Crosstalk between miR-203 and PKCθ regulates breast cancer stem cell markers

Protein kinase C theta (PKCθ) is expressed in ER-negative breast cancer and promotes cancer stem cells (CSCs) phenotype. PKCθ gene (PRKCQ) is predicted to be a target for tumor suppressor miR-203. Herein, we aim to validate this prediction and evaluate the ability of miR-203 to inhibit migration of breast cancer cell line enriched with CSCs, MDA-MB-231, via PRKCQ targeting.

Cells were transfected with miR-203 mimic, PRKCQ siRNA and negative control; then real-time PCR, migration assay, western blotting, reporter assay, and chromatin accessibility assay were performed.

Our findings displayed significant decrease in PRKCQ mRNA level and luciferase signals in cells with restored miR-203 expression, therefore, validated PRKCQ as a direct target of miR-203. Additionally, inhibiting PRKCQ by siRNA led to significant inhibition of miR-203 expression and significant decrease of chromatin accessibility at miR-203 promoter region 466-291 upstream TSS. Both of miR-203 re-expression and PRKCQ suppression resulted in altering migration ability of MDA-MB-231 through regulating AKT pathway and genes involved in breast cancer stem cells, CD44 and ALDH1A3. Expression of CDK5, GIV, and NANOG was significantly downregulated in miR-203 mimic-transfected cells, while PRKCQ siRNA-transfected cells displayed downregulation of OCT3/4, SOX2, and NANOG. Furthermore, we found that miR-224 expression was enhanced while miR-150 was downregulated after ectopic expression of miR-203.

The study highlighted the negative feedback loop between miR-203 and its target PRKCQ and the interplay between them in regulating genes involved in BCSCs. The study also concluded "microRNA-mediated microRNA regulation" as an event in breast cancer cells.