LPS-induced depolymerization of cytoskeleton and its role in TNF-alpha production by rat pneumocytes

Lipopolysaccharide (LPS) polymerizes microfilaments and microtubules in mac rophages and monocytes. Disrupting micro filaments or microtubules with cyt ochalasin D (CytoD) or colchicine can suppress LPS-induced tumor necrosis f actor-alpha (TNF-alpha) gene expression and protein production from these c ells. We have recently demonstrated that primary cultured rat alveolar epit helial cells can produce TNF-alpha on LPS stimulation. In the present study , we found that the LPS-induced. increase in TNF-alpha mRNA level and prote in production in alveolar epithelial cells was not inhibited by CytoD or co lchicine (1 nM to 10 mu M). In fact, LPS-induced TNF-alpha production was f urther enhanced by CytoD (1-10 mu M) and inhibited by jasplakinolide, a pol ymerizing agent for microfilaments. Immunofluorescent staining and confocal microscopy showed that LPS (10 mu g/ml) depolymerized microfilaments and m icrotubules within 15 min, which was prolonged until 24 h for microfilament s. These results suggest that the effects of LPS on the cytoskeleton and th e role of the cytoskeleton in mediating TNF-alpha production in alveolar ep ithelial cells are opposite to those in immune cells. This disparity may re flect the different roles between nonimmune and immune cells in host defens e..