Abstract
Inositol-(1,4,5)-triphosphate receptors (InsP(3)Rs) are ligand-gated Ca(2+) channels that control Ca(2+) release from intracellular stores and play a central role in a wide range of cellular responses. In most epithelial cells, InsP(3)Rs are not uniformly distributed within the endoplasmic reticulum (ER) membrane, with the consequence that agonist stimulation results in compartmentalized Ca(2+) signals. Despite these observations, little is known about the mechanisms that regulate the intracellular localization of InsP(3)Rs. Here, we report that exogenously expressed InsP(3)R1-GFP and endogenous InsP(3)R3 interact with the K-Ras-induced actin-binding protein (KRAP) in both differentiated and undifferentiated Madin-Darby canine kidney (MDCK) cells. KRAP mediates InsP(3)R clustering in confluent MDCK cells and functions as an adapter, linking InsP(3)Rs to vimentin intermediate filaments. Upon epithelial differentiation, KRAP and vimentin are both required for InsP(3)R accumulation at the periphery of MDCK cells. Finally, KRAP associates with vimentin in chicken B lymphocytes and with keratins in a breast cancer cell line devoid of vimentin. Collectively, our data suggest that intermediate filaments in conjunction with KRAP may govern the localization of InsP(3)Rs in a large number of cell types (including epithelial cells) and in various physiological or pathological contexts.