Autosomal recessive mutations in genes required for cytotoxicity are causative of a life-threatening, early-onset hyperinflammatory syndrome termed familial hemophagocytic lymphohistiocytosis (FHL). Mutations in UNC13D cause FHL type 3. UNC13D encodes Munc13-4, a member of the Unc13 protein family which control SNARE complex formation and vesicle fusion. We have previously identified FHL3-associated mutations in the first intron of UNC13D which control transcription from an alternative transcriptional start site. Using isoform specific antibodies, we demonstrate that this alternative Munc13-4 isoform with a unique N-terminus is preferentially expressed in human lymphocytes and platelets, as compared to the conventional isoform that was mostly expressed in monocytes and neutrophils. The distinct N-terminal of the two isoforms did not impact on Munc13-4 localization or trafficking to the immunological synapse of cytotoxic T cells. Moreover, ectopic expression of both isoforms efficiently restored exocytosis by FHL3 patient-derived Munc13-4 deficient T cells. Thus, we demonstrate that the conventional and alternative Munc13-4 isoforms have different expression pattern in hematopoietic cell subsets, but display similar localization and contribution to T cell exocytosis. The use of an alternative transcriptional starting site (TSS) in lymphocytes and platelets could be selected for increasing the overall levels of Munc13-4 expression for efficient secretory granule release.
Bibliographical noteFunding Information:
We thank Dr. Ute Becherer, and Dr. Elmar Krause for help with TIRF and confocal microcopy. Part of the imaging study was performed at the LCI facility/Nikon Center of Excellence, Karolinska Institutet, supported by grants from the Knut and Alice Wallenberg Foundation, Swedish Research Council, KI infrastructure, Center for Innovative Medicine and Jonasson center at the Royal Institute of Technology. Funding. This project was funded by the European Union's Horizon 2020 research and innovation program under the Marie Sk?odowska-Curie grant agreement No 794830 794830 -CL_Exocytosis to DG and by the Swedish Research Council, Swedish Foundation for Strategic Research, Swedish Cancer Foundation, Swedish Children's Cancer Foundation, Knut and Alice Wallenberg Foundation, the Karolinska Institute Research Foundation to YB. For the microscopy data, DG was supported by a fellowship from the European Federation of Immunology Societies (EFIS).
© Copyright © 2020 Galgano, Soheili, Voss, Torralba-Raga, Tesi, Cichocki, Andre, Rettig, Cavazzana and Bryceson.
- alternative intronic promoter/isoform
- familial hemophagocytic lymphohistiocytosis type 3
- intronic mutation
- lymphocyte cytotoxicity
- primary immunodeficiency