Abstract
Stress responses are highly nuanced and variable, but how this diversity is achieved by modulating receptor function is largely unknown. Corticotropin-releasing factor receptors (CRFRs), class B G protein-coupled receptors, are pivotal in mediating stress responses. Here we show that the two known CRFRs interact to form heteromeric complexes in HEK293 cells coexpressing both CRFRs and in vivo in mouse pancreas. Coimmunoprecipitation and mass spectrometry confirmed the presence of both CRF(1)R and CRF(2)βR, along with actin in these heteromeric complexes. Inhibition of actin filament polymerization prevented the transport of CRF(2)βR to the cell surface but had no effect on CRF(1)R. Transport of CRF(1)R when coexpressed with CRF(2β)R became actin dependent. Simultaneous stimulation of cells coexpressing CRF(1)R+CRF(2)βR with their respective high-affinity agonists, CRF+urocortin2, resulted in approximately twofold increases in peak Ca(2+) responses, whereas stimulation with urocortin1 that binds both receptors with 10-fold higher affinity did not. The ability of CRFRs to form heteromeric complexes in association with regulatory proteins is one mechanism to achieve diverse and nuanced function.