title: A novel Dutch mutation in UNC13D reveals an essential role of the C2B domain in munc13-4 function.
abstract: BACKGROUND
  UNC13D, encoding the protein munc13-4, is essential in intracellular trafficking and exocytosis of lytic granules. Mutations in this gene are associated with familial hemophagocytic lymphohistiocytosis type 3 (FHL3), a genetically heterogeneous, rare autosomal recessive immune disorder. How mutations affect function of munc13-4 is poorly understood. Since 2006 we genetically identified seven FHL patients with mutations in UNC13D.
  
  
  METHODS
  Here, we report for the first time a c.2695C>T (p.Arg899X) mutation in exon 28 of UNC13D in three young unrelated Dutch patients. The mutation causes a premature stop codon and encodes munc13-4(1-899), which lacks the C-terminal C2 domain. Genealogical research and haplotyping of the patient families demonstrated that a single ancestral founder introduced the mutation in the Netherlands. We then characterized the mutant protein phenotypically in cell biological and immunological assays.
  
  
  RESULTS
  Munc13-4(1-899) was correctly targeted to CD63-positive secretory lysosomes, although its stability was reduced and dynamic turnover on the granule membrane became uncoupled from receptor signaling. In accord, and in contrast to wild-type munc13-4, ectopically expressed mutant failed to rescue degranulation in cells with silenced endogenous munc13-4.
  
  
  CONCLUSIONS
  The functional and clinical data showed that this novel Dutch founder mutation leads to severe early onset of FHL3 due to misfolding and degradation of munc13-4(1-899).
authors.affiliation: Department of Cell Biology, UMC Utrecht, Utrecht, The Netherlands.
authors.forename: Edo D
authors.initials: ED
authors.lastname: Elstak
authors.forename: Maroeska
authors.initials: M
authors.lastname: te Loo
authors.forename: Kiki
authors.initials: K
authors.lastname: Tesselaar
authors.forename: Peter
authors.initials: P
authors.lastname: van Kerkhof
authors.forename: Jan
authors.initials: J
authors.lastname: Loeffen
authors.forename: Dimitris
authors.initials: D
authors.lastname: Grivas
authors.forename: Eric
authors.initials: E
authors.lastname: Hennekam
authors.forename: Jaap Jan
authors.initials: JJ
authors.lastname: Boelens
authors.forename: Peter M
authors.initials: PM
authors.lastname: Hoogerbrugge
authors.forename: Peter
authors.initials: P
authors.lastname: van der Sluijs
authors.forename: Marielle E
authors.initials: ME
authors.lastname: van Gijn
authors.forename: Lisette
authors.initials: L
authors.lastname: van de Corput
mesh_terms: D000818:Animals; D015550:Cell Degranulation / Q000235:genetics; D045744:Cell Line, Tumor; D018388:Codon, Terminator; D006801:Humans; D051359:Lymphohistiocytosis, Hemophagocytic / Q000235:genetics / Q000378:metabolism; D008247:Lysosomes / Q000235:genetics / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D009426:Netherlands; D017354:Point Mutation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D059748:Proteolysis; D051381:Rats; D060149:Tetraspanin 30 / Q000235:genetics / Q000378:metabolism
chemical_list: C554586:CD63 protein, human; C554588:Cd63 protein, rat; D018388:Codon, Terminator; D008565:Membrane Proteins; D011506:Proteins; D060149:Tetraspanin 30; C507969:UNC13D protein, human; C430713:Unc13d protein, rat