ATRA regulation of NF-κB binding. EMSAs and supershift assays showing binding to a palindromic NF-κB response element using nuclear extracts from NB4 cells treated with ATRA and TNF for various times. (A) ATRA is seen to heighten TNF-induced NF-κB binding after 2 hours and to increase these complexes alone after 48 and 72 hours (B-C). Supershift assays indicated that complexes induced by ATRA were composed primarily of p65 and p50 proteins. (D) In vitro kinase assay using GST-p65 as a substrate. While a slight increase in p65 phosphorylation is observed in response to TNF, no change is seen in response to ATRA.