The transfection-induced overexpression of IGF-binding protein-4 affects the secretory activity of porcine ovarian granulosa cells and their responseto hormones and IGF-I

The aim of our studies was to examine whether IGF-binding protein (IGFBP)-4 is involved in the control of the secretion of various ovarian substances and also the mediation of the effects of several hormones and growth factor s on this secretion. For this purpose, we carried out the transfection of p orcine granulosa cells with a cDNA sense construct, increasing IGFBP-4 synt hesis. We then compared the release of IGFBP-3, progesterone, oxytocin and IGF-1 by control and transfected cells cultured with and without porcine LH (100 ng/ml), porcine GH (100 ng/ml), IGF-I (10 ng/ml), oxytocin (10 ng/ml) and estradiol-17 beta (100 ng/ml). The concentration of IGFBP-4 produced w as assessed using ligand blotting, and the release of progesterone, oxytoci n, IGF-I and IGFBP-3 was evaluated using RIA/IRMA techniques. It was observed that GH, IGF-I, estradiol, LH and oxytocin alter the proges terone, oxytocin, IGF-I and IGFBP-3 release by porcine ovarian granulosa ce lls. Transfection of these cells with an IBFBP-4 cDNA expression construct significantly increased the IGFBP-4 accumulation in cell-conditioned medium . Furthermore, this transfection significantly reduced progesterone, oxytoc in and IGFBP-3 release, and increased IGF-I output in cells cultured in the absence or presence of GH, IGF-I, estradiol and LII. The addition of oxyto cin, but not of other tested substances, fully or partially prevented the e ffects of IGFBP-4 overexpression on IGFBP-3, IGF-I, but not on progesterone release. The present results suggested that IGFBP-4, as well as GH, IGF-I, estradiol , LH and oxytocin, is a potent regulator of porcine ovarian steroid (proges terone), nonapeptide hormone (oxytocin), growth factor (IGF-I) and growth f actor-binding protein (IGFBP-3) release. IGFBP-4 is an inhibitor of basal p rogesterone, oxytocin and IGFBP-3 release and a stimulator of IGF-I output by porcine ovarian cells. The action of IGFBP-4 on the ovary can be mediate d by (1) inhibition of oxytocin release, (2) suppression of receptor/postre ceptor events induced bq other hormones and IGF-I and (3) stimulation of IG F-I release.