Inhibiting PAD2 enhances the anti-tumor effect of docetaxel in tamoxifen-resistant breast cancer cells

Abstract

Background Tamoxifen resistance presents a huge clinical challenge for breast cancer patients. An understanding of the mechanisms of tamoxifen resistance can guide development of efficient therapies to prevent drug resistance. Methods We first tested whether peptidylarginine deiminase 2 (PAD2) may be involved in tamoxifen-resistance in breast cancer cells. The effect of depleting or inhibiting PAD2 in tamoxifen-resistant MCF-7 (MCF7/TamR) cells was evaluated both in vitro and in vivo. We then investigated the potential of Cl-amidine, a PAD inhibitor, to be used in combination with tamoxifen or docetaxel, and further explored the mechanism of the synergistic and effective drug regimen of PADs inhibitor and docetaxel on tamoxifen-resistant breast cancer cells. Results We report that PAD2 is dramatically upregulated in tamoxifen-resistant breast cancer. Depletion of PAD2 in MCF7/TamR cells facilitated the sensitivity of MCF7/TamR cells to tamoxifen. Moreover, miRNA-125b-5p negatively regulated PAD2 expression in MCF7/TamR cells, therefore overexpression of miR-125b-5p also increased the cell sensitivity to tamoxifen. Furthermore, inhibiting PAD2 with Cl-amidine not only partially restored the sensitivity of MCF7/TamR cells to tamoxifen, but also more efficiently enhanced the efficacy of docetaxel on MCF7/TamR cells with lower doses of Cl-amidine and docetaxel both in vivo and in vivo. We then showed that combination treatment with Cl-amidine and docetaxel enhanced p53 nuclear accumulation, which synergistically induced cell cycle arrest and apoptosis. Meanwhile, p53 activation in the combination treatment also accelerated autophagy processes by synergistically decreasing the activation of Akt/mTOR signaling, thus enhancing the inhibition of proliferation. Conclusion Our results suggest that PAD2 functions as an important new biomarker for tamoxifen-resistant breast cancers and that inhibiting PAD2 combined with docetaxel may offer a new approach to treatment of tamoxifen-resistant breast cancers.

Proteomic profiling of FBXW7‐mutant serous endometrial cancer cells reveals upregulation of PADI2, a potential therapeutic target

“…Two of these proteins, PADI2 (described above) and UCHL1, are potentially directly druggable 38,39 and exhibited increased total protein expression in all FBXW7 ‐mutant derivative cell lines across two genomically distinct backgrounds. Interestingly, UCHL1 promotes p53 signaling in nasopharyngeal carcinoma 40 and PADI2 facilitates p53 degradation in breast cancer cells 22 . This raises the possibility that the increase in PADI2 we observe is a response to increased UCHL1 protein expression, or vice versa.…”

“…Compared to normal tissue, PADI2 protein is increased in breast, cervical, colon, liver, lung, ovarian serous, thyroid, 20 and prostate cancers 21 . PADI2 mRNA expression is upregulated in tamoxifen‐resistant 22 and HER2/ERBB2 + breast cancers 23 . In contrast, in colon cancer, PADI2 mRNA and protein are decreased 24,25 and low mRNA correlates with poor prognosis 24 …”

The roles of PAD2‐ and PAD4‐mediated protein citrullination catalysis in cancers

“…Furthermore, PAD2 participates in drug resistance in breast cancer. PAD2 is highly upregulated in tamoxifen‐resistant MCF‐7 cells, and depletion of the PADI 2 gene or inhibition of PAD2 restores the sensitivity of these cells to tamoxifen 44 . Notably, inhibiting PAD2 with Cl‐amidine enhances the effects of docetaxel on tamoxifen‐resistant MCF‐7 cells 44 .…”

“…In addition, increased PAD2 enrichment on the PTN and MAGEA12 gene promoters has been detected in PADI2-overexpressing MCF-7 cells. 23 Citrullination on the histone H3 tail (at arginine residues 2, 8 and 17) on both the MAGEA12 and PTN gene promoters declines as PAD2 is depleted, suggesting that PAD2 regulates gene expression through histone tail citrullination.PADI2 gene or inhibition of PAD2 restores the sensitivity of these cells to tamoxifen 44. Notably, inhibiting PAD2 with Cl-amidine enhances the effects of docetaxel on tamoxifen-resistant MCF-7 cells 44.…”

“…23 Citrullination on the histone H3 tail (at arginine residues 2, 8 and 17) on both the MAGEA12 and PTN gene promoters declines as PAD2 is depleted, suggesting that PAD2 regulates gene expression through histone tail citrullination.PADI2 gene or inhibition of PAD2 restores the sensitivity of these cells to tamoxifen 44. Notably, inhibiting PAD2 with Cl-amidine enhances the effects of docetaxel on tamoxifen-resistant MCF-7 cells 44. Another study has reported that PAD2 is downregulated in Adriamycin-resistant MCF-7 cells but that overexpression of PAD2 does not enhance the sensitivity of these cells to Adriamycin 45.…”