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Liver receptor homolog-1 (LRH1) has been shown to promote tumor proliferation and development. However, the functions of LRH1 in mediating cancer cells chemoresistance are still not clear. Here, we found LRH1 levels were significantly elevated in primary breast cancer tissues in patients who developed early recurrence. Similarly, adriamycin (ADR)-resistant breast cancer cell lines also exerted high LRH1 expression. Indeed, overexpression of LRH1 attenuated cytotoxicity of chemotherapeutic drugs ADR and cisplatin (DDP) in breast cancer cells in vitro and in nude mice tumor model. Comet and BrdU assays showed overexpression of LRH1 blocked breast cancer cells DNA damage by chemotherapeutic drug, whereas depletion of LRH1 enhanced DNA damage. Remarkably, knockdown of LRH1 decreased the levels and foci of DNA damage marker γH2AX induced by ADR and DDP. Furthermore, plasmid end-joining assay indicated that knockdown of LRH1 significantly decreased non-homologous end-joining (NHEJ)-mediated double-strand break (DSB) repair efficiencies. Afterwards, we provided evidences that LRH1 promoted MDC1 transcription by directly activating MDC1 promoter and therefore increased γH2AX levels. Importantly, a LRH1-binding site mapped between -1812 and -1804 bp of the proximal MDC1 promoter was identified. Moreover, LRH1 and MDC1 mRNA levels were positively correlated in recurrent breast cancer samples. These results implied LRH1 enhanced breast cancer cell chemoresistance by upregulating MDC1 and attenuating DNA damage. Additionally, we elucidated the coactivator NCOA3 acted synergistically with LRH1 to promote MDC1 expression and chemoresistance. Altogether, LRH1-MDC1 signaling might be considered as a novel molecular target for designing novel therapeutic regimen in chemotherapy resistance breast cancer.

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Despite recent advances in the treatment of human colon cancer, the chemotherapy efficacy against colon cancer is still unsatisfactory. In the present study, effects of concomitant inhibition of the epidermal growth factor receptor (EGFR) and DNA methyltransferase were examined in human colon cancer cells. We demonstrated that decitabine (a DNA methyltransferase inhibitor) synergized with gefitinib (an EGFR inhibitor) to reduce cell viability and colony formation in SW1116 and LOVO cells. However, the combination of the two compounds displayed minimal toxicity to NCM460 cells, a normal human colon mucosal epithelial cell line. The combination was also more effective at inhibiting the AKT/mTOR/S6 kinase pathway. In addition, the combination of decitabine with gefitinib markedly inhibited colon cancer cell migration. Furthermore, gefitinib synergistically enhanced decitabine-induced cytotoxicity was primarily due to apoptosis as shown by Annexin V labeling that was attenuated by z-VAD-fmk, a pan caspase inhibitor. Concomitantly, cell apoptosis resulting from the co-treatment of gefitinib and decitabine was accompanied by induction of BAX, cleaved caspase 3 and cleaved PARP, along with reduction of Bcl-2 compared to treatment with either drug alone. Interestingly, combined treatment with these two drugs increased the expression of XIAP-associated factor 1 (XAF1) which play an important role in cell apoptosis. Moreover, small interfering RNA (siRNA) depletion of XAF1 significantly attenuated colon cancer cells apoptosis induced by the combination of the two drugs. Our findings suggested that gefitinib in combination with decitabine exerted enhanced cell apoptosis in colon cancer cells were involved in mitochondrial-mediated pathway and induction of XAF1 expression. In conclusion, based on the observations from our study, we suggested that the combined administration of these two drugs might be considered as a novel therapeutic regimen for treating colon cancer.