Endothelial Delta-like 4 (DLL4) promotes renal cell carcinoma hematogenous metastasis

The Notch ligand Delta-like 4 (DLL4) plays an important role in tumor angiogenesis, which is required for tumor invasion and metastasis. Here we showed that DLL4 was elevated in endothelium and Notch signaling was activated in renal cell carcinoma (RCC). Exogenous DLL4 induced RCC cell migration and invasion by activating intercellular Notch signaling. Importantly, the DLL4/Notch/Hey1/MMP9 cascades connecting the endothelium to the cancer cells in metastasis were identified. Knockdown of Hey1 decreased expression of MMP9 and attenuated tumor invasion. The clinical investigation on 120 cases of RCC specimens indicated that expressions of Hey1 and MMP9 correlated with DLL4 density. Moreover, univariate and multivariate analyses showed that tumor hematogenous metastasis not only was depended on microvessel density but was also associated with tumor size and DLL4 density. During 4-year surveillance, high-level of DLL4 density was associated with a higher probability of developing metastasis and being sensitive to target therapies. Our data suggest that RCC progression is caused in part by activated DLL4/Notch signaling, interaction of endothelium and cells, which can be therapeutically targeted.