title: CpG hypermethylation of the C-myc promoter by dsRNA results in growth suppression.
abstract: Deregulation of the c-myc proto-oncogene plays an important role in carcinogenesis. It is, therefore, commonly found to be overexpressed in various types of tumors. Downregulation of c-myc expression assumes great importance in tumor therapy because of its ability to promote and maintain cancer stem cells. Apart from post-transcriptional gene silencing (PTGS), siRNAs have also been shown to cause transcriptional gene silencing (TGS) through epigenetic modifications of a gene locus. This approach can potentially be used to silence genes for longer periods and at a much lesser dosage than PTGS. In this study, we have examined the effect of transfection of a novel siRNA directed against a CpG island encompassing the CT-I(2) region in the P2 promoter of c-myc in U87MG and other cell lines. Transient transfection with this siRNA resulted in c-myc promoter CpG hypermethylation and decreased expression of c-myc (both mRNA and protein) and its downstream targets. A decrease was also observed in the expression of some stemness markers (oct-4 and nanog). Stable transfection also confirmed the promoter CpG hypermethylation and reduced c-myc expression along with reduced cell proliferation and an increase in apoptosis and senescence. A significant decrease in c-myc levels was also observed in three other cancer cell lines after transient transfection under similar conditions. Thus this novel siRNA has the capability of becoming an effective therapeutic tool in malignancies with overexpression of c-myc and may be of particular use in the eradication of recalcitrant cancer stem cells.
authors: Department of Biochemistry, All India Institute of Medical Sciences, New Delhi 110029, India.
authors: Mohit
authors: M
authors: Mehndiratta
authors: Jayanth Kumar
authors: JK
authors: Palanichamy
authors: Arnab
authors: A
authors: Pal
authors: Mohita
authors: M
authors: Bhagat
authors: Anand
authors: A
authors: Singh
authors: Subrata
authors: S
authors: Sinha
authors: Parthaprasad
authors: P
authors: Chattopadhyay
mesh_terms: D000818:Animals; D015153:Blotting, Western; D018938:Caco-2 Cells; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D018899:CpG Islands / Q000235:genetics; D019175:DNA Methylation; D015536:Down-Regulation; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D020868:Gene Silencing; D016259:Genes, myc / Q000235:genetics*; D006801:Humans; D011401:Promoter Regions, Genetic / Q000235:genetics; D000090063:Proto-Oncogene Mas; D012330:RNA, Double-Stranded / Q000494:pharmacology*
chemical_list: C000715470:MAS1 protein, human; D000090063:Proto-Oncogene Mas; D012330:RNA, Double-Stranded