A ternary complex comprising FAK, PTPα and IP3 receptor 1 functionally engages focal adhesions and the endoplasmic reticulum to mediate IL-1-induced Ca2+ signalling in fibroblasts

Abstract

Ca2+ release is tightly sequestered in eukaryotic cells to enable fine spatio-temporal control of signalling but how Ca2+ release from the endoplasmic reticulum (ER) is linked to cell adhesions is not defined. We examined the spatial restriction of Ca2+ release through the inositol 1,4,5-triphosphate receptor 1 (IP3R1) in response to interleukin-1 (IL-1) and the functions of the adhesion-associated proteins, focal adhesion kinase (FAK) and protein tyrosine phosphatase-α (PTPα). In cultured fibroblasts IL-1 treatment promoted co-localization of PTPα and FAK with the ER and increased association of IP3R1 with PTPα and FAK at focal adhesions (FAs). GST pull-down assays of purified proteins demonstrated that PTPα and FAK directly interacted with IP3R1. These interactions depended on the focal adhesion-targeting (FAT) and band4.1-ezrin-radixin-moesin (FERM) domains of FAK. PTPα was required for the association of IP3R1 with Src, which mediated IP3R1 phosphorylation and consequently ER Ca2+ release. Collectively, these data indicate that PTPα and FAK, which are enriched in FAs, interact with IP3R1 at adjacent ER sites to spatially sequester IL-1-induced Ca2+ signalling.