Study On Blood DNA Methylation Profile Of Thyroid Cancer

It is considered at present that cancer is a genetics and epigenetics disease. Of all epigenetic modifications, hypermethylation, which represses transcription of the promoter regions of tumor suppressor genes leading to gene silencing, has been most extensively studied.To identify DNA methylation markers of thyroid cancer cases in blood samples, we used Illumina Infinium Human Methylation 27K BeadChip to screen the 24 genomic DNA samples for comprehensive DNA Methylation Profiling, and compared the differential methylation of multiple CpG sites between case and control group by Fisher, Pearson and Wilcoxon test. Diffscore>20 and<-20 was chose respectively as hypermethylation and hypomethylation standard. Through the preliminary screening there were 937 genes which were significant composing the methylation profile of thyroid cancer.βscore was calculated from diffscore. Through the variation analysis ofβscore we set two significant threshold. When choosing statistically significant threshold p<=5E-4,40 differentially methylated genes, including 29 high methylated genes and 11 low methylated genes, were identified.8 differentially methylated genes, including 7 high methylated genes and 1 low methylated gene, were identified(p<=1E-4).Then bioinformatics was undertook to analyze the differentially methylated genes with KEGG,REACTOM pathway database, JASPAR2010,TRANSFACTv11.3 Motif database, and GO analysis. Through these bioinformatics analysis we found these differentially methylated genes took part in a lot of biological pathway such as G_ALPHA_Q_SIGNALLING_EVENTS, WNT_SIGNALING, TIGHT_JUNCTION and so on.However, we screened 8 differentially methylated genes (p=1E-4), which had better ability of diagnosing thyroid cancer, the disease prediction had an average precision of 91.67% by thyroid cancer diagnosis model of our study's establishing with some variables from the epidemiological questionnaire.To confirm these aberrant methylated genes, we chose OXTR gene to do methylation specific PCR (MSP) after analyzing some references, laboratory data, related protein's function,biological pathway and so on. Recombinase-acid amplification was used to amplify OXTR gene in 15 thyroid cancer cases' and 15 normal controls'small DNA fragment from blood. OXTR gene methylated was named OXTR-M, as well as OXTR-U represented unmethylated OXTR gene. In cases, there 11 samples had OXTR-M and OXTR-U bands at the same time,4 samples emerged only OXTR-U band. The positive rate of OXTR-M reached 73%. On the other hand, in controls, only one control sample had OXTR-M and OXTR-U bands at the same time, others had OXTR-U band only. The positive rate of OXTR-U reached 93%.In this study we got the blood methylation profile of thyroid cancer as well as some significant differentially methylated genes with beadchip technique. We also confirm one differentially methylated gene OXTR had a higher express rate in thyroid cancer cases. Aberrant methylated genes play an important role in tumorigenesis and could act as molecular markers for thyroid cancer diagnosis in blood.