Heme oxygenase-1 (HO-1) is induced as an adaptive mechanism against oxidative stress in chondrocytes, which play an important role in the maintenance and degradation of cartilage. In the present study, we examined the role of protein kinase casein kinase (CK2) on peroxynitrite-induced expression of HO-1 in primary articular chondrocytes. 3-Μorpholinosydnonimine hydrochloride (SIN-1) has been shown to mediate cell death by activating apoptosis-related molecules in cells. In this study, we used a low concentration of SIN-1 that did not induce apoptosis to elucidate the mechanism by which SIN-1 upregulates HO-1 expression. In chondrocytes, SIN-1 induced HO-1 expression with spontaneous downregulation in a different manner than with high concentrations of SIN-1. Importantly, SIN-1 treatment of chondrocytes increased CK2 activation. Additionally, inhibition of CK2 with 4,5,6,7-tetrabromobenzotriazole (TBB) or siRNA did not induce HO-1 expression and reduced NF-E2-related factor 2 (Nrf2) accumulation in chondrocytes. Therefore, we examined whether CK2 directly regulates Nrf2, which is a transcription factor that regulates the expression of HO-1. Indeed, TBB treatment inhibited phosphorylation and nuclear translocation of Nrf2 in SIN-1-treated cells. Moreover, using an immunoprecipitation assay, we confirmed that SIN-1 treatment enhanced the interaction between CK2 and Nrf2. Taken together, our findings suggest that peroxynitrite activates Nrf2 via CK2 signaling, leading to the upregulation of HO-1 in primary chondrocytes.

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