Platelet tyrosine-specific protein phosphorylation is regulated by thrombin.

Abstract

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 pp6OC-S', primarily at Ser-12 and Tyr-527, although the effects of these phosphorylations on platelet pp60csrC function were not apparent. Together, these results suggest that tyrosine-specific protein kinases of uncertain identity are involved in signal transduction in platelets.The phosphorylation of proteins at tyrosine residues is implicated in normal and abnormal cell growth: several growth factor receptors are tyrosine-specific protein kinases, as are the transforming proteins of one class of acutely oncogenic retroviruses (13). The best-studied such retrovirus is Rous sarcoma virus, whose transforming gene v-src was derived from a cellular tyrosine kinase gene, c-src (22, 23). The protein-tyrosine kinase activity of the v-src gene product pp60vsrc has been activated by a C-terminal substitution and scattered point mutations (12). The transforming capacity of pp60v-src results, at least in part, from its increased kinase activity.Through alternative splicing, the c-src gene gives rise to two distinct proteins, both of about 60 kilodaltons (kDa) (16,18). Little is known about the physiological function of either c-src protein. A number of other proto-oncogene products are involved in the transduction of normal mitogenic signals (e.g., c-erbB [epidermal growth factor receptor], c-fms [colony-stimulating factor 1 receptor], c-sis [platelet-derived growth factor]). However, the tissue distribution of pp6Oc-src expression suggests that this is not its function; those cells which express the highest levels of pp60csrc do not divide. For example, postmitotic differentiated or differentiating neurons express high levels of both c-src proteins (1,3,7,8,17,21). Mammalian platelets, terminally differentiated cells with no growth potential, express still higher levels of the smaller c-src protein (9). These observations suggest that tyrosine-specific protein kinases in general, and pp60c-sr in particular, may regulate cellular processes that are distinct from growth control.We have chosen human platelets as a system for investigating the role of protein-tyrosine phosphorylation in differentiated cells. Platelets are relatively simple cell fragments (they do not syn...

Involvement of thromboxane A2 and tyrosine kinase in the synergistic interaction of platelet activating factor and calcium ionophore A23187 in human platelet aggregation

“…Many studies show that activation of platelets by some agonists increase the level of tyrosine phosphorylation resulting in the appearance of a new set of tyrosine-phosphorylated proteins (Ferrel and Martin, 1988;Golden and Yamamura, 1989). Increase in the phosphorylation of tyrosine residues is an early event in the signal transduction pathway for stimulation of platelets by PAF (Animesh et al, 1990).…”

Association of the protein tyrosine phosphatase PTP1C with the protein tyrosine kinase c‐Src in human platelets

“…Most tyrosine proteins are phosphorylated during platelet activation induced by physiological agonists such as thrombin and collagen [2][3][4], as well as by thapsgargin [5,6], or the monoclonal antibody P256 directed against the integrin C~Hb133, the receptor for fibrinogen also named glycoprotein IIb-IIIa [7]. Among the tyrosine phosphorylated proteins described in platelets, some have been detected in cellular contact regions and are related to platelet aggregation such as the focal adhesion kinase FAK [8].…”

“…Several protein tyrosine kinases (PTKs) have been identified ia platelets, c-Src is highly expressed together with some ~thers of the same family [2,3,9], Other soluble PTKs have ~lso been identified such as FAK, Syk, a tandem Src homolcgy 2 (SH2) domains kinase [10] and Matk, a Csk-like protein [: 1]. Modulation of platelet tyrosine kinase activity depends ~rnong others on intracellular Ca 2+ [6], on activation of pro-I fin kinase C, or on activation of the integrin O~iib [~ 3 [12].…”

Phase specific association of heterotrimeric GTP‐binding proteins with the actin‐based cytoskeleton during thrombin receptor‐mediated platelet activation

“…The platelet is, therefore, a suitable cell to assist understanding of the transmembrane signal transduction. Numerous intracellular molecular events during platelet activation have been reported: enhancement of phosphatidylinositol turnover and their key enzymes, increasing Ca 2+ influx, elevation of tyrosine kinase activities, and reorganization of the cytoskeleton [1][2][3][4]. Of particula r interest is the finding that several signal transducing molecuk's such as p60 c-"rc, phosphatidylinositol-3-kinase, phosphatidylinositol-4-kinase, phosphatidylinositol-4,5-kinase, diacylgycer~!…”