The Synthesis and Secretion of Inhibins

摘要

Inhibin A and B, dimeric glycoproteins comprising an alpha- and beta_(A/B)-subunit, negatively regulate follicle stimulating hormone (FSH) synthesis by the pituitary. The expression of alpha- and p-subunits within Sertoli cells of the testis and granulosa cells of the ovary is controlled by a range of transcription factors, including CREB, SP-1, Smads, and GATA factors. The inhibin alpha- and p-subunits are synthesized as precursor molecules consisting of an N-terminal propeptide and a C-terminal mature domain. Recently, we showed that hydrophobic residues within the propeptides of the a- and (3-subunits interact noncovalently with their mature domains, maintaining the molecules in a conformation competent for dimerization. Dimeric precursors are cleaved by proprotein conver-tases and mature inhibins are secreted from the cell noncovalently associated with their propeptides. Propeptides may increase the half-life of inhibin A and B in circulation, but they are readily displaced in the presence of the high-affinity receptors, betaglycan, and ActRII.