Insight into Ca2+- inositol 1,4,5-trisphosphate receptor 2 (IP3R2)-mediated unfolded protein response and apoptosis in scallop Patinopecten yessoensis under high temperature stress

Inositol 1,4,5-trisphosphate receptor 2 (IP₃R2) is an essential Ca²⁺ release channel protein located in the endoplasmic reticulum (ER), and plays a significant role in responding to various environmental stimuli. In the present study, the function of IP₃R2 from Yesso scallop Patinopecten yessoensis (PyIP₃R2) in regulating the Ca²⁺-mediated unfolded protein response (UPR) and apoptosis after high temperature (25 °C) treatment was investigated. Three MIR domains, one RYDR_ITPR domain, one RIH_assoc domain and one Ion_trans domain were identified in PyIP₃R2. Both D-myo-inositol-1,4,5-triphosphate (IP3, an activator of IP₃R) and high temperature significantly upregulated the mRNA expression level of PyIP₃R2 and genes related to apoptosis and the UPR, and also increased intracellular Ca²⁺ content (p < 0.05). Furthermore, the IP₃R antagonist 2-aminoethyl diphenylborinate (2-APB) had the opposite effect, decreasing intracellular Ca²⁺ content and the mRNA expression level of PyIP₃R2, glucose regulated protein 78 (PyGRP78) and PyCaspase-3 (p < 0.05). However, the apoptosis rate and Caspase-3 activity remained comparable to those in the injection control group. These findings indicate that PyIP₃R2 mediates UPR and apoptosis in scallop haemocytes by regulating Ca²⁺content and distribution, and providing insight into the cellular responses of scallops to high temperature.