title: Hemophagocytic lymphohistiocytosis caused by dominant-negative mutations in STXBP2 that inhibit SNARE-mediated membrane fusion.
abstract: Familial hemophagocytic lymphohistiocytosis (F-HLH) and Griscelli syndrome type 2 (GS) are life-threatening immunodeficiencies characterized by impaired cytotoxic T lymphocyte (CTL) and natural killer (NK) cell lytic activity. In the majority of cases, these disorders are caused by biallelic inactivating germline mutations in genes such as RAB27A (GS) and PRF1, UNC13D, STX11, and STXBP2 (F-HLH). Although monoallelic (ie, heterozygous) mutations have been identified in certain patients, the clinical significance and molecular mechanisms by which these mutations influence CTL and NK cell function remain poorly understood. Here, we characterize 2 novel monoallelic hemophagocytic lymphohistiocytosis (HLH)-associated mutations affecting codon 65 of STXPB2, the gene encoding Munc18-2, a member of the SEC/MUNC18 family. Unlike previously described Munc18-2 mutants, Munc18-2(R65Q) and Munc18-2(R65W) retain the ability to interact with and stabilize syntaxin 11. However, presence of Munc18-2(R65Q/W) in patient-derived lymphocytes and forced expression in control CTLs and NK cells diminishes degranulation and cytotoxic activity. Mechanistic studies reveal that mutations affecting R65 hinder membrane fusion in vitro by arresting the late steps of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE)-complex assembly. Collectively, these results reveal a direct role for SEC/MUNC18 proteins in promoting SNARE-complex assembly in vivo and suggest that STXBP2 R65 mutations operate in a novel dominant-negative fashion to impair lytic granule fusion and contribute to HLH.
authors.affiliation: Department of Pathology and Laboratory Medicine, and.
authors.forename: Waldo A
authors.initials: WA
authors.lastname: Spessott
authors.affiliation: Department of Pathology and Laboratory Medicine, and.
authors.forename: Maria L
authors.initials: ML
authors.lastname: Sanmillan
authors.affiliation: Department of Pathology and Laboratory Medicine, and.
authors.forename: Margaret E
authors.initials: ME
authors.lastname: McCormick
authors.affiliation: Division of Oncology, Department of Pediatrics, The Children's Hospital of Philadelphia, University of Pennsylvania, Philadelphia, PA;
authors.forename: Nishant
authors.initials: N
authors.lastname: Patel
authors.affiliation: Division of Bone Marrow Transplant and Immune Deficiency, and.
authors.forename: Joyce
authors.initials: J
authors.lastname: Villanueva
authors.affiliation: Division of Human Genetics, Cincinnati Children's Hospital Medical Center, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH; and.
authors.forename: Kejian
authors.initials: K
authors.lastname: Zhang
authors.affiliation: Division of Cancer Predisposition, Department of Oncology, St. Jude Children's Research Hospital, Memphis, TN.
authors.forename: Kim E
authors.initials: KE
authors.lastname: Nichols
authors.affiliation: Department of Pathology and Laboratory Medicine, and.
authors.forename: Claudio G
authors.initials: CG
authors.lastname: Giraudo
mesh_terms: D000328:Adult; D019943:Amino Acid Substitution; D002648:Child; D002675:Child, Preschool; D003062:Codon / Q000235:genetics; D005260:Female; D005799:Genes, Dominant; D006367:HeLa Cells; D006579:Heterozygote; D006801:Humans; D007223:Infant; D007694:Killer Cells, Natural / Q000276:immunology; D051359:Lymphohistiocytosis, Hemophagocytic / Q000235:genetics* / Q000276:immunology* / Q000378:metabolism; D008297:Male; D008561:Membrane Fusion / Q000235:genetics / Q000276:immunology; D008875:Middle Aged; D008954:Models, Biological; D008958:Models, Molecular; D051938:Munc18 Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D020125:Mutation, Missense; D011487:Protein Conformation; D054730:Protein Interaction Domains and Motifs; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D050600:SNARE Proteins / Q000276:immunology* / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology
chemical_list: D003062:Codon; D051938:Munc18 Proteins; D050505:Mutant Proteins; D050765:Qa-SNARE Proteins; D011994:Recombinant Proteins; D050600:SNARE Proteins; C541732:STX11 protein, human; C497940:STXBP2 protein, human