Abstract
YT-CB5, which had been continuously cultured with chrysotile B (CB) asbestos, showed impaired cytotoxicity with decreased expression of NKG2D and 2B4 NK cell-activating receptors. In the present study, the phosphorylation of extracellular signal-regulated kinase (ERK), which is known to induce degranulation downstream of many NK cell-activating receptors, was examined in YT-CB5 by flow cytometry and compared with the control line YT-Org. YT-CB5 exhibited impaired phosphorylation of ERK1/2 induced by the recognition of K562 cells, downstream of a process mediated by Src family kinase and phosphoinositide 3-kinase. YT-CB5 also exhibited impaired phosphorylation of ERK1/2 following incubation with K562 cells in the presence of anti-2B4 antibodies, where co-stimulation by 2B4 augmented the phosphorylation of ERK1/2 in YT-CB5 to a similar degree as in YT-Org. The phosphorylation of ERK1/2 induced by an inhibitor against phosphatase (PP) 1 and PP2A was also lower in YT-CB5 compared with YT-Org. Moreover, bead-bound antibodies to NKG2D, which contribute to cytotoxicity against K562 cells, induced negligible phosphorylation of ERK1/2 in YT-CB5, although antibodies to 2B4. induced a comparatively greater level of phosphorylation. Additionally, peripheral blood (PB-) NK cells with low expression of NKG2D showed lower phosphorylation of ERK1/2 mediated by anti-NKG2D antibodies compared with PB-NK cells with high expression of NKG2D. These results indicate that signal transduction events leading to the phosphorylation of ERK is impaired in YT-CB5 due to decreased expression of NKG2D. Further studies are required to clarify whether this suppressive effect of asbestos exposure on NK cells might promote lung cancer and mesothelioma in people who have inhaled asbestos.