Tamoxifen is included in the treatment protocol of
Tamoxifen is included in the treatment protocol of ER+ breast carcinoma patients routinely. Although tamoxifen improves patients' survival, unfortunately a large number of ER+ patients don't response to tamoxifen treatment (Yager and Davidson, 2006). Detection of molecular markers which could take a role in resistance progression is a considerable research interest. Generally, genetic and epigenetic variations contribute to tamoxifen refractory. Abnormal methylation pattern, as the most prevalent epigenetic modification, was reported to be involved in tumorigenesis and disease recurrence in a wide variety of malignancies. (Gao et al., 2013). DNMTs expression has been established as the key factors that could regulate methylation pattern in the human genome. (Das and Singal, 2004). It has been indicated previously that altered expression of DNMT1, DNMT3A, and DNMT3B are involved in lung cancer (Belinsky et al., 1996), ovarian cancer (Bai et al., 2012), acute and chronic myelogenous leukemia (Mizuno et al., 2001), hepatocellular carcinomas (Nagai et al., 2003), uterine cervical carcinoma (Luczak et al., 2012), prostate cancer (Patra et al., 2002), liver cancer (Oh et al., 2007), and melanoma (Deng et al., 2009). DNA methylation profile has been introduced as a potentially novel prognostic marker, which can predict tamoxifen response in breast cancer patients (Bai et al.). Hypermethylation of hormone receptor promoters including, 873 and progesterone receptors and the promoters of some tumor suppressor genes (TSGs) have been reported previously in patients who don't benefit from tamoxifen treatment (Bardou et al., 2003; Cui et al., 2005; Herynk and Fuqua, 2007). In the current study, protein expression pattern of all three types of DNMTs were immunohistochemically detected in ER+ breast carcinoma patients who received adjuvant tamoxifen. The results indicated that the protein expression of DNMT1, DNMT3A, and DNMT3B are higher in tamoxifen resistant patients in comparison to tamoxifen sensitive ones. We have indicated previously that mRNA expression of DNMT3A and DNMT3B were higher in tamoxifen resistance breast carcinoma patients in comparison to tamoxifen tamoxifen sensitive ones although the observed difference was not significant about DNMT1. microRNAs have been introduced as important mediators of post-transcriptional regulation of mRNAs, it has been indicated that miR-148a, miR-152, and miR-301 have the sequence complementarity to the 3′-UTR of DNMT1 and could target the transcript of DNMT1 and take roles in the regulation of DNMT1 expression (Braconi et al., 2010). mRNA expression analyses of all three DNMTs were performed in our previous study (Jahangiri et al., 2018a). Spearman correlation coefficient was performed to indicated the association between mRNA and protein expression of DNMTs. Data analysis revealed a positive correlation between mRNA and protein expression of DNMT1 (r: 289, P = 0.014), DNMT3A (r: 229, P = 0.053), and DNMT3B (r: 285, P = 0.015). Our present study was in line with other studies that indicated overexpression of DNMTs contributed to docetaxel resistance in human breast cancer cells (Kastl et al., 2010) and platinum resistance in ovarian cancer cells (Li et al., 2009). We also investigated the relationship between DNMTs expression and clinicopathological features of the tumors in TAM-S and TAM-R patients. Data analysis revealed that in TAM-S group, DNMT1, DNMT3A, and DNMT3B expression was significantly associated with high histologic grade and DNMT3B expression was observed in relation to lymphatic invasion (P = 0.034). In TAM-R patients, DNMT1 expression associated with the extracapsular nodal extension. DNMT3A and DNMT3B expression statistically correlated with high histologic grade and DNMT3A expression level was observed in relation to HER-2 status. A similar result was reported by Ben Gacemet al. who also showed that aberrant expression of DNMT1 and DNMT3A significantly correlated with high histologic grade in Tunisian breast carcinoma patients (Ben Gacem et al., 2012). Hypermethylation of TSGs which affect resistance progression could partially explain the poor prognosis in patients with high expression of DNMTs (Berry et al., 2000; Tanic et al., 2012). Aberrant expression of DNMTs was reported to be associated with poor prognosis in a large number of cancers. In the present study Kaplan–Meier survival analysis revealed that overexpression of DNMTs negatively correlated with patients' survival in all tamoxifen-treated breast carcinoma patients. Our study supports the previous finding which revealed that overexpression of DNMTs contributed to poor prognosis in lung cancer (Lin et al., 2007; Xing et al., 2008), oral cancer (Ben Gacem et al., 2012) and leukemia (Niederwieser et al., 2015). Also, it has been reported that DNMT1 overexpression is associated with increased death risk in renal cell carcinoma (Li et al., 2014) and gastric cancer (Cao et al., 2014). In the same manner, DNMT3B overexpression correlated with poor DFS and OS in diffuse large B-cell lymphoma patients (Amara et al., 2010) and primary acute myeloid leukemia (Niederwieser et al., 2015). High expression of DNMT3A in glioblastoma significantly decreases overall survival (Cheray et al., 2016). In contrary to our results, Husni et al. indicated that low expression of DNMT3A was associated with poor prognosis in lung adenocarcinoma patients (Husni et al., 2016).