Abstract
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.
Highlights
Neuroblastoma (NB) is the most common malignancy diagnosed in the first year of life
Because MYCN is inversely correlated with MHC class I (MHC I) [8,9,10], and MHC I is positively correlated with ERAP1 expression in human cell lines of various lineages [13, 14], we looked for expression patterns of MYCN, MHC I heavy chain, ERAP1, and ERAP2 by Western blotting (Fig. 1A) and of cell surface MHC I by flow cytometry (Fig. 1B) in a panel of human NB cell lines
Flow cytometry of the four cell lines in which p65 effectively upregulates MHC I heavy chain showed that MHC I surface expression was fairly proportional to the level of MHC I heavy chain in SH-EP and SH-SY5Y but not in IMR-32 and SK-N-BE[2]c in which only a marginal increase was noticeable (Fig. 4D). This poor surface MHC I expression may result from impaired expression of some components in MHC I–presenting machinery, such as β2m and TAP, other than MHC I heavy chain. These results indicate that NF-κB upregulates MHC I, ERAP1, and ERAP2 in NB cell lines, and the low expression of these genes is due to a low efficiency of NF-κB in activating target gene transcription, presumably consequence of a poor constitutive NF-κB nuclear expression, and/or the nuclear translocation as suggested by the tumor necrosis factor α (TNFα) unresponsiveness in several tested NB cell lines (Fig. 3A)
Summary
Neuroblastoma (NB) is the most common malignancy diagnosed in the first year of life. This tumor arises from neural crest cells and shows a wide range of clinical outcomes ranging from spontaneous regression to therapy-resistant progression. Patients bearing aggressive NB tumors have survival probabilities of
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
