Modulation of cystatin A expression in human airway epithelium related to genotype, smoking, COPD, and lung cancer.

The cathepsin inhibitor Cystatin A (CSTA) has antiapoptotic properties linked with neoplastic changes in squamous cell epithelium, where it has been proposed as a diagnostic and prognostic marker of lung cancer. Notably, cystatin A is upregulated in dysplastic epithelium, prompting us to hypothesize that it might be modulated in chronic obstructive pulmonary disease (COPD), a small airway epithelial (SAE) disorder that is a risk factor for non-small cell lung cancer (NSCLC) in a subset of smokers. Here we report that genetic variation, smoking, and COPD can all elevate levels of CSTA expression in lung small airway epithelia, with still further upregulation in squamous cell carcinoma (SCC), an NSCLC subtype. We examined SAE gene expression in 178 individuals, including healthy nonsmokers (n = 60), healthy smokers (n = 82), and COPD smokers (n = 36), with corresponding large airway epithelium (LAE) data included in a subset of subjects (n = 52). Blood DNA was genotyped by SNP microarray. Twelve SNPs upstream of the CSTA gene were found to associate with its expression in SAE. Levels were higher in COPD smokers than in healthy smokers, who, in turn, had higher levels than nonsmokers. CSTA gene expression in LAE was also smoking-responsive. Using publicly available NSCLC expression data we also found that CSTA was upregulated in SCC versus LAE and downregulated in adenocarcinoma versus smoke-exposed SAE. All phenotypes were associated with different proportional expression of CSTA to cathepsins. Our findings establish that genetic variability, smoking, and COPD all influence CSTA expression, as does SCC, supporting the concept that CSTA may make pivotal contributions to NSCLC pathogenesis in both early and late stages of disease development.