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This version published online on May 8, 2008
Molecular Endocrinology, doi:10.1210/me.2007-0457
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Submitted on October 3, 2007
Accepted on April 29, 2008

LUTEINIZING HORMONE RECEPTOR ACTIVATION IN OVARIAN GRANULOSA CELLS PROMOTES PROTEIN KINASE A-DEPENDENT DEPHOSPHORYLATION OF MAP2D

Maxfield P. Flynn, Evelyn T. Maizels, Amelia B. Karlsson, Thomas McAvoy, Jung-Hyuck Ahn, Angus C. Nairn, and Mary Hunzicker-Dunn*

From the Department of Cell and Molecular Biology, Northwestern University, Feinberg School of Medicine, Chicago, IL 60611; Laboratory of Molecular and Cellular Neuroscience, The Rockefeller University, New York, NY 10021; Department of Psychiatry, Yale University School of Medicine, New Haven, CT 06508

* To whom correspondence should be addressed. E-mail: mehd{at}wsu.edu.

The actions of luteinizing hormone (LH) to induce ovulation and luteinization of preovulatory follicles are mediated principally by activation of cAMP-dependent protein kinase (PKA) in granulosa cells. PKA activity is targeted to specific locations in many cells by A-kinase anchoring proteins (AKAPs). We previously showed that follicle-stimulating hormone (FSH) induces expression of microtubule-associated protein (MAP) 2D, an 80-kDa AKAP, in rat granulosa cells, and that MAP2D co-immunoprecipitates with PKA regulatory subunits in these cells. Here we report a rapid and targeted dephosphorylation of MAP2D at Thr256/Thr259 after treatment with human chorionic gonadotropin (hCG), an LH receptor agonist. This event is mimicked by treatment with forskolin or a cAMP analog and is blocked by the PKA inhibitor myristoylated-PKI, indicating a role for cAMP and PKA signaling in phospho-regulation of granulosa cell MAP2D. Furthermore, we show that Thr256/Thr259 dephosphorylation is blocked by the protein phosphatase 2A (PP2A) inhibitor okadaic acid and demonstrate interactions between MAP2D and PP2A by co-immunoprecipitation and microcystin-agarose pulldown. We also show that MAP2D interacts with glycogen synthase kinase (GSK) 3{beta} and is phosphorylated at Thr256/Thr259 by this kinase in the basal state. Increased phosphorylation of GSK3{beta} at Ser9 and the PP2A B56{delta} subunit at Ser566 is observed after treatment with hCG and appears to result in LH receptor-mediated inhibition of GSK3{beta} and activation of PP2A, respectively. Taken together, these results show that the phosphorylation status of the AKAP MAP2D is acutely regulated by LH receptor-mediated modulation of kinase and phosphatase activities via PKA.







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