Cell-cycle dependent micronucleus formation and mitotic disturbances induced by 5-azacytidine in mammalian cells

Abstract

Summary 5-Azacytidine was originally developed to treat human myelogenous leukemia. However, interest in this compound has expanded because of reports of its ability to affect cell differentiation and to alter eukaryotic gene expression. In an ongoing attempt to understand the biochemical effects of this compound, we examined the effects of 5-azacytidine on mitosis and on micronucleus formation in mammalian cells. In L5178Y mouse cells, 5-azacytidine induced micronuclei at concentrations at which we and others have already reported its mutagenicity at the tk locus. Using CREST staining and C-banding studies, we showed that the induced micronuclei contained mostly chromosomal fragments although some may have contained whole chromosomes. By incorporating BrdU into the DNA of SHE cells, we determined that micronuclei were induced only when the compound was added while the cells were in S phase. Microscopically visible effects due to 5-azacytidine treatment were not observed until anaphase of the mitosis following treatment or thereafter. 5-Azacytidine did not induce micronuclei via interference with formation of the metaphase chromosome arrangement in mitosis, a common mechanism leading to aneuploidy. SupravitalUV microscopy revealed that chromatid bridges were observed in anaphase and, in some cases, were sustained into interphase. In the first mitosis after 5-azacytidine treatment we observed that many cells were unable to perform anaphase separation. All of these observations indicate that 5-azacytidine is predominantly a clastogen through its incorporation into DNA.

Age-related changes in radiation-induced micronuclei among healthy adults

“…However, the in vitro micronucleus test is also suitable for the evaluation of genotoxicity (1)(2)(3)(4)(5)(6)(7) and is applied to human biomonitoring (8,9). Since radiationinduced micronuclei show a clear dependence on radiation dose and its quality (10)(11)(12)(13)(14), the micronucleus assay can be applied as a biological dosimeter.…”

Cell Cycle Disturbance in Relation to Micronucleus Formation Induced by the Carcinogenic Estrogen Diethylstilbestrol

“…However, DES as well as 5-azacytidine induced DNA hypomethylation in SHE cells [10]. In addition, 5-azacytidine has been shown to perturb G2 phase transit [11] and to induce micronuclei in SHE cells [12,13]. Cytogenetic analysis revealed that the ma jority of micronuclei induced by 5-azacytidine treatment did not contain whole chromosomes, but chromatin frag ments [12].…”

Cytogenetic anomalies and causes for their occurrence in somatic cells

“…For example, alkylation of the nucleotide pool may lead to aneuploidy through induction of nucleotide modifications of the centromeric region and, as a consequence, changes in the functional state of the kinetochore [75]. Aneuploidy may also be a consequence of interchromosome translocation [77]. It has been discovered that accelerated decondensation of the chromatin of individual chromosomes in connection with a disturbance in the kinetochore organization is apparently also accompanied by aneuploidy [76].…”