A 3'-transcribed region of the HLA-A2 gene mediates posttranscriptional stimulation by IFN-gamma.
The expression of several MHC class I genes is up-regulated at the transcriptional level by IFN-gamma. Posttranscriptional mechanisms also have been implicated, but not well characterized. To investigate the mechanism of IFN-gamma stimulation of the human MHC class I gene HLA-A2, several human tumor cell lines were transfected with reporter gene constructs driven by the HLA-A2 promoter. We have previously shown that the extended 525-bp HLA-A2 promoter alone, which includes a 5' IFN-stimulated response element consensus sequence, is not sufficient for IFN-gamma response in either K562 or Jurkat cells. In the current study, stable transfection of a genomic HLA-A2 gene construct, containing both 5'- and 3'-flanking sequences, resulted in stimulation of the gene by IFN-gamma. Nuclear run-on assays revealed that, unlike other class I genes, IFN-gamma stimulation of HLA-A mRNA accumulation occurs almost entirely through posttranscriptional mechanisms. RNA stability assays showed that the effect is not mediated by alteration of the half-life of the HLA-A2 mRNA. Formation of the 3' end was unaffected by IFN-gamma treatment. Sequences that mediate the majority of IFN-gamma induction of HLA-A2 mRNA reside in a 127-bp 3'-transcribed region of the gene. This region contains the terminal splice site, the usage of which is not affected by IFN-gamma treatment. These results demonstrate a novel posttranscriptional mechanism of regulation of MHC class I genes by IFN-gamma.
Massey Cancer Center, Virginia Commonwealth University, Richmond, VA 23298, USA.
S R
SR
Snyder
J F
JF
Waring
S Z
SZ
Zhu
S
S
Kaplan
J
J
Schultz
G D
GD
Ginder
D020413:3' Untranslated Regions / Q000276:immunology*; D017398:Alternative Splicing / Q000276:immunology; D001483:Base Sequence; D005786:Gene Expression Regulation / Q000276:immunology; D005805:Genes, MHC Class I / Q000276:immunology; D015234:HLA-A Antigens / Q000235:genetics / Q000378:metabolism; D015789:HLA-A2 Antigen / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism*; D006207:Half-Life; D006367:HeLa Cells; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology*; D019169:Jurkat Cells; D020014:K562 Cells; D012323:RNA Processing, Post-Transcriptional / Q000276:immunology*; D012333:RNA, Messenger / Q000378:metabolism; D014158:Transcription, Genetic / Q000276:immunology*; D014162:Transfection; D020298:U937 Cells
D020413:3' Untranslated Regions; D015234:HLA-A Antigens; D015789:HLA-A2 Antigen; D012333:RNA, Messenger; D007371:Interferon-gamma