Inhibition of vascular endothelial cell growth by activin-A.

The demonstration of type 2 activin receptor expression in human umbilical vein endothelial cells prompted an investigation of the effects of the activin/inhibin family of hormones on vascular endothelial cell growth. Recombinant activin-A inhibited [3H]methylthymidine uptake and growth of a panel of endothelial cell types; recombinant inhibin-A was without effect. Affinity cross-linking studies demonstrated the presence of type 1 and type 2 activin receptors on the surface of bovine aortic endothelial cells, while detailed analysis of type 2 activin receptor expression revealed both type 2 and type 2B activin receptor mRNA in all endothelial cell types analyzed. In addition, capillary endothelial cells were found to express activin-beta A subunit mRNA and protein, the levels of which were increased in response to transforming growth factor (TGF)-beta. Furthermore, activin-A and TGF-beta caused additive inhibition of capillary endothelial cell [3H]methylthymidine uptake. These findings implicate the activins in the regulation of endothelial cell function, and suggest that TGF-beta and activin may interact to inhibit capillary endothelial cell growth.