Cytokeratin (CK) 8 Expression in Non-Small-Cell Lung Cancer (NSCLC) and its Relation to Tumor Invasiveness and Patient Survival

ABSTRACT Purpose Type II intermediate filament protein CK8 is highly expressed in NSCLC. The role of CKs in tumor invasiveness is controversial. While circulating CKs have been used as tumor markers, the significance of circulating CK8 in NSCLC is undetermined. The significance of CK8 in NSCLC was assessed using cell lines and clinical samples. Methods We quantitatively evaluated expression of type I CK 18/19/20, type II CK 7/8, type III vimentin, and type V lamins among 12 NSCLC, 7 SCLC and 10 non-LC lines. Highly invasive NSCLC sublines were selected from two adenocarcinoma cell lines, A549 and HI1017, using a membrane invasion chamber system (MICS), and were assessed for CK 7/8/18/19 expression. Exogenous CK19 was induced by transfection, and endogenous CK 8/18/19 were knocked down by RNA interference (RNAi), followed by invasion assay using MICS. Circulating CK8 was assessed using sera from 60 NSCLC and 10 SCLC patients and ELISA. Results and discussion CK 8/18 were expressed in all NSCLC lines and CK8 was the dominant type II CK. The invasive sublines of A549 and HI1017 showed lower expression levels of CKs compared with their parental cells. Suppression of either CK8 or CK18 by RNAi led to a decrease in the total CK amount and increased invasiveness of both HI1017 and A549 cells. On the other hand, serum levels of CK8 in NSCLC patients correlated with progressing tumor clinical stage, and inversely correlated with survival in patients with NSCLC. Apparently contradictory results in the roles of CK8 as a negative regulator of tumor invasion and its prognostic impact on poor survival in NSCLC may suggest that circulating CK8 may reflect tumor burden rather than invasiveness of individual tumors.