Abstract 5756: The MicroRNA-17–92 Cluster Exhibits a Cell Intrinsic Anti-angiogenic Function in Endothelial Cells
MicroRNAs (miRs) are endogenously expressed small noncoding RNA molecules that are able to regulate gene expression on the posttranscriptional level by binding to the mRNAs of their target genes, thus inducing inhibition of translation or mRNA degradation. The miR-17–92 cluster (encoding miR-17, -18a, -19a, -20a, -19b and miR-92a) was shown to augment tumor angiogenesis if overexpressed in tumor cells. Whereas miR-92a was recently identified as negative regulator of vessel growth, the individual functions of the other members of the miR-17–92 cluster in endothelial cells is less clear and only a combination of miR-17, -18a and -20a was shown to partially rescue the defective angiogenesis under conditions of Dicer deficiency. To investigate the involvement of the individual members of the miR-17–92 cluster in angiogenesis, human umbilical vein endothelial cells (HUVECs) were transfected with precursor molecules for miR-17, -18a, -19a and -20a. Overexpression of the different members significantly inhibited 3D spheroid sprouting (Pre-17:10±3%,-18a: 28±5%,-19a: 45±4%,-20a: 33±8% of control) and impaired the assembly of capillary networks in vitro. Conversely, inhibition of miR-17 (142±15% of control), miR-18a (152±6% of control) and miR-20a (153±9% of control) augmented spheroid sprout formation. Next, we addressed the in vivo relevance by using antagomirs to block the individual miRs. Antagomir-17 (which also blocks miR-20a) significantly increased the number of lectin-positive vessels in matrigel plugs (190±26% of control), whereas antagomirs, which specifically affect miR-18a and miR-19a were less effective. Antagomir-17 additionally improved blood flow after hind limb ischemia (217±24% of control) and increased tumor growth (140±14% of control). To identify direct targets of miR-17, we combined microarray gene expression analysis with target prediction. Among others, Janus kinase 1 (Jak1) was significantly downregulated on mRNA (38±5% of control) and protein (41±14% of control) level by miR-17. In summary, we show that the individual members of the miR-17–92 clusters exhibit a cell intrinsic anti-angiogenic activity in endothelial cells. Inhibition of miR-17 efficiently increased neovascularization and tumor growth in vivo.