In the case of TGF-beta, inhibition of keratinocyte cell growth can be totally prevented by transformation with an intact early region 1a (E1a) oncogene. We show here that E1a-transformed keratinocytes become also partially resistant to growth inhibition by elevated 3',5'-cyclic adenosine monophosphate (cAMP) levels, as induced by treatment with forskolin, dibutyryl-cAMP, 8Br-cAMP, or 8Cl-cAMP. Resistance to cAMP is due to interference of E1a with signaling pathways downstream of protein kinase A (PKA) activation, as intracellular cAMP levels and PKA activity were found to be similar in control and E1a-transformed cells. Induction of c-fos expression by 8Br-cAMP occurs at the same time in both cell lines. Interestingly however, this effect is maintained longer in the case of E1a-transformed cells compared to the control. A truncated E1a mutant which is still able to bind to the p105-Rb gene product, p107, and p60/cyclin A, induces cAMP resistance at levels which are only slightly lower than those induced by an intact E1a oncogene. In contrast, an E1a mutant which binds only to a p300 cellular protein and induces a substantial level of TGF-beta resistance fails to induce cAMP resistance. Thus, E1a transformation counteracts the growth-inhibitory effects of cAMP as well as TGF-beta, but to a different degree and through an only partially overlapping mechanism.
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PMID:Counteracting effects of E1a transformation on cAMP growth inhibition. 839 67

In Xenopus oocytes, mitogen-activated protein (MAP) kinase can be activated by progesterone treatment or by microinjection of cyclin A, both of which lead to activation of the cdc2 protein kinase. The tyrosine kinase pp60v-src has previously been shown to accelerate progesterone-induced oocyte maturation and to increase the phosphorylation of ribosomal protein S6 by pp90rsk, most likely by activating MAP kinase. In extracts of resting oocytes, MAP kinase kinase and MAP kinase were activated by addition of pp60v-src or cyclin A. Activation by pp60v-src was blocked by a dominant-negative p21ras protein (RAST), but activation by cyclin A/cdc2 was unaffected. Thus these two pathways that converge at MAP kinase kinase but are clearly divergent upstream of a p21ras-dependent step can be studied in a cell-free system.
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PMID:Reconstitution of p21ras-dependent and -independent mitogen-activated protein kinase activation in a cell-free system. 839 92

Interleukin 6 (IL-6) induces in M1 myeloblastic cells growth arrest and terminal differentiation toward monocytes. It is reported here that IL-6 reduced by 5- to 20-fold the tyrosine phosphorylation of cellular proteins in these cells. The same-fold reduction was also observed in M1 cells that were transfected with the BCR-ABL deregulated protein kinase. In these stable clones, the levels of tyrosine phosphorylation of cellular proteins were 30- to 100-fold higher than in the parental cells. IL-6 did not reduce the expression levels or the inherent tyrosine kinase activity of BCR-ABL p210. By measuring the protein-tyrosine-phosphatase (PTPase; protein-tyrosine-phosphate phosphohydrolase, EC 3.1.3.48) activity in crude cell lysates, we found that protein dephosphorylation resulted, at least partially, from induction of PTPase activity by IL-6. The induction of PTPase in the BCR-ABL-transfected clones was not sufficient to confer the minimal protein phosphorylation levels characteristic of IL-6-treated cells. Yet, the transfected M1 clones showed normal growth and differentiation responses to IL-6. None of the gene responses to IL-6 including suppression in the levels of c-myc, c-myb, and cyclin A mRNA; junB and c-jun mRNA induction; and dephosphorylation of retinoblastoma protein were rescued by the BCR-ABL oncogene. The functional relevance of PTPase induction by IL-6 is discussed.
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PMID:Induction of protein-tyrosine-phosphatase activity by interleukin 6 in M1 myeloblastic cells and analysis of possible counteractions by the BCR-ABL oncogene. 842 78

Originally identified as a 'mitotic cyclin', cyclin A exhibits properties of growth factor sensitivity, susceptibility to viral subversion and association with a tumor-suppressor protein, properties which are indicative of an S-phase-promoting factor (SPF) as well as a candidate proto-oncogene. Other recent studies have identified human cyclin D1 (PRAD1) as a putative G1 cyclin and candidate proto-oncogene. However, the specific enzymatic activities and, hence, the precise biochemical mechanisms through which cyclins function to govern cell cycle progression remain unresolved. In the present study we have investigated the coordinate interactions between these two potentially oncogenic cyclins, cyclin-dependent protein kinase subunits (cdks) and the Rb tumor-suppressor protein. The distribution of cyclin D isoforms was modulated by serum factors in primary fetal rat lung epithelial cells. Moreover, cyclin D1 was found to be phosphorylated on tyrosine residues in vivo and, like cyclin A, was readily phosphorylated by pp60c-src in vitro. In synchronized human osteosarcoma cells, cyclin D1 is induced in early G1 and becomes associated with p9Ckshs1, a Cdk-binding subunit. Immunoprecipitation experiments with human osteosarcoma cells and Ewing's sarcoma cells demonstrated that cyclin D1 is associated with both p34cdc2 and p33cdk2, and that cyclin D1 immune complexes exhibit appreciable histone H1 kinase activity. Immobilized, recombinant cyclins A and D1 were found to associate with cellular proteins in complexes that contain the p105Rb protein. This study identifies several common aspects of cyclin biochemistry, including tyrosine phosphorylation and the potential to interact directly or indirectly with the Rb protein, that may ultimately relate membrane-mediated signaling events to the regulation of gene expression.
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PMID:Two potentially oncogenic cyclins, cyclin A and cyclin D1, share common properties of subunit configuration, tyrosine phosphorylation and physical association with the Rb protein. 847 54

Cyclin A was initially characterized as a 'mitotic cyclin', believed to function exclusively at the G2-to-M phase transition; however, recent studies have provided compelling evidence that cyclin A additionally functions earlier in the mammalian somatic cell cycle as a putative 'S-phase-promoting factor'. Moreover, numerous inconsistencies have arisen concerning the temporal induction, subcellular localization, subunit configuration, covalent modification and proteolytic destruction of cyclin A, as well as the physiological function of the cyclin A-associated protein kinase complexes. Utilizing precisely synchronized human MG-63 osteosarcoma cells, the present study demonstrates that cyclin A mRNA and protein are clearly expressed in late G1 prior to S-phase entry, as is cyclin A-associated kinase activity and concomitant phosphorylation of the Rb protein. A series of monospecific cyclin A antibodies were generated and utilized to confirm that multiple covalent modifications of cyclin A occur during the course of the cell cycle, and to characterize the subcellular dynamics in additional detail. Pharmacological blockade with mimosine was utilized to further delineate cyclin A expression and to distinguish the temporal induction from the mechanisms of enzyme activation. Subcellular fractionation and immunocytochemical staining localized nascent cyclin A to the cytoplasm, and revealed a distinct translocation to the nucleus during the G1-to-S phase transition. The results of these studies support a multistage model of cyclin A metabolism and enzyme activation.
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PMID:G1 expression and multistage dynamics of cyclin A in human osteosarcoma cells. 850 85


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