Methylation of CIITA promoter IV causes loss of HLA-II inducibility by IFN-gamma in promyelocytic cells.
The human promyelocytic cell line THP-1 expresses high level of HLA class II (HLA-II) molecules after IFN-gamma treatment. Here, we report a variant of THP-1 that does not express HLA-II after IFN-gamma. The variant's HLA-II phenotype is constant over time in culture and it is not related to a defective IFN-gamma-signalling pathway. Transfection of CIITA, the HLA-II transcriptional activator, under the control of a cytomegalovirus promoter rescues high level of HLA-DR surface expression in the variant indicating that the biosynthetic block resides in the expression of CIITA and not in the CIITA-dependent transactivation of the HLA-II promoters. Treatment of the variant with 5-azacytidine (5-aza), which inhibits CpG methylation, restores inducibility of HLA-II by IFN-gamma both at transcriptional and phenotypic level and antigen presenting and processing function of the variant. DNA studies demonstrate that the molecular defect of the THP-1 variant originates from the methylation of the CIITA promoter IV. Furthermore, treatment with 5-aza produces a substantial demethylation of CIITA promoter IV and a significant increase of IFN-gamma-dependent HLA-II expression in another myelomonocytic cell line, U937. Therefore hyper-methylation of CIITA promoter IV may be a relevant mechanism of epigenetic control preventing HLA-II IFN-gamma inducibility in the myelomonocytic cell lineage.
De Lerma Barbaro
Andrea
A
Department of Clinical and Biological Sciences, Unit of General Pathology and Immunology, School of Medicine, Università of Insubria, Varese, Italy. a.delermabarbaro@uninsubria.it
De Ambrosis
Alessandro
A
Banelli
Barbara
B
Li Pira
Giuseppina
G
Aresu
Ottavia
O
Romani
Massimo
M
Ferrini
Silvano
S
Accolla
Roberto S
RS
D017951:Antigen Presentation; D001374:Azacitidine / Q000494:pharmacology; D019175:DNA Methylation / Q000187:drug effects; D042381:Granulocyte Precursor Cells / Q000187:drug effects / Q000378:metabolism*; D006684:HLA-DR Antigens / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007371:Interferon-gamma / Q000235:genetics / Q000378:metabolism*; D008213:Lymphocyte Activation; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D011401:Promoter Regions, Genetic; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D020298:U937 Cells
D006684:HLA-DR Antigens; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D015534:Trans-Activators; D007371:Interferon-gamma; D001374:Azacitidine