JAM-1 induces HUVEC proliferation and tube formation. (A) The proliferation of HUVECs stably transfected with mock (•) or JAM-1 (○) constructs was quantified by counting cell number. (B) Cells as in panel A were treated with bFGF and assayed for BrdU incorporation. Anti–JAM-1 significantly inhibited bFGF-induced proliferation (*P < .01). (C) In vitro Matrigel tube formation assay. Serum-starved mock-transfected (i, iii), JAM-1–transfected (ii, iv), Δ-257–transfected (v), and Y→F–transfected (vi) HUVECs were assayed for tube formation in the presence or absence of bFGF as indicated. Original magnification × 100.