Immunohistochemical localization of LLC1 in human tissues and its limited expression in non-small cell lung cancer

We have shown both LLC1 expression in the lung epithelium by in situ hybridization and its inactivation in lung cancer by epigenetic modification. However, LLC1 protein's cellular localization or its role in normal lung or cancer tissues has not yet been evaluated. In the present study, a monoclonal antibody against recombinant LLC1 was produced, and immunohistochemical staining was performed on arrays including various human tissues, normal lung and non-small cell lung cancer (NSCLC) tissues for LLC1 localization. The immunohistochemical results showed LLC1 expression in the cilia of normal-airway epithelial cells and in the cytoplasm of type II pneumocytes in bronchiectatic patients, but no expression in most of the NSCLC tissues, which is consistent with our previous report positing LLC1 as a tumor suppressor. However, LLC1 over-expression in NSCLC cell lines NCI-H1299 and NCI-H23 did not show any change in proliferation or migration, which does not indicate any LLC1 tumor-suppressor role. As for the other human tissues, LLC1 was localized in renal tubular cells, pancreatic acinar cells, and epithelial cells of the stomach, duodenum, and gallbladder. In summary, our findings suggest that LLC1 is not a tumor suppressor, and that it is localized in the cilia of the normal lung epithelium but is absent in most NSCLC cases, probably due to the loss of cilia during lung carcinogenesis.