Progesterone together with estradiol promotes luteinizing hormone β-subunit mRNA stability in rat pituitary cells cultured in vitro

Abstract

The present study examined the role of ovarian steroids, estradiol and/or progesterone in the regulation of luteinizing hormone beta-subunit (LH-beta) mRNA levels and LH release in the rat anterior pituitary cells cultured in vitro. When estradiol (10 nmol/l) and/or progesterone (100 nmol/l) were added to the cultures, neither estradiol or progesterone nor both together altered the basal LH-beta mRNA levels or LH release. Continuous exposure to gonadotropin-releasing hormone (GnRH, 0.2 nmol/l) for 24 h markedly induced LH-beta mRNA accumulation, and in this experimental condition, progesterone alone and progesterone + estradiol further augmented GnRH-induced LH-beta mRNA levels and LH release. Then we explored further the possibility that ovarian steroids are involved in modulating LH-beta mRNA stability in cultured rat pituitary cells where transcription was inhibited by actinomycin D. Anterior pituitary cells were preincubated with GnRH (0.2 nmol/l) for 16 h and, after removing GnRH from culture medium, the cells were incubated further in the presence of actinomycin D (5 mumol/l) for 24 h. The LH-beta mRNA levels gradually declined to about 30% of the control values (zero time point after GnRH removal) in a time-dependent manner. During this period, either progesterone alone or progesterone + estradiol clearly blocked the degradation of LH-beta mRNA species. These results indicate that ovarian steroids promote LH-beta mRNA stability, thereby contributing to the maintenance of GnRH-stimulated LH-beta mRNA levels.

Regulation of gonadotropin subunit gene transcription

“…Similarly, while E 2 blocked bovine LH CAT promoter activity in OVX transgenic mice, the combination of E 2 and P 4 was no more effective than E 2 alone (McNeilly et al 1996). In vitro, neither P 4 nor E 2 + P 4 altered LH mRNA levels in female rat pituitary cells, but P 4 alone or in combination with E 2 augmented the GnRH-induced increase in LH mRNA, perhaps by blocking LH mRNA degradation (Park et al 1996). Glucocorticoids do not appear to regulate LH mRNA; B had no effect on LH mRNA levels in cultured rat pituitary cells (Kilen et al 1996) and dexamethasone did not alter the activity of the rat LH promoter (Shupnik & Rosenzweig 1991).…”

Co-localisation of gonadotrophins and granins in gonadotrophs at different stages of the oestrous cycle in sheep

“…Moreover, LH and -GSU mRNA polyadenylation increased after pulsatile GnRH administration in rats (Weiss et al 1992), and decreased after progesterone treatment in ovine pituitary cultures (Wu & Miller 1991). However, progesterone alone or in combination with oestradiol further enhanced GnRH-induced LH mRNA stability in cultured rat pituitary cells (Park et al 1996). Additionally, administration of activin to rat anterior pituitary cell cultures treated with actinomycin D increased the half-life of FSH mRNA from 3·1 to 6·5 h (Carroll et al 1991).…”

“…Interestingly, polyadenylation of gonadotrophin subunit mRNAs was induced in response to GnRH stimulation in rats (Weiss et al 1992, Clayton 1993, Chedrese et al 1994, while progesterone (but not oestradiol) induced shortening of -GSU and LH mRNA 3 -poly(A) tail in ovine pituitary primary cell culture (Wu & Miller 1991). GnRH-induced stabilisation of LH mRNA was improved by administering GnRH in conjunction with gonadal-derived steroids such as progesterone alone, or in combination with oestrogen in cultured rat pituitary cells (Park et al 1996). Stabilisation of FSH mRNA was further improved by addition of testosterone in conjunction with GnRH in castrate male rats (Paul et al 1990) or activin A in male rat pituitary primary cell culture (Carroll et al 1991).…”

Hormonal regulation of mRNA stability and RNA-protein interactions in the pituitary

“…For example, the mRNA stability of the -subunit was increased six-to sevenfold in the presence of gonadotropin releasing hormone (GnRH) in T 3 pituitary cells (Chedrese et al 1994). Similarly, GnRH stabilized LH mRNA, and this stabilization was further augmented by progesterone, or a combination of estrogen and progesterone (Park et al 1995). Interestingly, FSH subunit mRNA, but not -subunit or LH mRNA, was stabilized by testosterone in male rat gonadotropes (Paul et al 1990).…”

“…This sequence does not  2. Summary of pituitary-derived genes that are known to be regulated by hormones et al (1990) mRNA stabilized by GnRH; GnRH-induced mRNA stability augmented with progesterone or progesterone+estrogen Park et al (1995) LH/FSH/TSH -subunit mRNA stabilized six-to sevenfold by GnRH Chedrese et al (1994) Dex, Dexamethasone.…”