Production of cytokeratin 19 fragment by human squamous lung cancer cell lines.

Cytokeratins form part of the cytoskeleton of both normal and malignant epithelium. A novel tumor marker measuring cytokeratin 19 (CK-19) fragment has been introduced and proven to be suitable for monitoring therapy 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 unknown. We studied the CK-19 fragment produced by two human squamous cell lung cancer cell lines. In Western blotting analysis, culture supernatants of both cell lines displayed bands of 37 and 40 kDa, which represented the CK-19 fragment and the intact CK-19, respectively. Gel filtration demonstrated that a part of soluble CK-19 was released as a large complex form in culture supernatants. The level of CK-19 fragment in culture supernatants increased during the exponential growth phase. CK-19 level decreased by an addition of a cytotoxic agent to non-significant level though the transient release of CK-19 fragment occurred during the first 2 days. After all, soluble CK-19 fragments were detected in culture supernatants of human lung cancer cell lines and its level reflected proliferating cancer cells though it was not determined whether CK-19 fragments were released directly from live cells.