As shown in Fig. transcriptionally through ETS conserved binding ABT sites in the promoters by getting together with ETS2. Elevated expression of Np73 promotes tumor progression by mediating angiogenesis and survival. Therapeutic targeting of downstream Np73 signaling pathways by rebastinib inhibits growth of established tumors and extends survival in preclinical models of glioblastoma. Conclusion Aberrant expression of Np73 in GBM promotes tumor progression through autocrine and paracrine signaling dependent on Tie2 activation by ANGPT1. Disruption of this signaling by rebastinib improves tumor response to treatment in glioblastoma. mice (Envigo). Ten mice for each group were used. For the survival studies with rebastinib, luciferase-labeled DBTRG or CHLA-200 cells were used. Detailed method description for the mice and zebrafish studies can be found in the Supplementary Methods. Statistical Analyses Data were graphed and analyzed using GraphPad Prism 7 software. Error bars represent mean standard deviation (SD) from triplicate measurements from 1 experiment. Most of the experiments were repeated at least 2 times with similar results. Differences between 2 groups were analyzed by Students 0.01, *** 0.001, **** 0.0001. Np73 Expression Prolongs Survival, Promotes Intracranial Growth, and Induces Tumor Vascularization of GBM We next examined the biologic consequence of high levels of Np73 expression in GBM. To determine how Np73 expression in GBM affects survival, we first utilized a zebrafish orthotopic xenograft model. DBTRG-shCtr, DBTRG-shNp73, SJGBM2-Ctr, or SJGBM2-Np73 GBM cell lines (Supplementary Figure 1E) were transplanted into the midbrain region of embryonic zebrafish and the larvae were analyzed over time. As shown in Fig. 2A, zebrafish implanted with DBTRG cells, expressing high levels of Np73, had a significantly decreased survival compared with Np73 knockdown (DBTRG-shNp73) implanted zebrafish. Conversely, overexpression of Np73 in SJGBM2 cells was associated with decreased survival (Fig. 2B). Next, we evaluated whether Np73 promotes intracranial growth of GBM. Luciferase-labeled DBTRG-shCtr, DBTRG-shNp73, SJGBM2-Ctr, or SJGBM2-Np73 cells were implanted into the caudate nucleus FZD4 of mice. Tumor growth has evaluated weekly by bioluminescence imaging. As shown in Fig. 2C, inhibition of Np73 in DBTRG cells significantly reduced tumor growth. In contrast, overexpression of Np73 in SJGBM2 cells significantly increased growth of intracranially injected tumors (Fig. 2D). Overall, our data indicate that aberrant expression of Np73 in GBM plays a crucial role in the malignant growth of this deadly ABT disease. Open in a separate window Fig. 2 Np73 expression increases tumor progression. (A) Inhibition of Np73 isoform in DBTRG cells significantly extended zebrafish survival. (B) Overexpression of Np73 in SJGBM2 cells significantly reduced zebrafish survival. (A, B) KaplanCMeier survival curves with log-rank test (**** 0.0001). Right, representative confocal images of transplanted casper zebrafish 5 days posttransplant. (C, D) Np73 promotes intracranial growth of gliomas in mice. Bioluminescent signal intensity was determined at the ABT indicated days as described in the Methods section. Significant variations between 2 groups was determined by Students 0.05, ** 0.01. (E) Np73 expression in GBM induces tumor vascularization. Representative IHC images for CD34 staining in GBM sections are shown. Scale bar = 200 m. Below, quantification of MVD in each type of intracranial glioma was determined as described in Materials and Methods. 0.05, ** 0.01. GBMs are among the most vascularized tumors in humans.15 We consequently evaluated whether expression of Np73 in GBM cell lines stimulates tumor vascularization (angiogenesis) in GBM. Using an endothelial tube formation assay, we demonstrated that stable overexpression of Np73 in the SJGBM2 cell line significantly increased the number of endothelial tubes formed, conversely knockdown of Np73 significantly decreased endothelial tube formation (Supplementary Figure 2A, B). To further investigate the role of Np73 expression in tumor angiogenesis, IHC was performed using a CD34-specific antibody. As shown in Fig. 2E, inhibition of Np73 resulted in a significant decrease of CD34-positive vessel formation in tumor tissues compared with the control group as determined by microvessel density (MVD). Furthermore, tumors derived from mice implanted with GBM cells overexpressing Np73 displayed a significant increase of CD34-positive vessel formation (Fig. 2E). Together, our results provide strong evidence that aberrant expression of Np73 plays a crucial role in GBM angiogenesis. Np73 Forms Complexes with ETS2 to Regulate ANGPT1 and Tie2 Expression in GBM Given that p73 isoforms are proteins with sequence-specific DNA binding properties, we hypothesized that.