Expression of an X-family DNA polymerase, pol lambda, in the respiratory epithelium of non-small cell lung cancer patients with habitual smoking

DNA polymerase lambda, pol λ, is a eukaryotic member of the X-family DNA polymerases that is involved in two modes of DNA repair, i.e. base excision repair (BER) or non-homologous end joining (NHEJ). Using immunohistochemical approaches, we have observed pol λ expression in human tissues, particularly in the respiratory system of lung cancer patients. pol λ proteins were distributed in the nuclei of the epithelial cells in the bronchi, bronchioles and alveoli. Intriguingly, the level of pol λ expression in the bronchiolar epithelia significantly correlated with the amount of habitual smoking in the individuals. Conversely, pol λ expression in cancer tissues did not correlate with the smoking status of the patients. Pol λ expression was sometimes discrepant between the tumor tissues and adjacent bronchioles. More importantly, tumors without pol λ expression that occurred in heavy smokers significantly tended to be at an advanced clinical stage. Pol λ may thus be involved in the DNA repair processes counteracting DNA damage caused by tobacco smoke in the respiratory system.