Effects of 5-azacytidine on methylation and expression of specific DNA sequences in C3H 10T1/2 cells.

Abstract

The present study indicates that the transient exposure of C3H 1OT1/2 mouse embryo fibroblasts to 5-azacytidine leads to extensive loss of methylation of the protooncogene c-mos and the P-globin locus at the cell population level and in at least 40 isolated subclones. These changes persisted, even when the cells were serially passaged for many generations without further exposure to the drug. Even though the amount of demethylation, assessed through differential digestion by the restriction enzymes HpaII and MspI, was quite extensive, neither locus was transcribed at a detectable level. This nonselective analysis suggests, therefore, that loss of DNA methylation is not sufficient per se to induce the expression of certain loci. Presumably, the expression of these loci requires additional factors, some of which may be related to cell lineage and differentiation.

Enhanced in vitro Reactivation of Herpes Simplex Virus Type 2 from Latently Infected Guinea-pig Neural Tissues by 5-Azacytidine

“…Similarly, treatment with 5-AZC induced Epstein-Barr virus early antigens in latently infected human lymphoid cells (Ben-Sasson et al, 1981). Furthermore, an increase in hepatitis B virus core transcripts (Korba et al, 1985) as well as expression of retrovirus type C and type A sequences (Hsiao et al, 1986;Lasneret et al, 1983) and genomes (Jaenisch et al, 1985) have been demonstrated after 5-AZC treatment. We therefore hypothesized that methylation of the HSV genome might be involved in the induction 0000-8084 © 1988 SGM Short communication or maintenance of the latent state by down-regulating viral gene expression and that druginduced hypomethylation might, therefore, enhance reactivation of latent HSV-2.…”

“…The extent of demethylation due to 5-AZC, however, exceeds the amount incorporated, which may relate to the inhibition of the DNA methyltransferase by the drug (Jones, 1985). Once demethylation occurs, it is inherited clonally and some genes activated by demethylation are transcribed in progeny cells (Hsiao et al, 1984;Compere & Palmiter, 1981).…”

Notes on the role of dynamic DNA methylation in mammalian development

“…It has been nearly 40 y since it was suggested that genomic methylation patterns could be transmitted via maintenance methylation during S phase and might play a role in the dynamic regulation of gene expression during development [Holliday R, Pugh JE (1975) Science 187(4173):226-232; Riggs AD (1975) Cytogenet Cell Genet 14(1): [9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. This revolutionary proposal was justified by "... our almost complete ignorance of the mechanism for the unfolding of the genetic program during development" that prevailed at the time.…”

DNA Methylation and Differentiation

“…Treatment of chicken cells with 5-aza-CR caused hypomethylation Rat cells (138) and transcriptional activation of the ev-1 endogenous retroviral locus (128). Drug-induced activation of viruses in human (129,130), murine (131)(132)(133)(134)(135)(136), and rat systems (137,138) has also been reported. In most cases, the inactive proviral genomes were hypermethylated and exhibited decreased 5-methylcytosine levels once activated by 5-aza-CR treatment.…”