Proteomics-based identification of secreted protein dihydrodiol dehydrogenase as a novel serum markers of non-small cell lung cancer

Identification of secreted proteins of lung cancer could provide new candidates of serum biomarkers for cancer diagnosis and prognosis evaluation. In this study, non-small cell lung cancer (NSCLC) cell line A549 was cultured. Proteins in the conditioned medium of A549 were recovered and the proteome analysis was subsequently performed. Secreted proteins of A549 were identified using mass spectrometry and database search. Fourteen human proteins were identified, including peptidyl-prolyl cis-trans isomerase A, manganese superoxide dismutase, peroxiredoxin 1, phosphatidylethanolamine-binding protein, glutathione S-transferase P, PGP9.5, alpha enolase, phosphoglycerate mutase 1, galectin-1 and dihydrodiol dehydrogenase (DDH). DDH was selected for further analysis using RT-PCR, immunoblotting, immunohistochemical staining and ELISA in NSCLC patients. Compared with normal lung tissues, higher DDH mRNA and protein expression level were found in 15 NSCLC cancer tissues (p<0.05). DDH overexpression was identified to be located in cytoplasm and cell membrane by immunohistochemical staining in NSCLC tissue. The serum level of DDH was significantly higher in NSCLC patients (n=64) than nonmalignant lung tumor (n=20) and healthy controls (n=20) (p<0.05). The results show that DDH was one of the secreted proteins in NSCLC. It can serve as a tissue marker and a novel serological marker of NSCLC. Identification of secreted proteins could be a feasible and effective strategy to search potential serum biomarkers of cancer.