Bcl-3 and NFkappaB p50-p50 homodimers act as transcriptional repressors in tolerant CD4+ T cells.
The transcriptional events that control T cell tolerance are still poorly understood. To investigate why tolerant T cells fail to produce interleukin (IL)-2, we analyzed the regulation of NFkappaB-mediated transcription in CD4(+) T cells after tolerance induction in vivo. We demonstrate that a predominance of p50-p50 homodimers binding to the IL-2 promoter kappaB site in tolerant T cells correlated with repression of NFkappaB-driven transcription. Impaired translocation of the p65 subunit in tolerant T cells was a result from reduced activation of IkappaB kinase and poor phosphorylation and degradation of cytosolic IkappaBs. Moreover, tolerant T cells expressed high amounts of the p50 protein. However, the increased expression of p50 could not be explained by activation-induced de novo synthesis of the precursor p105, which was constitutively expressed in tolerant T cells. We also demonstrate the exclusive induction of the IkappaB protein B cell lymphoma 3 (Bcl-3) in tolerant T cells as well as its specific binding to the NFkappaB site. These results suggest that the cellular ratio of NFkappaB dimers, and thus the repression of NFkappaB activity and IL-2 production, are regulated at several levels in tolerant CD4(+) T cells in vivo.
Grundström
Susanna
S
Active Biotech Research Center, Scheelevägen 22, S-223 63 Lund, Sweden. susanna.grundstrom@medhs.ki.se
Anderson
Per
P
Scheipers
Peter
P
Sundstedt
Anette
A
D000818:Animals; D000081242:B-Cell Lymphoma 3 Protein; D001665:Binding Sites; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D019281:Dimerization; D004789:Enzyme Activation; D015870:Gene Expression; D051550:I-kappa B Kinase; D020672:I-kappa B Proteins / Q000378:metabolism; D007108:Immune Tolerance / Q000235:genetics; D007376:Interleukin-2 / Q000235:genetics; D051379:Mice; D008822:Mice, Transgenic; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D052002:NF-kappa B p50 Subunit; D011401:Promoter Regions, Genetic / Q000235:genetics; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000032:analysis; D016693:Receptors, Antigen, T-Cell, alpha-beta / Q000235:genetics / Q000502:physiology; D012097:Repressor Proteins / Q000502:physiology*; D051996:Transcription Factor RelA; D014157:Transcription Factors; D014158:Transcription, Genetic
D000081242:B-Cell Lymphoma 3 Protein; C000631344:BCL3 protein, human; C000631345:Bcl3 protein, mouse; C083487:I kappa B beta protein; D020672:I-kappa B Proteins; D007376:Interleukin-2; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; C000606204:NFKBIA protein, human; C000606205:Nfkbia protein, mouse; D021122:Protein Subunits; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger; D016693:Receptors, Antigen, T-Cell, alpha-beta; D012097:Repressor Proteins; C484522:TCR Vbeta3 protein, human; D051996:Transcription Factor RelA; D014157:Transcription Factors; D000072000:NF-KappaB Inhibitor alpha; D004247:DNA; D017346:Protein Serine-Threonine Kinases; C496564:Chuk protein, mouse; D051550:I-kappa B Kinase; C496562:Ikbkb protein, mouse; C496566:Ikbke protein, mouse