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The Role of Signal Regulation via RING-type Ubiquitin Ligase (Roquin) Over-Expression In Vitro and Ex Vivo T Cell Activation
Several types of white blood cells, such as T cells, B cells, and macrophages, are involved in the immune response. In particular, the processes of T-cell activation play a crucial role in an adaptive immune response, whereby the T-cell receptor (TCR) engages with an antigen and signals a cascade that leads to the activation of transcription factors (AP-1, NF-κB, and NFAT) that are critically involved in cytokine production. Roquin, encoded by the RC3H1 gene and characterized as an immune regulator, was recently identified as a novel RING-type ubiquitin ligase family member, but the mechanisms by which Roquin proteins regulate T-cell responses are unclear. To elucidate the role of Roquin in vitro, murine lymphoma EL-4 cells were used. Roquin overexpressing Tcells became hyper-responsive upon anti-CD3/CD28 stimulation in vitro and were a major source of cytokines such as IL-2, TNF-α, IL-6, and IL-10. Upon activation, these cells showed preferentially enhanced production of IL-2 and TNF-α, but not IFN-γ. To clarify the important role of Roquin in the T-cell response ex vivo, we generated T-cell-specific Roquin-transgenic (Tg) mice having a higher expression of Roquin in T cells as compared to wild-type mice. Using Roquin-Tg mice, we studied whether immune responses are affected ex vivo. Roquin-Tg CD4+ T cells showed enhanced production of IL-2 or TNF-α to TCR stimulation with anti-CD28 costimulation via up-regulation of CD28. T-cell proliferation also increased in Roquin-Tg CD4+ T cells after anti-CD3/CD28 treatment. Further studies on the role of Roquin in the regulation of primary T-cell activation, survival, and differentiation may be anticipated.
