The role of caspase 3 in producing cytokeratin 19 fragment (CYFRA21-1) in human lung cancer cell lines

The CYFRA 21-1 assay, which detects cytokeratin 19 (CK19) fragment, is wide ly used as a tumor marker for lung cancer, particularly non-small cell lung cancer. However, the reason that some lung cancer cell lines release CYFRA 21-1 in culture supernatants and others do not remains unclear. We hypothe sized that the release of CYFRA 21-1 might be related to the expression of CK19 and caspase 3. In order to prove this, the quantities of mRNA for CK19 were evaluated by the competitive reverse transcriptase-polymerase chain r eaction (RT-PCR). CK19 protein synthesis was also evaluated by Western blot ting and immunohistochemistry, and the levels of CYFRA 21-1 in the culture supernatant were measured by an immunoradiometric assay. The expression of mRNA for caspase 3 was evaluated by the RT-PCR, and caspase 3 protein synth esis was also evaluated by immunohistochemistry. In 13 lung cancer cell lin es, the amounts of mRNA for CK19 correlated with the levels of CYFRA 21-1 i n culture supernatants, results of Western blotting for CK19, and positivit ies of immunohistochemistry for CK19. In 5 cell lines that produced a signi ficant amount of CYFRA 21-1, the level of CYFRA 21-1 correlated with the po sitivity of RT-PCR for caspase 3 and immunohistochemistry for caspase 3. Th is suggests that caspase 3 played a role in the formation of CYFRA 21-1. In addition, the specific inhibitor of caspase 3 significantly inhibited the release of CYFRA 21-1 in culture supernatants. In conclusion, we demonstrat e that caspase 3, which cleaves several intermediate filaments and carries out cell apoptosis, played an important role in producing CYFRA 21-1 in hum an lung cancer cell lines. (C) 2001 Wiley-Liss, Inc.