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

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.