Syntaxin11 deficiency inhibits CRAC channel priming to suppress cytotoxicity and gene expression in T lymphocytes independent of membrane trafficking.

Mutations in Syntaxin11 (STX11), a Q-SNARE, result in a fatal immune disorder known as familial hemophagocytic lymphohistiocytosis 4 (FHLH4) in human patients. A key diagnostic feature of FHLH4 is defective T and natural killer cell cytotoxicity. Here, we show that STX11 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. STX11 depletion strongly inhibited SOCE, CRAC currents, NFAT activation, interleukin-2 gene expression, and degranulation in FHLH4 patient T lymphocytes and cell lines without affecting membrane trafficking. Remarkably, defects of cytolytic granule exocytosis, as well as interleukin-2 expression, could be reversed by ionomycin in patient T lymphocytes, and a constitutively active, H134S, mutant of Orai1 rescued calcium entry in STX11-depleted cells. Further analyses showed that STX11 'primes' Orai1 for optimal on-site multimeric assembly, which was Stim independent but required for gating. Priming of ion channel pore subunits is, therefore, a primary function of specific SNAREs which may have preceded their role in membrane trafficking and vesicle fusion.