Interleukin-20 promotes angiogenesis in a direct and indirect manner.

IL-20 belongs to the IL-10 family and is involved in the pathogenesis of keratinocyte hyperproliferation in vivo. Endothelial cells express IL-20 receptors. To explore the function of IL-20 on endothelial cells, we treated human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells (HMECs) with human IL-20 and analyzed its effect on endothelial cells. IL-20 induced proliferation of endothelial cells and the activity was specifically blocked by anti-human-IL-20 monoclonal antibody and soluble (s)IL-20 receptor (R)1 and sIL-20R2. An alternatively spliced variant of IL-20 was isolated and also was shown to induce proliferation of HUVECs and HMECs. Treatment of HUVECs with both IL-10 and IL-20 demonstrated that IL-10 antagonized the activity of IL-20 because it diminished IL-20-induced proliferation of HUVECs. IL-20 significantly induced HUVECs migration and vascular tube formation on Matrigel in vitro. In vivo, IL-20 also enhanced tumor angiogenesis. Incubation of IL-20 with HUVECs induced transcripts of bFGF, VEGF, MMP-2, MMP-9, and IL-8. Furthermore, incubation of HUVECs with IL-20 induced phosphorylation of ERK1/2, p38, and JNK. Thus, IL-20 is a pleiotropic cytokine and promotes angiogenesis.