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Involvement of protein kinase C in crystalline silica-induced activation of the MAP kinase and AP-1 pathway

¹Pathology and Physiology Research Branch, Health Effects Laboratory Division, National Institute for Occupational Safety and Health, Morgantown, West Virginia; and ²Nelson Institute of Environmental Medicine, New York University, School of Medicine, Tuxedo, New York

Submitted 28 January 2005 ; accepted in final form 9 September 2005

Crystalline silica has long been well established as a fibrogenic agent, and recent evidence has implicated it as a potential human carcinogen. However, the mechanisms of silica-induced disease development and progression are not well understood. Our previous studies demonstrated that crystalline silica is able to activate activator protein-1 (AP-1) through mitogen-activated protein kinase (MAPK) pathways. The present study investigates the possible involvement of protein kinase C (PKC) in silica-induced activation of the MAPK/AP-1 signal transduction pathway. Treatment of mouse epidermal cells (JB6 cell line) with freshly fractured silica stimulated translocation of PKC and PKC from the cytosol to the membrane and activated AP-1 transcription activity. Pretreatment of cells with PKC inhibitors, including RO-32-0432, calphostin C, and bisindolylmaleimide I, inhibited silica-induced AP-1 activation and phosphorylation of ERKs and p38 kinase. These inhibitory effects by PKC inhibitors were dose dependent. Furthermore, overexpression of dominant negative mutant (DNM) of PKC or PKC markedly blocked AP-1 activation as well as phosphorylation of ERKs and p38 kinase induced by freshly fractured silica. These results demonstrate that PKC and PKC are essential in silica-induced AP-1 activation through the MAP kinase (ERKs and p38 kinases) pathway.

protein kinase C; mitogen-activated protein kinase; activator protein-1; silica