title: Galpha12 regulates epithelial cell junctions through Src tyrosine kinases.
abstract: Regulation and assembly of the epithelial cell junctional complex involve multiple signaling mechanisms, including heterotrimeric G proteins. Recently, we demonstrated that Galpha12 binds to the tight junction scaffolding protein ZO-1 through the SH3 domain and that activated Galpha12 increases paracellular permeability in Madin-Darby canine kidney (MDCK) cells (Meyer et al. J Biol Chem 277: 24855-24858, 2002). In the present studies, we explore the effects of Galpha12 expression on tight and adherens junction proteins and examine downstream signaling pathways. By confocal microscopy, we detect disrupted tight and adherens junction proteins with increased actin stress fibers in constitutively active Galpha12 (QLalpha12)-expressing MDCK cells. The normal distribution of ZO-1 and Na-K-ATPase was altered in QLalpha12-expressing MDCK cells, consistent with loss of polarity. We found that the tyrosine kinase inhibitor genistein and the Src-specific inhibitor PP-2 reversibly abrogated the QLalpha12 phenotype on the junctional complex. Junctional protein localization was preserved in PP-2- or genistein-treated QLalpha12-expressing cells, and the increase in paracellular permeability as measured by transepithelial resistance and [3H]mannitol flux was prevented by the inhibitors. Src activity was increased in QLalpha12-expressing MDCK cells as assessed by Src autophosphorylation, and beta-catenin tyrosine phosphorylation was also increased, although there was no detectable increase in Rho activity. Taken together, these results indicate that Galpha12 regulates MDCK cell junctions, in part through Src tyrosine kinase pathways.
authors.affiliation: Renal Division, Brigham and Women's Hospital and Harvard Medical School, Harvard Institutes of Medicine, 77 Avenue Louis Pasteur, Boston, MA 02115, USA.
authors.forename: Tobias N
authors.initials: TN
authors.lastname: Meyer
authors.forename: Jennifer
authors.initials: J
authors.lastname: Hunt
authors.forename: Catherine
authors.initials: C
authors.lastname: Schwesinger
authors.forename: Bradley M
authors.initials: BM
authors.lastname: Denker
mesh_terms: D022005:Adherens Junctions / Q000201:enzymology / Q000502:physiology; D000818:Animals; D002460:Cell Line; D004285:Dogs; D004847:Epithelial Cells / Q000201:enzymology / Q000502:physiology*; D044365:GTP-Binding Protein alpha Subunits, G12-G13 / Q000502:physiology*; D007365:Intercellular Junctions / Q000201:enzymology / Q000502:physiology*; D019061:src-Family Kinases / Q000502:physiology*
chemical_list: D019061:src-Family Kinases; D044365:GTP-Binding Protein alpha Subunits, G12-G13