Human melanocyte and several breast cancer cell lines have elevated Src activity with concomitant hypophosphorylation of Tyr530. Biochemical analyses showed that these cells have elevated levels of PTP activity, which correlates with reduced phosphorylation on the C terminal residue AS-1404 DMXAA of Src and may have an important role in controlling Src kinase activity. The ability of PTP 1B to modulate Src activity has been demonstrated in mouse Lcell fibroblasts. Rare activating mutations in Src that are truncated at codon 531 have been reported in some cases of advanced colon cancer patients. The Src 531 mutation resulted in the production of a stop at codon 531, one residue beyond the regulatory Tyr530. Due to the lack of a C terminal regulatory region, phosphorylation of Tyr530 did not result in a closed conformation and the mutated Src remained constitutively active.
5. Regulation of Src Activity by Receptor Tyrosine Kinases Src can acts as an upstream or downstream modulator of several receptor molecules, as well as nonreceptor tyrosine kinases, which are responsible for the robustness and persistence of RTK signaling. Src acts as a signal transducer from BMS-599626 the cell surface receptors by sequential phosphorylation of tyrosine residues on substrates. Src participates in the activation of various downstream signaling pathways through molecular interactions with growth factor receptors such as the epidermal growth factor receptor family, hepatocyte growth factor receptor, integrin cell adhesion receptors, steroid hormone receptors, G protein coupled receptors, focal adhesion kinase and cytoskeleton components.
Src can activate the phosphatidylinositol 3 kinase Akt, growth factor receptor bound protein 2 Ras Raf mitogenactivated protein kinase, Jak signal transducers and activators of transcription as well as FAK paxillinp130 Crk associated substrate cascades that are most crucial for cell cycle progression, survival, and proliferation. Aberrant expression and activation of Src occurs in several tumor types and has been correlated with poor clinical outcome, which has stimulated interest in using Src kinase inhibitors as therapeutic cancer agents, some of which have entered the clinical trial stage. A variety of Src binding proteins have been detected that compete for binding to the protein,s SH domains and disturb the intramolecular interactions that allow the activation of Src kinase.
v Src cellular counterpart forms activated dimerized receptors via its SH2 domain binding to specific phosphotyrosine residues in the plateletderived growth factor receptor juxtamembrane region. Other reports have suggested that activated PDGFR can phosphorylate tyrosine residues in the SH2/SH3 domain of Src and subsequently activate Src. FAK is another kinase molecule able to bind to the Src SH2 domain and activate the kinase activity. Additional examples of regulators are FAK binding partners p130Cas and PTP. Recently, p130Cas, a protein that is thought to function as a docking protein because of its large number of binding motifs, has been demonstrated to bind to Src SH2 and SH3 domains, resulting in Src activation. Nef and Sin are examples of proteins that can bind to SH3 domains and activate the Src family members Hck and Src, respectively. There is al
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