PU.1 and Multiple IFN Regulatory Factor Proteins Synergize to Mediate Transcriptional Activation of the Human IL-1β Gene

Abstract

Both lymphoid and myeloid cells express two related members of the IFN regulatory factor (IRF) family of transcription factors, specifically IRF-4 and IFN consensus binding protein (ICSBP or IRF-8). We previously reported that macrophages express IRF-4 and in combination with the ETS-like protein PU.1 can synergistically activate a human IL-1β reporter gene. Here we report that this synergy is mediated by a composite PU.1/IRF element located within an upstream enhancer known to confer cytokine- and LPS-inducible expression. In macrophages, synergistic activation of IL-1β reporter gene expression was preferentially mediated by IRF-4, whereas IRF-4 and ICSBP were equally capable of synergizing with PU.1 when coexpressed in fibroblasts. Furthermore, coexpression of IRF-1 and IRF-2 dramatically increased the capacity of both PU.1/IRF-4 and PU.1/ICSBP to induce IL-1β reporter gene expression in fibroblasts. The additional synergy observed with IRF-1 and IRF-2 coexpression is mediated by a region of DNA distinct from either the IL-1β enhancer or promoter. We also assessed the capacity of these transcription factors to activate endogenous IL-1β gene when overexpressed in human embryonic kidney 293 cells. Although ectopic expression of PU.1 alone was sufficient to activate modest levels of IL-1β transcripts, endogenous IL-1β expression was markedly increased following coexpression of additional IRF proteins. Thus, maximal expression of both a human IL-1β reporter gene and the endogenous IL-1β gene was observed in cells that coexpressed PU.1, IRF-4 (or ICSBP), IRF1, and IRF2. Together, our observations suggest that these factors may function together as an enhanceosome.

Identification of IRF-8 and IRF-1 target genes in activated macrophages

“…The stoichiometry between the interacting partners was not determined and it is possible that several PEST domains interact with an IAD, as observed on promoters of several macrophage specific genes, such as IL-12, IL-1β, and ISG15 Marecki et al 2001b). …”

Transcriptional regulation of granulocyte and monocyte development

“…Pip or Interferon consensus sequence binding protein (ICSBP, can interact with PU.1 in monocytic cells, enabling trans-activation via a hybrid DNA-element binding element (Meraro et al, 1999;Marecki et al, 2001). However, an essential role for Pip or ICSBP interaction for PU.1 activity in myeloid cells has not been established.…”

Correlation between differentiation plasticity and mRNA expression profiling of CD34+-derived CD14− and CD14+ human normal myeloid precursors

“…[40][41][42][43] Recently, PPARd and BCL-6 have been demonstrated to regulate MCP1 (CCL2) monocyte chemokine transcription. 44,45 IRFs, [46][47][48] …”