Regulation of ER Stress‐Associated Gene Expression by Lifeguard in Human Breast Cancer Cells

Abstract

ABSTRACT Background Despite significant advances in breast cancer therapy, resistance to apoptosis remains a major obstacle to successful treatment. Lifeguard (LFG), an antiapoptotic membrane protein, has been implicated in breast cancer progression; however, its role in endoplasmic reticulum (ER) stress‐associated molecular responses and apoptosis‐related gene regulation remains incompletely understood. Aims This study aimed to investigate molecular changes associated with LFG‐targeted siRNA treatment and reduced LFG mRNA expression in human breast cancer cells. Methods and Results The triple‐negative breast cancer cell line MDA‐MB‐231 and the non‐tumorigenic mammary epithelial cell line MCF10A were transfected with LFG‐specific siRNA. LFG mRNA expression was analyzed by quantitative RT‐PCR. Furthermore, ER stress‐ and apoptosis‐related gene expression was examined using an RT2 Profiler PCR Array, and intracellular calcium‐associated fluorescence was assessed by fluorescence‐based calcium imaging. LFG mRNA expression was markedly reduced following LFG‐specific siRNA treatment in MDA‐MB‐231 cells, whereas a more moderate reduction was observed in MCF10A cells. LFG‐targeted siRNA treatment was associated with altered intracellular calcium‐associated fluorescence and differential expression of several ER stress‐ and apoptosis‐related genes, including upregulation of CREB3L3, SREBF1, and INHBE, as well as downregulation of EDEM1, HSPA2, and RRM2. Conclusions These findings demonstrate that LFG‐targeted siRNA treatment and reduced LFG mRNA expression are associated with changes in intracellular calcium‐related responses and ER stress‐ and apoptosis‐associated gene expression, particularly in MDA‐MB‐231 cells. Further studies are required to determine the underlying mechanisms and establish the functional role of LFG in these cellular responses.