title: Role of cortactin in dynamic actin remodeling events in gonadotrope cells.
abstract: GnRH induces marked activation of the actin cytoskeleton in gonadotropes; however, the physiological consequences and cellular mechanisms responsible have yet to be fully elucidated. The current studies focus on the actin scaffolding protein cortactin. Using the gonadotrope-derived αT3-1 cell line, we found that cortactin is phosphorylated at Y(421), S(405), and S(418) in a time-dependent manner in response to the GnRH agonist buserelin (GnRHa). GnRHa induced translocation of cortactin to the leading edge of the plasma membrane where it colocalizes with actin and actin-related protein 3 (Arp3). Incubation of αT3-1 cells with the c-src inhibitor phosphoprotein phosphatase 1, blocked tyrosine phosphorylation of cortactin, reduced cortactin association with Arp3, and blunted actin reorganization in response to GnRHa. Additionally, we used RNA silencing strategies to knock down cortactin in αT3-1 cells. Knockdown of cortactin blocked the ability of αT3-1 cells to generate filopodia, lamellipodia, and membrane ruffles in response to GnRHa. We show that lamellipodia and filopodia are capable of LHβ mobilization in primary pituitary culture after GnRHa treatment, and disruption of these structures using jasplakinolide reduces LH secretion. Collectively, our findings suggest that after GnRHa activation, src activity leads to tyrosine phosphorylation of cortactin, which facilitates its association with Arp3 to engage the actin cytoskeleton. The reorganization of actin by cortactin potentially underlies GnRHa-induced secretory events within αT3-1 cells.
authors.affiliation: College of Arts and Sciences, Department of Zoology and Physiology (A.M.N., M.G.D.), University of Wyoming, Laramie, Wyoming 82071; College of Veterinary Medicine and Biomedical Science, Departments of Microbiology, Immunology, and Pathology (J.D.W.) and Biomedical Sciences (C.M.C.), Colorado State University, Ft Collins, Colorado, 80523; and College of Veterinary Medicine, Department of Biomedical Sciences (M.S.R.), Cornell University, Ithaca, New York 14853.
authors.forename: Amy M
authors.initials: AM
authors.lastname: Navratil
authors.forename: Melissa G
authors.initials: MG
authors.lastname: Dozier
authors.forename: Jennifer D
authors.initials: JD
authors.lastname: Whitesell
authors.forename: Colin M
authors.initials: CM
authors.lastname: Clay
authors.forename: Mark S
authors.initials: MS
authors.lastname: Roberson
mesh_terms: D051378:Actin-Related Protein 3 / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000818:Animals; D002460:Cell Line; D051356:Cortactin / Q000378:metabolism*; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism*; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology; D008297:Male; D051379:Mice; D010749:Phosphoprotein Phosphatases / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D010902:Pituitary Gland / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism; D012756:Sheep
chemical_list: D051378:Actin-Related Protein 3; D000199:Actins; D051356:Cortactin; D007987:Gonadotropin-Releasing Hormone; D016392:Proto-Oncogene Proteins pp60(c-src); D010749:Phosphoprotein Phosphatases