[ERK, JNK/AP-1 pathway was involved in silica-induced cell cycle changes]

To investigate the alteration of activator protein-1 (AP-1) luciferase activity in human embryo lung fibroblasts (HELF) after exposed to silica, and the role of mitogen activated protein kinase (MAPK)/AP-1 pathway on silica-induced cell cycle changes.

After HELF cells were treated with 200 microg/ml silica, immunofluorescence assays were employed to detect the translocation and the phosphorylation level of extracellular signal-regulated protein kinase (ERK) and c-Jun N-terminal kinase (JNK), flow cytometry was used to detect the distributions of cell cycle, the dominant negative mutant of ERK, JNK and p38 were applied to detect the upstream or downstream relationship of signaling pathways.

After HELF-AP-1 cells were exposed to 200 microg/ml silica 6, 12, 24 h respectively, silica exposure lead to AP-1 activation in a time-dependent manner, inducing significant AP-1 activation at 6 h, reaching a maximum activation at 12 h, and having a little decrease at 24 h. After silica exposure 1 h, phosphorylation level of ERK and JNK increased mainly in cytoplasm, however, after exposure 2 h, they translocated to nucleus. The proportion of cells in G1 phases was decreased from (63.80 +/- 9.57)% to (32.23 +/- 7.22)%, and the proportion of cells in S phases was increased from (35.17 +/- 10.33)% to (66.00 +/- 8.07)% after exposed to silica 24 h. Curcumin, a chemical inhibitor of AP-1, impaired the decrease of cells in G1 phases. Furthermore we found expression of dominant-negative mutant of ERK and JNK impaired silica-induced AP-1 activation, whereas, dominant-negative mutant of p38 did not show the effect.

These result suggested that 200 microg/ml silica exposure can induce AP-1 activation, induce cell cycle changes through ERK, JNK/AP-1-dependent pathway.