Nuclear Factor-κB (NF-κB) Mediates a Protective Response in Cancer Cells Treated with Inhibitors of Fatty Acid Synthase

The efficacy of drugs used to treat cancer can be significantly attenuated by adaptive responses of neoplastic cells to drug-induced stress. To determine how cancer cells respond to inhibition of the enzyme fatty acid synthase (FAS), we focused on NF-kappa B-mediated pathways, which can be activated by various cellular stresses. Treating lung cancer cells with C93, a pharmacological inhibitor of FAS, results in changes indicative of a rapid initiation of NF-kappa B signaling, including translocation of RelA/p65 NF-kappa B to the nucleus, activation of a transfected NF-kappa B-luciferase reporter, and increased expression of NF-kappa B dependent transcripts, IL-6, IL-8, and COX-2. Verifying that these responses to C93 are specifically related to inhibition of FAS, we confirmed that levels of these same transcripts increase in response to siRNA targeting FAS. Inhibiting this NF-kappa B response (either by transfecting a mutant I kappa B alpha or treating with bortezomib) resulted in increased cell killing by C93, indicating that the NF-kappa B response is protective in this setting. Because inhibiting FAS leads to accumulation of intermediate metabolites of fatty acid biosynthesis, we then questioned whether protein kinase C (PKC) is involved in this response to metabolic stress. Immunofluorescence microscopy revealed that C93 treatment results in cellular translocation of PKC alpha and PKC beta isoforms and increased PKC alpha-dependent phosphorylation of the I kappa B alpha subunit of NF-kappa B. Furthermore, inhibiting PKC activity with RO-31-8220 or PKC alpha isoform-specific siRNA attenuates C93-induced I kappa B alpha phosphorylation and NF-kappa B activation and also potentiates C93-induced cell killing. These results suggest a link between PKC and NF-kappa B in protecting cancer cells from metabolic stress induced by inhibiting FAS.