Src Tyrosine Kinases Mediate Crystalline Silica-Induced NF-κB Activation through Tyrosine Phosphorylation of IκB-α and p65 NF-κB in RAW 264.7 Macrophages

Protein tyrosine kinases (PTKs) and mitogen-activated protein kinases (MAPKs) have been demonstrated to play a crucial role in the signaling pathways induced by silica. In the present study, we investigated whether Src family TKs play a role in crystalline silica-induced NF-kappaB activation and whether NF-kappaB activation requires Src TK-dependent MAPK activity in RAW 264.7 cells, a mouse peritoneal macrophage cell line. Selective Src TK inhibitors, damnacanthal or PP1, inhibited silica-induced NF-kappaB activation in a dose-dependent manner. Furthermore, these kinase inhibitors suppressed silica-induced tyrosine phosphorylation of IkappaB-alpha and p65 NF-kappaB. Within a similar time frame, c-Src and Lck were physically associated with IkappaB-alpha and with p65 NF-kappaB. Silica stimulated the phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/2), but not p38 MAPK and c-Jun NH(2)-terminal kinase 1 and 2 (JNK1/2). Damnacanthal or PP1 substantially blocked the silica-induced activation of ERK1/2. Moreover, PD98059, an inhibitor of ERK1/2, or SB203580, an inhibitor of p38 MAPK, failed to inhibit silica-induced NF-kappaB activation. These results suggest that c-Src and Lck act for silica-induced NF-kappaB activation by mediating the tyrosine phosphorylations of IkappaB-alpha and p65 NF-kappaB. However, the Src TK-dependent activation of ERK1/2 may not be involved in the silica signaling pathway leading to NF-kappaB activation.