PARENT SESSION
SLIDE SESSION 8. SIGNAL TRANSDUCTION
Chairs: Teresa Woodruff, Mary Hunziker-Dunn, Chun-Ying Ku (Trainee)
Univ Ottawa-Morisset 218
2:30 PM-4:30 PM
58
FSH AMPLIFIES IGF-I-MEDIATED PROTEIN KINASE SIGNALING CASCADES IN RAT SERTOLI CELLS.
Khan, Shafiq1, Ndjountche, Lilianne 2, Pratchard, Lauren 1, Davis, John2, 1 2
ABSTRACT- FSH and IGF-I are both important determinants of testicular development and Sertoli cell function. The present studies were performed to determine the actions of FSH and IGF-I on phosphatidylinositol (PI) 3-kinase/Akt and Erk mitogen-activated protein kinase (p42 and p44 MAPKs) signaling in immature rat Sertoli cells. Primary cultures of rat Sertoli cells were prepared from 10 d old rats. After 6 days Sertoli cells were treated with IGF-I, FSH or IGF-I plus FSH. In some experiments cultures were treated with 8-Br-cAMP (40 
M), dibutyryl-cAMP (40 M), or forskolin (10 M). Following treatments, cell lysates were prepared and the activation state of CREB, Akt and Erk MAPK was determined by Western blot analysis using phosphorylation site-specific antibodies. IGF-I (0-100 ng/ml) had little effect on CREB phosphorylation, but rapidly increased the phosphorylation of Akt and Erks 1 and 2 in a concentration dependent manner. Maximal stimulatory effects were observed at 10-20 ng/ml IGF-I. The action of IGF-I was mimicked by treatment with high levels of insulin (5 g/ml). Treatment with FSH (0.9 IU/ml), cAMP analogues or forskolin for 20 minutes increased CREB and Erk phosphorylation, but had little effect on Akt phosphorylation. However, when cultures were treated with FSH (0.06-0.9 IU/ml) for 10 minutes prior to addition of IGF-I for 10 minutes, we observed that FSH caused a concentration dependent increase in IGF-I-induced Akt and Erk phosphorylation. Longer incubations (1-4 hrs) with FSH alone resulted in the elevation of Akt phosphorylation implicating the production of endogenous IGF-I in the action of FSH. IGF-I- and FSH-dependent Akt phosphorylation was inhibited by LY29400 (10 M), which inhibits PI 3-kinase. The present study demonstrates that immature rat Sertoli cells possess multiple protein kinase signaling cascades which are regulated by IGF-I and FSH. Furthermore, FSH amplifies IGF-I-mediated Erk MAPK and PI 3-kinase/Akt signaling in Sertoli cells. The results provide evidence for intracellular signaling mechanisms that may be required development and function of Sertoli cells. Supported by the VA, USDA (9903453) and NIEHS (ES10232).
KEY WORDS: Sertoli cells, FSH, IGF-1, Testis