Knockdown of E-cad did not increase EGFR protein stability. 24 hours after PCI-37A and 686LN cells were transfected with siRNA, cells were treated with cycloheximide (CHX) (Sigma-Aldrich) at 10 g/ml for 0, 2, 4 and 12 hrs. The EGFR protein level remained unchanged for up to 4 hours, and then declined after 12 hours of treatment with CHX in the tested SCCHN cell lines with E-cad knockdown. The experiment was repeated once. Activity of CHX was confirmed with a protein known to be regulated at the transcriptional level by Western analysis.