Novel ORAI1 Mutation Disrupts Channel Trafficking Resulting in Combined Immunodeficiency

Fang Yu,Khaled Abouhazima,Bernice Lo,Amel Hassan,Mehdi Adeli,Khaled Machaca,Rafah Mackeh,Nourhen Agrebi,Khadija Khudabakhsh

doi:10.1007/s10875-021-01004-8

Abstract

Store-operated Ca2+ entry (SOCE) represents a predominant Ca2+ influx pathway in non-excitable cells. SOCE is required for immune cell activation and is mediated by the plasma membrane (PM) channel ORAI1 and the endoplasmic reticulum (ER) Ca2+ sensor STIM1. Mutations in the Orai1 or STIM1 genes abolish SOCE leading to combined immunodeficiency (CID), muscular hypotonia, and anhidrotic ectodermal dysplasia. Here, we identify a novel autosomal recessive mutation in ORAI1 in a child with CID. The patient is homozygous for p.C126R mutation in the second transmembrane domain (TM2) of ORAI1, a region with no previous loss-of-function mutations. SOCE is suppressed in the patient’s lymphocytes, which is associated with impaired T cell proliferation and cytokine production. Functional analyses demonstrate that the p.C126R mutation does not alter protein expression but disrupts ORAI1 trafficking. Orai1-C126R does not insert properly into the bilayer resulting in ER retention. Insertion of an Arg on the opposite face of TM2 (L135R) also results in defective folding and trafficking. We conclude that positive side chains within ORAI1 TM2 are not tolerated and result in misfolding, defective bilayer insertion, and channel trafficking thus abolishing SOCE and resulting in CID.

Highlights

Store-operated Ca2+ entry (SOCE) is ubiquitous Ca2+ influx pathway that regulates cellular signaling [1,2,3,4]
We describe a novel mutation in ORAI1 that abolishes SOCE and causes combined immunodeficiency (CID) associated with recurring viral and bacterial infections, neutropenia, muscular hypotonia, and anhidrosis in an infant
We show that the patient has largely normal immune cell development, yet T cells are defective in cytokine production and proliferation (Fig. 2a–d)

Summary

Introduction

Store-operated Ca2+ entry (SOCE) is ubiquitous Ca2+ influx pathway that regulates cellular signaling [1,2,3,4]. SOCE is triggered downstream of PLC-linked agonists that result in the production of IP3 and Ca2+ release from stores. STIM1 recruits ORAI1 through diffusional trapping and gates it open to trigger Ca2+ influx [1,2,3]. Gain-of-function (GoF) and loss-of-function (LoF) mutations in either ORAI1 or STIM1 in humans lead to distinct pathologies [3, 5,6,7]. Autosomal dominant GoF mutations in ORAI1 that result in excessive Ca2+ influx including p.S97C, p.G98S, p.L138F, and p.P245L, develop TAM/Stormorken syndrome with no obvious immune phenotype [3, 8,9,10]. Recessive LoF mutations that abolish SOCE, including p.A88SfsX25, p.R91W, p.G98R, p.A103E/p.L194P

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Conclusion