A FACTOR-INDUCED BY DIFFERENTIATION SIGNALS IN CELLS OF THE MACROPHAGE LINEAGE BINDS TO THE GAMMA-INTERFERON ACTIVATION SITE

Rapid transcriptional induction of genes in response to gamma interfer on (IFN-gamma) is mediated by the IFN-gamma activation site (GAS) and its cognate protein, the IFN-gamma activation factor (GAF). We describ e a GAS-associated, differentiation-induced factor (DIF) as a potentia l molecular link between the activities of IFN-gamma and of growth and differentiation factors. DIF DNA binding was activated by colony-stim ulating factor 1 in murine macrophages and also during tetradecanoyl p horbol acetate-induced differentiation or IFN-gamma treatment in myelo id U937 cells. INF-gamma activation of DIF decreased significantly upo n monocytic differentiation. DIF binding to DNA was inhibited by antip hosphotyrosine antibodies and could be induced by treatment of U937 ce lls with vanadate. Unlike GAF, DIF-DNA complexes did not contain the 9 1-kDa protein (p91) from ISGF-3. DIF bound with high affinity to GAS f rom the promoters of the IFP 53/tryptophanyl-tRNA synthetase and Fc ga mma RI genes, intermediate affinity to the Ly6A/E GAS, and low affinit y to the guanylate-binding protein GAS. DIF may belong to a family of cytokine- or growth factor-induced factors binding with variable affin ities to GAS-related elements: the interleukin-6-responsive acute-phas e response factor associated with GAS from different IFN-inducible pro moters but with a different preference of binding compared with DIF. T he sis-inducible element of the c-fos promoter bound GAF but not DIF. However, the sis-inducible element could be changed by point mutation to compete for GAF and DIF binding. Our data show DIF to be a novel DN A-binding protein which is activated in response to differentiating si gnals. Moreover, they suggest that a family of cytokine- or growth fac tor-regulated proteins integrates and coordinates the responses to cyt okines and to growth and differentiation factors by binding to GAS-rel ated elements.