title: Loss of glucocorticoid receptor expression by DNA methylation prevents glucocorticoid induced apoptosis in human small cell lung cancer cells.
abstract: Human small cell lung cancer (SCLC) is highly aggressive, and quickly develops resistance to therapy. SCLC cells are typically insensitive to glucocorticoids due to impaired glucocorticoid receptor (GR) expression. This is important as we have previously shown that expression of a GR transgene induces cell death in-vitro, and inhibits tumor growth in-vivo. However, the underlying mechanism for loss of GR expression is unknown. The SCLC cell line, DMS79, has low GR expression, compared to non-SCLC cell lines and normal bronchial epithelial cells. Retroviral GR expression in DMS79 cells caused activation of the apoptotic pathway as evidenced by marked induction of caspase-3 activity. Methylation analysis of the GR promoter revealed some methylation in the 1D, and 1E promoters of the GR gene, however the ubiquitous constitutively active 1C promoter was heavily methylated. In the 1C promoter there was a highly significant increase in DNA methylation in a panel of 14 human SCLC cell lines compared to a mixed panel of GR expressing, and non-expressing cell lines, and to peripheral blood mononuclear cells. Furthermore, within the panel of SCLC cell lines there was a significant negative correlation seen between methylation of the 1C promoter, and GR protein expression. Reversal of GR gene methylation with DNA methyltransferase inhibition caused increased GR mRNA and protein expression in SCLC but not non-SCLC cells. This resulted in increased Gc sensitivity, decreased Bcl-2 expression and increased caspase-3 activity in SCLC cells. These data suggest that DNA methylation decreases GR gene expression in human SCLC cells, in a similar manner to that for conventional tumor suppressor genes.
authors: Faculty of Medical and Human Sciences, Manchester Academic Health Sciences Centre, University of Manchester, Manchester, United Kingdom.
authors: Paul
authors: P
authors: Kay
authors: George
authors: G
authors: Schlossmacher
authors: Laura
authors: L
authors: Matthews
authors: Paula
authors: P
authors: Sommer
authors: Dave
authors: D
authors: Singh
authors: Anne
authors: A
authors: White
authors: David
authors: D
authors: Ray
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics; D001374:Azacitidine / Q000494:pharmacology; D001483:Base Sequence; D053148:Caspase 3 / Q000378:metabolism; D045744:Cell Line, Tumor; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation / Q000187:drug effects*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology*; D057809:HEK293 Cells; D006801:Humans; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic / Q000235:genetics; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism*; D055752:Small Cell Lung Carcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D019076:Transgenes / Q000235:genetics
chemical_list: D004791:Enzyme Inhibitors; D005938:Glucocorticoids; D019253:Proto-Oncogene Proteins c-bcl-2; D011965:Receptors, Glucocorticoid; D053148:Caspase 3; D001374:Azacitidine