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Molecular Endocrinology

Year: 2010  |  Volume: 24  |  Issue: 3  |  Page No.: 632 - 643

Prostaglandin F2{alpha} Represses IGF-I-Stimulated IRS1/Phosphatidylinositol-3-Kinase/AKT Signaling in the Corpus Luteum: Role of ERK and P70 Ribosomal S6 Kinase

E Arvisais, X Hou, T. A Wyatt, K Shirasuna, H Bollwein, A Miyamoto, T. R Hansen, B. R Rueda and J. S. Davis


Little is known about the early intracellular events that contribute to corpus luteum regression. Experiments were designed to determine the effects of prostaglandin F2 (PGF2) on phosphatidylinositol-3-kinase (PI3K)/Akt signaling in the corpus luteum in vivo and in vitro. Treatment of midluteal-phase cows with a luteolytic dose of PGF2 resulted in a rapid increase in ERK and mammalian target of rapamycin (mTOR)/p70 ribosomal protein S6 kinase (p70S6K1) signaling and a rapid suppression of Akt phosphorylation in luteal tissue. In vitro treatment of primary cultures of luteal cells with PGF2 also resulted in an increase in ERK and mTOR/p70S6K1 signaling and a diminished capacity of IGF-I to stimulate PI3K, Akt, and protein kinase C activation. Accounting for the reductions in PI3K and Akt activation observed in response to PGF2 treatment, we found that PGF2 promoted the phosphorylation of serine residues (307, 612, 636) in the insulin receptor substrate 1 (IRS1) peptide sequence in vivo and in vitro. Serine phosphorylation of IRS1 was associated with reduced formation of IGF-I-stimulated IRS1/PI3Kp85 complexes. Furthermore, treatment with inhibitors of the MAPK kinase 1/ERK or mTOR/p70S6K1 signaling pathways prevented PGF2-induced serine phosphorylation of IRS1 and abrogated the inhibitory actions of PGF2 on Akt activation. Taken together, these experiments provide compelling evidence that PGF2 treatment stimulates IRS1 serine phosphorylation, which may contribute to a diminished capacity to respond to IGF-I. It seems likely that the rapid changes in phosphorylation events are among the early events that mediate PGF2-induced corpus luteum regression.

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