The impact of ITPR3 mutations on immunity

Project Summary The inositol trisphosphate receptors (ITPR1, ITPR2, ITPR3) are present in the endoplasmic reticulum, forming homo- or hetero- tetrameric complexes to control calcium release. Upon binding to the second messenger, inositol 1,4,5 trisphosphate (IP3), the ITPR controlled release of calcium controls differentiation, proliferation, and death processes for every cell type in the body. We identified the same single allelic mutation in the Inositol Tris Phosphate Receptor Type 3 (ITPR3) in two unrelated children. The missense mutation creates a p.Arg2524Cys amino acid substitution within the calcium channel. These children have immunodeficiency, Charcot-Marie Tooth disease and partial to complete anhidrosis. While autosomal recessive ITPR3 mutations cause one form of CMT syndrome, immune system problems and sweating defects are not normally seen. In fact, most single allelic mutations in ITPR3 are benign due to compensatory functions by ITPR1 and ITPR2. To understand the basis for the more widespread clinical presentation our two patients with the single allelic p.R2524C variant, as well as an expanding number being reported elsewhere, we genocopied the mutation in mice. Our preliminary findings suggest this Itpr3 p.R2524C variant forms a cell-type specific dominant negative. In the current proposal, we will determine the impact of this Itpr3 mutation on cell signaling in the immune, neuronal, and eccrine systems. A characterization of the T and B cells of the adaptative immune system will be done with a combination of functional assays and signaling studies. Additionally, a characterization of the Schwann cells of the peripheral nervous system and eccrine cells will be undertaken. The studies will be complemented with knockdown approaches using shRNA technologies to determine if functionality can be restored by selectively targeting Itpr3.