TY - JOUR T1 - H2 RELAXIN IS A BIASED LIGAND RELATIVE TO H3 RELAXIN AT THE RELAXIN FAMILY PEPTIDE RECEPTOR 3 (RXFP3) JF - Molecular Pharmacology JO - Mol Pharmacol DO - 10.1124/mol.109.061432 SP - mol.109.061432 AU - Emma T van der Westhuizen AU - Arthur Christopoulos AU - Patrick M. Sexton AU - John D Wade AU - Roger J. Summers Y1 - 2010/01/01 UR - http://molpharm.aspetjournals.org/content/early/2010/02/12/mol.109.061432.abstract N2 - Relaxin family peptide 3 receptors (RXFP3) are activated by H3-relaxin to inhibit forskolin-stimulated cAMP accumulation and stimulate ERK1/2 phosphorylation. In this study we sought to identify novel signaling pathways coupled to RXFP3 and to investigate whether other members of the relaxin peptide family activated these pathways. Two patterns of signaling were observed in RXFP3-expressing Chinese hamster ovary (CHO)-K1 and human embryonic kidney (HEK)-293 cells (CHO-RXFP3 and HEK-RXFP3) and murine septal neuron, SN56, cell lines. 1. Strong inhibition of forskolin-stimulated cAMP accumulation, extracellular signal-regulated kinase (ERK) 1/2 activation and nuclear factor (NF)-κB reporter gene activation in cells stimulated with H3 relaxin with weaker activity observed for H2 relaxin, porcine relaxin or INSL3 and; 2. Strong stimulation of activator protein (AP)-1 reporter genes by H2 relaxin, with weaker activation observed with H3 or porcine relaxin. Two distinct ligand binding sites were identified on RXFP3-expressing cells using two different radioligands. 125I-insulin-like peptide (INSL) 5 A-chain/relaxin-3 B-chain chimera bound with high affinity to the RXFP3-expressing cells with competition by H3 relaxin or a H3 relaxin B-chain dimeric peptide, consistent with previous reports. Binding studies with 125I-H2 relaxin revealed a distinct binding site with potent competition observed with H2 relaxin, H3 relaxin or INSL3 and weaker competition with porcine relaxin. Thus H3 relaxin potently activates all signaling pathways coupled to RXFP3, whereas H2 relaxin is an AP-1 biased ligand relative to H3 relaxin.The American Society for Pharmacology and Experimental Therapeutics ER -