NF-kappaB, and not MYCN, regulates MHC class I and endoplasmic reticulum aminopeptidases in human neuroblastoma cells.
Neuroblastoma (NB) is the most common solid extracranial cancer of childhood. Amplification and overexpression of the MYCN oncogene characterize the most aggressive forms and are believed to severely downregulate MHC class I molecules by transcriptional inhibition of the p50 NF-kappaB subunit. In this study, we found that in human NB cell lines, high MYCN expression is not responsible for low MHC class I expression because neither transfection-mediated overexpression nor small interfering RNA suppression of MYCN affects MHC class I and p50 levels. Furthermore, we identified NF-kappaB as the immediate upstream regulator of MHC class I because the p65 NF-kappaB subunit binds MHC class I promoter in chromatin immunoprecipitation experiments, and MHC class I expression is enhanced by p65 transfection and reduced by (a) the chemical NF-kappaB inhibitor sulfasalazine, (b) a dominant-negative IKBalpha gene, and (c) p65 silencing. Moreover, we showed that the endoplasmic reticulum aminopeptidases ERAP1 and ERAP2, which generate MHC class I binding peptides, are regulated by NF-kappaB, contain functional NF-kappaB-binding elements in their promoters, and mimic MHC class I molecules in the expression pattern. Consistent with these findings, nuclear p65 was detected in NB cells that express MHC class I molecules in human NB specimens. Thus, the coordinated downregulation of MHC class I, ERAP1, and ERAP2 in aggressive NB cells is attributable to a low transcriptional availability of NF-kappaB, possibly due to an unknown suppressor other than MYCN.
Forloni
Matteo
M
Research Center, Ospedale Bambino Gesù, Rome, Italy.
Albini
Sonia
S
Limongi
Maria Zaira
MZ
Cifaldi
Loredana
L
Boldrini
Renata
R
Nicotra
Maria Rita
MR
Giannini
Giuseppe
G
Natali
Pier Giorgio
PG
Giacomini
Patrizio
P
Fruci
Doriana
D
D000626:Aminopeptidases / Q000235:genetics / Q000378:metabolism*; D015153:Blotting, Western; D045744:Cell Line, Tumor; D047369:Chromatin Immunoprecipitation; D005434:Flow Cytometry; D015395:Histocompatibility Antigens Class I / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D015778:Minor Histocompatibility Antigens; D000071447:N-Myc Proto-Oncogene Protein; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D009447:Neuroblastoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D015513:Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D021381:Protein Transport / Q000187:drug effects; D034622:RNA Interference; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D015395:Histocompatibility Antigens Class I; C459801:MYCN protein, human; D015778:Minor Histocompatibility Antigens; D000071447:N-Myc Proto-Oncogene Protein; D016328:NF-kappa B; D009687:Nuclear Proteins; D015513:Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D000626:Aminopeptidases; C464841:ERAP1 protein, human; C503944:ERAP2 protein, human