Epigenetic Study Of Folic Acid In Cancer Based On Methylation And MiRNA-mRNA Integrated Regulatory Network

Folic acid(FA,folate)is an essential B vitamin for human body.Folic acid and its metabolites have important physiological and biochemical functions in vivo:1)participate in the biosynthesis of nucleotides;2)folate serves as both donor and acceptor of methyl groups in many one-carbon metabolism reactions,including DNA methylation.The whole genome methylation level and abnormal methylation status of specific oncogenes or tumor suppressor genes can promote the occurrence and development of tumors,so the lack of folate will directly induce cancer.Therefore,maintaining adequate folate levels and normal folate metabolism is very beneficial for cancer prevention.Abundant epidemiological evidence has shown that,insufficient dietary folate intake may increase the risk of various cancers,including breast cancer(BC)and colorectal cancer(CRC),and folate intake is negatively correlated with the incidence rate of related cancers.In breast cancer,the change of estrogen level before and after menopause becomes the cut-off point of breast cancer heterogeneity.The genetic characteristics,epigenetic changes and pathological features between premenopausal breast cancer(pre-BC)and postmenopausal breast cancer(post-BC)are all different,moreover,the prognosis of pre-BC is worse than that of post-BC,and the chemotherapy sensitivity is lower.At the same time,among many risk factors of breast cancer,obesity is an independent prognostic factor.Overweight and obesity are the risk factors of various cancers,which can increase the risk of postmenopausal breast cancer,but reduce the risk of premenopausal breast cancer.The molecular mechanism of the abnormal epidemiological phenomenon that obesity is negatively correlated with pre-BC is still unclear.Previous statistical analysis of population data from NHANES database of the United States conducted by our research group shows that:the content of folate in red blood cells(RBC)of overweight and obese people was higher than that of normal weight people.It is suggested that folate may play an anti-cancer role in the protective effect of obesity on pre-BC.Except BC,folate is also closely related to CRC.On the one hand,the absorption region of folate in human body is small intestine;on the other hand,colorectal mucosa and epithelial tissue regenerate rapidly,which is more sensitive to abnormal metabolism of essential nutrients.Therefore,folate is closely related to the occurrence and development of digestive system cancer,especially CRC.Epidemiological studies have shown that local folate deficiency exists in the intestinal tissues of patients with CRC.This research group had confirmed that the lack of folate in mice will activate tumor-induced Wnt signaling pathway,leading to a significant increase in tumor incidence and tumor multiplicity in colorectal areas.Based on the above two aspects of research background,in this study,clinical samples of premenopausal women's breast tissue and colon epithelial cells of Apc^1638N/+knockout mice were selected as the research objects,the research method of combining classical molecular biology experiments with emerging cross technology bioinformatics analysis was adopted,two epigenetic mechanisms of folate in Pre-BC and CRC were explored:methylation and miRNA-mRNA interaction.The main contents and conclusions are as follows:1.Folic acid plays a protective role in inhibiting breast cancer risk in premenopausal obese women by regulating epigenetic methylation.In a state of obesity,the breast tissue folate status of premenopausal women will be improved and enhanced with the increase of BMI.In the meantime,the overall methylation level of genome will also increase simultaneously,and the expression of tumor suppressor genes SFRP1 and MLH1 will also increase significantly.The methylation level of MLH1 promoter region was positively correlated with breast tissue folate content.It is suggested that the metabolism of breast tissue folate in premenopausal women may be affected by obesity factors,which may inhibit the occurrence of breast cancer through genome-wide methylation and specific methylation of breast cancer related genes.2.Folic acid is involved in the tumorigenic signal pathway of CRC through regulating miRNA-mRNA integrated interaction network,and then affects the occurrence and development of CRC.The folate deficiency animal model of Apc^1638N/+gene knockout mice showed that folate deficiency could significantly increase tumor incidence and multiplicity in colorectal region of mice,and affect the differential expression of miRNA,thus 15 DE-miRNA molecules were identified.Finally,a visualized miRNA-mRNA interaction network of Wnt/apoptosis/cell cycle signaling pathway related to folate regulation was constructed.The representative miRNA-mRNA negative regulatory pairs in the signal pathway interaction network were screened and identified:for example,mmu-mi R-27a/Sfrp1 and mmu-mi R-361/Ctbp2 in Wnt signaling pathway miRNA-mRNA interaction network;mmu-mi R-690/Kras in Apotosis interaction network;and mmu-mi R-21/Stag2 in cell cycle interaction network.So far,the docking of DE-miRNA in colon epithelium of mice model lacking of one carbon vitamin and DEGs of adjacent tissues in mice model of colorectal cancer interfered by gavage of folate was successfully realized,it also integrates miRNA and mRNA of tumor signaling pathway related to folate metabolism.According to the miRNA mRNA integrated interaction network,folic acid may regulate the oncogenic signal pathway of colorectal cancer by regulating the interaction between miRNA and target genes,and then affect the evolution of malignant tumors.To sum up,this paper studies the molecular mechanism of folate affecting the occurrence and development of breast cancer and colorectal cancer through epigenetic pathways such as methylation and miRNA-mRNA interaction.The results provide a new theoretical exploration and experimental basis for further understanding the antitumor mechanism of folic acid.It is a theoretical basis for folate to be included in conventional cancer chemopreventive supplements by promoting preventive medicine and pu blic health policy.