Syntaxin11 Deficiency Inhibits CRAC Channel Priming to Suppress Cytotoxicity and Gene Expression in T Lymphocytes Independent of Membrane Trafficking.

Abstract

Mutations in Syntaxin11, 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 (NK) 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 cell (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 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 Syntaxin11 depleted cells. Further analyses showed that Syntaxin11 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.