TOX2 nuclear-cytosol translocation is linked to leukemogenesis of acute T-cell leukemia by repressing TIM3 transcription.

Nuclear factors TOX and TOX2 upregulate TIM3 expression and lead to T-cell exhaustion in malignancies. Here, we demonstrate two distinct TIM3 expression patterns (high & low) with high TOX and TOX2 levels in T-cell acute lymphoblastic leukemia (T-ALL) specimens and cell lines. However, the mechanisms regulated by TOX and TIM3 signaling in leukemogenesis are unclear. We found that TOX and TOX2 proteins each directly upregulated HAVCR2 transcription, while the cellular localization of TOX2 was different in Jurkat and MOLT3 cells (nucleus) and lymphoblastic cell T2 and normal T cells (cytoplasm). Nuclear TOX and TOX2 formed a protein complex and repressed HAVCR2 promoter activity by recruiting transcriptional corepressor LCOR and deacetylase HDAC3. The nuclear-cytosol translocation of TOX2 was deacetylation-dependent and cooperatively mediated by deacetylase Sirt1 and kinase TBK1. Radiation damage induced TOX2 nuclear translocation and decreased Sirt1, TIM3, and caspase 1 expression in normal T cells. Accordingly, knockdown of TOX, TOX2 or LCOR; HDAC3 inhibition; or TIM3 overexpression induced Jurkat cell apoptosis in vitro and slow growth in vivo. Thus, our findings demonstrate a novel regulatory mechanism involving TOX-TOX2 and the TIM3 pathway in the leukemogenesis of T-ALL.