Dynamic communication between TRPC3 and IP3R shape Ca2+ signaling signatures.

Abstract

Physical and functional coupling between TRPC channels and IP3 receptors (IP3R) has been proposed as a pivotal mechanism in cellular Ca2+ signaling. Here we set out to explore the impact of TRPC3-IP3R communication at the level of spatiotemporal organisation of Ca2+ signaling. The low affinity Ca2+ sensor R-GECO1.2 was fused as a reporter to the C-terminus of TRPC3 and the channel function of this construct was modified specifically by point mutations. Cytoplasmic Ca2+ changes at the TRPC3 channels expressed in HEK293 cells originated from both the entry of Ca2+ through the TRPC channel and Ca2+ mobilization via IP3R. Local Ca2+ changes within the TRPC3 signaling domain were predominantly biphasic with IP3R-dependent initial Ca2+ transients, while exclusively monophasic signals were recorded when all three IP3R isoforms were lacking. Abrogation of Ca2+ entry through TRPC3 by mutational impairment of Ca2+ permeability (E630Q), cation permeation (E630K), or DAG sensitivity (G652A), promoted local Ca2+ oscillations. Ca2+ signals at E630Q, E630K, and G652A channels featured initial Ca2+ transients along with oscillatory activity. By contrast, oscillations and initial Ca2+ transients, were virtually lacking, when the TRPC3 channels were sensitized by subthreshold stimulation of phospholipase C. TIRF imaging provided evidence for dynamic colocalization of TRPC3 and IP3R. Our results suggest that TRPC3-mediated Ca2+ entry controls IP3R activity at ER-PM junctions to shape Ca2+ signaling signatures and enable specificity of downstream signaling.