A phosphotyrosine displacement mechanism for activation of Src by PTPα

Abstract

Protein tyrosine phosphatase α (PTPα) is believed to dephosphorylate physiologically the Src protooncogene at phosphotyrosine (pTyr)527, a critical negative-regulatory residue. It thereby activates Src, and PTPα overexpression neoplastically transforms NIH 3T3 cells. pTyr789 in PTPα is constitutively phosphorylated and binds Grb2, an interaction that may inhibit PTPα activity. We show here that this phosphorylation also specifically enables PTPα to dephosphorylate pTyr527. Tyr789→Phe mutation abrogates PTPα-Src binding, dephosphorylation of pTyr527 (although not of other substrates), and neoplastic transformation by overexpressed PTPα in vivo. We suggest that pTyr789 enables pTyr527 dephosphorylation by a pilot binding with the Src SH2 domain that displaces the intramolecular pTyr527-SH2 binding. Consistent with model predictions, we find that excess SH2 domains can disrupt PTPα-Src binding and can block PTPα-mediated dephosphorylation and activation in proportion to their affinity for pTyr789. Moreover, we show that, as predicted by the model, catalytically defective PTPα has reduced Src binding in vivo. The displacement mechanism provides another potential control point for physiological regulation of Src-family signal transduction pathways.

CUTL1 promotes tumor cell migration by decreasing proteasome-mediated Src degradation

“…To ensure that the differences in spreading were not due to clonal biases in the Src-overexpressing Panc1 clones, we transiently overexpressed Src in CUTL1 Csk is transcriptionally regulated by CUTL1 in several cell lines Csk is able to phosphorylate human Src at Tyr530 which is located in the C-terminal tail of Src (Zheng et al, 2000). More than 95% of cellular Src is phosphorylated at the Csk-specific tyrosine residue 530 representing an important mechanism in the regulation of basal Src activity (Zheng et al, 2000).…”

“…More than 95% of cellular Src is phosphorylated at the Csk-specific tyrosine residue 530 representing an important mechanism in the regulation of basal Src activity (Zheng et al, 2000). When phosphorylated at Tyr530, the activity of Src is reduced to low basal levels, thereby protecting cells from the potential oncogenic activity of the src protooncogene (Zheng et al, 2000).…”

“…More than 95% of cellular Src is phosphorylated at the Csk-specific tyrosine residue 530 representing an important mechanism in the regulation of basal Src activity (Zheng et al, 2000). When phosphorylated at Tyr530, the activity of Src is reduced to low basal levels, thereby protecting cells from the potential oncogenic activity of the src protooncogene (Zheng et al, 2000). The activity of Src phosphorylated at the C-terminal Tyr530 can be increased either by dephosphorylation of Tyr530 or by phosphorylation at other tyrosine residues, for example, after the stimulation of integrin receptors with fibronectin (Moarefi et al, 1997;Ma et al, 2000).…”

“…Under basal conditions, 90-95% of Src is phosphorylated by the C-terminal src kinase (Csk) at the Cterminal Tyr527 in mice or Tyr530 in humans (Zheng et al, 2000). Through phosphorylation at Tyr527, Csk stabilizes Src in a dormant form with low basal activity (Roskoski, 2004).…”

Contribution of Bone Tissue Modulus to Breast Cancer Metastasis to Bone

“…Integrin binding to the ligands in the matrix results in integrin clustering and activation of enzymes including kinases (e.g., focal adhesion kinase (FAK)) and phosphatases (e.g., tyrosine phosphatase-α (RPTP-α)) that regulate signal transduction within the cell [50,61]. RPTP-α can activate Src family kinases (SFKs) within about 300 ms after application of a force on fibronectin beads [65][66][67]. Phosphorylation of mitogen-activated protein kinase (MAPK) has also been reported to increase in response to mechanical stress, suggesting that integrins sense forces regulating gene expression by activation of the MAPK pathway [68], which is known to be downstream of TGF-β signaling [69].…”