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

The E2F transcription factor has been found in association with the cyclin A protein, and this complex accumulates during the S phase of the cell cycle, suggesting that E2F may play a role in cell cycle control. In independent studies, cyclin A has been shown to be associated with two other proteins, the Rb-related p107 protein and the cdc2-related p33 cdk2 protein kinase. Through an analysis of the E2F-cyclin A complex, we now find that both the p107 protein and the cdc2-related p33cdk2 kinase are components of the previously described complex. Moreover, the complex possesses H1 kinase activity. These results thus define a cyclin A-cdk2 kinase complex that possesses sequence-specific DNA binding activity. This suggests that the cdk2 kinase may phosphorylate other DNA-bound substrates, and that one role of the E2F factor may be to localize this protein kinase to the DNA.
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PMID:A cyclin A-protein kinase complex possesses sequence-specific DNA binding activity: p33cdk2 is a component of the E2F-cyclin A complex. 131 73

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.
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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

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.
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PMID:Involvement of the cell-cycle inhibitor Cip1/WAF1 and the E1A-associated p300 protein in terminal differentiation. 777 29

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.
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PMID:Regulation of the retinoblastoma protein-related p107 by G1 cyclin complexes. 779 74

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

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

p107 is a retinoblastoma protein-related phosphoprotein that, when overproduced, displays a growth inhibitory function. It interacts with and modulates the activity of the transcription factor, E2F-4. In addition, p107 physically associates with cyclin E-CDK2 and cyclin A-CDK2 complexes in late G1 and at G1/S, respectively, an indication that cyclin-dependent kinase complexes may regulate, contribute to, and/or benefit from p107 function during the cell cycle. Our results show that p107 phosphorylation begins in mid G1 and proceeds through late G1 and S and that cyclin D-associated kinase(s) contributes to this process. In addition, E2F-4 binds selectively to hypophosphorylated p107, and G1 cyclin-dependent p107 phosphorylation leads to the dissociation of p107-E2F-4 complexes as well as inactivation of p107 G1 blocking function.
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PMID:Regulation of the retinoblastoma protein-related protein p107 by G1 cyclin-associated kinases. 864 55

Cells which are highly proliferative typically lack expression of differentiated, lineage-specific characteristics. Id2, a member of the helix-loop-helix (HLH) protein family known to inhibit cell differentiation, binds to the retinoblastoma protein (pRb) and abolishes its growth-suppressing activity. We found that Id2 but not Id1 or Id3 was able to bind in vitro not only pRb but also the related proteins p107 and p130. Also, an association between Id2 and p107 or p130 was observed in vivo in transiently transfected Saos-2 cells. In agreement with these results, expression of Id1 or Id3 did not affect the block of cell cycle progression mediated by pRb. Conversely, expression of Id2 specifically reversed the cell cycle arrest induced by each of the three members of the pRb family. Furthermore, the growth-suppressive activities of cyclin-dependent kinase inhibitors p16 and p21 were efficiently antagonized by high levels of Id2 but not by Id1 Id3. Consistent with the role of p16 as a selective inhibitor of pRb and pRb-related protein kinase activity, p16-imposed cell cycle arrest was completely abolished by Id2. Only a partial reversal of p21-induced growth suppression was observed, which correlated with the presence of a functional pRb. We also documented decreased levels of cyclin D1 protein and mRNA and the loss of cyclin D1-cdk4 complexes in cells constitutively expressing Id2. These data provide evidence for important Id2-mediated alterations in cell cycle components normally involved in the regulatory events of cell cycle progression, and they highlight a specific role for Id2 as an antagonist of multiple tumor suppressor proteins.
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PMID:Id2 specifically alters regulation of the cell cycle by tumor suppressor proteins. 864 64

The major transforming protein of HPV-16 is encoded by the E7 gene. This has been shown to cooperate with EJ-ras in the immortalisation of primary rodent cells and with the viral E6 gene in the immortalisation of primary human keratinocytes. HPV-16 E7 protein has been shown to bind to a number of cellular proteins involved in the control of cell growth; including pRB, p107 and cyclin A. Loss of pRb or p107 binding results in the loss of transforming activity. In this paper we demonstrate that HPV-16 E7 can also complex with the core component of TFIID, the TATA Box Binding Protein (TBP). This interaction is partly dependent upon phosphorylation of the E7 protein by cellular casein kinase II (CKII), since phosphorylation of E7 by CKII increases the affinity with which E7 binds TBP. Similar results are also obtained with the Adenovirus Ela protein, indicating a conservation of function between these two viral oncoproteins. Mutation of the CKII site to two acidic amino acids significantly increases the affinity of E7 for TBP, indicating that the incorporation of two negative charges at this region of E7 is important in regulating the interaction with TBP.
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PMID:HPV-16 E7 and adenovirus E1a complex formation with TATA box binding protein is enhanced by casein kinase II phosphorylation. 864 72

In this study, we have extensively modified the Rb-binding domain of polyomavirus large T antigen. Mutant polyomavirus large T antigens were tested for their ability to bind pRb and p107 in vitro and assayed for their capacity to immortalize primary rat embryo fibroblasts in vivo. Polyomavirus large T antigen bound pRb and p107 through a common region located between amino acids 141 to 158, containing the consensus Rb-binding sequence D/N-L-X-C-X-E. Substitution of any amino acid within the core Rb-binding sequence abolished pRb and p107 binding in vitro and immortalization activity in vivo. Substitution of amino acids outside the core Rb-binding sequence reduced pRb and p107 binding in vitro and decreased or abolished immortalization of rat embryo fibroblasts in vivo. Although duplication of the Rb-binding domain within the polyomavirus large T antigen results in a molecule that can bind at least twice as much pRb and p107 in vitro, this mutant displayed an essentially wild-type level of immortalization activity. More importantly, we found that the addition of acidic residues within the casein kinase II consensus phosphorylation region flanking the Rb-binding domain, or the deletion of amino acids 256 to 272, increased the immortalizing activity of the mutant polyomavirus large T antigen. These two mutants displayed a greater than wild-type level of pRb binding in vitro, while in contrast, a decreased affinity for p107 binding in vitro was observed. Together, these results indicate that while pRb binding appears to be an essential event for immortalization, there is no tight correlation between the frequency of immortalization and the absolute level of pRb binding in vitro, indicating that other large T antigen functions are important for cellular immortalization.
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PMID:Functional implications of mutations within polyomavirus large T antigen Rb-binding domain: effects on pRb and p107 binding in vitro and immortalization activity in vivo. 867 70


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