Bioactivity of recombinant prorelaxin from the marmoset monkey

The hormone relaxin (RLX) is generally present in the serum of humans and p rimates as a heterodimer, though some unprocessed prohormone may also be pr esent. In order to test whether this proRLX is biologically relevant for hu man or primate physiology, recombinant marmoset monkey proRLX was synthesiz ed in a baculovirus-infected cell system and tested in different bioassays. Marmoset proRLX is > 70% identical to human H2 proRLX, especially in the s o-called receptor-binding region of the B-peptide. The bioassay systems use d were (a) cAMP production by human endometrial stromal cells and (b) cAMP production by the human monocyte cell line THP-1. In both bioassay systems recombinant proRLX showed comparable EC50 values to pure porcine heterodime ric relaxin (porcine relaxin, 1.5-2.0 nM; marmoset prorelaxin 4.0-5.0 nM). Additionally, recombinant marmoset prorelaxin was shown to stimulate steroi dogenesis in primary cultures of marmoset ovarian theca cells, though with a lower apparent activity than porcine relaxin. It thus appears that precur sor processing of human or primate relaxin is not an essential prerequisite for the acquisition of bioactivity, as it is for the closely related hormo ne insulin, and that circulating prorelaxin is physiologically relevant. (C ) 2001 Elsevier Science B.V. All rights reserved.