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This Article Full Text Full Text (PDF) Data Supplement All Versions of this Article: jimmunol.0803693v1 183/5/3188    most recent Alert me when this article is cited Alert me if a correction is posted Citation Map Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Permissions Google Scholar Articles by Zhou, J. X. Articles by Morse, H. C. PubMed PubMed Citation Articles by Zhou, J. X. Articles by Morse, H. C., III

IFN Regulatory Factor 8 Regulates MDM2 in Germinal Center B Cells¹

Laboratory of Immunopathology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, MD 20852

IFN regulatory factor 8 (IRF8) is a transcription factor that affects the differentiation and function of myeloid, dendritic, and B cells. Herein we report that IRF8 regulates the expression of Mdm2, a suppressor of p53-dependent and -independent apoptosis pathways, in germinal center (GC) B cells. In GC B cells of IRF8-deficient mice, Mdm2 transcripts were greatly down-regulated, and MDM2 protein was poorly expressed in GC of Irf8^–/– mice. Small interfering RNA-induced repression of IRF8 in a GC-derived B cell line resulted in decreased expression of MDM2 at the protein level but increased expression of p53 and p21. We found that IRF8 binds to the Mdm2 P2 promoter, and that cotransfection of an IRF8 expression vector with an Mdm2 reporter construct stimulated significant increases in reporter activity. Additionally, transcripts of the p53 target Pmaip1 (Noxa) were significantly increased in IRF8-deficient GC B cells as well as in the IRF8 knockdown B cell line. Finally, cells deficient in IRF8 exhibited growth suppression and increased sensitivity to apoptosis induced by etoposide or IL-21. These results suggest that by regulating MDM2, IRF8 might allow GC B cells to tolerate physiological DNA breaks that otherwise would trigger apoptosis.

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 the Intramural Research Program of the National Institute of Allergy and Infectious Diseases, National Institutes of Health.

² J.X.Z. and C.H.L. contributed equally to the experimental work.

³ Address correspondence and reprint requests to Dr. Jeff X. Zhou and Dr. Herbert C. Morse III, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 5640 Fishers Lane, Rockville, MD 20852. E-mail addresses: jeffxzhou{at}gmail.com and hmorse{at}niaid.nih.gov

⁴ Abbreviations used in this paper: GC, germinal center; SHM, somatic hypermutation; CSR, class switch recombination; DSB, double-strand break; IRF, IFN regulatory factor; siRNA, small interfering RNA; WT, wild type; PNA, peanut lectin (agglutinin); IECS, IRF/Ets composite site; qPCR, quantitative real-time RT-PCR; ChIP, chromatin immunoprecipitation.

⁵ The online version of this article contains supplemental material.