Syntaxin11 Deficiency Inhibits CRAC Channel Priming to Suppress Cytotoxicity and Gene Expression in FHLH4 Patient T Lymphocytes

Mutations in Syntaxin11, a Q-SNARE, result in a fatal immune disorder known as familial hemophagocytic lymphohistiosis 4 (FHLH4) in human patients. A key diagnostic feature of FHLH4 is defective T and natural killer cell cytotoxicity. Here we show that Syntaxin11 directly binds and regulates Orai1, the pore forming subunit of calcium release activated calcium (CRAC) channels. CRAC channels enable store-operated calcium entry (SOCE) from the extracellular space and are crucial for granule exocytosis and nuclear factor of activated T cells (NFAT) dependent gene expression in activated lymphocytes. Syntaxin11 depletion strongly inhibited SOCE, CRAC currents, NFAT activation, interleukin-2 gene expression and degranulation in FHLH4 patient T lymphocytes and cell lines. Remarkably, defects of granule exocytosis as well as interleukin-2 expression could be reversed by ionomycin induced calcium influx in patient T lymphocytes and a constitutively active, H134S, mutant of Orai1 rescued calcium entry in Syntaxin11 depleted cells. Further mechanistic analyses showed that Syntaxin11 primes Orai1 subunits for correct on-site assembly which is a prerequisite for functional entrapment and gating of CRAC channels by the endoplasmic reticulum resident Stim1. We propose that priming of ion channel pore subunits is a primary and conserved function of specific SNAREs which likely preceded their role in vesicle fusion.