Novel heterozygous mutation in STX11 in a pediatric patient with Evans syndrome.

ERRA, LORENZO; COLADO, ANA; FERNANDEZ, J; BRUNELLO, F; GORIS, V; VISHNOPOLSKA, SEBASTIÁN; MARTINEZ MAYER, J; AVALOS, V.; VILLA, M; OLEASTRO, M; MARTI, MARCELO A.; POZNER, ROBERTO G.; BORGE, MERCEDES; DANIELIAN, S; ALMEJUN, MARÍA BELÉN

Virtual

Congreso; Reunión de Sociedades de Biociencias.; 2021

SAIC

Natural killer (NK) and CD8+ T cells play an important role in the immuneresponse. STX11 encodes a t-SNARE protein necessary forthe final fusion of lytic granules with the plasma membrane of thesecells. Biallelic mutations in STX11 results to a “particular” FamilialHemophagocytic Lymphohistiocytosis type 4. Heterozygous mutationshave been identified in several patients, although the clinical/functional relevance of these mutations remains poorly understood.Our aim was to determine the functional relevance of an heterozygousSTX11 variant (R129P) identified in a pediatric patient diagnosedwith Evans syndrome. Targeted sequencing showed that thepatient’s mother was heterozygous for the mutation.PBMC from healthy donors (HD), patient, mother and a patient withChediak Higashi syndrome (negative control, NC) were used.We analysed degranulation capacity of CD8+T cells and degranulationand cytotoxicity ability of NK cells, using flow cytometry assays.We observed a reduction of all these functions in the R129P-STX11patient and mother in comparison to HD. Nevertheless, these reductionswere less defective than observed in NC cells. IL-2 in vitrotreatment restored these functions.The RNA levels (qPCR) of patient and mother were similar to HD butthe protein expression (WB) was reduced.Finally, we performed in-silico structural analysis of R129P substitutionusing available STX11:Munc18-2 complex structure. R129 ispart of a helix in the NHabc domain displaying a rich hydrogen bondnetwork with Munc18-2. In this context, this variant is expected notonly to impact helix stability, but also protein-protein interaction.Altogether, we demonstrated that the novel R129P-STX11 mutationcan play a pathogenic role by impairing degranulatory activity of NKand CD8+T cells and cytotoxic activity of NK cells. The aberrantfunctionality of NK cells have been reported in several autoimmunedisorders. This novel mutation may explain the clinical patient EvansSyndrome phenotype.