Different levels of control prevent interferon-γ-inducible HLA-class II expression in human neuroblastoma cells

Abstract

The HLA class II expression is controlled by the transcriptional activator CIITA. The transcription of CIITA is controlled by different promoters, among which promoter-IV is inducible by IFN-c. We analysed the regulation of HLA class II molecules by IFN-c in a large series of human neuroblastoma cell lines. No induction of surface or intracellular HLA class II molecules and of specific mRNA was observed, in all neuroblastomas, with the exception of a nonprototypic cell line, ACN. In a large subset of neuroblastomas IFN-c induced expression of CIITA mRNA, derived from promoter-IV, which was not methylated. In contrast, in another subset of neuroblastomas, CIITA was not inducible by IFN-c and CIITA promoter-IV was either completely or partially methylated. Interestingly, the use of DNA demethylating agents restored CIITA gene transcriptional activation by IFN-c, but not HLA class II expression. The defect of HLA class II was not related to alterations in RFX or NF-Y transcription factors, as suggested by EMSA or RFX gene transfection experiments. In addition, the transfection of a functional CIITA cDNA failed to induce HLA class II expression in typical neuroblastoma cells. Confocal microscopy and Western blot analysis suggested a defective nuclear translocation and/or reduced protein synthesis in CIITA-transfected NB cells. Altogether, these data point to multiple mechanisms preventing HLA class II expression in the neuroblastoma, either involving CIITA promoter-IV silencing, or acting at the CIITA post-transcriptional level.

Epigenetic regulation of MHC-II and CIITA genes

“…Studies on uveal melanoma cells, T-cell acute lymphocytic leukemia cells and developmental tumors all reveal increased DNA methylation that, when treated with 5-azacytidine, restore the IFN-g inducibility of CIITA and, subsequently, of MHC-II [32][33][34][35]. Neuroblastoma cells also can respond to 5-azacytidine; however, despite restored CIITA expression, MHC-II expression is not activated, revealing that the genes encoding both CIITA and MHC-II are silenced in these tumors through distinct mechanisms [36]. Metastatic breast-tumor lines with decreased CIITA expression compared with nonmetastatic cells also show restored IFN-g inducibility following 5-azacytidine treatment, although the methylation status of the CIITApIV promoter is unclear in this study [37].…”

Polycomb Repressive Complex 2 Confers BRG1 Dependency on the CIITA Locus

“…MHC class II-peptide complexes activate the helper arm of the adaptive immune response, which has several critical roles in immunity, including activation of killer T cells. CIITA is often downregulated and/or unresponsive to IFN-g in cancer cells (7,26,28,(37)(38)(39)(40)(41)(42)(43)(44)(45), or in some cases its activity is redirected through translocation and fusion to other regulators (46). Re-expression of CIITA in various cancers improves immunogenicity and can lead to both tumor clearance and sustained antitumor immunological memory (reviewed in Ref.…”

Mini‐review: Specificity and expression of CIITA, the master regulator of MHC class II genes

“…Moreover, the inability to induce MHCII expression in response to IFN-+ is often associated with tumor cells of non-hematopoietic origin [58,[95][96][97][98][99][100]. There is growing evidence that this inability to express MHCII results from epigenetic silencing of the MHC2TA gene [95][96][97][98][99][100][101][102].…”

“…There is growing evidence that this inability to express MHCII results from epigenetic silencing of the MHC2TA gene [95][96][97][98][99][100][101][102]. The regulatory regions of the MHC2TA gene have been found to be hypermethylated at CpG dinucleotides in MHCII -T cell leukemias, B cell lymphomas and various tumor cells that are unable to express MHCII upon exposure to IFN-+ , including teratocarcinoma, choriocarcinoma, neuroblastoma, erythroleukemia and small cell lung cancer [95,97,[100][101][102]. Histone deacetylation rather than DNA hypermethylation has been implicated in silencing of MHC2TA expression in several squamous cell carcinoma cell lines [103].…”

“…Moreover, the inability to induce MHCII expression in response to IFN-+ is often associated with tumor cells of non-hematopoietic origin [58,[95][96][97][98][99][100]. There is growing evidence that this inability to express MHCII results from epigenetic silencing of the MHC2TA gene [95][96][97][98][99][100][101][102]. The regulatory regions of the MHC2TA gene have been found to be hypermethylated at CpG dinucleotides in MHCII -T cell leukemias, B cell lymphomas and various tumor cells that are unable to express MHCII upon exposure to IFN-+ , including teratocarcinoma, choriocarcinoma, neuroblastoma, erythroleukemia and small cell lung cancer [95,97,[100][101][102].…”