title: Cell signaling associated with Na(+)/K(+)-ATPase: activation of phosphatidylinositide 3-kinase IA/Akt by ouabain is independent of Src.
abstract: Exposure of intact cells to selective inhibitors of Na(+)/K(+)-ATPase such as ouabain activates several growth-related cell signaling pathways. It has been suggested that the initial event of these pathways is the binding of ouabain to a preexisting complex of Src with Na(+)/K(+)-ATPase of the plasma membrane. The aim of this work was to evaluate the role of Src in the ouabain-induced activation of phosphatidylinositide 3-kinase 1A (PI3K1A) and its downstream consequences. When fibroblasts devoid of Src (SYF cells) and controls (Src(++) cells) were exposed to ouabain, PI3K1A, Akt, and proliferative growth were similarly stimulated in both cell lines. Ouabain-induced activation of Akt was not prevented by the Src inhibitor PP2. In contrast, ERK1/2 were not activated by ouabain in SYF cells but were stimulated in Src(++) cells; this was prevented by PP2. In isolated adult mouse cardiac myocytes, where ouabain induces hypertrophic growth, PP2 also did not prevent ouabain-induced activation of Akt and the resulting hypertrophy. Ouabain-induced increases in the levels of co-immunoprecipitation of the α-subunit of Na(+)/K(+)-ATPase with the p85 subunit of PI3K1A were noted in SYF cells, Src(++) cells, and adult cardiac myocytes. In conjunction with previous findings, the results presented here indicate that (a) if there is a preformed complex of Src and Na(+)/K(+)-ATPase, it is irrelevant to ouabain-induced activation of the PI3K1A/Akt pathway through Na(+)/K(+)-ATPase and (b) a more likely, but not established, mechanism of linkage of Na(+)/K(+)-ATPase to PI3K1A is the ouabain-induced interaction of a proline-rich domain of the α-subunit of Na(+)/K(+)-ATPase with the SH3 domain of the p85 subunit of PI3K1A.
authors.affiliation: Department of Biochemistry and Cancer Biology, College of Medicine and Life Sciences, University of Toledo Health Science Campus , Toledo, Ohio 43614, United States.
authors.forename: Jian
authors.initials: J
authors.lastname: Wu
authors.forename: Evgeny E
authors.initials: EE
authors.lastname: Akkuratov
authors.forename: Yan
authors.initials: Y
authors.lastname: Bai
authors.forename: Cassie Miller
authors.initials: CM
authors.lastname: Gaskill
authors.forename: Amir
authors.initials: A
authors.lastname: Askari
authors.forename: Lijun
authors.initials: L
authors.lastname: Liu
mesh_terms: D000818:Animals; D002460:Cell Line; D058543:Class Ia Phosphatidylinositol 3-Kinase / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D051379:Mice; D010042:Ouabain / Q000494:pharmacology*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects*; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D019061:src-Family Kinases / Q000378:metabolism
chemical_list: D010042:Ouabain; D058543:Class Ia Phosphatidylinositol 3-Kinase; D019061:src-Family Kinases; D051057:Proto-Oncogene Proteins c-akt; D000254:Sodium-Potassium-Exchanging ATPase