CYTOKINE-INDUCIBLE EXPRESSION IN ENDOTHELIAL-CELLS OF AN I-KAPPA-B-ALPHA-LIKE GENE IS REGULATED BY NF-KAPPA-B

The transient expression of many different genes is mediated by the in ducible transcription factor p50-p65 NFchiB, which in turn is regulate d by, complex formation with its inhibitor IchiBalpha. We describe her e that in porcine aortic endothelial celts, either IL-1alpha, TNFalpha or LPS upregulates an inhibitor of NFchiB which we refer to as ECI-6. ECI-6 is by structural and functional criteria an IchiBalpha protein, the porcine homologue of MAD-3, pp40 and RL/IF-1. We have studied the promoter of the ECI-6/IchiBalpha gene and provide three lines of evid ence that its expression is directly regulated by NFchiB. First, the 5 ' regulatory region of ECI-6/IchiBalpha contains two sites that bind N FchiB in electrophoretic mobility shift assays. Second, expression fol lowing transfection of an ECI-6/IchiBalpha promoter-luciferase reporte r construct is dependent on a co-transfected NFchiB-p65 subunit. Third , pretreatment of endothelial cells with antioxidants, agents that inh ibit activation of NFchiB, inhibit the expression of ECI-6/IchiBalpha. We conclude that the regulated expression of ECI-6/IchiBalpha could r epresent a novel feedback mechanism by which NFchiB downregulates its own activity after transient activation of target genes has been achie ved.