Abstract
PURPOSE: Tissue factor (TF), the transmembrane receptor for factor VIIa (FVIIa), has key regulatory functions in coagulation as well as in tumour progression and metastasis. Small-cell lung cancer (SCLC) metastasises more aggressively than non-small-cell lung cancer (NSCLC). Previously, we described the transition of SCLC cell line H69 to adherent growth and TF expression. Here, we explored the differential expression of TF and its functional impact on morphology and matrix metalloproteinase (MMP) secretion. METHODS: The constitutional TF expression was evaluated in a panel of established NSCLC and SCLC cell lines. Furthermore, in three stress-selected adherent SCLC H69 cells, TF and MMP expressions were determined by mRNA, protein, and activity measurements. RNA interference-mediated TF down-regulation and FVIIa stimulation were used to study the impact of TF on cellular functions. RESULTS: NSCLC cells expressed high TF antigen (median 3.75 ng/mg; range 0.31-65.2 ng/mg protein, n = 8), while SCLC expressed none or low TF (median 0.07 ng/mg; range 0-0.39 ng/mg protein, n = 6). However, selected H69 adherent cells markedly expressed TF (range: 4.8-44.3 ng/mg protein, n = 3) and secreted MMP-2 and MMP-9. FVIIa stimulated MMP-2 and MMP-9 secretion in H69adh cells, whereas TF down-regulation diminished MMP-2 and MMP-9 expression and promoted reversion to suspension growth. CONCLUSIONS: Our data show the significance of TF expression in the reversible growth phenotype of H69. Because TF, MMP expression, and adherence are highly relevant to cancer metastasis, this study suggests a novel mechanism of adaptation, thereby adding to the understanding of SCLC biology and its aggressiveness.