Molecular and Cellular Endocrinology 173 (2001) 29–40 Biochemical characterization and expression analysis of the Xenopus lae6is corticotropin-releasing hormone binding protein

Corticotropin-releasing hormone (CRH) plays a key role in the regulation of responses to stress. The presence of a high affinity binding protein for CRH (CRH-BP) has been reported in mammals. We have characterized the biochemical properties and expression of CRH-BP in the South African clawed frog, Xenopus lae6is. Apparent inhibition constants (Ki[app]) for different ligands were determined by competitive binding assay. Xenopus CRH-BP (xCRH-BP) exhibited a high affinity for xCRH (Ki[app]1.08 nM) and sauvagine (1.36 nM). Similar to rodent and human CRH-BPs, the frog protein binds urotensin I and urocortin with high affinity, and ovine CRH with low affinity. RT-PCR analysis showed that xCRH-BP is expressed in brain, pituitary, liver, tail, and intestine. Brain xCRH-BP mRNA is expressed at a relatively constant level throughout metamorphosis and increases slightly in the metamorphic frog. By contrast, the gene is strongly upregulated in the tail at metamorphic climax. Thus, regulation of xCRH-BP gene expression is tissue specific. Because xCRH-BP binds CRH-like peptides with high affinity the protein may regulated, the bioavailability of CRH in amphibia as it does in mammals. © 2001 Elsevier Science Ireland Ltd. All rights reserved