Irradiation-induced regulation of plasminogen activator inhibitor type-1 and vascular endothelial growth factor in six human squamous cell carcinoma lines of the head and neck.

PURPOSE: It has been shown that plasminogen activator inhibitor type-1 (PAI-1) and vascular endothelial growth factor (VEGF) are involved in neo-angiogenesis. The aim of this study was to investigate the irradiation-induced regulation of PAI-1 and VEGF in squamous cell carcinomas of the head and neck (SCCHN) cell lines of varying radiation sensitivity.

METHODS AND MATERIALS: Six cell lines derived from SCCHN were investigated in vitro. The colorimetric AlamarBlue assay was used to detect metabolic activity of cell lines during irradiation as a surrogate marker for radiation sensitivity. PAI-1 and VEGF secretion levels were measured by enzyme-linked immunosorbent assay 24, 48, and 72 h after irradiation with 0, 2, 6, and 10 Gy. The direct radioprotective effect of exogenous PAI-1 was measured using the clonogenic assay. For regulation studies, transforming growth factor-beta1 (TGF-beta1), hypoxia-inducible factor-1alpha (HIF-1alpha), hypoxia-inducible factor-2alpha (HIF-2alpha), or both HIF-1alpha and HIF-2alpha were downregulated using siRNA.

RESULTS: Although baseline levels varied greatly, irradiation led to a comparable dose-dependent increase in PAI-1 and VEGF secretion in all six cell lines. Addition of exogenous stable PAI-1 to the low PAI-1-expressing cell lines, XF354 and FaDu, did not lead to a radioprotective effect. Downregulation of TGF-beta1 significantly decreased VEGF secretion in radiation-sensitive XF354 cells, and downregulation of HIF-1alpha and HIF-2alpha reduced PAI-1 and VEGF secretion in radiation-resistant SAS cells.

CONCLUSIONS: Irradiation dose-dependently increased PAI-1 and VEGF secretion in all SCCHN cell lines tested regardless of their basal levels and radiation sensitivity. In addition, TGF-beta1 and HIF-1alpha could be partly responsible for VEGF and PAI-1 upregulation after irradiation.