Elucidating the molecular mechanism of Syntaxin11 function in cytotoxic T lymphocytes (P3032)

Abstract

Abstract Cytotoxic T lymphocytes (CTL) play a crucial role in eliminating virus infected and cancer cells through exocytosis of perforin and granzymeB containing lytic granules (LGs). Soluble NSF Attachment Protein Receptors (SNAREs) function as executors of exocytosis. The importance of SNAREs and SNARE associated proteins in CTL function and LG exocytosis is evident in the form of Familial Hemophagocytic Lymphohistiocytosis (FHL). Mutations within Syntaxin11 (Stx11), a Qa-SNARE protein, result in FHL subtype-4, however the mechanism by which Stx11 malfunction leads to this severe phenotype remains unknown. Here, we investigate the molecular mechanism of Stx11 function in primary human CTLs. High resolution live cell imaging with CTLs before and after target cell contact showed sequential polarization of Stx11 followed by LGs to the immunological synapse. Using TIRF (total internal reflection fluorescence) microscopy we further showed an association of LGs with plasma membrane-bound Stx11 at the IS. Further, knockdown studies using Stx11 specific siRNA resulted in a strong reduction of both LG fusion and dwell time at the IS. We therefore propose that Stx11 is required for the final fusion of LG at the IS, explaining the severe FHL4 phenotype.