PARENT SESSION
PLATFORM SESSION 10. OVARY II: FOLLICLE GROWTH / PERIOVULATORY EVENTS

Monday, August 2, 2004
2:00 PM–4:00 PM
Buchanan A106
Chair: Jon Hennenbold Co-Chair: Tara Swan

(294) REGULATION OF MICROTUBULE ASSOCIATED PROTEIN 2D EXPRESSION BY GLUCOCORTICOIDS IN GRANULOSA CELLS.

Peters, Carl¹, Maizels, Evelyn¹, Alam, Hena ¹, Hunzicker-Dunn, Mary¹, ¹ Northwestern University, Chicago, IL

ABSTRACT- Glucocorticoids are known to have a variety of effects on grnaulosa cells that implicate them as important for follicular growth and differentiation. For example, glucocorticoids have been shown to enhance the gonadotrophin induced steroidogenesis of granulosa cells as well as protect granulosa cells from apoptosis by increasing Bcl-2 expression. In addition, glucocorticoids may also participate in orchestrating the intracellular signaling events of granulosa cells as we have shown that treatment of granulosa cells with dexamethasone (Dex) induces the expression of an 80 kD A-kinase anchoring protein that we have indentified as the microtubule associated protein 2D (MAP2D). We now show that MAP2D epxression is increased in as little as 24 hours, attains maximal expression at 48 hours and maintains this maximal expression up to 72 hours. Dex induced expression of MAP2D is blocked by the insulin-like growth factor 1 receptor (IGF-1R) inhibitor AG538. This effect with the previous report that Dex maintains IGF-1 RNA expression in cultured granulosa cells. Similarly we found that Dex treatment maintains expression of insuling receptor substrate-1 (IRS-1) protein and that AG538 inhibits IRS-1 expression. IRS-1 is well characterized for its important role in IGF signaling including activation of phosphatidylinositol-3 (PI-3) kinase and subsequently Akt. Treatment with PI-3 kinase inhibitors (wortmannin and LY294002) blocked Dex induced MAP2D expression and maintainence of IRS-1 exprssion. Furthermore directly stimulating IGF-1R by addition of exogenous IGF1 induced MAP@D expression that was inhibited by AG538 or by inhibition of PI-3 kinase. These results suggest that glucocorticoids maitn functional signaling through the IGF pathway not only at the previously characterized level of receptor agonist but also at the level of receptor substrate. The signaling through this pathway and active PI-3 kinase are necessary for expression of MAP2D which, functioning as an AKAP, may integrate future signaling events as the follicle matures. Supported by HD21921.

KEY WORDS: glucocorticoids, phosphatidylinositol-3 kinase, microtubule associated protein 2d, insulin-like growth factor