IRE1 modulates expression of a set of tumor suppressor miRNAs in luminal breast cancer cells.

To explore the regulatory mechanism by which inositol-requiring enzyme 1 (IRE1) regulates oncogenic factors, particularly RAB3B, in luminal breast cancer cells, we blocked IRE1 activity in breast cancer cell lines by using the IRE1 inhibitor 4μ8C or expressing IRE1 dominant-negative for miRNA microarray analysis. SUM52 and SUM225 lines with high-level IRE1 expression were treated with 4μ8C for 2 days. The IRE1 kinase dominant-negative mutant K599A or K907A was also used to suppress IRE1 kinase or RNase activity in SUM52 cells. The miRNA microarray analysis revealed a landscape change in miRNA expression profiling in IRE1-inhibited luminal breast cancer cells. Using a criterion of p < 0.05 in miRNA analysis, we identified 41 miRNAs in both SUM52 and SUM225 cells that were altered after inhibiting IRE1 activity. Additionally, we exogenously overexpressed wild-type IRE1 in human nontumorigenic mammary epithelial MCF10A cells and then performed miRNA array assays. When we combined miRNA data from both IRE1 inhibition models in breast cancer cells and exogenous overexpression of IRE1 in MCF10A cells (p<0.05), we identified 5 miRNAs (3607-3p, 374a-5p, 4764-3p, 516a-3p, and 6073) that were upregulated in IRE1-inhibited breast cancer cells and downregulated in MCF10A-IRE1 cells. Total RNAs from SUM52, SUM225, or MCF10A cells that were treated with IRE1 inhibitor 4μ8C or transducted with the IRE1 dominant-negative K599A, K907A, or wild-type IRE1 were harvested, frozen, and sent to the LC Sciences (Houston, TX, USA) for miRNA analysis.