Evidence that IFN-gamma does not affect MHC class II gene expression at the post-transcriptional level in a mouse macrophage cell line

Abstract

Mouse class II major histocompatibility complex genes have been shown to be regulated at the level of transcription for both tissue-specific and inducible expression. In particular, IFN-gamma induction of the class II genes has been shown to occur at the transcriptional level, although the role that additional post-transcriptional mechanisms of regulation may play in this induction is not known. To evaluate IFN-gamma effects on transcriptional and post-transcriptional events of class II gene expression, we examined the rate of decline of class II transcription, steady-state mRNA, and cell surface protein following the removal of IFN-gamma from maximally stimulated WEHI-3 cells (an IFN-gamma inducible, myelomonocytic cell line). We determined that transcription of class II genes almost completely returned to baseline levels eight hours after removal of IFN-gamma. However, the steady-state level of class II mRNA's required 4 days, and membrane Ia expression required 5 days to return to baseline levels. This decay was linear and allowed us to determine a half-life value of 16-20 h for class II transcripts. These data demonstrate that, following removal of IFN-gamma from fully stimulated cells, transcription of the class II genes declined rapidly, but mRNA was quite long-lived. We also assessed the class II mRNA stability in unstimulated WEHI-3 cells and the B-cell lymphoma. A20/2J, by actinomycin D treatment and northern blot analysis. In agreement with the IFN-gamma washout experiments, transcripts from all four class II genes were quite long-lived in these cell types, with a half-life greater than ten hours. These data support the concept that IFN-gamma acts primarily at the level of class II transcription and argues against IFN-gamma playing a major role in post-transcriptional modulation of class II expression.

Human chromosome 16 encodes a factor involved in induction of class II major histocompatibility antigens by interferon gamma.

“…in the human-RAG cell hybrids requires, likewise, the presence of human chromosomes 6 and 21, in addition to chromosome 16. In some of these hybrids, when all three of these human chromosomes were present, induction of cell-surface HLA-DR antigens was also observed.…”

“…However, the various DNA-binding proteins known to interact with class II gene promoters are not affected by IFN-y treatment (13). Furthermore, inhibitor studies have led to controversial results regarding the requirement for protein synthesis (14,15), for posttranscriptional regulation (16,17), or for the involvement of protein kinase C (18,19) in class II MHC antigen induction by IFN-y.…”

Capsaicin inhibits IFN-γ-induced MHC class II expression by suppressing transcription of class II transactivator gene in murine peritoneal macrophages

“…For instance, Cellell-Young et al reported that 7-and 12-fold increases in the MHC mRNA levels in cultured macrophage cells treated with IFN-γ for 24 h and 48 h are accompanied by 3-and 9-fold increases in cell surface levels of MHC protein, respectively [38]. In addition, Kern et al reported that, after the removal of IFN-γ from cultured medium, the increased levels of MHC class II mRNA and protein levels on cell surface reverted to baseline with similar time course [39]. Thus, there is a close connection between mRNA levels and cell surface protein levels of MHC class II in macrophages.…”

MHC Class II levels and intracellular localization in human dendritic cells are regulated by calmodulin kinase II

“…This difference in protein levels is paralleled by differences in protein t 1/2 of MHC Class II: ϳ10 h in macrophages versus 52 h in mature DC [68,81]. In contrast, stimulation-induced increases in MHC Class II mRNA levels are prolonged in macrophages (Ͼ48 h) and only transient in DC [10,16,82]. In addition, macrophages express three isoforms of CIITA-pI, pIII, pIV-with a predominance of pI, whereas DC express only pI and pIII, and the levels of each are approximately equal [20,42].…”