Alterations in expression and methylation of specific gene in livers of rats fed a cancer promoting methyl-deficient diet

Abstract

We have reported earlier that hypomethylated DNA is rapidly induced in the livers of male Fischer rats fed an extremely methyl-deficient diet (MDD). The early effects of dietary methyl deficiency on the expression of several genes in the livers of such animals have now been investigated. Poly(A)+ RNA was isolated from the livers of rats fed MDD or a similar diet supplemented with adequate supplies of choline, methionine, folic acid and vitamin B12 (CSD) for periods ranging from 1 to 4 weeks. The levels of mRNAs for the c-myc and c-fos protooncogenes in livers of rats given either MDD or the liver carcinogen, 2-acetylaminofluorene (AAF), were compared by Northern blot analysis with those in livers of animals given control diets. Both AAF and MDD induced significant elevations in levels of mRNAs specific for these two genes. After 1 week of MDD intake, large increases in the levels of c-myc and c-fos mRNAs and a smaller increase in the levels of c-Ha-ras mRNAs were observed. In contrast, there were marked decreases in the levels of mRNAs for epidermal growth factor receptor and for epidermal growth factor. These effects on mRNA accumulation persisted and were further enhanced during a 4 week period of MDD feeding. The appearance of hypomethylated DNA in the livers of these MDD-fed rats coincided with the observed changes in levels of mRNA for these genes associated with the regulation of cell growth. Increases in levels of mRNA for c-fos, c-Ha-ras and c-myc were correlated with loss of methylation at specific sites within these genes as early as 1 week after the start of MDD feeding. These combined observations are consistent with the hypothesis that methyl-deficient diets are cancer promoting and/or carcinogenic, at least in part, because they induce hypomethylation of DNA with concomitant alterations in the regulation of gene expression.

Increase in Plasma Homocysteine Associated with Parallel Increases in Plasma S-Adenosylhomocysteine and Lymphocyte DNA Hypomethylation

“…Cellular methyltransferases that have been shown experimentally to be inhibited by SAH include catecholamine-O-methyltransferase (39), phosphatidylethanolamine methyltransferase (46), histone methyltransferase (18), DNA methyltransferase (18,26,47), tRNA and mRNA methyltransferases (48,49), acetylserotonin methyltransferase (50), and histamine N-methyltransferase (51). The functional consequences of decreased cellular methylation are significant and include central nervous system demyelination (52,53), reduced neurotransmittor synthesis (39,50), decreased chemotaxis and macrophage phagocytosis (54,55), altered membrane phospholipid composition and membrane fluidity (56,58), altered gene expression (23,59,60), and cell differentiation (61,62). It is likely that the K i for SAH varies with different cellular methyltransferases and also varies according to tissue priorities and subcellular methyltransferase distribution (63).…”

Biological Effects of Polyamines on the Prevention of Aging-associated Diseases and on Lifespan Extension

“…Moreover, it was reported that a diet deficient in methyl groups provoked the demethylation of c-myc, c-fox, H-ras, and p-53 genes (Bhave et al, 1988;Christman et al, 1993;Dizik et al, 1991;Pogribny et al, 1995;Zapisek et al, 1992). In other studies, supplementation of methyl groups affected the methylation status and gene expression of several genes (Garcea et al, 1989;Kano et al, 2013).…”

Perspectives in cancer chemoprevention.

“…In contrast, methyl-rich (fortified with choline and methionine) diets prevent or reduce these effects in the liver (147)(148)(149). Changes in the expression levels of protooncogenes and decreased expression of growth factors and growth factor receptors occur in animals on methyl-deficient diets (143,150,151). The increased protooncogene expression correlates with hypomethylation of the protooncogenes (143,150).…”

“…Changes in the expression levels of protooncogenes and decreased expression of growth factors and growth factor receptors occur in animals on methyl-deficient diets (143,150,151). The increased protooncogene expression correlates with hypomethylation of the protooncogenes (143,150). Collectively, these data suggest that hypomethylation of DNA results in changes in the expression of genes involved in cellular growth control (143,148).…”