Role of the VEGFR3/VEGFD receptor axis in TGFbeta1 activation of primary prostate cell lines.

Background: Reports indicate that vascular endothelial growth factor receptor type 3 (VEGFR3) regulates cellular functions such as invasion, proliferation, and chemo-resistance. However, the exact function of the VEGFR3 signaling axis in prostate epithelial cells is poorly characterized.
Methods: The goal of this study was to evaluate whether TGFbeta1 in combination with VEGFD can promote pre-malignant invasive activities of intermediate basal cells (IBC-10a) isolated from human prostate cancer (Gleason score 6).
Results: hTERT immortalized IBC-10a cells normally grew as confluent "cobblestoned" monolayers, but treatment with TGFbeta1 (10 ng/ml for 2-6 hr) dissociated the cell-cell junctions and induced VEGFR3 translocation to the cell surface. This event was not inhibited by 10 microM cycloheximide or puromycin, indicating transcription and protein synthesis were not required. We further discovered that TGFbeta1 in combination with VEGFD induced a significant increase in the invasive activity of IBC-10a cells (>26% and 53% after 24 and 48 hr, respectively) in modified Boyden Chamber assays. TGFbetaRII receptor antibodies specifically blocked TGFbeta1 induction of VEGFR3 translocation to the cell surface and blocked VEGFD-induced invasion. Zymograms revealed that TGFbeta1 (and not VEGFR3) stimulated the secretion of MMP-2 and MMP-9, presumably to promote cell invasion. The cell invasion assays confirmed that antibodies specific for TGFbetaII receptor, MMP-2 and MMP-9 and VEGFR3, independently blocked TGFbeta1-induced invasion.
Conclusions: For the first time, we have demonstrated the mechanism by which TGFbeta1 stimulates VEGFD/VEGFR3 receptor axis activation leading to increased cell migration and invasion by primary intermediate basal cell cultures.