CRH-BP: the regulation and function of a phylogenetically conserved binding protein.

Corticotropin Releasing Hormone-Binding Protein (CRH-BP), a 37 kDa secreted glycoprotein, binds both CRH and urocortin with high affinity and is structurally unrelated to the CRH receptors. CRH-BP orthologues have been identified in multiple invertebrate and vertebrate species. It is strongly conserved throughout evolution, suggesting the maintenance of a structural conformation necessary for biological activity. CRH-BP is an important modulator of CRH activity; it inhibits CRH-induced ACTH secretion from pituitary corticotropes and may exert similar actions at central sites of CRH release. While the function of CRH-BP is thought to be primarily inhibitory, recent studies indicate that novel functional roles may exist in both the brain and pituitary. Regulation of CRH-BP expression by stress and metabolic factors are consistent with in vivo models of altered CRH-BP expression. Positive regulation of pituitary CRH-BP by reproductive hormones suggests that additional interactions between the stress and reproductive axes may exist. While recent research has focused on the evolutionary conservation, expanded sites of expression, regulation and in vivo function of CRH-BP, a more complete understanding of the central and peripheral functions of CRH-BP and its mechanisms of action will help elucidate its potential role in the etiology or treatment of disorders of CRH dysregulation.