BIOACTIVATION OF MULLERIAN-INHIBITING SUBSTANCE DURING GONADAL DEVELOPMENT BY A KEX2 SUBTILISIN-LIKE ENDOPROTEASE/

During male gonadal development Mullerian duct regression is mediated by the actions of the hormone Mullerian inhibiting substance (MIS), a member of the transforming growth factor beta superfamily. MIS is cons idered to be unique among members of this superfamily because bioactiv ation of MIS via proteolytic processing is hypothesized to occur at it s target organ, the Mullerian duct. We find instead that the majority of MIS is processed and secreted from the embryonic testes as a comple x in which the mature region remains noncovalently associated with the the prodomain. In addition, pie have identified two candidate endopro teases that are expressed in the testes and that may be capable of pro cessing MIS in vivo. These kex2/subtilisin-like enzymes, PC5 and furin , are members of the proprotein convertase family that have been impli cated in hormone bioactivation via proteolytic processing after dibasi c amino acid cleavage recognition sites. Coexpression of PC5 and MIS i n transfected mammalian cells results in efficient processing and bioa ctivation of MIS. Our results suggest that MIS is a natural substrate for PC5, thereby supporting a role for prohormone convertases in the a ctivation of transforming growth factor beta-related hormones during d evelopment.