Bortezomib suppresses focal adhesion kinase expression via interrupting nuclear factor-kappa B

Abstract Aims Bortezomib is a potent proteasome inhibitor currently used to treat various malignancies with promising results. To explore the role of bortezomib in reducing cancer cell migration and inducing apoptosis, we evaluated the effects of bortezomib on the expression of focal adhesion kinase (FAK). Main methods Various types of cancer cells including lung cancer A549, H1299; a breast cancer MCF7; a hepatocellular carcinoma Huh7, and a tongue squamous cell carcinoma SCC-25 were treated with different concentrations of bortezomib or MG-132 as indicated for 24 h. Protein and mRNA levels were determined by Western blotting and real-time PCR. Apoptosis was analyzed by caspase 3 cleavage and activity. FAK promoter and NFκB binding activities were measured by luciferase-reporter method. NFκB subunit p65 binding capacity was determined by electrophoretic mobility shift assay (EMSA) and chromatin immunoprecipitation (ChIP) analysis. Key findings Both bortezomib and another proteasome inhibitor, MG-132, significantly reduced FAK expression, suppressed cancer cell migration and increased cell apoptosis. Results of real-time PCR and promoter activity assay revealed that bortezomib decreased FAK expression through transcriptional inactivation. Results of FAK promoter activity and ChIP assays in A549 and H1299 cells indicated that bortezomib suppressed FAK activity through a p53-independent pathway. Furthermore, reduction of NFκB binding capacity demonstrated by EMSA and ChIP assay suggested that NFκB plays an important role in bortezomib suppressing FAK expression. Significance These results suggested that FAK is downregulated by bortezomib through a proteasome-dependent NFκB inhibitory mechanism. Thus, FAK could be a potential molecular target of bortezomib for therapeutic strategy.