The anti-inflammatory activity of Phellinus linteus (Berk. & MA 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 C delta (PKC delta), but not PKC alpha/beta II, in a time-dependent manner. PL-induced HO-1 expression was dramatically released by GF109203X, a general inhibitor of PKC, and rottlerin, a specific PKC delta inhibitor but not by Go6976, a selective inhibitor for PKC alpha/beta. Additionally, PL treatment resulted in a marked increase in antioxidant response element (ARE)-driven transcriptional activity, which was dependent on PKC delta but not PKC alpha. An increase by PL treatment in the ARE-driven transcriptional activity was further enhanced by Nrf2, whereas it was diminished by Keapl. Furthermore, pretreatment of rottlerin and overexpression of PKC delta (K376R), a kinase-inactive form of PKC delta, 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 (NIMP-9) and its promoter activity were suppressed by PL, which were dependent upon PKC delta. The present findings indicate that Phellinus linteus gives rise to an anti-inflammatory activity though the PKC delta/Nrf2/ARE signaling to the up-regulation of HO-I in an in vitro inflammation model. (C) 2007 Published by Elsevier Ireland Ltd.