title: Cross-talk between serine/threonine protein phosphatase 2A and protein tyrosine phosphatase 1B regulates Src activation and adhesion of integrin αIIbβ3 to fibrinogen.
abstract: Integrin α(IIb)β(3) signaling mediated by kinases and phosphatases participate in hemostasis and thrombosis, in part, by supporting stable platelet adhesion. Our previous studies indicate that the genetic manipulation of PP2Acα (α isoform of the catalytic subunit of protein phosphatase 2A) negatively regulate the adhesion of human embryonal kidney 293 cells expressing α(IIb)β(3) to fibrinogen. Here, we demonstrated that small interference RNA (siRNA) mediated knockdown of PP2Acα in 293 α(IIb)β(3) cells led to the dephosphorylation of Src Tyr-529, phosphorylation of Src Tyr-418 and an increased Src kinase activity. Conversely, overexpression of PP2Acα decreased the basal Src activity. Pharmacological inhibition of PP2Ac in human platelets or PP2Acα knockdown in primary murine megakaryocytes resulted in Src activation. PP2Acα-depleted 293 α(IIb)β(3) cells did not alter the serine (Ser) phosphorylation of Src but enhanced the Ser-50 phosphorylation of protein tyrosine phosphatase 1B (PTP-1B) with a concomitant increase in the PTP-1B activity. Src activation in the PP2Acα-depleted 293 α(IIb)β(3) cells was abolished by siRNA mediated knockdown of PTP-1B. Pharmacological inhibition of Src or knockdown of Src, PTP-1B blocked the enhanced activation of extracellular signal-regulated kinase (ERK1/2) and the increased adhesiveness of PP2Acα-depleted 293 α(IIb)β(3) cells to fibrinogen, respectively. Thus, inactivation of PP2Acα promotes hyperphosphorylation of PTP-1B Ser-50, elevates PTP-1B activity, which dephosphorylates Src Tyr-529 to activate Src and its downstream ERK1/2 signaling pathways that regulate α(IIb)β(3) adhesion. Moreover, these studies extend the notion that a cross-talk between Ser/Thr and Tyr phosphatases can fine-tune α(IIb)β(3) outside-in signaling.
authors.affiliation: Department of Medicine, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Subhashree
authors.initials: S
authors.lastname: Pradhan
authors.forename: Nawaf
authors.initials: N
authors.lastname: Alrehani
authors.forename: Vimal
authors.initials: V
authors.lastname: Patel
authors.forename: Tanvir
authors.initials: T
authors.lastname: Khatlani
authors.forename: K Vinod
authors.initials: KV
authors.lastname: Vijayan
mesh_terms: D000818:Animals; D000906:Antibodies / Q000494:pharmacology; D002460:Cell Line; D005340:Fibrinogen / Q000235:genetics / Q000378:metabolism*; D005434:Flow Cytometry; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D051379:Mice; D010766:Phosphorylation / Q000187:drug effects; D019039:Platelet Glycoprotein GPIIb-IIIa Complex / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1 / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics / Q000502:physiology; D019061:src-Family Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
chemical_list: C412373:AG 1879; D000906:Antibodies; D019039:Platelet Glycoprotein GPIIb-IIIa Complex; D011743:Pyrimidines; D034741:RNA, Small Interfering; D005340:Fibrinogen; D019061:src-Family Kinases; D054648:Protein Phosphatase 2; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1