Knockdown of A-kinase anchor protein 4 inhibits proliferation of triple-negative breast cancer cells in vitro and in vivo.

Triple-negative breast cancers are the most aggressive subtypes with poor prognosis due to lack of targeted cancer therapy. Recently, we reported an association of A-kinase anchor protein 4 expression with various clinico-pathological parameters of breast cancer patients. In this context, we examined the effect of knockdown of A-kinase anchor protein 4 on cell cycle, apoptosis, cellular proliferation, colony formation, migration, and invasion in triple-negative breast cancer cells. We also examined the synergistic cytotoxic effect of paclitaxel on A-kinase anchor protein 4 downregulated triple-negative breast cancer cells. Knockdown of A-kinase anchor protein 4 resulted in significant reduction in cellular growth and migratory abilities. Interestingly, we also observed enhanced cell death in A-kinase anchor protein 4 downregulated cells treated with paclitaxel. Knockdown of A-kinase anchor protein 4 in cell cycle resulted in G0/G1 phase arrest. Knockdown of A-kinase anchor protein 4 also led to increased reactive oxygen species generation as a result of upregulation of NOXA and CHOP. In addition, levels of cyclins, cyclin-dependent kinases, anti-apoptotic molecules, and mesenchymal markers were reduced in A-kinase anchor protein 4 downregulated cells. Moreover, downregulation of A-kinase anchor protein 4 also caused tumor growth reduction in in vivo studies. These data together suggest that A-kinase anchor protein 4 downregulation inhibits various malignant properties and enhances the cytotoxic effect of paclitaxel, and this combinatorial approach could be useful for triple-negative breast cancer treatment.