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Induction of Class II Transactivator: A Role for PRDM1/Blimp-1 in Regulation of Cytokine Signaling1
Section of Experimental Hematology, Leeds Institute of Molecular Medicine, University of Leeds, Leeds, United Kingdom
MHC class II is expressed in restricted lineages and is modulated in response to pathogens and inflammatory stimuli. This expression is controlled by MHC CIITA, which is transcribed from multiple promoters. Although factors required for induction of CIITA are well characterized, less is known about the mechanisms leading to repression of this gene. During plasma cell differentiation, B lymphocyte-induced maturation protein-1 (PRDM1/Blimp-1) represses promoter (p)III of CIITA, responsible for constitutive expression in B cells. pIV is inducible by IFN-
in epithelia, macrophages and B cells. An IFN regulatory factor-element (IRF-E) in CIITA-pIV, which is bound by IRF-1 and IRF-2, is necessary for this response. This site matches the PRDM1/Blimp-1 consensus binding site, and PRDM1/Blimp-1 is expressed in cell lineages in which this promoter is operative. We, therefore, investigated whether PRDM1 regulates CIITA-pIV and found that PRDM1 bound to CIITA-pIV in vivo and the IRF-E in vitro. PRDM1 repressed IFN--mediated induction of a CIITA-pIV luciferase reporter in a fashion dependent on an intact consensus sequence and competes with IRF-1/IRF-2 for binding to the IRF-E and promoter activation. In human myeloma cell lines that express IRFs, PRDM1 occupancy of CIITA-pIV was associated with resistance to IFN- stimulation, while short interfering RNA knockdown of PRDM1 led to up-regulation of CIITA. Our data indicate that PRDM1 is a repressor of CIITA-pIV, identifying a target of particular relevance to macrophages and epithelia. These findings support a model in which PRDM1/Blimp-1 can modulate the cellular response to IFN- by competing with IRF-1/IRF-2 dependent activation of target promoters.
The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
1 This work was supported by a Medical Research Council Clinician Scientist Fellowship (R.M.T.) and a Leeds University Research Fellowship (G.M.D.).
2 Address correspondence and reprint requests to Dr. Gina M. Doody, Section of Experimental Hematology, Leeds Institute of Molecular Medicine, St. James’s University Hospital, University of Leeds, Leeds LS9 7TF, U.K. E-mail address: medgmd{at}leeds.ac.uk
3 Abbreviations used in this paper: MHC-II, MHC class II; Blimp-1, B lymphocyte-induced maturation protein-1; FL, full length; PRDI, positive regulatory domain I; PRDM1, PR-domain containing protein-1; IRF, IFN regulatory factor; IRF-E, IRF-element; ChIP, chromatin immunoprecipitation; p, promoter; GAS, IFN- activation sequence; siRNA, short interfering RNA.
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