SUMOylated NICD in endothelial cell suppresses tumor angiogenesis

The abnormal vascular in tumor promotes tumor cells proliferation and metastasis. Endothelial cell (EC), which is usually dysfunctional in tumor microenvironment, affects angiogenesis and vascular function. Neurogenic locus notch homolog protein 1 (NOTCH1) signaling pathway plays a critical role in vascular endothelial growth factor (VEGF) signaling and angiogenesis by driving its intracellular domain (N1ICD) to nucleus and activates downstream signaling. However, regulatory mechanism of N1ICD remains unclear. Small ubiquitin-like modifier (SUMO) proteins express widely and regulate gene expression, stability, and signal transduction via protein post-translational modification. Our previous study has confirmed that N1ICD could be SUMOylated. In the current study, we first found that SUMOylated N1ICD in ECs negatively regulated angiogenic signaling by enhancing the activity and protein stability of N1ICD. To reveal the role of SUMOylated NICD in tumor angiogenesis, we generated inducible endothelial SUMO1-N1ICD knock-in (SUMO1-N1ICDecKI) mice. Xenograft tumor was produced by subcutaneous injection of mice Lewis Lung Cancer cells on the back and analyzed by volume measurement. SUMO1-N1ICDecKI mice developed smaller tumor than WT mice at 14 days after injection. Immunofluorescence (IF) staining of EC marker also indicated that vessel density of tumors in SUMO1-N1ICDecKI mice was much lower than tumors in WT mice. To further explore the mechanism, VEGFR2 and p-VEGFR2 was measured by IF staining. Increased levels of endothelial-specific N1ICD SUMOylation correlated with lower VEGFR2 expression and p-VEGFR2 signal. On the other hand, we also detected platelet-derived growth factor β (PDGFRβ) to measure vascular integrity. Surprisingly, vessels with enhanced N1ICD SUMOylation associated with more PDFGFβ+ pericyte coverage, indicating that endothelial N1ICD SUMOylation promotes vessel stability. Taken together, we conclude that endothelial-specific N1ICD SUMOylation suppressed tumor growth and tumor angiogenesis while protected vascular integrity.