The Role of Protein-tyrosine Phosphatase 1B in Integrin Signaling

Abstract

Protein-tyrosine phosphatase 1B (PTP1B) is a key negative regulator of insulin and leptin signaling and a novel therapeutic target for the treatment of type 2 diabetes, obesity, and other associated metabolic syndromes. Because PTP1B regulates multiple signal pathways and it can both enhance and antagonize a cellular event, it is important to establish the physiological relevance of PTP1B in these processes. In this study, we utilize potent and selective PTP1B inhibitors to delineate the role of PTP1B in integrin signaling. We show that down-regulation of PTP1B activity with small molecule inhibitors suppresses cell spreading and migration to fibronectin, increases Tyr 527 phosphorylation in Src, and decreases phosphorylation of FAK, p130Cas , and ERK1/2. In addition, PTP1B "substrate-trapping" mutants bind Tyr 527 -phosphorylated Src and protect it from dephosphorylation by endogenous PTP1B. These results establish that PTP1B promotes integrin-mediated responses in fibroblasts by dephosphorylating the inhibitory pTyr 527 and thereby activating the Src kinase. We also show that PTP1B forms a complex with Src and p130Cas , and that the proline-rich motif PPRPPK (residues 309 -314) in PTP1B is essential for the complex formation. We suggest that the specificity of PTP1B for Src pTyr 527 is mediated by protein-protein interactions involving the docking protein p130Cas with both Src and PTP1B in addition to the interactions between the PTP1B active site and the pTyr 527 motif.

Protein tyrosine phosphatase PTP1B in cell adhesion and migration

“…27 Remarkably, the positive role of PTP1B in cell motility was frequently associated with the stimulation of integrin-dependent signaling. 3,4,12,17,18,22 In contrast, the negative effect of PTP1B on cell motility was related to antagonizing signaling from growth factor receptor tyrosine kinases. [24][25][26][27] In a recent quantitative study, we analyzed the intrinsic motility and migration parameters of PTP1B-null cells (KO cells) in an isotropic 2-D fibronectin substratum.…”

“…17 Src activation by PTP1B was further demonstrated in several different cell models. 3,4,12,18,[45][46][47] Using a combination of time lapse, total internal reflection fluorescence microscopy, and BiFC we were able to visualize ER-bound PTP1B/ Src complexes as small fluorescent puncta distributed uniformly at the plasma membrane in contact with the substrate. 8 The substrate trap mutation (D181A) in PTP1B and the tyrosine 529 at the C-tail of Src were both required for BiFC to occur, as well as the plasma membrane targeting motif of Src.…”

“…PTP1B was shown to promote cell adhesion and motility in fibroblasts, 17,18 neurons, 3,19 platelets, 4 and several tumor cell lines. 12,[20][21][22] An inhibitory role has been described in fibroblasts, 23,24 primary aortic smooth muscle cells, 25 ovarian cancer cells, 26 and in glioblastoma multiforme tumor cell invasion in mice.…”

Identification of new genes associated with breast cancer progression by gene expression analysis of predefined sets of neoplastic tissues

“…It is involved in leptin and insulin signaling and in several other signaling pathways such as growth factor and integrin mediated processes. 57 Several studies demonstrated that changes in abundance and distribution of PTPases could impair insulin signal transduction, causing insulin resistance. 58 Aberrant insulin signaling, which leads to insulin resistance, hyperinsulinaemia and increased concentrations of endogenous estrogen and androgen, was linked to high breast cancer risk by clinical and experimental evidence.…”

Physiological Signaling Specificity by Protein Tyrosine Phosphatases

“…In contrast, TC-PTP and PTP-1B dephosphorylate similar but largely distinct sets of non-RTK substrates. For example, PTP-1B targets include the Src family kinases (SFKs) (8,13,43) and JAK2 (14,28,49,80), whereas TC-PTP targets the SFKs (71) and JAK1 (60). These observations point to the fact that, despite their high similarity between their PTP domains, PTP-1B and TC-PTP can target different substrates.…”