Identification of E2F1 as an important transcription factor for the regulation of tapasin expression.
HER-2/neu overexpression in tumor cells caused abnormalities of MHC class I surface expression due to impaired expression of components of the antigen-processing machinery (APM) including the low molecular weight proteins, the transporter associated with antigen processing (TAP), and the chaperone tapasin, whereas the expression of MHC class I heavy chain as well as β(2)-microglobulin was only marginally affected. This oncogene-mediated deficient APM component expression could be reverted by interferon-γ treatment, suggesting a deregulation rather than structural alterations as underlying molecular mechanisms. To determine the level of regulation, the transcriptional activity of APM components was analyzed in HER-2/neu(-) and HER-2/neu(+) cells. All major APM components were transcriptionally down-regulated in HER-2/neu(+) when compared with HER-2/neu(-) cells, which was accompanied by a reduced binding of RNA polymerase II to the APM promoters. Site-directed mutagenesis of the p300- and E2F-binding sites in the APM promoters did not reconstitute the oncogene-mediated decreased transcription rate with the exception of tapasin, which was restored in HER-2/neu(+) cells to levels of wild type tapasin promoter activity in HER-2/neu(-) fibroblasts. The E2F-directed control of tapasin expression was further confirmed by chromatin immunoprecipitation analyses showing that E2F1 and p300 bind to the tapasin and APM promoters in both cell lines. Moreover, siRNA-mediated silencing of E2F1 was associated with an increased tapasin expression, whereas transient overexpression of E2F1 launch a reduced tapasin transcription, suggesting that E2F1 is an essential transcription factor for tapasin.
Bukur
Juergen
J
Institute of Medical Immunology, Martin Luther University Halle-Wittenberg, 06112 Halle, Saale, Germany.
Herrmann
Felix
F
Handke
Diana
D
Recktenwald
Christian
C
Seliger
Barbara
B
D000818:Animals; D050687:E2F1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000502:physiology*; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D016297:Mutagenesis, Site-Directed; D041681:NIH 3T3 Cells; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism; D020218:Response Elements / Q000502:physiology*; D001613:beta 2-Microglobulin / Q000235:genetics / Q000378:metabolism; D050880:p300-CBP Transcription Factors / Q000235:genetics / Q000378:metabolism
D050687:E2F1 Transcription Factor; D026901:Membrane Transport Proteins; D018719:Erb-b2 Receptor Tyrosine Kinases; D001613:beta 2-Microglobulin; D050880:p300-CBP Transcription Factors; C493754:E2f1 protein, mouse; C107762:tapasin; C524056:Erbb2 protein, mouse