Low molecular weight heparin downregulates tissue factor expression and activity by modulating growth factor receptor-mediated induction of nuclear factor-κB

Treatment of cancer patients with low molecular weight heparin (LMWH) appears to have beneficial effects. In this study, the influence of low molecular weight heparin (LMWH) on tissue factor (TF) expression and activity in five cell lines from various tissues was analysed and explored. Incubation of cells with LMWH (0–2000 μg/ml) resulted in the downregulation of TF mRNA expression which was both LMWH concentration-dependent and time-dependent. Downregulation of TF was also measured as decreased cellular TF antigen and activity. Consistently, incubation of cells with LMWH suppressed the nuclear localisation and the transcriptional activity of NFκB. Decreased TF mRNA was largely achievable by incubating the cells with an NFκB inhibitor alone whilst incubation with betulinic acid to activate NFκB reversed the inhibitory influence of LMWH. Cells were also incubated with a range of concentrations of EGF (0–10 ng/ml), bFGF (0–20 ng/ml) or VEGF (0–4 ng/ml) in the presence or absence of LMWH (200 μg/ml) for 24 h and TF antigen measured. Inclusion of LMWH reduced TF expression in response to EGF, bFGF or VEGF but TF expression was partially restored by increasing concentrations of the growth factors. We conclude that LMWH downregulates TF expression in vitro through a mechanism that involves interference with the function of growth factors which in turn is mediated through the downregulation of the transcriptional activity of NFκB. This mechanism may also explain some of the beneficial influences attributed to LMWH therapy in the treatment of cancer patients.

► Downregulation of TF by LMWH in vitro was shown for the first time and a coherent mechanism for TF suppression identified. ► The mechanism involves the prevention of nuclear translocation of NFκB by interfering with growth factor receptor function. ► LMWH downregulates cellular TF antigen/activity gradually since cellular TF reservoirs are depleted at differing rates. ► The study explains the reported suppression of TF in vivo by LMWH at therapeutic doses. ► A new RT-PCR-based procedure for the absolute quantification of TF mRNA is developed and described.