MOLECULAR AND BIOCHEMICAL-CHARACTERIZATION OF THE MOUSE-BRAIN CORTICOTROPIN-RELEASING HORMONE-BINDING PROTEIN

A 37 kDA corticotropin-releasing hormone-binding protein (CRH-BP), distinct from the CRH receptor, is expressed in rat anterior pituitary corticotrophs and many regions of the brain, suggesting that CRH-BP may modulate the biological activity of CRH. In these studies a mouse brain CRH-BP (mCRH-BP) cDNA has been isolated and characterized. The 1666 nucleotide mCRH-BP cDNA is expressed in brain and pituitary and encodes a 322 amino acid protein that is highly homologous to human and rat CRH-BPs. Recombinant mCRH-BP, expressed in cultured mammalian cells, binds human CRH (K-d(app)= 0.56 nM and K-i(app)= 0.37 nM) and the alpha-helical (9-41) CRH antagonist (Ki(app)= 0.28 nM) with high affinity, but exhibits much weaker affinity for ovine CRH (K-i(app)= 206 nM). Recombinant mCRH-BP also blocks CRH-induced adrenocorticotropin release from AYT-20 cells. Additional biochemical characterization of the binding activity of mCRH-BP indicates that hRH-BP and CRH receptor utilize different molecular interactions to bind CRH.