An INF2-dependent actin-mediated step in Inositol 1,4,5-trisphosphate receptor cluster formation and activity

Intracellular calcium signaling plays a vital role in regulating various cellular processes including gene regulation, motility, metabolism and cell death. Inositol 1,4,5-trisphosphate receptors (IP3R) on the Endoplasmic Reticulum (ER) are a major cation channel that regulates stimulus-induced calcium release from the ER. While several molecular players regulate activity of IP3R, its regulation by actin filaments were uncharacterized. Here we show that actin filaments polymerized by a specific actin nucleator INF2 facilitates agonist-induced IP3R activity. Our results demonstrate that INF2-mediated actin filaments regulate formation and/or stability of IP3R clusters on the ER that have been previously shown to be hotspots of ER calcium release. Using cell-biological and biochemical techniques we further show that INF2 physically interacts with IP3R isoforms, often at IP3R clusters. While INF2-IP3R interaction is independent of INF2-activity, the ability of INF2 to mediate IP3R clusters is dependent on its actin polymerization activity. Finally, we demonstrate that in addition to its calcium mobilization activity, INF2 on ER specifically regulates IP3R cluster positioning to mediate ER-mitochondrial contacts and facilitate ER to mitochondrial calcium transfer. Overall, these results reveal an actin-dependent step in regulation of IP3R activity both in terms of ER calcium release and modulation of ER-mitochondrial contacts. HighlightsO_LIINF2-mediated actin filaments potentiate agonist-induced IP3R-mediated ER calcium release without affecting the ER calcium stores per se. C_LIO_LIER-localization of INF2 is dispensable for its role on IP3R activity. Moreover INF2-mediated actin filaments affect the activity of all IP3R isoforms. C_LIO_LIINF2 interacts with IP3R in an activity and actin filament independent manner through its C-terminal region. C_LIO_LIINF2 regulates IP3R cluster formation in actin-filament dependent manner and thereby regulates IP3R activity. C_LIO_LIFurther we show that ER-localized INF2 specifically regulate IP3R cluster positioning thereby promoting ER to mitochondrial contact and calcium transfer. C_LI