Biochemical characterization and expression analysis of the Xenopus laevis 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 laevis. Apparent inhibition constants (K(i[app])) for different ligands were determined by competitive binding assay. Xenopus CRH-BP (xCRH-BP) exhibited a high affinity for xCRH (K(i[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.
Department of Biology, University of Michigan, Ann Arbor, MI 48109-1048, USA.
R A
RA
Valverde
A F
AF
Seasholtz
D N
DN
Cortright
R J
RJ
Denver
D000595:Amino Acid Sequence; D029845:Amphibian Proteins; D000818:Animals; D001483:Base Sequence; D001667:Binding, Competitive; D015153:Blotting, Western; D001921:Brain / Q000378:metabolism; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007814:Larva / Q000378:metabolism; D051379:Mice; D008969:Molecular Sequence Data; D009928:Organ Specificity; D036361:Peptide Hormones; D010455:Peptides / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013623:Tail / Q000378:metabolism; D054832:Urocortins; D014579:Urotensins / Q000378:metabolism; D014982:Xenopus laevis / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
D029845:Amphibian Proteins; D002352:Carrier Proteins; D036361:Peptide Hormones; D010455:Peptides; D012333:RNA, Messenger; D054832:Urocortins; D014579:Urotensins; C067133:corticotropin releasing factor-binding protein; C025727:sauvagine; D003346:Corticotropin-Releasing Hormone; C029676:urotensin I