The anti-inflammatory activity of Phellinus linteus (Berk. & M.A. Curt.) is mediated through the PKCδ/Nrf2/ARE signaling to up-regulation of heme oxygenase-1

It has been reported that heme oxygenase-1 (HO-1) mediates the anti-inflammatory activity of the n-BuOH subfraction (PL) prepared from fruiting bodies of Phellinus linteus. This continuing work aimed to elucidate the signaling pathway to the up-regulation of HO-1 by PL. In RAW264.7 macrophage cells, PL was able to enhance phosphorylation of protein kinase Cδ (PKCδ), but not PKCα/βII, in a time-dependent manner. PL-induced HO-1 expression was dramatically released by GF109203X, a general inhibitor of PKC, and rottlerin, a specific PKCδ inhibitor but not by Gö6976, a selective inhibitor for PKCα/β. Additionally, PL treatment resulted in a marked increase in antioxidant response element (ARE)-driven transcriptional activity, which was dependent on PKCδ but not PKCα. An increase by PL treatment in the ARE-driven transcriptional activity was further enhanced by Nrf2, whereas it was diminished by Keap1. Furthermore, pretreatment of rottlerin and overexpression of PKCδ (K376R), a kinase-inactive form of PKCδ, partly blocked the suppression by PL of nitric oxide (NO) production and inducible nitric oxide synthase (iNOS) expression, and iNOS promoter activity, which were elevated in the lypopolysaccharide (LPS)-activated macrophages. Similarly, expression of matrix metalloproteinase-9 (MMP-9) and its promoter activity were suppressed by PL, which were dependent upon PKCδ. The present findings indicate that Phellinus linteus gives rise to an anti-inflammatory activity though the PKCδ/Nrf2/ARE signaling to the up-regulation of HO-1 in an in vitro inflammation model.