KRAS-induced actin-interacting protein regulates inositol 1,4,5-trisphosphate-receptor-mediated calcium release

KRAS-induced actin-interacting protein (KRAP) was originally characterized as a filamentous- actin-interacting protein. We have recently found that KRAP is an associated molecule with inositol 1,4,5-trisphosphate (IP3) receptor (IP3R) and is responsible for the proper subcellular localization of IP3R. Since it remains unknown whether KRAP regulates the IP3R-mediated Ca2+ signaling, we herein examined the effects of KRAP on the IP3R-mediated Ca2+ release by Ca2+ imagings in the cultured HEK293 or MCF7 cells. Reduction of KRAP protein by KRAP-specific siRNA diminishes ATP-induced Ca2+ release and the ATP-induced Ca2+ release is completely quenched by the pretreatment with the IP3R inhibitor but not with the ryanodine receptor inhibitor, indicating that KRAP regulates IP3R-mediated Ca2+ release. To further reveal mechanistic insights into the regulation of IP3R-mediated Ca2+ release by KRAP, we examined the effects of the KRAP-knockdown on the releasable Ca2+ content of intracellular Ca2+ stores. Consequently, reduction of KRAP does not affect the amount of ionophore- or Ca2+-ATPase inhibitor-induced Ca2+ release in the HEK293 cells, indicating that releasable Ca2+ content of intracellular Ca2+ stores is not altered by KRAP. Thus, KRAP is involved in the proper regulation of IP3R-mediated Ca2+ release.

► Reduction of KRAP inhibits IP3R-mediated Ca2+ release in the cultured cells.
► KRAP does not affect the releasable Ca2+ content of intracellular Ca2+ stores.
► KRAP does not affect the IP3-binding itself to the receptor in vitro.
► KRAP is involved in the proper IP3-mediated Ca2+ signaling.