Methylation and serum response factor mediated in the regulation of gene ARRDC3 in breast cancer

Breast cancer poses a serious threat to women's life and health and many factors contribute to breast cancer including gene mutation and epigenetics. Gene ARRDC3 was usually repressed in breast cancer and methylation in promoter was reported to be involved in gene ARRDC3 expression regulation. To this end, the methylation status for gene ARRDC3 promoter was assayed by the Massarray quantitative method. The results indicated that different methylation level CpG sites including CpG_6, CpG_13.14, CpG_17.18, and CpG_25 existed between the tumor tissue and the adjacent normal tissue. In order to further verify whether methylation participated in gene ARRDC3 expression, three cell lines were treated with methylation inhibitor Aza-2'-deoxycytidine including A-375, HepG2, and MDA-MB-231. The results revealed that methylation inhibition observably increased ARRDC3 mRNA expression. Then we confirmed the effective length of promoter through the fluorescence report assay used for further analysis. The results showed that the 1746 bp length promoter produced the maximum fluorescence signal. To obtain the direct evidence that methylation in gene ARRDC3 promoter mediated in ARRDC3 expression regulation, the promoter plasmid was methylated by M.SssI enzyme and subjected to the fluorescence report assay. The results showed that methylation in the promoter markedly suppressed relative luciferase activity. In addition, the ecRNA was also analyzed for the methylation regulation and results illustrated that the ecRNA did not regulate ARRDC3 promoter methylation. However, several methylation CpG sites were found to be around CpG_25 site such as TGCATGG, TTGCAA, TTCGTA, and ATAGTT. These sites provide a good clue for further research in methylation for gene ARRDC3 expression regulation. Furthermore, the possible transcription factors involved in the ARRDC3 regulation were investigated by western blot, luciferase activity analysis and ChiP assay. These results documented that gene ARRDC3 expression was improved by SRF and that the methylation affected the interaction between the promoter and SRF. Lastly, the inhibition role of gene ARRDC3 on breast cancer was probed in vivo and in vitro and our results demonstrated that ARRDC3 could inhibit breast cancer growth through the STAT3 signal pathway. In summary, Gene ARRDC3 was inhibited by promoter methylation and was promoted by transcription factor SRF by binding the promoter region and the inhibition on breast cancer growth was exerted by ARRDC3 through STAT3 signal pathway.