Role Of Protein Tyrosine Phosphatases Research Articles

Insulin Receptor Kinase Phosphorylates Protein Tyrosine Phosphatase Containing Src Homology 2 Regions and Modulates Its PTPase Activity in Vitro

To clarify the role of protein tyrosine phosphatase (PTPase) containing a pair of Src homology 2 (SH2) regions upon insulin signaling, we studied the interactions between the insulin receptor and SH-PTP2 coupled to glutathione-S-transferase. A full length SH-PTP2 was phosphorylated by insulin receptor kinase and associated with the insulin receptor in vitro. The N-terminal SH2 domain was more phosphorylated than the other SH2 domain of SH-PTP2. However, both SH2 domains of SH-PTP2 were necessary for association with insulin receptors. Phosphorylation of the SH2 domains of SH-PTP2 resulted in decreased PTPase activities toward the phosphorylated insulin receptor. These results indicate that the insulin receptor can negatively regulate SH-PTP2 activity by means of phosphorylating the SH2 domains.

The role of protein tyrosine phosphatases in lymphocyte activation and differentiation.

Protein tyrosine phosphorylation is involved in the regulation of every facet of biological phenomena. Signal transduction mechanisms operative in lymphocyte development, activation, and differentiation have been studied intensively, and are also found to support this premise. In this review, I focus on the crucial problems surrounding CD45, a prototypic receptor-type protein tyrosine phosphatase (RPTP) of the immune system: (1) the role of CD45 for antigen receptor-initiated signaling in T and B cells, (2) the physiological relevance of CD45 isoforms, (3) potential regulatory mechanisms of CD45 PTP activity, and (4) the clinical significance of structural abnormalities in PTP. Furthermore, other PTPs that may be important to the exquisite functioning of the immune system are reviewed.

Induction of tyrosine phosphorylation and T-cell activation by vanadate peroxide, an inhibitor of protein tyrosine phosphatases.

Rapid tyrosine phosphorylation of key cellular proteins is a crucial event in the transduction of activation signals to T-lymphocytes. The regulatory role of protein tyrosine phosphatases (PTPases) in this process was explored by studying the effects of a powerful PTPase inhibitor, vanadate peroxide (pervanadate), on the activation cascade of Jurkat human leukaemic T-cells. Pervanadate induced activation of the tyrosine kinases lck and fyn (4- and 3-fold respectively) and a dramatic increase in tyrosine phosphorylation of cellular proteins, notably phospholipase C gamma 1. After this event, we observed a rise in intracellular Ca2+ concentration, corresponding to an influx. This effect required surface expression of the CD45 PTPase and was not observed in CD45-deficient variants of Jurkat cells. In the CD45-negative variant, the effect of pervanadate on tyrosine phosphorylation was globally decreased and some phosphorylated substrates were specifically missing. Pervanadate also stimulated transcription of the c-fos gene and accumulation of its mRNA as well as several other hallmarks of T-lymphocyte activation such as surface expression of the CD69 antigen and the interleukin 2 receptor alpha-chain (CD25). Pervanadate synergized with signals delivered by T-cell antigen receptor engagement or by a phorbol ester to induce interleukin 2 production. Pervanadate activated NF-kappa B, as shown by an increase in DNA-binding activity of this transcription factor. We thus conclude that PTPases play a crucial role in the negative regulation of signal transduction culminating in T-lymphocyte activation. Moreover, induction of tyrosine phosphorylation appears sufficient per se to initiate a complete activation programme.

Structure and function of SH2-domain containing tyrosine phosphatases

The importance of tyrosyl phosphorylation in regulating growth factor-receptor-mediated signal transduction is firmly established, but the roles of protein tyrosine phosphatases (PTPases) in these pathways are unclear. PTPases that contain src-homology 2 (SH2) domains, which mediate interactions with specific phosphotyrosyl proteins, probably play an important role in early signaling events following growth factor stimulation. In this review, the two mammalian SH2-containing PTPases, SH-PTP1 and SH-PTP2, are described and their possible roles in signal transduction discussed. In addition, the implications of recent genetic studies in the mouse and Drosophila, which shed light on the actions of these PTPases in physiology and pathology, will be addressed.

Chromosomal assignment of the gene for protein tyrosine phosphatase HPTP delta.

Protein tyrosine phosphatase (PTP) negatively regulates the effect of protein tyrosine kinases and is implicated in the regulation of a variety of biological phenomena such as cell activation, differentiation and neoplastic transformation. To gain insight into the role of PTPs, we cloned the human receptor‐type FTP gene and assigned the chromosome harboring the gene for HPTPδ by using DNAs from human‐mouse hybrid cell lines and by fluorescence in situ hybridization. The results clearly demonstrated that HPTPδ gene maps to human chromosome 9p24.

Src Homology 2 Domains of Protein Tyrosine Phosphatase Are Phosphorylated by Insulin Receptor Kinase and Bind to the COOH-Terminus of Insulin Receptors in Vitro

To clarify the role of protein tyrosine phosphatases(PTPase) containing Src homology 2 (SH2) regions on insulin signaling, we investigated the interactions between SH2 regions of PTPase and insulin receptors. We made a pair of SH2 domains of PTP1C and SH-PTP2 fusion proteins coupled to glutathione-S-transferase (GST) using pGEX-3X expression vector. After incubating with insulin, insulin receptors were incubated with SH2 proteins in the presence of 100 μ ATP at 4°C for 3 hr, and then immunoprecipitated and analyzed by SDS-PAGE. We found that SH2 domains of SH-PTP2 were phosphorylated, but not those of PIP1C by insulin receptor kinase and the SH2 domains of SH-PTP2, but not those of PTP1C, directly bound to the phosphorylated COOH-terminus of insulin receptors in vitro.

The role of protein tyrosine phosphatases in density-dependent growth control of normal rat kidney cells

In normal rat kidney cells protein tyrosine phosphatases (PTPases) play a role in attaining density-dependent growth arrest after stimulation with mitogens. The PTPase inhibitor sodium orthovanadate prevents density-dependent growth inhibition of EGF-treated cells and mimicks in that respect the action of TGFβ and retinoic acid. However, enhanced PTPase activity is not obligatory for maintaining cells in a density-arrested state. In contrast to TGFβ and retinoic acid, vanadate is unable to restimulate density-inhibited cells, indicating that different mechanisms are operating. Yet, vanadate is strongly potentiating the effect of low concentrations of TGFβ but not of retinoic acid, implicating that tyrosine phosphorylation is linked to TGFβ action and that PTPase may represent a negative control element in the TGFβ signaling pathway.