Co-activator p120 is increased by gonadotropins in the rat ovary and enhances progesterone receptor activity

A full-length cDNA encoding rat p120 was cloned, and expression of the gene in the ovary was examined by Northern blotting. Tissue localization of p120 was examined by in situ hybridization. Cellular functions of p120 were studied by co-transfection of rat p120 gene together with estrogen receptor (ER)-alpha, ER-beta, androgen receptor (AR), or progesterone receptor (PR) genes.A full-length cDNA encoding rat p120 was characterized as a protein with 957 amino acid residues. Rat p120 was expressed ubiquitously, but strongly in the ovary and the testis. Expression of p120 mRNA was also induced in vivo by PMSG or PMSG/hCG treatment. Strong expression of p120 mRNA was observed in the granulosa cells of pre-ovulatory large antral follicles. Progesterone receptor was co-localized with p120 in the large antral follicles. Co-transfection experiments revealed that rat p120 activated AR, ER-alpha, ER-beta, and PR in the presence of their respective ligands.These observations suggest that rat p120 is strongly induced in the ovarian granulosa cells, and may work together with PR in the granulosa cells of ovulatory follicles to promote the ovulation process.Follicular growth is primarily controlled by pituitary gonadotropins LH and FSH in assistance with various intraovarian factors that also play essential and significant roles in development. FSH stimulates proliferation and differentiation of granulosa cells of small follicles in the ovary, and promotes their development to pre-ovulatory follicles [1-3]. During the differentiation of the granulosa cells, steroid hormone synthesizing enzymes are induced in the cells [4]. Estrogen and progesterone produced in the ovary work primarily on the uterus or the mammary gland, but the steroids also regulate pituitary gonadotropin secretion through positive and negative feedback systems of hypothalamus-pituitary-ganadal axis [5]. These steroid hormones also work on the ovary in either a paracrine or an autocrine fashion [6]. Progesterone