Expression of liver X receptors in normal and refractory carcinoma tissues of the human lung and pancreas.

Liver X receptors (LXRs) participate not only in maintaining cholesterol homeostasis but also in controlling cellular growth in many types of normal and tumor cells. We previously reported that LXR alpha was aberrantly expressed in human oral squamous cell carcinoma (HOSCC) tissues and cell lines, and that LXR stimulation led to significant reduction of proliferation of HOSCC cells via accelerating cholesterol efflux. Since LXRs and downstream proteins involved in cholesterol metabolism could be also applied as therapeutic targets in small cell lung carcinoma (SCLC) and pancreatic ductal adenocarcinoma (PDAC), we herein analyzed the distribution of LXR proteins in these refractory cancers as well as in normal human lung and pancreatic tissues. LXR beta was observed in ciliated epithelial cells, bronchial gland epithelia, type II alveolar epithelia and alveolar macrophages of the lung, and was less expressed in bronchial basal cells and type I alveolar epithelia. In addition, LXR beta was detected in epithelium of the pancreatic duct and acinar cells of the pancreas, and was weakly expressed in pancreatic islet cells. By contrast, LXR alpha expression was restricted to alveolar macrophages, and was not evident in any types of epithelial cells in the lung and pancreas. We also demonstrated that LXR beta but not LXRa was abundantly expressed in nine cases of SCLC and twenty cases of PDAC tissues. These findings provide basic information for evaluating the efficacy of LXR-targeted treatment in SCLC and PDAC.