Knockdown of TM9SF4 triggering ER stress exerts anti-growth effect on drug-resistant breast cancer cells

[Speaker] Yifei Zhu:1
[Co-author] Xiaoqiang Yao:1
1:Chinese University of Hong Kong, Hong Kong

Drug-resistance of chemotherapy is the leading cause of mortality in breast cancer patients. Understanding how drug-resistant cancer cell survival is of great importance for the breast cancer therapy. Here, we identified a key protein, TM9SF4, namely transmembrane 9 superfamily, isoform 4, which play vital role in drug-resistant breast cancer survival. TM9SF4 is significantly up-regulated in drug-resistant breast cancer cells MCF-7/ADM compared to its parental wildtype cell line MCF-7/WT. Knockdown of TM9SF4 using lenti-TM9SF4-shRNA dramatically decreased cell viability and induced cell death of MCF-7/ADM. Moreover, drug-resistant xenografts derived from animal model also showed a significantly reduced growth rate after the delivery of lenti-TM9SF4-shRNA. The underlying mechanism may be related to the triggering of ER stress, leading to unfolded protein response, which will induce apoptosis/necrosis, causing cell death. Our study provides TM9SF4 as a promising target for the overcoming of drug-resistance in clinical breast cancer therapy.
90% breast cancer patients die from drug-resistance. Drug-resistance is one of the bottlenecks in breast cancer treatment.
TM9SF4 stands for transmembrane 9 superfamily protein, isoform 4. TM9SF4 function is essentially unknown.
When the unfolded or misfolded proteins are abundant, it leads to ER stress, and the unfolded protein response (UPR) is elicited, which restores the homeostatic functions of the ER.
Cell culture: Wild-type MCF-7 (MCF-7/WT) (ATCC) and MCF-7/ADM cells were cultured. MCF-7/ADM cells were derived by exposing MCF-7 cells to stepwise increasing concentrations of adriamycin over 8 months.
Western blot: Measurements of the protein level.
CYQUANT assay and Edu assay: Cell viability and proliferation rate analysis.
Immunofluorescence: Detection of the expression and distribution of TM9SF4 and ER marker in breast cancer cells.
Flow cytometry: Apoptosis/necrosis and aggresomes detection.
TM9SF4 expression level was up-regulated in drug-resistant MCF-7 cells (MCF-7/ADM).
Knockdown of TM9SF4 reduced MCF-7/ADM cell proliferation rate and caused cell death.
Knockdown of TM9SF4 increased ER stress and protein misfolding in MCF-7/ADM cells.
TM9SF4 is essential for drug-resistant breast cancer cell survival.
The underlying mechanism may involve ER stress, which triggers unfolded protein response, inducing cell apoptosis/necrosis.
Our study provides TM9SF4 as a promising target in drug-resistant breast cancer therapy.

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