The effect of thyroid hormones and 5-azacytidine on transcription of malic enzyme and 6-phosphogluconate dehydrogenase genes

Great attention is now being paid to elucidating the correlation between the nature of DNA methylation and the functional status of the cell, since DNA methylation is thought to be one of the factors responsible for the regulation of gene activity [1]. Earlier, we studied the effect of thyroid hormones on DNA methylation in rat liver in rive and in vitro using the following approaches: deterruination of msC content in total nuclear DNA from rat liver at various levels of thyroid hormones; comparative study of DNA methylase activity in ceil nuclei and investigation of accepter properties of DNA, chromatin, and intact nuclei in the methylation reaction performed in vitro in the presence of bacterial DNA methylases. As was shown, DNA is relatively hypomethylated after injection of triiodothyroni,fle (T3) in both thyroidectomized and intact rats, and simultaneously we recorded a decrease in DNA methylase activity. These experiments led us to conclude that thyroid hormones block the system of DNA methylation [2]. The aim of the present study was to analyze how the blocking of DNA methylation impacts the functional activity of thyroid hormone-responsive genes.