Evidence that IFN-gamma does not affect MHC class II gene expression at the post-transcriptional level in a mouse macrophage cell line.
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.
Kern
M J
MJ
Department of Microbiology and Immunology, Albert B Chandler Medical Center, University of Kentucky, Lexington 40536-0084.
Stuart
P M
PM
Omer
K W
KW
Woodward
J G
JG
D000818:Animals; D015152:Blotting, Northern; D002460:Cell Line; D003609:Dactinomycin / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D006207:Half-Life; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis / Q000235:genetics*; D007371:Interferon-gamma / Q000494:pharmacology*; D007700:Kinetics; D008264:Macrophages / Q000187:drug effects; D008285:Major Histocompatibility Complex / Q000187:drug effects*; D051379:Mice; D012333:RNA, Messenger / Q000187:drug effects; D014158:Transcription, Genetic / Q000187:drug effects*
D000949:Histocompatibility Antigens Class II; D012333:RNA, Messenger; D003609:Dactinomycin; D007371:Interferon-gamma