Regulation of chicken Heparin-binding EGF-like Growth Factor (HB-EGF) Expression by EGF and TGF-a in the cultured ovarian granulosa cells

Abstract

Our previous study demonstrated that both epidermal growth factor (EGF) and its receptor (EGFR) are expressed in the chicken ovary, suggesting that EGF might play a paracrine/autocrine role in controlling ovarian functions. To further examine whether other EGF family members were involved in vertebrate ovarian development, we investigated the expression of heparin-binding EGFlike Growth factor (HB-EGF), a member of EGF family, in the chicken ovary. Interestingly, like EGF, HB-EGF was also expressed in all of the developing follicles from the adult chicken ovary and its highest expression was noticed in the smallest follicles (<1mm). The co-expression of EGF and HB-EGF promotes us to elucidate their possible interactions in the chicken ovary. Using semi-quantitative RT-PCR, we noticed that mouse epidermal growth factor (mEGF) strongly increased the expression of HB-EGF in the cultured ovarian granulose cells in clear time- and dose-dependant manners. The effect of EGF (150 nM) reached the maximal level at 2 h of treatment. In consistent with this finding, recombinant human transforming growth factor α (rhTGFα) (10 nM) also strongly induced HB-EGF expression and its action was much more potent than EGF. Interestingly, phorbol-12-myristate-13-acetate (PMA, 100 nM), a protein kinase C (PKC) activator, could mimic the stimulatory effects of EGF and TGFα on HB-EGF expression. However, the stimulatory effect of EGF on HB-EGF expression was substantially reduced by an MEK inhibitor (PD98059, 50 uM), but not by a PKC inhibitor, suggesting that the regulation of HB-EGF expression by EGF is primarily mediated by MEK-MAPK signaling pathway. In summary, the expression of HB-EGF in the chicken ovary, together with the up-regulation of HB-EGF expression by EGF and TGFα, suggests that ovarian HB-EGF, like EGF, might play an important role in ovarian development and its expression level is tightly controlled by intra-ovarian EGF and other EGF family members, probably, including HB-EGF itself.