Progesterone Inhibits Basal and Gonadotropin-Releasing Hormone Induction of Luteinizing Hormone β-Subunit Gene Expression

Abstract

LH and FSH play critical roles in mammalian reproduction by mediating steroidogenesis and gametogenesis in the gonad. Gonadal steroid hormone feedback to the hypothalamus and pituitary influences production of the gonadotropins. We previously demonstrated that progesterone differentially regulates the expression of the LH and FSH β-subunits at the level of the gonadotrope: FSHβ transcription is induced, whereas LHβ is repressed. In this study, we investigated the mechanism of progesterone repression of LHβ gene expression using immortalized gonadotrope-derived LβT2 cells. The progesterone suppression of both basal and GnRH-induced LHβ gene expression occurs in a hormone- and receptor-dependent manner. Chromatin immunoprecipitation demonstrates that the hormone-bound progesterone receptor (PR) is recruited to the endogenous mouse LHβ promoter. In addition, suppression requires both the amino-terminal and DNA-binding regions of PR. Furthermore, progesterone suppression does not require direct PR binding to the promoter, and, thus, PR is likely recruited to the promoter via indirect binding through other transcription factors. These data demonstrate that the molecular mechanism for progesterone action on the LHβ promoter is distinct from FSHβ, which involves direct PR binding to the promoter to produce activation. It also differs from androgen repression of LHβ gene expression in that, rather than Sp1 or steroidogenic factor-1 elements, it requires elements within −300/−250 and −200/−150 that also contribute to basal expression of the LHβ promoter. Altogether, our data indicate that progesterone feedback at the level of the pituitary gonadotrope is likely to play a key role in differential production of the gonadotropin genes.