PLAC8 promotes adriamycin resistance via blocking autophagy in breast cancer.

Yongxia Chen,Jichun Zhou,Yifeng Gu,Chenpu Xu,Jian Ruan,Dengdi Hu,Zhaoqing Li,Linbo Wang,Peng Shen,Wenxian Hu,Misha Mao,Yunlu Jia,Cong Chen,Qun Wei,Jun Shen,Lini Chen,Jingjing Yang

doi:10.1111/jcmm.16706

Abstract

Adriamycin (ADM) is currently one of the most effective chemotherapeutic agents in breast cancer treatment. However, growing resistance to ADM could lead to treatment failure and poor outcome. PLAC8 was reported as a novel highly conserved protein and functioned as an oncogene or tumour suppressor in various tumours. Here, we found higher PLAC8 expression was correlated with worse outcome and aggressive phenotype in breast cancer. Breast cancer patients with higher PLAC8 expression showed potential ADM resistance. In vitro experiments further confirmed that PLAC8 inhibited by siRNA or enforced overexpression by infecting pcDNA3.1(C)‐PLAC8 plasmid correspondingly decreased or increased ADM resistance. Subsequently, we demonstrated that ectopic PLAC8 expression in MCF‐7/ADMR cell blocked the accumulation of the autophagy‐associated protein LC3 and resulted in cellular accumulation of p62. Rapamycin‐triggered autophagy significantly increased cell response to ADM, while the autophagy inhibitor 3‐MA enhanced ADM resistance. 3‐MA and PLAC8 could synergistically cause ADM resistance via blocking the autophagy process. Additionally, the down‐regulation of p62 by siRNA attenuated the activation of autophagy and PLAC8 expression in breast cancer cells. Thus, our findings suggest that PLAC8, through the participation of p62, inhibits autophagy and consequently results in ADM resistance in breast cancer. PLAC8/p62 pathway may act as novel therapeutic targets in breast cancer treatment and has potential clinical application in overcoming ADM resistance.

Highlights

MethodsWe analyzed the expression profile of PLAC8 in breast cancer tissues and breast cancer cell lines, and explored the correlation of PLAC8 expression levels with patients’ outcomes and ADM response
Adriamycin (ADM) is currently one of the most effective chemotherapeutic agents in breast cancer treatment
Higher PLAC8 expression was correlated with poorer outcome and aggressive phenotype in breast cancer, and breast cancer patients with higher PLAC8 expression showed potential ADM resistance

Summary

Methods

We analyzed the expression profile of PLAC8 in breast cancer tissues and breast cancer cell lines, and explored the correlation of PLAC8 expression levels with patients’ outcomes and ADM response. One ADM resistant MCF-7 breast cancer cell (MCF-7/ADM) and its parental cell was used as in vitro models to identify the underlying mechanism of PLAC8 and ADM resistance. Breast cancer cells were transfected with PLAC8 knockdown and overexpression vectors, and MTT and colony formation assays were performed to test the cell response to ADM. Combining treatment of autophagy inhibitor/inducer and PLAC8 downregulation/upregulation revealed the participation of PLAC8 in autophagy pathway to synergistically regulate ADM resistance in breast cancer. Human breast cancer cell line, MCF-7, T47D, BCAP37, MDA-MB231, MDA-MB-453, MDA-MB-436, MDA-MB-468, HBL-100 and HCL-1937 were purchased from the Cell Bank of the Chinese Academy of Sciences and stored in liquid nitrogen. ADM-resistant MCF-7 cells (MCF-7/ADM) was derived from the human breast cancer cell MCF-7, which was maintained in the presence of 1 ug/ml ADM. A double concentration of ADM was applied when the cells became tolerable. Cells were cultured in RPMI 1640 medium (Invitrogen, Carlsbad, CA, USA) supplemented with 10% fetal bovine serum (GIBREAST CANCERO) and grew at 37 °C with 5% CO2 and 95% humidity

Results

Discussion

Conclusion