DNA Alkylating Agents Alleviate Silencing of Class II Transactivator Gene Expression in L1210 Lymphoma Cells

Abstract

MHC class II (Ia) Ag expression is inversely correlated with tumorigenicity and directly correlated with immunogenicity in clones of the mouse L1210 lymphoma (1 ). Understanding the mechanisms by which class II Ag expression is regulated in L1210 lymphoma may facilitate the development of immunotherapeutic approaches for the treatment of some types of lymphoma and leukemia. This study demonstrates that the variation in MHC class II Ag expression among clones of L1210 lymphoma is due to differences in the expression of the class II transactivator (CIITA). Analysis of stable hybrids suggests that CIITA expression is repressed by a dominant mechanism in class II-negative L1210 clones. DNA-alkylating agents such as ethyl methanesulfonate and the chemotherapeutic drug melphalan activate CIITA and class II expression in class II negative L1210 cells, and this effect appears to be restricted to transformed cell lines derived from the early stages of B cell ontogeny. Transient transfection assays demonstrated that the CIITA type III promoter is active in class II− L1210 cells, despite the fact that the endogenous gene is not expressed, which suggests that these cells have all of the transacting factors necessary for CIITA transcription. An inverse correlation between methylation of the CIITA transcriptional regulatory region and CIITA expression was observed among L1210 clones. Furthermore, 5-azacytidine treatment activated CIITA expression in class II-negative L1210 cells. Collectively, our results suggest that 1) CIITA gene expression is repressed in class II− L1210 cells by methylation of the CIITA upstream regulatory region, and 2) treatment with DNA-alkylating agents overcomes methylation-based silencing of the CIITA gene in L1210 cells.

Inactivation of class II transactivator by DNA methylation and histone deacetylation associated with absence of HLA-DR induction by interferon-γ in haematopoietic tumour cells

“…DNA methylation is known to be involved in the regulation of CIITA and MHC gene expression in several tumour cell types, including trophoblast-derived cells, a subset of lymphoma cells, and squamous cell carcinoma (Morris et al, 2000;Nie et al, 2001;Murphy et al, 2002;Moreau et al, 2003). Our results suggest that DNA methylation of CIITA-PIV is also a major cause of HLA-DR suppression in haematopoietic tumour cells, especially those derived from T-cells and myeloid cells.…”

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]. 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].…”

“…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].…”

Cytosine arabinoside induces costimulatory molecule expression in acute myeloid leukemia cells

“…[1][2][3][4][5][6][7][8][9][10][11] For example, in mouse lymphoma cells, DNA-alkylating agents alleviate silencing of class II transactivator gene. 12 Another possible mechanism could be the upregulation and/or neoexpression of costimulatory molecules or cytokines by tumor cells. For example, Mokyr and co-workers 13,14 showed that in the MOPC-315 mouse plasmacytoma, melphalan, mitomycin, and g-irradiation enhanced CD80, INF-b, and TNF-a expression.…”