Graham Burdge’s research study is an important step forward in being able to help nutritionists devise dietary recommendations for folic acid intake to the general population and to those at risk of cancers
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The breast cancer associated genes BRCA1 and 2 are critical for repair of double stranded DNA damage in all cells. Silencing or decreased transcription due to increased DNA methylation of BRCA promoters is involved causally in sporadic breast and ovarian cancer. Such silencing increases genomic instability and hence underpins the tumorigenic process.
Interventions that prevent methylation of the BRCA genes may, therefore, reduce the risk of cancer. Folate is a critical cofactor in 1-carbon metabolism linked to DNA methylation. Folate status has been shown to be negatively associated with risk of some cancers including breast and ovarian.
However, there is uncertainty in the literature as to whether the synthetic folate, folic acid protects against or promotes cancer. We have shown previously that folic acid supplementation of juvenile rats induced a tissue-specific, persistent changes in the methylation of BRCA1 which were associated with altered mRNA and protein expression. Such tissue-specific effects may underlie the conflicting reports of about the effect of folic acid on cancer risk.
To address this, we tested the hypothesis that: folic acid treatment induces, through altered epigenetic regulation, dose-dependent, cell-specific changes in BRCA1 and BRCA2 transcription, and so modifies capacity for protection against DNA damage.
Normal cells and their cancer counterparts were treated with physiological concentrations of folic acid. We found that FA treatment induced dose-related increase in BRCA1 mRNA expression in liver (HepG2), breast epithelial (Hs578T) carcinomas, and in BRCA2 in liver (HepG2), breast (Hs578T, MCF7 and MDA-MB-157) cancer cells.
Folic acid did not affect the corresponding normal cells or on any of the leukocyte or ovarian cell lines tested. Folic acid induced increased BRCA1 protein expression in Hs578T, but not HepG2 cells, while BRCA2 protein levels were undetectable. Folic acid treatment did not alter DNA repair in liver-derived cells, while there were transient effects on breast-derived cells.
There was no effect of FA treatment on BRCA1 or 2 DNA methylation, although there was some variation in the methylation of specific CpG loci between cell lines. Overall, these findings show that the effects of folic on BRCA-related outcomes differ between cells lines, but the biological consequences of induced changes in BRCA expression appear to be limited.
Thus it appears unlikely that altered epigenetic regulation of BRCA1 or 2 is the primary mechanism underlying the effects of folic acid on tumorigenesis. In order to gain novel insights into the differential effects of FA on cancer cells, we analysed the expression of the transcriptome of two breast cancer cell lines and compared these with the findings with a non-cancer cell line.
We found that the three major pathways that were altered by FA treatment in all three cell types showed marked, cell type-related differences in the expression of individual genes within these pathways. This provides highly novel information about the mechanism by which FA may induce different responses in different cell types.
This project tested the hypothesis that: Folic acid can change the way in which the tumour-preventing genes BRCA1 and BRCA2 work in a manner that protects cells from cancer-related damage. However, we predict that this effect differs between normal and cancer cells, and between cells from different tissues in the body.
The genes BRCA1 and 2 are important for repairing damaged DNA in all cells and so prevent the formation of cancers. Impaired function of these genes is important in cancers of the breast and ovary. However, most of these cancers do not involve mutations in BRCA genes. Instead, the processes which control how these genes work are altered in a way that reduces their ability to repair damaged DNA.
The vitamin folic acid is involved in controlling the function of BRCA genes. Our findings show that more folic acid may increase the activity of the BRCA genes in some cells, but decrease it on others. In order to make safe dietary recommendations for consumption of folic acid, including dietary changes to prevent or help treat cancers, we need to understand why different tissues respond differently to folic acid.
We tested in the laboratory how different types of cells, normal and cancer, respond to folic acid treatment. We then investigated how this affects the control of the BRCA genes and their ability to repair damaged DNA.
We found that, as we predicted, folic acid did improve the activity of the BRCA genes in some, but not all, cell types that were tested. However, these effects did not protect the cells from damage. Consequently, we then tested the effect of folic acid on all the genes that are active in the cells and found that folic acid affected different genes in different cells.
We did not find changes in the processes that control the BRCA genes that we expected, but it is still possible that these control mechanisms may be affected in other genes.
Our findings are an important step forward in being able to help nutritionists devise dietary recommendations for folic acid intake to the general population and to those at risk of cancers.
