Regulation of the activity of IFN-γ promoter elements during Th cell differentiation

Before they can deliver their effector functions, CD4⁺ Th cells must differentiate into Th1 or Th2 subsets. We have prepared reporter transgenic mice that express the luciferase gene under the control of proximal (prox·(IFN-γ)) and distal (dist·(IFN-γ)) regulatory elements from the IFN-γ promoter to permit investigation of mechanisms that regulate IFN-γ gene transcription during Th cell differentiation. Precursor Th cells (pTh) contain high levels of cAMP response element binding protein-activation transcription factor-1 (CREB-ATF1) proteins that bind these promoter elements from the IFN-γ gene, and these cells fail to express promoter activity. Restimulated effector Th (eTh) cells have reduced levels of CREB-ATF1 proteins, their nuclear extracts exhibit reduced CREB-ATF1 binding and greater Jun and Jun-ATF2 binding to dist·(IFN-γ), and eTh cells express promoter activity. CREB directly competes with effector T cell nuclear proteins for dist·(IFN-γ) binding, and overexpression of CREB inhibits both prox·(IFN-γ)and dist·(IFN-γ)-directed transcription in Jurkat T cells. IL-12-stimulated Th1 differentiation increases dist·(IFN-γ) activity in restimulated eTh1 cells; eTh1 nuclear extracts form increased levels of Jun- ATF2-dist·(IFN-γ) complexes. Taken together, these data suggest that both de-repression and trans-activation contribute to the induction of IFN-γ gene transcription during Th1 differentiation.