Submitted on January 28, 2005
Accepted on September 9, 2005
Involvement of Protein Kinase C in Crystalline Silica-induced Activation of the MAP Kinase AP-1 Pathway
Min Ding1*, Chuanshu Huang2, Yongju Lu2, Linda Bowman2, Vince Castranova2, and Val Vallyathnan2
1 Nelson Institute of Environmental Medicine, New York University School of Medicine, Tuxedo, NY, USA
2 Pathology and Physiology Research Branch, National Institute for Occupational Safety and Health, Morgantown, WV, USA
* To whom correspondence should be addressed. E-mail: Mid5{at}cdc.gov.
Crystalline silica has long been well established as a fibrogenic agent and recent evidence have been implicated 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 epithermal cells (JB6 cell line) with freshly fractured silica stimulated translocation of PKC alpha and PKC epsilon 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, over-expression of dominant negative mutant (DNM) of PKC alpha and PKC epsilon markedly blocked AP-1 activation induced by freshly fractured silica. Over-expression of DNM-PKC alpha and DNM-PKC epsilon also abolished the silica-induced phosphorylation of ERKs and p38 kinase. These results demonstrate that PKC alpha and PKC epsilon are essential in silica-induced AP-1 activation through the MAP kinase (ERKs and p38 kinases) pathway.
