CLONING AND CHARACTERIZATION OF HUMAN UROCORTIN

Urocortin, a new member of the CRF peptide family which also includes urotensin I and sauvagine, was recently cloned from the rat midbrain. The synthetic replicate of urocortin was found to bind with high affin ity to type 1 and type 2 CRF receptors and, based upon its anatomic lo calization within the brain, was proposed to be a natural ligand for t he type 2 CRF receptors. Using a genomic library, we have cloned the h uman counterpart of rat urocortin and localized it to human chromosome 2. Human and rat urocortin share 95% identity within the mature pepti de region. Synthetic human urocortin binds with high affinity to CRF r eceptor types 1, 2 alpha, and 2 beta, stimulates cAMP accumulation fro m cells stably transfected with these receptors, and acts in vitro to release ACTH from dispersed rat anterior pituitary cells. In addition, the CRF-binding protein binds human urocortin with high affinity and can prevent urocortin-stimulated ACTH secretion in vitro, The inhibito ry effect of the CRF-binding protein on human urocortin can be blocked by biologically inactive CRF fragments, such as CRF(9-33).