Editors' ChoiceImmunology

SUMO wrestles PKC to the immunological synapse

Sci. Signal.  27 Oct 2015:
Vol. 8, Issue 400, pp. ec307
DOI: 10.1126/scisignal.aad7107

When the T cell receptor (TCR) on the surface of a T cell is engaged by peptide antigen bound to the major histocompatibility complex on the surface of an antigen-presenting cell (APC), an immunological synapse is formed at the contact point between the cells. The central region of the immunological synapse consists of clusters of signaling TCRs, which are surrounded by a ring enriched in the coreceptor CD28 and protein kinase C θ (PKCθ). Immunological synapse formation is required for T cell activation and proliferation. Wang et al. found that PKCθ in CD4+ T cells was subjected to posttranslational modification by SUMO1 (small ubiquitin-like molecule 1) in response to stimulation of the TCR and CD28. Mass spectrometry analysis showed that Lys325 and Lys506 of PKCθ were the major SUMOylated residues, and a mutant PKCθ [PKCθ(2KR)] in which both sites were mutated to arginines failed to undergo TCR-stimulated SUMOylation in transfected T cells. PKCθ-deficient mouse CD4+ T cells that were retrovirally reconstituted with PKCθ(2KR) exhibited impaired expression of activation markers and reduced proliferation in response to stimulation. In vitro kinase assays showed that the lack of SUMOylation of PKCθ(2KR) did not affect its catalytic activity. PKCθ and the SUMOylating E3 ligase PIASxβ were coimmunoprecipitated from stimulated primary human CD4+ T cells. Microscopic analysis demonstrated that incubation of wild-type CD4+ T cells with antigen-loaded APCs resulted in the recruitment of PKCθ and PIASxβ to the immunological synapse. Although PKCθ(2KR) was also recruited to the immunological synapse of stimulated transfected T cells, it was not localized with CD28 in the ring surrounding TCRs, but had a more diffuse distribution. This diffuse pattern of PKCθ was also observed in stimulated wild-type CD4+ T cells in which PIASxβ was knocked down. Furthermore, blocking PKCθ SUMOylation disrupted TCR-stimulated interactions between PKCθ, CD28, and the actin-binding protein filamin A, and the localization of filamin A at the immunological synapse. Together, these results suggest that TCR-stimulated SUMOylation of PKCθ is required for stable immunological synapse formation and effective TCR signaling.

X.-D. Wang, Y. Gong, Z.-L. Chen, B.-N. Gong, J.-J. Xie, C.-Q. Zhong, Q.-L. Wang, L.-H. Diao, A. Xu, J. Han, A. Altman, Y. Li, TCR-induced sumoylation of the kinase PKC-θ controls T cell synapse organization and T cell activation. Nat. Immunol. 16, 1195–1203 (2015). [PubMed]

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