AP‐1 is activated by relaxin family peptides in cells expressing the relaxin family peptide receptor 3 (RXFP3)

Abstract

Relaxin‐3 is a neuropeptide involved in appetite regulation and stress behaviour in rats. RXFP3 is the cognate receptor for relaxin‐3 that is coupled to cAMP inhibition and ERK1/2 activation in CHO‐K1 and HEK293 cell lines recombinantly expressing the receptor. Competition for [125I]‐INSL5/H3 relaxin chimera binding is observed with H3 relaxin and the B‐chain of H3 relaxin, but not with any other relaxin family peptides. We identified that H3 relaxin but also H2 relaxin and porcine relaxin activate transcription from AP‐1 elements in CHO and HEK cells transiently expressing human RXFP3 receptors, measured using a reporter gene. H2 relaxin was more potent at activating transcription than either H3 relaxin or porcine relaxin. Experiments with inhibitors of p38 MAPK (RWJ67657, 10 μM), MEK1/2 (PD98059, 20μM) and JNK (SP600125, 10μ M) showed that AP‐1 activation involved p38 MAPK in CHO‐K1 cells stimulated with H3 relaxin, H2 relaxin or porcine relaxin. In HEK293 cells, AP‐1 activation in response to H3 relaxin or porcine relaxin involved p38 MAPK, MEK1/2 and JNK, but, when stimulated with H2 relaxin, it involved only a MEK1/2 pathway. We propose that different relaxin family peptides interact at different sites on RXFP3, to activate distinct signalling pathways.This research was supported by National Health and Medical Research Council Project Grants 436713 and 454375