Relaxin activates peroxisome proliferator-activated receptor γ (PPARγ) through a pathway involving PPARγ coactivator 1α (PGC1α).
Relaxin activation of its receptor RXFP1 triggers multiple signaling pathways. Previously, we have shown that relaxin activates PPARγ transcriptional activity in a ligand-independent manner, but the mechanism for this effect was unknown. In this study, we examined the signaling pathways of downstream of RXFP1 leading to PPARγ activation. Using cells stably expressing RXFP1, we found that relaxin regulation of PPARγ activity requires accumulation of cAMP and subsequent activation of cAMP-dependent protein kinase (PKA). The activated PKA subsequently phosphorylated cAMP response element-binding protein (CREB) at Ser-133 to activate it directly, as well as indirectly through mitogen activated protein kinase p38 MAPK. Activated CREB was required for relaxin stimulation of PPARγ activity, while there was no evidence for a role of the nitric oxide or ERK MAPK pathways. Relaxin increased the mRNA and protein levels of the coactivator protein PGC1α, and this effect was dependent on PKA, and was completely abrogated by a dominant-negative form of CREB. This mechanism was confirmed in a hepatic stellate cell line stably that endogenously expresses RXFP1. Reduction of PGC1α levels using siRNA diminished the regulation of PPARγ by relaxin. These results suggest that relaxin activates the cAMP/PKA and p38 MAPK pathways to phosphorylate CREB, resulting in increased PGC1α levels. This provides a mechanism for the ligand-independent activation of PPARγ in response to relaxin.
From the Medical Research Service, The Department of Veterans Affairs, Nebraska-Western Iowa Health Care System, Omaha, Nebraska 68105 and the Departments of Biochemistry & Molecular Biology, Internal Medicine and Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska 68198.
Sudhir
S
Singh
From the Medical Research Service, The Department of Veterans Affairs, Nebraska-Western Iowa Health Care System, Omaha, Nebraska 68105 and the Departments of Biochemistry & Molecular Biology, Internal Medicine and Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska 68198.
Ronda L
RL
Simpson
From the Medical Research Service, The Department of Veterans Affairs, Nebraska-Western Iowa Health Care System, Omaha, Nebraska 68105 and the Departments of Biochemistry & Molecular Biology, Internal Medicine and Pharmacology & Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska 68198 rgbennet@unmc.edu.
Robert G
RG
Bennett
D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D006801:Humans; D008024:Ligands; D020935:MAP Kinase Signaling System / Q000235:genetics; D047495:PPAR gamma / Q000096:biosynthesis* / Q000235:genetics; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D010766:Phosphorylation; D043562:Receptors, G-Protein-Coupled / Q000096:biosynthesis* / Q000235:genetics; D018000:Receptors, Peptide / Q000096:biosynthesis* / Q000235:genetics; D012065:Relaxin / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000235:genetics*; D014157:Transcription Factors / Q000096:biosynthesis* / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics / Q000378:metabolism
C115163:CREB1 protein, human; D017362:Cyclic AMP Response Element-Binding Protein; D008024:Ligands; D047495:PPAR gamma; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; C417543:RXFP1 protein, human; D043562:Receptors, G-Protein-Coupled; D018000:Receptors, Peptide; D014157:Transcription Factors; D012065:Relaxin; D017868:Cyclic AMP-Dependent Protein Kinases; D048051:p38 Mitogen-Activated Protein Kinases
Peroxisome Proliferator-activated Receptor γ Coactivator 1-α (PGC-1a)(PPARGC1A); Peroxisome Proliferator-activated receptor (PPAR); Protein Kinase A (PKA); Relaxin; Relaxin Family Peptide Receptor 1 (RXFP1); cAMP Response Element-binding Protein (CREB); p38 MAPK