ErbB4-encoded novel miRNAs act as tumor suppressors by regulating ErbB/PI3K signaling.

BACKGROUND: ErbB/PI3K signaling is widely recognized as a critical modulator of malignancy and miRNAs have been found to play a crucial role in the regulation of this pathway.

OBJECTIVE: This study aimed to identify novel miRNAs related to the ErbBs loci and investigate the functional effects of these miRNAs on ErbB/PI3K signaling in cancer progression.

MATERIALS AND METHODS: Bioinformatics tools and RNA-seq data were used to discover novel miRNAs in breast and colon cancer cells. Gene expression levels were determined using RT-qPCR. Western blotting and dual-luciferase assays were used to identify the regulatory mechanism between ErbB4-miR1/2 and related genes. The effects of ErbB4-miR1/2 on cell proliferation, viability, ROS production, and migration were assessed by PI-flow cytometry, colony formation, MTT, ROS, scratch, and transwell assays in SKBR3 and SW480 cells.

RESULTS: MicroRNA prediction tools, RNA-seq data, RT-qPCR, and sequencing results identified ErbB4-miR1 and ErbB4-miR2 (ErbB4-miR1/2) as novel miRNAs encoded by ErbB4 gene. ErbB4-miR1/2 were downregulated in breast and colon tumor tissues and also in different cancerous cells. RT-qPCR and dual-luciferase assays revealed that ErbB2 and ErbB3 genes are regulated by ErbB4-miR1/2. Consistently, a decrease in the p-AKT/AKT protein ratio verified the suppressive effect of ErbB4-miR1/2 on ErbB/PI3K activity. Furthermore, ErbB4-miR1/2 overexpression suppressed cell proliferation, viability, and migration, and increased ROS production.

CONCLUSIONS: ErbB4-miR1/2 are novel tumor suppressor miRNAs which attenuate ErbB/PI3K signaling in breast and colon cancer cells.