Protein 4.1N is required for translocation of inositol 1,4,5-trisphosphate receptor type 1 to the basolateral membrane domain in polarized Madin-Darby canine kidney cells

Protein 4.1N was identified as a binding molecule for the C-terminal cytoplasmic tail of inositol 1,4,5-trisphosphate receptor type 1 (IP₃R1) using a yeast two-hybrid system. 4.1N and IP₃R1 associate in both subconfluent and confluent Madin-Darby canine kidney (MDCK) cells, a well studied tight polarized epithelial cell line. In subconfluent MDCK cells, 4.1N is distributed in the cytoplasm and the nucleus; IP₃R1 is localized in the cytoplasm. In confluent MDCK cells, both 4.1N and IP₃R1 are predominantly translocated to the basolateral membrane domain, whereas 4.1R, the prototypical homologue of 4.1N, is localized at the tight junctions (Mattagajasingh, S. N., Huang, S. C., Hartenstein, J. S., and Benz, E. J., Jr. (2000) J. Biol. Chem. 275, 30573-30585), and other endoplasmic reticulum marker proteins are still present in the cytoplasm. Moreover, the 4.1N-binding region of IP₃R1 is necessary and sufficient for the localization of IP₃R1 at the basolateral membrane domain. A fragment of the IP₃R1-binding region of 4.1N blocks the localization of co-expressed IP₃R1 at the basolateral membrane domain. These data indicate that 4.1N is required for IP₃R1 translocation to the basolateral membrane domain in polarized MDCK cells.