title: Laminin regulates PI3K basal localization and activation to sustain STAT5 activation.
abstract: Extracellular matrix (ECM) is a key regulator of tissue morphogenesis and functional differentiation in the mammary gland. We showed recently that laminin-111 (LN1) together with prolactin induces β-casein expression in mammary epithelial cells (MECs) by sustaining STAT5 activation. Others have shown that Rac1 is required for integrin-mediated STAT5 activation, but molecules upstream of Rac1 remain to be elucidated. Here, we show that exposure to three-dimensional (3D) laminin-rich ECM (LrECM) gels changes the localization of phosphoinositide 3-kinase (PI3K) in MECs from diffuse to basal accompanied with the activation of PI3K-Rac1 signaling pathway. We show by co-immunoprecipitation that Rac1 associates with STAT5, and that LrECM treatment enhances this interaction. Blocking PI3K with LY294002 inhibits LrECM-dependent Rac1 activation, attenuates sustained STAT5 phosphorylation and blocks β-casein gene transcription. These results indicate that PI3K is a key mediator of the LN1-induced signaling cascade which controls the activity of transcription factors essential for tissue-specific gene expression.
authors.affiliation: Department of Molecular and Biomedical Pharmacology, University of Kentucky, Lexington, USA. Ren.xu2010@uky.edu
authors.forename: Ren
authors.initials: R
authors.lastname: Xu
authors.forename: Virginia A
authors.initials: VA
authors.lastname: Spencer
authors.forename: Dinah Levy
authors.initials: DL
authors.lastname: Groesser
authors.forename: Mina J
authors.initials: MJ
authors.lastname: Bissell
mesh_terms: D000818:Animals; D002364:Caseins / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D016764:Cell Polarity / Q000187:drug effects; D002867:Chromones / Q000494:pharmacology; D047468:Immunoprecipitation; D007797:Laminin / Q000494:pharmacology*; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000032:analysis*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011401:Promoter Regions, Genetic; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D015398:Signal Transduction; D020830:rac1 GTP-Binding Protein / Q000037:antagonists & inhibitors / Q000378:metabolism
chemical_list: D002364:Caseins; D002867:Chromones; D007797:Laminin; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D050799:STAT5 Transcription Factor; D020830:rac1 GTP-Binding Protein; C121346:laminin 1; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one