Membrane topology and immunolocalization of CHIF in kidney and intestine

Corticosteroid hormone-induced factor (CHIF) is an aldosterone-induced gene , the function of which is yet unknown. It is specifically expressed in kid ney collecting duct (CD) and distal colon and is upregulated by either Nadeprivation or K+ loading. Hence, it may play a role in epithelial electrol yte transport. Previous studies have characterized regulation and tissue di stribution of CHIF mRNA but provided no information on the protein itself. The present paper addresses this issue by using Western blotting, immunoche mistry, and in vitro translation. CHIF is an similar to8-kDa membranal prot ein, and protease digestion experiments suggest that its COOH tail faces th e cell interior. The protein is abundant in distal colon, kidney medulla, a nd papilla but cannot be detected in a variety of other tissues. Confocal i mmunocytochemistry demonstrates that CHIF is present in the basolateral mem brane of CD principal cells and distal colon surface cells, with occasional intracellular staining. Dexamethasone and low Na+ intake increase the abun dance of CHIF. Unlike previous Northern data, induction of CHIF protein by low-Na+ intake was apparent not only in the distal colon but also in the ki dney.