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Submitted on February 9, 2007
Accepted on September 14, 2007
Department of Applied Animal Science, Graduate School of Biosphere Science, Hiroshima University, 1–4-4 Kagamiyama Higashi-Hiroshima, 739-8528, Japan; Department of Molecular and Cellular Biology, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030
* To whom correspondence should be addressed. E-mail: mashimad{at}hiroshima-u.ac.jp.
The epidermal growth factor (EGF)-like growth factors, amphiregulin (AREG) and epiregulin (EREG), are expressed in murine cumulus oocyte complexes (COCs) where they impact the function of cumulus cells and oocyte maturation during LH-mediated ovulation. Since TACE/ADAM17 is essential for ectodomain shedding of AREG and EREG from surface of other cell types, the expression and function of TACE/ADAM17 was analyzed in a porcine COC culture system in which FSH and LH mediated expansion and oocyte meiotic maturation have been well-characterized and shown to occur between 20–40h. In this model, Areg, Ereg and Tace/Adam17 mRNAs increased significantly with maximum levels observed between 5–20 h of culture with FSH+LH. TACE/ADAM17 protein and protease activity were up-regulated markedly at 10 h and maintained to 40h. Treatment of COCs with the TACE/ADAM17 selective inhibitor, TAPI-2 significantly suppressed in a time-dependent manner downstream targets of EGFR activation such as ERK1/2 phosphorylation, Ptgs2, Has2 and Tnfaip6 mRNA expression, hormone-induced COC expansion and meiotic maturation of the oocytes. Addition of EGF to COCs cultured in the presence of FSH/LH reversed the inhibitory effects of TAPI-2 on these ovulation related processes. Gonadotropin-induced phosphorylation of ERK1/2 was also inhibited in rat granulosa cells treated with TAPI-2 or following transfection with Tace/Adam17 siRNA. Induced expression of Tnfaip6 mRNA was also reduced by Tace/Adam17 siRNA. Thus, TACE/ADAM17 is induced and the activity is involved in porcine COC expansion as well as oocyte meiotic maturation through the activation of EGFR in cumulus cells.
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