Waldo A. Spessott, Maria L. Sanmillan, Margaret E. McCormick, Nishant  Patel , Joyce Villanueva, Kejian Zhang,  Kim E. Nichols  and Claudio G. Giraudo. (2015) Familial hemophagocytic lymphohistiocytosis caused by a novel dominant-negative mutation in STXBP2 that inhibits SNARE-mediated membrane fusion. Blood. 125(10): 1566-1577. PMCID: PMC4351505.

In this manuscript we demonstrate for first time a dominant-negative mode of action of an HLH-associated genetic mutation. The familial form of HLH (f-HLH) is generally considered an autosomal recessive disorder. Nonetheless, there exist many HLH patients who harbor monoallelic mutations in genes such as PRF1, UNC13D, STX11 and STXBP2. Commonly,  these patients are not considered as having the familial form of HLH and as a consequence, are not being treated with the only known curative therapy – hematopoietic stem cell transplantation. In this work we evaluated for first time in the field the effect of specific mutations on the function of FHL proteins using in vitro assays developed in our lab. This manuscript will have major implications by allowing for a better understanding of HLH pathogenesis and facilitating therapeutic decisions. In this manuscript we also proposed a mechanism by which other monoallelic mutations might act in a dominant-negative fashion.

Waldo A. Spessott, Maria L. Sanmillan, Margaret E. McCormick, Vineet K.Kulkarni  andClaudio G. Giraudo. (2017). SM protein Munc18-2 facilitates transition for Syntaxin 11-mediated lipid mixing to complete fusion for T-lymphocyte cytotoxicity. P.N.A.S.-USA. 14:114(11) E2176-E2185.

In this manuscript we showed by using in-vitro fusion assays that lipid-anchored STX11 and its cognate SNARE proteins, SNAP23 and Vamp8, mainly support outer membrane hemifusion. Strikingly, complete fusion is stimulated by addition of Munc18-2-wt to the assay, but not of Munc18-2 mutants that cannot bind STX11. Our data support a direct role of SM proteins in controlling membrane fusion outcomes of lipid-anchored SNAREs by promoting SNARE complex assembly. This novel mechanism likely regulates other cell-type specific exocytic processes such as platelet secretion.

Kou, X., Xu, X., Chen, C., Sanmillan, M. L., Cai, T., Zhou, Y., Giraudo, C., Le, A. and Shi, S. (2018) The Fas/Fap-1/Cav-1 complex regulates IL-1RA secretion in mesenchymal stem cells to accelerate wound healing. Sci Transl Med 10: 432.

In this study we found that Fas binds with Fas-associated phosphatase–1 (Fap-1) and caveolin-1(Cav-1) to activate a common soluble N-ethylmaleimide–sensitive factor (NSF) attachment protein receptor (SNARE)–mediated membrane fusion mechanism to release small extracellular vesicles (sEVs) in MSCs. Moreover, we revealed that MSCs produce and secrete interleukin-1 receptor antagonist (IL-1RA) associated with sEVs to maintain rapid wound healing in the gingiva via the Fas/Fap-1/Cav-1 cascade. Tumor necrosis factor–a (TNF- a) serves as an activator to up-regulate Fas and Fap-1 expression via the nuclear factor kB pathway to promote IL-1RA release. This study identifies a previously unknown Fas/Fap-1/Cav-1 axis that regulates SNARE-mediated sEV and IL-1RA secretion in stem cells, which contributes to accelerated wound healing.