Transcriptional regulation of UCP4 by NF-κB and its role in mediating protection against MPP⁺ toxicity

Mitochondrial uncoupling protein-4 (UCP4) enhances neuronal cell survival in MPP⁺-induced toxicity by suppressing oxidative stress and preserving intracellular ATP and mitochondrial membrane potential. UCP4 expression is increased by MPP⁺, but its regulation is unknown. Using serial human UCP4 promoter-luciferase reporter gene constructs, we identified and characterized several cis-acting elements that can regulate UCP4 expression. Core promoter activity exists within 100bp upstream of the transcription initiation site (TIS=+1). Both CAAT box (-33/-27) and Sp1 (-62/-49) elements are crucial and act synergistically in its transcription. We identified a NF-κB putative binding site at -507/-495. Mutation of this site significantly decreased UCP4 promoter activity. Activation of NF-κB by TNFα or cycloheximide increased, whereas its inhibition by 4-hydroxy-2-nonenal or transfection of pIκBαM suppressed, UCP4 promoter activity. NF-κB inhibition significantly suppressed the MPP⁺-induced increase in UCP4 expression. MPP⁺ increased specific binding of NF-κB protein complexes to this site in electrophoretic mobility shift assay. Both UCP4 knockdown and NF-κB inhibition exacerbated MPP⁺-induced cell death. We present the first direct evidence that UCP4 is regulated by NF-κB, mediated via a functional NF-κB site in its promoter region, and that UCP4 has a significant role in NF-κB prosurvival signaling, mediating its protection against MPP⁺ toxicity.