CCN1 stimulated endothelial proliferation and angiogenesis in vitro. (A) Proliferation of HUVECs was determined by BrdU incorporation in the absence (control) and in the presence of 1, 10, and 100 ng/mL CCN1 or 50 ng/mL VEGF for 16 hours. (B) Proliferation of HUVECs was determined by BrdU incorporation after 16 hours of incubation with supernatants (SN) from CD34⁺ cells unstimulated (control), stimulated with 100 ng/mL CCN1 for 24 hours or preabsorbed with a neutralizing antibody (AB) against CCN1. Unspecific control IgG did not show effects (data not shown). Increase in proliferation was significant different from control levels (*P < .05). (C) HUVECs were cultured in Matrigel for 24 hours in the absence (control) or in the presence of 100 ng/mL CCN1 or 50 ng/mL VEGF. (D) HUVECs were cultured in Matrigel for 24 hours with supernatants (SN) from CD34⁺ cells unstimulated (control) or stimulated with 100 ng/mL CCN1 for 24 hours. Increase in tube-like structures was significant different from control levels (*P < .05).