Western blot analysis was performed as described previously (15 (link)). In brief, cells were lysed with ice-cold lysis buffer, and the lysates were centrifuged at 20,000 × g for 10 minutes at 4 °C. Cell lysates containing equal amounts of protein were resolved using sodium dodecyl sulfate–polyacrylamide gel electrophoresis, transferred to nitrocellulose membranes, and incubated with different primary antibodies. Protein expression was detected using a horseradish peroxidase–conjugated secondary antibody (Bio-Rad, Hercules, CA) and electrochemiluminescence reagent (Amersham Biosciences, Pittsburg, PA). For the quantification of protein expression, the band intensities were measured using ImageJ, RRID:SCR_003070 (National Institutes of Health, Bethesda, MD) (16 (link)) and normalized first to β actin and then to its respective positive control (expression in HN31, UMSCC4, or C33A, as noted in the figures).