ERp44 C160S/C212S mutants regulate IP₃R₁ channel activity

Previous studies have indicated that ERp44 inhibits inositol 1,4,5-trisphosphate (IP₃)-induced Ca²⁺ release (ⅡCR) via IP₃R₁, but the mechanism remains largely unexplored. Using extracellular ATP to induce intracellular calcium transient as an ⅡCR model, Ca²⁺ image, pull down assay, and Western blotting experiments were carried out in the present study. We found that extracellular ATP induced calcium transient via IP3Rs (ⅡCR) and the ⅡCR were markedly decreased in ERp44 overexpressed Hela cells. The inhibitory effect of C160S/C212S but not C29S/T396A/ΔT(331-377) mutants of ERp44 on ⅡCR were significantly decreased compared with ERp44. However, the binding capacity of ERp44 to L3V domain of IP₃R₁ (1L3V) was enhanced by ERp44 C160S/C212S mutation. Taken together, these results suggest that the mutants of ERp44, C160/C212, can more tightly bind to IP₃R₁ but exhibit a weak inhibition of IP₃R₁ channel activity in Hela cells.