Endocrine Abstracts

Inhibins are members of the Transforming Growth Factor-β (TGF-β) superfamily of pleiotrophic growth and differentiation factors that includes activins and bone morphogenetic proteins (BMPs). Inhibins were characterized originally as providing negative endocrine feedback from the gonads to the pituitary gland to regulate Follicle Stimulating Hormone (FSH) secretion. More recently, inhibin has been shown to antagonise activin and BMP action in engineered cell systems through binding to betaglycan, thereby providing a hypothesis for a local autocrine/paracrine role of inhibin in the tissues that produce them. Our focus has been to test this hypothesis of inhibin action in several endocrine cell systems.

Inhibin antagonizes a number of actions of activin: on FSH production by mouse pituitary LβT2 cells, GnRH receptor promoter activity in mouse Leydig-like TM3 cells and LβT2 cells, 17α-hydroxylase activity in mouse adrenal cells (AC), and production of latent matrix metalloproteinases in human endometrial cells. However, unlike activin, reversal of the BMP inhibitory action on 17α-hydroxylase in AC cells by inhibin was reduced by higher concentrations of BMP agonists. This can be attributed in part, to the suppression of betaglycan expression by BMPs, with consequent reduction in inhibin binding to betaglycan. This data confirms the central role of betaglycan in inhibin action in endocrine cells, and shows that betaglycan is dynamically regulated in part by BMPs. We conclude that inhibins integrate the multiple inputs from members of the TGF-β superfamily through a hierarchy of interactions involving the regulation and action of betaglycan.

Supported by the NH&MRC of Australia (RegKeys #241000 & #198705).