NF-κB protein levels in NB4 cells. Western blot of NF-κB protein levels in NB4 cells in response to RA demonstrates that increased NF-κB binding in response to ATRA is not attributed to increased NF-κB family member levels. NB4 whole cell extract (30 μg) was analyzed for NF-κB subunit levels in response to ATRA for the time periods indicated. Antibodies were used at a dilution of 1:500.