H2 relaxin is a biased ligand relative to H3 relaxin at the relaxin family peptide receptor 3 (RXFP3).
Relaxin family peptide 3 receptors (RXFP3) are activated by H3-relaxin to inhibit forskolin-stimulated cAMP accumulation and stimulate extracellular signal-regulated kinase (ERK) 1/2 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, ERK1/2 activation and nuclear factor (NF)-kappaB reporter gene activation in cells stimulated with H3 relaxin, with weaker activity observed for H2 relaxin, porcine relaxin, or insulin-like peptide (INSL) 3 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. (125)I-INSL5 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 (125)I-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.
Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Parkville, Victoria, Australia.
Emma T
ET
van der Westhuizen
Arthur
A
Christopoulos
Patrick M
PM
Sexton
John D
JD
Wade
Roger J
RJ
Summers
D000469:Alkaline Phosphatase / Q000235:genetics / Q000378:metabolism; D000818:Animals; D016466:CHO Cells; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D008024:Ligands; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D010920:Placenta / Q000201:enzymology; D011247:Pregnancy; D043562:Receptors, G-Protein-Coupled / Q000235:genetics* / Q000378:metabolism; D018000:Receptors, Peptide / Q000235:genetics; D012065:Relaxin / Q000378:metabolism* / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology
D008024:Ligands; C095068:RLN2 protein, human; C417543:RXFP1 protein, human; C472867:RXFP2 protein, human; C410092:RXFP3 protein, human; C480239:RXFP4 protein, human; D043562:Receptors, G-Protein-Coupled; D018000:Receptors, Peptide; D005576:Colforsin; D012065:Relaxin; D000242:Cyclic AMP; D048049:Extracellular Signal-Regulated MAP Kinases; D048052:Mitogen-Activated Protein Kinase 3; D000469:Alkaline Phosphatase