Epigenetic Regualtion For The Expression Of DACT1and Molecular Mechanism For Its Suppressive Effects On Cell Proliferation And Migration In Breast Cancer

According to global cancer statistics, the morbidity and mortality ofbreast cancer have ranked the top in females worldwide. Although thecomprehensive therapies for breast cancer had been improved during thepast decade, there is no promising therapy for advanced breast cancer inwhich Disease-Free Survival and Overall survival is worse than that in breastcancer at early stage. Actively and effectively improving the early diagnosisof breast cancer had been proved to be the key element of treatment of breastcancer. Epigenetic is the hot spot of the medical basic scientific research, andvery important for better understanding the occurrence and development ofbreast cancer. Among them, the studies of DNA methylation of tumorsuppressor genes (TSGs) have provided a potentially possibility for the earlydiagnosis of breast cancer.DACT1(dapper, antagonist of beta-catenin, homolog1Xenopuslaevis) belongs to DAPPER family. Previous study had indicated thatDACT1was downregulated and regarded as a TSG in hepatic carcinoma, lung cancer and gastric cancer. These results had suggested that DACT1could act as a new TSG in breast cancer. To demonstrate our hypothesis,RT-PCR, immunohistochemistry, MSP were performed to examine DACT1expression and its promoter methylation status in breast cancer cell lines,primary breast carcinomas and normal breast tissues, and then cellularfunction assays were used to verify whether DACT1could inhibit breastcancer cell proliferation and migration. Besides, we had use western blot toanalyse the effect of DACT1on Wnt/β-catenin signaling pathway. Resultsshowed that mRNA expression level of DACT1was frequentlydownregulated or silenced in89%(8/9) of breast cancer cell lines andprimary breast tumors, and the protein level was also lower in primary breastcancers when compared to paired adjacent tissues. Furthermore, promotermethylation of DACT1was detected in55.6%(5/9) of breast cancer celllines and29.9%(40/134) of primary tumors, but not in any tumor adjacenttissues or normal breast tissues. Treatment of breast cancer cell lines with5-aza-2’-deoxycytidine and trichostatin A can activate DACT1expressionalong with promoter demethylation. The functional assays showed thatectopic expression of DACT1can inhibit cell proliferation and migrationthrough antagonizing Wnt/β-catenin signaling pathway.In summary, our study demonstrated that DACT1was epigeneticallyinactivated by promoter methylation and could be considered as a TSG inbreast cancer...