Bifunctional Alkylating Agent-Induced p53 and Nonclassical Nuclear Factor κB Responses and Cell Death Are Altered by Caffeic Acid Phenethyl Ester: A Potential Role for Antioxidant/Electrophilic Response-Element Signaling

Bifunctional alkylating agents (BFA) such as mechlorethamine (nitrogen mustard) and bis-(2-chloroethyl) sulfide (sulfur mustard; SM) covalently modify DNA and protein. The roles of nuclear factor κB (NF-κB) and p53, transcription factors involved in inflammatory and cell death signaling, were examined in normal human epidermal keratinocytes (NHEK) and immortalized HaCaT keratinocytes, a p53-mutated cell line, to delineate molecular mechanisms of action of BFA. NHEK and HaCaT cells exhibited classical NF-κB signaling as degradation of inhibitor protein of NF-κBα (IκBα) occurred within 5 min after exposure to tumor necrosis factor-α. However, exposure to BFA induced nonclassical NF-κB signaling as loss of IκBα was not observed until 2 or 6 h in NHEK or HaCaT cells, respectively. Exposure of an NF-κB reporter gene-expressing HaCaT cell line to 12.5, 50, or 100 μM SM activated the reporter gene within 9 h. Pretreatment with caffeic acid phenethyl ester (CAPE), a known inhibitor of NF-κB signaling, significantly decreased BFA-induced reporter gene activity. A 1.5-h pretreatment or 30-min postexposure treatment with CAPE prevented BFA-induced loss of membrane integrity by 24 h in HaCaT cells but not in NHEK. CAPE disrupted BFA-induced phosphorylation of p53 and p90 ribosomal S6 kinase (p90RSK) in both cell lines. CAPE also increased nuclear factor E2-related factor 2 and decreased aryl hydrocarbon receptor protein expression, both of which are involved in antioxidant/electrophilic response element (ARE/EpRE) signaling. Thus, disruption of p53/p90RSK-mediated NF-κB signaling and activation of ARE/EpRE pathways may be effective strategies to delineate mechanisms of action of BFA-induced inflammation and cell death signaling in immortalized versus normal skin systems.