From transcription to cell surface expression, the induction of MHC class II I-A alpha by interferon-gamma in macrophages is regulated at different levels.
Using mouse bone marrow-derived macrophages we determined the role of interferon (IFN)-gamma at the different steps in expression of the I-A alpha chain of MHC class II molecules, from transcription to the cell surface. Levels of transcription, RNA, and protein were low in cells not stimulated with IFN-gamma. Treatment with IFN-gamma for 24 or 48 h induced an increase in mRNA levels (7- and 12-fold) that did not correlate with the increase in transcription (2.5- and 2.7-fold). The half-life of mRNA was not modified by IFN-gamma. These data suggest a block at the level of translation. In fact, IFN-gamma increased ribosome loading, which confirms regulation at the translational level. Treatment with IFN-gamma increased protein synthesis (6-fold after 48 h) and level of expression at the cell surface (3- and 9-fold after 24 and 48 h, respectively). Interestingly, treatment with IFN-gamma also increased the I-A alpha protein half-life from 2 to 6-7 h. This is the first attempt to determine qualitatively and quantitatively the regulation of an inducible gene at all the putative levels of control. The data indicate that IFN-gamma plays a critical role in MHC class II protein expression in macrophages through the regulation of different steps, from transcription to surface expression.
Cullell-Young
M
M
Departament de Fisiologia (Biologia del macròfag), Facultat de Biologia and Fundació August Pi i Sunyer, Campus de Bellvitge, Universitat de Barcelona, Av. Diagonal 645, 08028 Barcelona, Spain.
Barrachina
M
M
López-López
C
C
Goñalons
E
E
Lloberas
J
J
Soler
C
C
Celada
A
A
D000818:Animals; D002462:Cell Membrane / Q000276:immunology; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis* / Q000235:genetics*; D007371:Interferon-gamma / Q000494:pharmacology*; D007700:Kinetics; D008264:Macrophages / Q000187:drug effects* / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins; D014158:Transcription, Genetic / Q000187:drug effects
D000949:Histocompatibility Antigens Class II; D012333:RNA, Messenger; D011994:Recombinant Proteins; D007371:Interferon-gamma