PRODUCTION OF CYTOKERATIN-19 FRAGMENT BY HUMAN SQUAMOUS LUNG-CANCER CELL-LINES

Cytokeratins form part of the cytoskeleton of both normal and malignan t epithelium. A novel tumor marker measuring cytokeratin 19 (CK-19) fr agment has been introduced and proven to be suitable for monitoring th erapy and following cases of non-small cell lung cancer, squamous cell lung cancer in particular. However, whether the serum level of CK-19 fragment reflects the number of proliferating tumor mass remains unkno wn. We studied the CK-19 fragment produced by two human squamous cell lung cancer cell lines. In Western blotting analysis, culture supernat ants of both cell lines displayed bands of 37 and 40 kDa, which repres ented the CK-19 fragment and the intact CK-19, respectively. Gel filtr ation demonstrated that a part of soluble CK-19 was released as a larg e complex form in culture supernatants. The level of CK-19 fragment in culture supernatants increased during the exponential growth phase. C K-19 level decreased by an addition of a cytotoxic agent to non-signif icant level though the transient release of CK-19 fragment occurred du ring the first 2 days. After all, soluble CK-19 fragments were detecte d in culture supernatants of human lung cancer cell lines and its leve l reflected proliferating cancer cells though it was not determined wh ether CK-19 fragments were released directly from live cells.