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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have shown previously that pp60c-src is a substrate for protein kinase C in vivo and that the target of protein kinase C phosphorylation in mammalian pp60c-src is serine 12. We now demonstrate that in addition to tumor promoters, all activators of phosphatidylinositol turnover that we have tested in fibroblasts (platelet-derived growth factor, fibroblast growth factor, serum, vasopressin, sodium orthovanadate, and prostaglandin F2 alpha) lead to the phosphorylation of pp60c-src at serine 12. In addition to stimulating serine 12 phosphorylation in pp60c-src, platelet-derived growth factor treatment of quiescent fibroblasts induces phosphorylation of one or two additional serine residues and one tyrosine residue within the N-terminal 16 kilodaltons of the enzyme and activates its immune complex protein-tyrosine kinase activity.
Mol Cell Biol 1988 Aug
PMID:Platelet-derived growth factor induces multisite phosphorylation of pp60c-src and increases its protein-tyrosine kinase activity. 246 76

Intact human platelets, terminally differentiated cells with no growth potential, were found to possess unusually high levels of tyrosine-specific protein phosphorylation. The physiological platelet activator thrombin transiently elevated platelet phosphotyrosine content, apparently through stimulation of one or more tyrosine-specific protein kinases. Immunoblotting with antiphosphotyrosine antiserum showed that thrombin caused dramatic changes in the tyrosine phosphorylation of a number of individual protein bands and that these changes occurred in three distinct temporal waves. Most but not all of the protein bands phosphorylated at tyrosine in response to thrombin were also tyrosine phosphorylated in response to chilling or the combination of ionophore A23187 and tetradecanoylphorbol acetate. Thrombin stimulated the phosphorylation of the tyrosine kinase pp60c-src, primarily at Ser-12 and Tyr-527, although the effects of these phosphorylations on platelet pp60c-src function were not apparent. Together, these results suggest that tyrosine-specific protein kinases of uncertain identity are involved in signal transduction in platelets.
Mol Cell Biol 1988 Sep
PMID:Platelet tyrosine-specific protein phosphorylation is regulated by thrombin. 246 41

We have compared the properties of pp60c-src from the mouse pituitary tumor cell line, AtT20, and from mouse fibroblasts. In vitro, pp60c-src phosphotransferase activity from AtT20 cells is 2- to 3-fold that of mouse NIH 3T3 fibroblast pp60c-src. In analyzing the reason for this elevation in specific activity, we found that pp60c-src from AtT20 cells differs structurally in at least three ways from pp60c-src in fibroblasts. First, AtT20 cells and primary rat anterior pituitary cells express low levels of the neuronal form of pp60c-src. Second, pp60c-src from AtT20 cells is phosphorylated at two additional N-terminal serine residues. Last, AtT20 pp60c-src is phosphorylated to a lower overall stoichiometry.
Mol Endocrinol 1989 Jan
PMID:AtT20 cells express modified forms of pp60c-src. 246 57

We used myristylated and nonmyristylated c-src-based variants and phosphotyrosine-specific antibodies to reevaluate the role of tyrosine phosphorylation in cellular transformation by pp60src. Prior methods used to detect tyrosine-phosphorylated proteins failed to discriminate predicted differences in tyrosine phosphorylation which are clearly observed with phosphotyrosine-specific antibodies and Western blotting (immunoblotting). Here we report the observation of a 120,000-Mr protein whose phosphorylation on tyrosine correlates with the induction of morphological transformation. p120 was not observed in cells overexpressing the regulated, nononcogenic pp60c-src, whereas phosphorylation of p120 was greatly enhanced in cells expressing activated, oncogenic pp60527F. Furthermore, phosphorylation of p120 was not induced by expression of the activated but nonmyristylated src variant pp602A/527F, which is transformation defective. p120 partitioned preferentially with cellular membranes, consistent with the observation that transforming src proteins are membrane associated. Although a number of additional putative substrates were identified and partially characterized with respect to intracellular localization, tyrosine phosphorylation of these proteins was not tightly linked to transformation.
Mol Cell Biol 1989 Feb
PMID:Transformation-specific tyrosine phosphorylation of a novel cellular protein in chicken cells expressing oncogenic variants of the avian cellular src gene. 246 3

To examine how amino acid sequences outside of the catalytic domain of pp60c-src influence the functional activity of this protein, we have introduced deletion mutations within the amino-terminal half of pp60c-src. These mutations caused distinct changes in the biochemical properties of the c-src gene products and in the properties of cells infected with retroviruses carrying these mutant c-src genes. Cells expressing the c-srcNX protein, which contains a deletion of amino acids 15 to 89, displayed a refractile, spindle-shaped morphology, formed intermediate-sized, tightly packed colonies in soft agar, and contained elevated levels of cellular phosphotyrosine-containing proteins. Thus, deletion of amino acids 15 to 89 can activate the kinase activity and transforming potential of the c-src gene product. Deletion of amino acids 112 to 225, however, did not increase the kinase activity or transforming ability of pp60c-src; indeed, deletion of these sequences in c-srcHP suppressed phenotypic alterations induced by pp60c-src. Cells expressing the c-srcNP or c-srcBS gene products (containing deletions of amino acids 15 to 225 and 55 to 169, respectively) displayed a fusiform, refractile morphology and formed diffuse colonies in soft agar; the mutant proteins displayed an increased in vitro protein-tyrosine kinase activity. However, only a few cellular proteins contained elevated levels of phosphotyrosine in vivo. Thus, deletions downstream of amino acid 89 severely restricted the ability of c-src to phosphorylate cellular substrates in vivo without affecting the intrinsic tyrosine kinase activity of the c-src gene product. These results suggest the existence of at least two modulatory regions within the amino-terminal half of pp60c-src that are important for the regulation of tyrosine kinase activity and for the interaction of pp60c-src with cellular substrates.
Mol Cell Biol 1989 Mar
PMID:Deletions within the amino-terminal half of the c-src gene product that alter the functional activity of the protein. 247 Oct 59

In previous studies examining the potential role of pp60c-src in cellular proliferation, we demonstrated that C3H10T1/2 murine embryo fibroblasts overexpressing transfected chicken genomic c-src displayed an epidermal growth factor (EGF)-induced mitogenic response which was 200 to 500% of the response exhibited by parental control cells (Luttrell et al., Mol. Cell. Biol. 8:497-501, 1988). In order to examine specific structural and functional requirements for pp60c-src in this event, 10T1/2 cells were transfected with chicken c-src genes encoding pp60c-src deficient in tyrosine kinase activity (pm430), myristylation, (pm2A), or a domain hypothesized to modulate the interaction with substrates or regulatory components (dl155). Neomycin-resistant clonal cell lines overexpressing each of the mutated c-src genes were assayed for EGF mitogenic responsiveness by measuring [3H]thymidine incorporation into acid-precipitable material or into labeled nuclei. The results were compared with those obtained with lines overexpressing the cDNA form of wild-type (wt) c-src or control cells transfected with the neomycin resistance gene only. As previously described for cells overexpressing wt genomic c-src (Luttrell et al., 1988), clones overexpressing wt cDNA c-src also exhibited enhanced EGF mitogenic responses ranging from approximately 300 to 400% of the control cell response. In contrast, clones overexpressing unmyristylated, modulation-defective, or kinase-deficient c-src not only failed to support an augmented response to EGF but also exhibited EGF responses lower than that of the control cells. Furthermore, there were no significant differences in the mitogenic responses to 10% fetal calf serum among any of the cells tested. These results indicate that pp60(c-scr) can potentiate mitogenic signaling generated by EGF but not all growth factors. This potentiation requires the utilization of pp60(c-scr) myristylation, and modulatory and tyrosine kinase domains and can me mediated by cDNA-encoded as well as by genome-encoded wt pp60(c-scr).
Mol Cell Biol 1989 Apr
PMID:pp60c-src tyrosine kinase, myristylation, and modulatory domains are required for enhanced mitogenic responsiveness to epidermal growth factor seen in cells overexpressing c-src. 247 Oct 64

The proto-oncogene c-src has been implicated in the development and mature function of the nervous system. pp60c-src, the protein product of the c-src gene, is a tyrosine protein kinase that is highly enriched in fetal neural tissue. pp60c-src appears in two phases of neuronal development. Neuroectodermal cells of gastrulating embryos first express pp60c-src around the time of commitment to neuronal or glial pathways. Later, committed neuroepithelial cells express pp60c-src near the onset of terminal neuronal differentiation. Immunocytochemical analyses of pp60c-src in developing chick retina, telencephalon, and cerebellum show immunoreactivity concentrated in regions rich in growth cones and neurites. Moreover, pp60c-src is concentrated approximately 10-fold in a biochemical fraction from fetal rat brain that is enriched in nerve growth cone membranes. These results point toward a function for pp60c-src in neurite outgrowth. A functional role for other proto-oncogenes in the development of the nervous system was indicated from a study of the expression of a battery of proto-oncogenes during the retinoic acid-induced differentiation of the mouse embryonal carcinoma cell line P19 to a neuronal phenotype. Nuclear runoff transcription of the proto-oncogenes c-src, c-fms, c-sis, N-ras, c-myc, and c-fos was observed in proliferating and retinoic acid-treated cells.
Mol Chem Neuropathol 1989 Feb
PMID:c-src and other proto-oncogenes implicated in neuronal differentiation. 247 50

The product of the c-src proto-oncogene, pp60c-src, is phosphorylated at Ser-17 by cyclic AMP-dependent protein kinase A and at Ser-12 by calcium-phospholipid-dependent protein kinase C (when stimulated by 12-O-tetradecanoyl phorbol acetate). We tested the effects of Ser----Ala and Ser----Glu mutations at these sites in pp60c-src and in pp60c-src(F527) (a mutant whose transforming activities are enhanced by Tyr-527----Phe mutation) by transfecting single-, double-, and triple-mutant src expression plasmids into NIH 3T3 cells. Tryptic phosphopeptide analyses of the mutant proteins confirmed prior biochemical identifications of the phosphorylation sites and showed that neither separate nor coordinate mutations at Ser-12 and Ser-17 affected Tyr-416, Tyr-527, or Ser-48 phosphorylation or prevented mitosis-specific phosphorylations of either pp60c-src or pp60c-src(F527). Ser-12 mutation did not affect phosphorylation of the Ser-17-containing peptide, but mutation of Ser-17 significantly increased phosphorylation at Ser-12. Specific kinase activities (both with and without in vivo 12-O-tetradecanoyl phorbol acetate treatment) and the abilities of pp60c-src and pp60c-src(F527) to induce foci, transformed morphologies, and anchorage-independent growth were unaffected by any of the serine mutations. Thus, pp60c-src transforming activity in NIH 3T3 cells is relatively insensitive to phosphorylation at these sites, but there is a suggestion that Ser-17 phosphorylation may have a subtle regulatory effect.
Mol Cell Biol 1989 Jun
PMID:Mutation of amino acids in pp60c-src that are phosphorylated by protein kinases C and A. 247 54

A promoter of the nuclear proto-oncogene fos was activated by cotransfection with the viral src gene. Ability to transactivate the c-fos promoter was dependent on tyrosine kinase activity, because (i) src mutants which have reduced tyrosine kinase activity due to mutation of Tyr-416 to Phe showed lower promoter activation, (ii) pp60c-src mutants which have increased tyrosine kinase activity due to mutation of Tyr-527 to Phe also augmented c-fos promoter induction, and (iii) mutation in the ATP-binding site of pp60v-src strongly suppressed c-fos promoter activation. Tyrosine kinase activity alone, however, was not sufficient for promoter activation, because of pp60v-src mutant which lacked its myristylation site and consequently membrane association showed no increased c-fos promoter activation. Both the tyrosine kinase- and membrane-association-defective mutants were also unable to induce transformation. Therefore, phosphorylation of membrane-associated substrates appears to be required for both gene expression and cellular transformation by the src protein. Two regions of the c-fos promoter located between positions -362 and -324 and positions -323 and -294 were responsive to src stimulation. We believe that protein tyrosine phosphorylation represents an important step of signal transduction from the membrane to the nucleus.
Mol Cell Biol 1989 Jun
PMID:Gene regulation by tyrosine kinases: src protein activates various promoters, including c-fos. 247 55

The biological and biochemical properties of pp60c-src are regulated, in part, by phosphorylation at Tyr-416 and Tyr-527. The tyrosine kinase and transforming activities of pp60c-src are suppressed by phosphorylation at Tyr-527, whereas full activation of pp60c-src requires phosphorylation at Tyr-416. To test specifically the significance of the negatively charged phosphate moieties on these tyrosine residues, we have substituted the codons for both residues with codons for either Glu or Gln. A negatively charged Glu at position 527 was unable to mimic a phosphorylated Tyr at this position, and, in consequence, the mutated pp60c-src was activated and transforming. Similarly, substitution of Tyr-416 with Glu was unable to stimulate the activities of the enzyme. However, mutagenesis of Tyr-416 to Gln (to form the mutant 416Q) activated the kinase activity approximately twofold over that observed for wild-type pp60c-src. When introduced into the mutant 527F (containing Phe-527 instead of Tyr), the double mutant 416Q-527F exhibited weak transforming activity. This is in contrast to the other double mutants 416E-527F and 416F-527F, which were nontransforming. The biochemical basis by which 416Q activates pp60c-src is not understood but probably involves some local conformational perturbation. Deletion of residues 519 to 524 (RH5), a region previously shown to be necessary for association with middle-T antigen, led to loss of phosphorylation at Tyr-527 and activation of the enzymatic and focus-forming activities of pp60c-src. Hence, the sequences necessary for complex formation with middle-T antigen may also be required by the kinase(s) which phosphorylates Tyr-527 in vivo. This suggests that normal cells contain cellular proteins which are analogous to middle-T antigen and whose action regulates the activity of pp60c-src by controlling phosphorylation or dephosphorylation at residue 527.
Mol Cell Biol 1989 Sep
PMID:pp60c-src variants containing lesions that affect phosphorylation at tyrosines 416 and 527. 247 63


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