Twist1 and Etv5 are part of a transcription factor network defining T helper cell identity

Abstract

CD4 T helper cells control immunity to pathogens and the development of inflammatory disease by acquiring the ability to secrete effector cytokines. Cytokine responsiveness is a critical component of the ability of cells to respond to the extracellular milieu by activating Signal Transducer and Activator of Transcription factors that induce the expression of other transcription factors important for cytokine production. STAT4 is a critical regulator of Th1 differentiation and inflammatory disease that attenuates the gene-repressing activity of Dnmt3a. In the absence of STAT4, genetic loss of Dnmt3a results in de-repression of a subset of Th1 genes, and a partial increase in expression that is sufficient to observe a modest recovery of STAT4-dependent inflammatory disease. STAT4 also induces expression of the transcription factors Twist1 and Etv5. We demonstrate that Twist1 negatively regulates Th1 cell differentiation through several mechanisms including physical interaction with Runx3 and impairing STAT4 activation. Following induction by STAT3-activating cytokines including IL-6, Twist1 represses Th17 and Tfh differentiation by directly binding to, and suppressing expression of, the Il6ra locus, subsequently reducing STAT3 activation. In contrast, Etv5 contributes only modestly to Th1 development but promotes Th differentiation by directly activating cytokine production in Th9 and Th17 cells, and Bcl6 expression in Tfh cells. Thus, the transcription factors Twist1 and Etv5 provide unique regulation of T helper cell identity, ultimately impacting the development of cell-mediated and humoral immunity.