Tyrosine phosphorylation of the fission yeast cdc2 + protein kinase regulates entry into mitosis
TL;DR: The cdc2+ protein kinase (pp34) is found to be phosphorylated on tyrosine as well as serine and threonine residues in exponentially growing Schizosaccharomyces pombe, establishing that tyrosines phosphorylation/dephosphorylation directly regulates pp34 function.
Abstract: The cdc2+ protein kinase (pp34) is found to be phosphorylated on tyrosine as well as serine and threonine residues in exponentially growing Schizosaccharomyces pombe. At mitosis, the level of pp34 phosphorylation on both threonine and tyrosine residues decreases. The single detectable site of tyrosine phosphorylation in pp34 has been mapped to Tyr 15, a residue within the presumptive ATP-binding domain. Substitution of this tyrosine by phenylalanine advances cells prematurely into mitosis, establishing that tyrosine phosphorylation/dephosphorylation directly regulates pp34 function.
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TL;DR: In this article, an improved two-hybrid system was employed to isolate human genes encoding Cdk-interacting proteins (Cips) and found that CIP1 is a potent, tight-binding inhibitor of Cdks and can inhibit the phosphorylation of Rb by cyclin A-Cdk2.
5,726 citations
TL;DR: The onset of M-phase is regulated by a mechanism common to all eukaryotic cells and requires p34cdc2 dephosphorylation and association with cyclin.
Abstract: The onset of M-phase is regulated by a mechanism common to all eukaryotic cells. Entry into M-phase is determined by activation of the p34cdc2 protein kinase which requires p34cdc2 dephosphorylation and association with cyclin.
2,798 citations
TL;DR: The protein-tyrosine kinase oncogenes will be the primary focus of the review as discussed by the authors, however, biochemical connections between the protein tyrosine Kinases and oncoproteins of the Ras,Raf,Fos,Jun, and Rel families as well as the protein kinase C family are also discussed.
2,686 citations
TL;DR: Cyclin D2-Cdk4 complexes bind competitively to and down-regulate the activity of p27 and may thereby act in a pathway that reverses Cdk2 inhibition and enables G1 progression.
Abstract: Cell-cell contact and TGF-beta can arrest the cell cycle in G1. Mv1Lu mink epithelial cells arrested by either mechanism are incapable of assembling active complexes containing the G1 cyclin, cyclin E, and its catalytic subunit, Cdk2. These growth inhibitory signals block Cdk2 activation by raising the threshold level of cyclin E necessary to activate Cdk2. In arrested cells the threshold is set higher than physiological cyclin E levels and is determined by an inhibitor that binds to cyclin E-Cdk2 complexes. A 27-kD protein that binds to and prevents the activation of cyclin E-Cdk2 complexes can be purified from arrested cells but not from proliferating cells, using cyclin E-Cdk2 affinity chromatography. p27 is present in proliferating cells, but it is sequestered and unavailable to interact with cyclin E-Cdk2 complexes. Cyclin D2-Cdk4 complexes bind competitively to and down-regulate the activity of p27 and may thereby act in a pathway that reverses Cdk2 inhibition and enables G1 progression.
1,934 citations
TL;DR: It seems likely that most malignancies arise from the collaborative effects of dominant and recessive lesions, andumeration of the number of tumor suppressor genes afflicted in any given tumor may be greater.
1,643 citations
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TL;DR: Phylogenetic mapping of the conserved protein kinase catalytic domains can serve as a useful first step in the functional characterization of these newly identified family members.
Abstract: In recent years, members of the protein kinase family have been discovered at an accelerated pace. Most were first described, not through the traditional biochemical approach of protein purification and enzyme assay, but as putative protein kinase amino acid sequences deduced from the nucleotide sequences of molecularly cloned genes or complementary DNAs. Phylogenetic mapping of the conserved protein kinase catalytic domains can serve as a useful first step in the functional characterization of these newly identified family members.
4,838 citations
TL;DR: It is inferred that pp60src is a novel protein kinase and that the modification of proteins via the phosphorylation of tyrosine is essential to the malignant transformation of cells by Rous sarcoma virus.
Abstract: The protein kinase activity associated with pp60src, the transforming protein of Rous sarcoma virus, was found to phosphorylate tyrosine when assayed in an immunoprecipitate. Despite the fact that a protein kinase with this activity has not been described before, several observations suggest that pp60src also phosphorylates tyrosine in vivo. First, chicken cells transformed by Rous sarcoma virus contain as much as 8-fold more phosphotyrosine than do uninfected cells. Second, phosphotyrosine is present in pp60src itself, at one of the two sites of phosphorylation. Third, phosphotyrosine is present in the 50,000-dalton phosphoprotein that coprecipitates with pp60src extracted from transformed chicken cells. We infer from these observations that pp60src is a novel protein kinase and that the modification of proteins via the phosphorylation of tyrosine is essential to the malignant transformation of cells by Rous sarcoma virus. pp60sarc, the closely related cellular homologue of viral pp60src, is present in all vertebrate cells. This normal cellular protein, obtained from both chicken and human cells, also phosphorylated tyrosine when assayed in an immunoprecipitate. This is additional evidence of the functional similarity of these structurally related proteins and demonstrates that all uninfected vertebrate cells contain at least one protein kinase that phosphorylates tyrosine.
2,061 citations
1,835 citations
TL;DR: Data indicate that elements of the mechanism by which the cell cycle is controlled are likely to be conserved between yeast and humans.
Abstract: A human homologue of the cdc2 gene has been cloned by expressing a human cDNA library in fission yeast and selecting for clones that can complement a mutant of cdc2. The predicted protein sequence of the human homologue is very similar to that of the yeast cdc2 gene. These data indicate that elements of the mechanism by which the cell cycle is controlled are likely to be conserved between yeast and humans.
1,081 citations
TL;DR: This chapter discusses the detection and quantification of phosphotyrosine in proteins, and describes the kinases associated with the cell surface receptors for two polypeptide growth factors, epidermal growth factor and platelet-derived growth factor, and with the transforming proteins of at least five genetically distinct groups of retroviruses.
Abstract: Publisher Summary This chapter discusses the detection and quantification of phosphotyrosine in proteins. Protein kinases can be differentiated according to their amino acid specificity. Casein kinases of type II and the cAMP-dependent kinases phosphorylate serine, while casein kinases of type I phosphorylate threonine and, to a lesser extent, serine. Another group of kinases with strict specificity for tyrosine is described in the chapter. Most tyrosine-specific protein kinase activities detected to date are implicated in cell growth control. They include the kinases associated with the cell surface receptors for two polypeptide growth factors, epidermal growth factor (EGF) and platelet-derived growth factor (PDGF), and with the transforming proteins of at least five genetically distinct groups of retroviruses. The activity of a tyrosine protein kinase in the cell is apparent from an increase in the gross level of phosphotyrosine in cell proteins. The induction of a cellular tyrosine protein kinase by growth factors or the introduction of a viral tyrosine protein kinase by infection can raise the proportion of acid-stable protein bound phosphate present as phosphotyrosine 5–10 times. Phosphatases specific for tyrosine are as yet poorly characterized, but may be inhibited by traces of Zn 2+ or by adding free phosphotyrosine or analogs. The simplest strategy is to lyse cells directly into a denaturing solution, or to stop an in vitro reaction with denaturing agents.
991 citations