Molecular analysis of the novel L243R mutation in STXBP2 reveals impairment of degranulation activity

Laura Viñas-Giménez, Laura Donadeu, Laia Alsina, Rafael Rincón, Elena Álvarez de la Campa, Ana Esteve-Sole, Albert Català, Roger Colobran, Xavier de la Cruz, Joan Sayós, Mónica Martínez-Gallo*

*Corresponding author for this work

Research output: Contribution to journalArticleResearchpeer-review

Abstract

The presence of mutations in PRF1, UNC13D, STX11 and STXBP2 genes in homozygosis or compound heterozygosis results in immune deregulation. Most such cases lead to clinical manifestations of haemophagocytic lymphohistiocytosis (HLH). In the present study, we analyzed degranulation and cytotoxicity in a pediatric patient with a late presentation of HLH associated with Epstein–Barr virus infection. Remarkably, the results of the degranulation assay showed reduction of CD107a median fluorescence intensity (MFI) and absent cytotoxicity. Genetic analysis identified compound heterozygous mutations in STXBP2 gene: a previously reported splicing defect in exon 15 (c.1247-1G>C, p.V417LfsX126) and a novel missense mutation in exon 9 (c.728T>G, p.L243R). Transfection experiments of STXBP2-L243R or STXBP2-WT constructs showed an undetectable protein expression of the STXBP2-L243R mutation. The residue L243 is highly preserved evolutionarily; moreover, computational analysis of its structure revealed its participation in the rich network of interactions that stabilizes domains 2 and 3 of the protein. Altogether, we demonstrated by molecular and in silico analysis that the new L243R mutation in STXBP2 plays a pathogenic role that, together with the p.Val417Leufsc mutation, shows the synergistic negative effect of these two mutations on STXBP2 function, leading to a decrease of degranulatory activity in vivo.

Original languageEnglish
Pages (from-to)440-450
Number of pages11
JournalInternational Journal of Hematology
Volume111
Issue number3
DOIs
Publication statusPublished - 1 Mar 2020

Keywords

  • Cell degranulation
  • Cytotoxic T-lymphocytes
  • Epstein–Barr virus infection
  • Familial hemophagocytic lymphohistiocytosis
  • Munc18-1 protein
  • Munc18-2 protein
  • Natural killer cells

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