KRAS-induced actin-interacting protein is required for the proper localization of inositol 1,4,5-trisphosphate receptor in the epithelial cells

Abstract

Three inositol 1,4,5-trisphosphate receptor (IP 3R) subtypes are differentially expressed among tissues and function as the Ca 2+ release channel on specialized endoplasmic reticulum (ER) membranes. The proper subcellular localization of IP 3R is crucial for its proper function, but this molecular mechanism is unclear. KRAS-induced actin-interacting protein (KRAP) was originally identified as a cancer-related molecule, and is involved in the regulation of whole-body energy homeostasis and pancreatic exocrine system. We herein identified IP 3R as an associated molecule with KRAP in vivo, and the association was validated by the co-immunoprecipitation and confocal immunostaining studies in mouse tissues including liver and pancreas. The association of KRAP with IP 3R was also observed in the human epithelial cell lines including HCT116, HeLa and HEK293 cells. Intriguingly, KRAP interacts with distinct subtypes of IP 3R in a tissue-dependent manner, i.e. IP 3R1 and IP 3R2 in the liver and IP 3R2 and IP 3R3 in the pancreas. The NH 2-terminal amino acid residues 1–610 of IP 3R are critical for the association with KRAP and KRAP–IP 3R complex resides in a specialized ER but not a typical reticular ER. Furthermore, the localization of particular IP 3R subtypes in tissues from KRAP-deficient mice is obviously disturbed, i.e. IP 3R1 and IP 3R2 in the liver and IP 3R2 and IP 3R3 in the pancreas. These findings demonstrate that KRAP physically associates with IP 3R and regulates the proper localization of IP 3R in the epithelial cells in vivo and cultured cells, and might shed light on the Ca 2+ signaling underlying physiological cellular programs, cancer development and metabolism-related diseases.