Abstract 2389: uPA and uPAR siRNA inhibits angiogenesis by blocking nuclear localization of angiogenin and angiopoietin1 signaling in glioblastoma cell lines

Transcriptional inactivation of uPA and uPAR system in the glioblastoma cell line SNB19 inhibited angiogenesis both in vitro and in vivo. To decipher this mechanism and extend our studies to other glioblastoma cell lines, U87MG and U87 SPARC-overexpressing cell lines were subjected to uPA, uPAR and U2 (bicistronic construct against uPA and uPAR) downregulation by siRNA. In the present study, the bicistronic construct against uPA and uPAR caused significant inhibition of angiogenesis by in vitro angiogenesis assay and in vivo dorsal skin fold chamber models in both cell lines. Increased apoptosis was seen in siRNA downregulated gliomablastoma cells when compared with control cells by FACS analysis. MTT assay revealed significant inhibition of proliferation by U2 siRNA treatment in both cell lines. Transfection with siRNA against uPA and uPAR in co-cultures of glioma cells with endothelial cells showed significant inhibition of angiopoeitin1, IL-6, GRO and GM-CSF while SPARC-overexpressing U87 cells had decreased secretion of angiogenin, GRO, MCP-1, PDGFBB, VEGF and angiopoietin1 by protein array analysis. Bicistronic construct showed decreased levels of angiogenin by ELISA and Western blot in endothelial cells and in cocultures with cancer cells. Transcriptional inactivation of uPA and uPAR showed significant downregulation of angiogenin-induced phosphorylation of ERK, JNK and Akt signaling in endothelial cells. Nuclear translocation of angiogenin in semi-confluent human umbilical vein endothelial cells treated with conditioned medium from siRNA-transfected U87 SPARC-overexpressing cells was inhibited as shown by Western blot and immunofluorescence analyses. Conditioned medium from U87MG and U87 SPARC-overexpressing cells transfected with uPA, uPAR and U2 siRNA plasmids significantly inhibited the phosphorylation of Tie2 receptor in endothelial cells. uPA and uPAR downregulation significantly downregulated MMP-2 levels by gelatin zymography in co-cultures and in single cultures of cancer cells. Matrix metalloproteinase array analysis showed significant inhibition of MMP-3 in co-cultures of U2-transfected SPARC-overexpressing glioma cells. Overall, our results suggest that the simultaneous downregulation of uPA and uPAR inhibits angiogenesis by inhibition of nuclear localization of angiogenin, angiopoeitin 1 signaling and MMP-2 downregulation in endothelial cells. In summary, these results identify novel mechanisms by which the bicistronic construct against