Type 3 Inositol 1,4,5-Trisphosphate Receptor is a Crucial Regulator of Calcium Dynamics Mediated by Endoplasmic Reticulum in HEK Cells

Being the largest the Ca(2+) store in mammalian cells, endoplasmic reticulum (ER)-mediated Ca(2+) signalling often involves both Ca(2+) release via inositol 1, 4, 5-trisphosphate receptors (IP(3)R) and store operated Ca(2+) entries (SOCE) through Ca(2+) release activated Ca(2+) (CRAC) channels on plasma membrane (PM). IP(3)Rs are functionally coupled with CRAC channels and other Ca(2+) handling proteins. However, it still remains less well defined as to whether IP(3)Rs could regulate ER-mediated Ca(2+) signals independent of their Ca(2+) releasing ability. To address this, we generated IP(3)Rs triple and double knockout human embryonic kidney (HEK) cell lines (IP(3)Rs-TKO, IP(3)Rs-DKO), and systemically examined ER Ca(2+) dynamics and CRAC channel activity in these cells. The results showed that the rate of ER Ca(2+) leakage and refilling, as well as SOCE were all significantly reduced in IP(3)Rs-TKO cells. And these TKO effects could be rescued by over-expression of IP(3)R3. Further, results showed that the diminished SOCE was caused by NEDD4L-mediated ubiquitination of Orai1 protein. Together, our findings indicate that IP(3)R3 is one crucial player in coordinating ER-mediated Ca(2+) signalling.