title: Protein phosphatase 2A interacts with the Src kinase substrate p130(CAS).
abstract: In this study, we report that the Src substrate Cas (p130 Crk-associated substrate) associates with protein phosphatase 2A (PP2A), a serine/threonine phosphatase. We investigated this interaction in cells expressing a temperature-sensitive mutant form of v-Src. v-Src activation (by shifting cells from the nonpermissive to the permissive temperature) led to an increase in the tyrosine phosphorylation of v-Src and Cas, as well as in the association between v-Src and Cas. v-Src has previously been shown to bind to PP2A and to phosphorylate the catalytic subunit of PP2A, resulting in inhibition of phosphatase activity. We found that the association between v-Src and PP2A decreased as cells were shifted to the permissive temperature. In contrast, the levels of PP2A that co-immunoprecipitated with Cas increased when v-Src was activated. We obtained similar results in pull-down experiments with immobilized Microcystin, a PP2A inhibitor. Serine/threonine phosphorylation of Cas has previously been shown to occur in a cell cycle regulated matter. Treatment of NIH3T3 cells with okadaic acid, a PP2A inhibitor, augments the serine/threonine phosphorylation of Cas that occurs at mitosis. Furthermore, PP2A dephosphorylates serine residues on Cas in vitro. Taken together, our results suggest that PP2A may be involved in the cell cycle-specific dephosphorylation of Cas.
authors.affiliation: Department of Physiology and Biophysics, School of Medicine, State University of New York at Stony Brook, Stony Brook, NY 11794-8661, USA.
authors.forename: N
authors.initials: N
authors.lastname: Yokoyama
authors.forename: W T
authors.initials: WT
authors.lastname: Miller
mesh_terms: D016475:3T3 Cells; D000818:Animals; D050719:Crk-Associated Substrate Protein; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051379:Mice; D052998:Microcystins; D009154:Mutation; D019319:Okadaic Acid / Q000494:pharmacology; D015688:Oncogene Protein pp60(v-src) / Q000235:genetics / Q000378:metabolism*; D010456:Peptides, Cyclic / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000378:metabolism* / Q000502:physiology; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010769:Phosphothreonine / Q000378:metabolism; D054648:Protein Phosphatase 2; D011506:Proteins; D050717:Retinoblastoma-Like Protein p130; D015398:Signal Transduction; D013696:Temperature
chemical_list: C493842:Bcar1 protein, mouse; D050719:Crk-Associated Substrate Protein; D004791:Enzyme Inhibitors; D052998:Microcystins; D010456:Peptides, Cyclic; D010750:Phosphoproteins; D011506:Proteins; D050717:Retinoblastoma-Like Protein p130; D010769:Phosphothreonine; D010768:Phosphoserine; D019319:Okadaic Acid; C078588:microcystin; D015688:Oncogene Protein pp60(v-src); D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2