1. DNA alkylating agents alleviate silencing of class II transactivator gene expression in L1210 lymphoma cells.
- Author
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Murphy SP, Holtz R, Lewandowski N, Tomasi TB, and Fuji H
- Subjects
- 5' Untranslated Regions drug effects, Animals, B-Lymphocytes drug effects, B-Lymphocytes metabolism, B-Lymphocytes pathology, Cell Differentiation drug effects, Cell Differentiation genetics, Cell Differentiation immunology, Clone Cells, DNA Methylation drug effects, Ethyl Methanesulfonate pharmacology, Histocompatibility Antigens Class II biosynthesis, Hybridomas, Leukemia L1210 metabolism, Leukemia L1210 pathology, Mice, Mice, Inbred DBA, Promoter Regions, Genetic drug effects, Trans-Activators antagonists & inhibitors, Trans-Activators biosynthesis, Trans-Activators metabolism, Transcription, Genetic drug effects, Transcription, Genetic immunology, Transfection, Tumor Cells, Cultured, Antineoplastic Agents, Alkylating pharmacology, Gene Expression Regulation, Neoplastic drug effects, Gene Expression Regulation, Neoplastic immunology, Gene Silencing drug effects, Genes, MHC Class II drug effects, Leukemia L1210 genetics, Leukemia L1210 immunology, Nuclear Proteins, Trans-Activators genetics
- 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.
- Published
- 2002
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