Protease-activated receptor-2 activates NQO-1 via Nrf2 stabilization in keratinocytes

Abstract

BACKGROUND: Protease-activated receptor-2 (PAR-2) mediates inflammation and immune responses by serine proteinases. NF-E2-related factor 2 (Nrf2) confers protection against tissue injury through antioxidant responses to oxidative stress induced by a variety of factors, including electrophilic chemicals, hydrogen peroxide, and ultraviolet irradiation. OBJECTIVE: In this study, we investigated if PAR-2 activation can stimulate Nrf2 signaling to preserve homeostasis in keratinocytes. METHODS: We performed western blotting, real-time reverse transcription polymerase chain reaction, and immunocytochemistry of keratinocyte cultures, as well as immunohistochemical labeling of human skin samples. Short interfering RNA (siRNA) was employed to confirm the effects of PAR-2 activation. RESULTS: PAR-2 activation with a selective PAR-2 agonist peptide increased the nuclear level of Nrf2 protein and subsequently induced phase II enzyme expression. Nrf2 signaling via PAR-2 activation was confirmed with experiments using PAR-2-siRNA-treated keratinocytes. The activation of an Nrf2-targeted gene by PAR-2 activation was not induced by new production of Nrf2 but by prolonged stabilization of Nrf2. Lesional skin samples from vitiligo patients showed significantly lower expression of PAR-2 and Nrf2 than control skin samples. CONCLUSION: Collectively, PAR-2 activation enhanced nuclear Nrf2 translocation, and PAR-2-mediated Nrf2 activation was attributable to existing Nrf2 stabilization rather than de novo production. Our findings suggest that in addition to induction of inflammation, PAR-2 can play a chemopreventative role via Nrf2 stabilization in keratinocytes.