Functional role of CD105 in TGF-beta1 signalling in murine and human endothelial cells

Angiogenesis is important in health and several disease states. CD105 is a proliferation-associated and hypoxia-inducible transmembrane protein abundantly expressed in angiogenic endothelial cells. CD105 is a receptor for transforming growth factors (TGF)-beta1 and -beta3. The exact mechanisms for CD105 regulation of vascular development have not been fully elucidated.

In this study, an antisense approach to create a murine and a human stably transfected endothelial cell line expressing a reduction in CD105 protein was used.

We showed that inhibition of CD105 in cultured murine and human endothelial cells enhanced the ability of TGF-beta1 to suppress growth and migration, and influenced TGF-beta1 promoter activity. TGF-beta1 not only reduced the length of the capillary-like structures, but also caused mortality in CD105-deficient murine antisense cells compared to control cultures. To determine whether CD105 affected TGF-beta1-induced gene expression, a luciferase assay in transiently transfected cells with p3TP-Lux promoter constructs was performed. Both murine and human antisense transfectants showed a significant increase in p3TP-Lux promoter activity. Further studies on the functional importance of CD105 was undertaken in irradiated normoxic and hypoxic cells. The levels of pro- and anti-apoptotic markers were also evaluated. There was an increase in pro-apoptotic marker (p53), but a reduction in anti-apoptotic marker (Bcl-2) in CD105-deficient cells.

These results provide direct evidence that CD105 antagonises the inhibitory effects of TGF-beta1 on human and murine vascular endothelial cells and that normal cellular levels of CD105 are required for the formation of new blood vessels.