Long Non-Coding RNA (lncRNA) 91H Confers Tamoxifen Resistance in ER+ Breast Cancer Cells through Inhibiting mTOR Signaling Pathway.

Objective: Estrogen receptor-positive (ER+) breast cancers are the most often diagnosed subtype of breast tumors, in which the development of tamoxifen resistance remains a major impediment. The effect of long non-coding RNA (lncRNA) on therapy resistance is beginning to emerge. The lncRNA 91H, a recently identified lncRNA involved in tumorigenesis, is also overexpressed in breast cancer. The purpose of this study was to explore the role of 91H in the biological function and tamoxifen resistance of ER+ breast cancer cells.

Methods: MCF-7 and T47D cells were transfected for 91H silence. CCK-8 assay was performed to examine cell viability and drug sensitivity. Cell cycle and apoptosis were analyzed using flow cytometry. Cell migration capacity was determined by wound healing assay. The protein level was analyzed by Western blotting.

Results: MCF-7 and T47D cells with 91H knockdown exhibited lower capacities of cell proliferation and migration. In addition, knockdown of 91H resulted in significantly increased sensitivity to tamoxifen and a higher ratio of apoptosis induced by tamoxifen. Furthermore, the protein level of p-mTOR was notably inhibited through downregulating 91H expression. And the mTOR inhibitor together with tamoxifen presented synergistic effect on the inhibition of cell viability.

Conclusion: Our study highlights that 91H might serve as a potential target for ER+ breast cancer patients who have acquired tamoxifen resistance.