Identification and characterization of a soluble splice variant of corticotropin-releasing hormone receptor 2ß.
R. T. EVANS; A. F. SEASHOLTZ
Society for Neuroscience. 2009.
The primary hypothalamic mediator of the mammalian neuroendocrine stress response, corticotropin-releasing hormone (CRH), signals through two G-protein coupled receptors, CRH receptor (CRH-R) 1 and 2. In rodents, there are two isoforms of CRH-R2, α and ß, that use different promoters and 5' exons, but splice to a common set of downstream exons and therefore exhibit similar pharmacologies. An mRNA splice variant of the a isoform of CRH-R2 (called soluble(s) CRH-R2α) was identified in mouse, and it encodes the ligand-binding extracellular domain but terminates with a unique C-terminal tail prior to any transmembrane domains . It was proposed that the sCRH-R2α splice variant would therefore encode a soluble decoy receptor, inhibiting CRH activity similarly to the canonical CRH binding protein. However, recent work by our laboratory demonstrated that the sCRH-R2α protein fails to traffic through the secretory pathway due to an ineffective signal peptide and is degraded by the proteasome. While this prevents sCRH-R2α from functioning as a decoy receptor, we have recently identified an analogous soluble splice variant of the ß isoform of CRH-R2, termed sCRH-R2ß. sCRH-R2ß mRNA encodes the same decoy receptor-like features as sCRH-R2α, but importantly, the sCRH-R2ß protein contains a distinct N-terminus and signal peptide sequence. In contrast to sCRH-R2α, sCRH-R2ß's signal peptide appears to mediate ER translocation, allowing the appropriate trafficking and secretion of sCRH-R2ß, as demonstrated by immunofluorescence and western blot analysis of transfected Cos-1 cells. This secretion appropriately positions sCRH-R2ß to sequester CRH and other CRH-like ligands and function as a soluble decoy receptor.