Immunohistochemical distribution of sphingosine kinase 1 in normal and tumor lung tissue

Sphingosine kinase 1 (SK1) is a key enzyme critical to the sphingolipid metabolic pathway responsible for catalyzing the formation of the bioactive lipid sphingosine-1-phosphate. SK1-mediated production of sphingosine-1-phosphate has been shown to stimulate such biological processes as cell growth, differentiation, migration, angiogenesis, and inhibition of apoptosis. In this study, cell type-specific immunolocalization of SK1 was examined in the bronchus/terminal bronchiole of the lung. Strong immunopositive staining was evident at the apical surface of pseudostratified epithelial cells of the bronchus and underlying smooth muscle cells, submucosal serous glands, immature chondrocytes, type 11 alveolar cells, foamy macrophages, endothelial cells of blood vessels, and neural bundles. Immunohistochemical screening for SK1 expression was performed in 25 samples of normal/tumor patient matched non-small-cell lung cancer tissue and found that 25 of 25 tumor samples (carcinoid [5 samples], squamous [10 samples], and adenocarcinoma tumors [10 samples]), exhibited overwhelmingly positive immunostaining for SK1 as compared with patient-matched normal tissue. In addition, an approximately 2-fold elevation of SK1 mRNA expression was observed in lung cancer tissue versus normal tissue, as well as in several other solid tumors. Taken together, these findings define the localization of SK1 in lung and provide clues as to how SK1 may play a role in normal lung physiology and the pathophysiology of lung cancer.