Clear cell renal cell carcinoma (ccRCC) is a highly angiogenic cancer. Manic fringe (MFng) is elevated in ccRCC compared to the normal kidney. However, its role in ccRCC tumour angiogenesis remains elusive. This study seeks to determine the expression pattern of MFng in ccRCC blood vessels and its role in angiogenesis. The association between MFng and the blood vessels was established through online compendia, immunohistochemistry and qPCR analyses. The anti-angiogenic potential of lentiviral-mediated MFng knockdown in endothelial cells (EC shMFng) was assessed for viability, proliferation, apoptosis, migration, adhesion, cell cycle, vessel sprouting, and molecular expression of adhesion and apoptosis markers. Finally, EC shMFng were co-cultured with 786-0 renal cancer cells to determine their impact on cancer cell migration. The online dataset analyses and immunostaining on ccRCC tissues revealed high expression of MFng in ECs. MFng and CD31/PECAM-1 genes were up-regulated in ccRCC tissue samples compared to normal kidney tissues. EC shMFng demonstrated decreased cell viability due to G1 cell cycle arrest and reduced Ki-67 protein expression. In addition, shMFng down-regulated endothelial adhesion molecules and hindered EC migration, network formation and sprouting, compared to their respective empty vector (EV) controls. Co-culture assay of EC shMFng with 786-0 renal cancer cells inhibited cancer cell migration. These findings underscore the potential role of MFng in ECs in influencing renal cancer cell migration, thus opening an avenue for anti-angiogenic strategy targeting MFng to treat ccRCC.
Delta-like 4 (DLL4) and Jagged1 (JAG1) are two key Notch ligands implicated in tumour angiogenesis. They were shown to have opposite effects on mouse retinal and adult regenerative angiogenesis. In tumours, both ligands are upregulated but their relative effects and interactions in tumour biology, particularly in tumour response to therapeutic intervention are unclear. Here we demonstrate that DLL4 and JAG1 displayed equal potency in stimulating Notch target genes in HMEC-1 endothelial cells but had opposing effects on sprouting angiogenesis in vitro. Mouse DLL4 or JAG1 expressed in glioblastoma cells decreased tumour cell proliferation in vitro but promoted tumour growth in vivo. mDLL4-expressing tumours showed fewer but larger vessels whereas mJAG1-tumours produced more vessels. In both tumour types pericyte coverage was decreased but the vessels were more perfused. Both ligands increased tumour resistance towards anti-VEGF therapy but the resistance was higher in mDLL4-tumours versus mJAG1-tumours. However, their sensitivity to the therapy was restored by blocking Notch signalling with dibenzazepine. Importantly, anti-DLL4 antibody blocked the effect of JAG1 on tumour growth and increased vessel branching in vivo. The mechanism behind the differential responsiveness was due to a positive feedback loop for DLL4-Notch signalling, rendering DLL4 more dominant in activating Notch signalling in the tumour microenvironment. We concluded that DLL4 and JAG1 promote tumour growth by modulating tumour angiogenesis via different mechanisms. JAG1 is not antagonistic but utilises DLL4 in tumour angiogenesis. The results suggest that anti-JAG1 therapy should be explored in conjunction with anti-DLL4 treatment in developing anti-Notch therapies in clinics.