Themis Functions As A Cytoplasmic Adaptor And Nuclear Transcription Factor In Developing Thymocytes And Mature T Cells

Abstract THEMIS functions in the cytoplasm as an adaptor molecule which dampens TCR signaling. During thymic development, THEMIS sets the affinity threshold for activation, enabling the selection of conventional T cells in response to low affinity antigens. Although these events occur in the cytoplasm, THEMIS possess a nuclear localization signal (NLS) and a significant amount of THEMIS resides in the nucleus. To investigate the importance of THEMIS in the nucleus, we deleted the Themis NLS to force THEMIS in the cytoplasm. Surprisingly, T cell development was impaired similar to the Themis null mice, suggesting that THEMIS may have important roles in the nucleus as well. Alternatively, we established Themis mutant mice, in which THEMIS localized exclusively in the nucleus or where THEMIS was constantly present in both compartments. Normal conventional T cells were absent in both mutant mice. Since lack of THEMIS or the constant presence of THEMIS in the cytoplasm or nucleus or both, all resulted in aberrant T cell development it indicated that the translocation of THEMIS to or/and from the nucleus is essential for its function. To examine the role of THEMIS in T cells in the periphery, we generated mutant mice where THEMIS is expressed normal during thymic development but altered post-thymically. Adoptive transfer of naïve CD4 T cells with altered THEMIS expression into RAG deficient host induced enhanced sever colitis and furthermore, we observed that forced localization of THEMIS in the nucleus redirects the polarization of CD4 T cells toward the pathogenic TH17 helper lineage. These findings identify a dual function for THEMIS as a cytoplasmic adaptor during TCR signaling and a nuclear factor directing gene expression in thymocytes and mature T cells.