The predicted structure of the autosomal recessive polycystic kidney disease protein, fibrocystin, suggests that it may function as a receptor, but its function remains unknown. To understand its function, we searched for proteins that interact with the intracellular C-terminus of fibrocystin using the yeast two-hybrid system. From the screening, we found calcium modulating cyclophilin ligand (CAML), a protein involved in Ca2+ signaling. Immunofluorescent analysis showed that both proteins are co-localized in the apical membrane, primary cilia, and the basal body of cells derived from the distal nephron Epitope-tagged expression constructs of both proteins were co-immunoprecipitated from COS7 cells. The intracellular C-terminus of fibrocystin interacts with CANIL, a protein with an intracellular distribution that is similar to that of PKD2. Fibrocystin may participate in regulation of intracellular Ca2+ in the distal nephron in a manner similar to PKD1 and PKD2 that are involved in autosomal dominant polycystic kidney disease. (c) 2005 Elsevier Inc. All rights reserved.