A Critical Analysis of the Role of SNARE Protein SEC22B in Antigen Cross-Presentation

Publication date: 27 June 2017
Source:Cell Reports, Volume 19, Issue 13
Author(s): S. Julia Wu, Yashar S. Niknafs, Stephanie H. Kim, Katherine Oravecz-Wilson, Cynthia Zajac, Tomomi Toubai, Yaping Sun, Jayendra Prasad, Daniel Peltier, Hideaki Fujiwara, Israel Hedig, Nathan D. Mathewson, Rami Khoriaty, David Ginsburg, Pavan Reddy
Cross-presentation initiates immune responses against tumors and viral infections by presenting extracellular antigen on MHC I to activate CD8⁺ T cell-mediated cytotoxicity. In vitro studies in dendritic cells (DCs) established SNARE protein SEC22B as a specific regulator of cross-presentation. However, the in vivo contribution of SEC22B to cross-presentation has not been tested. To address this, we generated DC-specific Sec22b knockout (CD11c-Cre Sec22b^fl/fl) mice. Contrary to the paradigm, SEC22B-deficient DCs efficiently cross-present both in vivo and in vitro. Although in vitro small hairpin RNA (shRNA)-mediated Sec22b silencing in bone-marrow-derived dendritic cells (BMDCs) reduced cross-presentation, treatment of SEC22B-deficient BMDCs with the same shRNA produced a similar defect, suggesting the Sec22b shRNA modulates cross-presentation through off-target effects. RNA sequencing of Sec22b shRNA-treated SEC22B-deficient BMDCs demonstrated several changes in the transcriptome. Our data demonstrate that contrary to the accepted model, SEC22B is not necessary for cross-presentation, cautioning against extrapolating phenotypes from knockdown studies alone.

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Teaser

SEC22B has been characterized as a crucial mediator of antigen cross-presentation. Using DC-specific Sec22b knockout mice, Wu et al. demonstrate that SEC22B is not necessary for cross-presentation and that the Sec22b shRNA sequences used in prior studies impact cross-presentation through off-target effects. They identify potential cross-presentation mediators for future investigation.


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