Nuclear factor KB (NF-κB) is a transcription factor that is critical for the inducible expression of multiple cellular and viral genes. Using the electrophoretic mobility shift assay, we demonstrated that DNA binding activity of NF-κB was abolished by proteolysis with μ- and m-calpains in vitro. The proteolysis of NF-κB by calpains and hence the abolition of its DNA binding was prevented by calpastatin, calpain inhibitor I and proteasome inhibitor. We also provided evidence that calpains degrade the Cterminal domain of NF-κB by Western blot using anti-NF-κB (p65) C-terminal antibody. These observations indicate that calpains regulate gene expression through processing of NF-κB.
