Post-transcriptional inhibition of CD40 gene expression in microglia by transforming growth factor-beta.
Microglia are one of the major glial cell types within the central nervous system, and can function as immune effector cells upon activation. CD40 is a cell surface receptor belonging to the TNF receptor family that plays a critical role in the regulation of immune responses. In this study, we investigated the expression of CD40 on microglia, and the role of transforming growth factor-beta (TGF-beta), an immunosuppressive cytokine, in regulating CD40 expression. Microglia constitutively express very low levels of CD40, and IFN-gamma enhances CD40 mRNA and protein expression in these cells. IFN-gamma-induced CD40 mRNA expression is partially sensitive to the protein synthesis inhibitor puromycin, suggesting that ongoing protein synthesis is necessary for optimal induction of CD40 mRNA by IFN-gamma. TGF-beta inhibits IFN-gamma-induced CD40 protein and mRNA expression. Inhibition of IFN-gamma-induced CD40 mRNA levels by TGF-beta in microglia is not due to inhibition of CD40 transcription; rather, inhibition is due to enhanced degradation of CD40 mRNA. These results indicate that TGF-beta can inhibit expression of an immunologically important receptor, CD40, in microglia, and does so at the post-transcriptional level by destabilizing CD40 mRNA. TGF-beta inhibition of CD40 expression may be one of the mechanisms by which TGF-beta exerts its suppressive effects on immune responses.
Department of Cell Biology, University of Alabama at Birmingham, 35294-0005, USA.
V T
VT
Nguyen
W S
WS
Walker
E N
EN
Benveniste
D000818:Animals; D019013:CD40 Antigens / Q000235:genetics* / Q000378:metabolism; D002460:Cell Line; D016207:Cytokines / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D051379:Mice; D017628:Microglia / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism; D011499:Protein Processing, Post-Translational; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins; D015398:Signal Transduction; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D019013:CD40 Antigens; D016207:Cytokines; D012333:RNA, Messenger; D011994:Recombinant Proteins; D016212:Transforming Growth Factor beta; D007371:Interferon-gamma