SH2 domain protein E and ABL signaling regulate blood vessel size

Blood vessels in different vascular beds vary in size, which is essential for their function and fluid flow along the vascular network. Molecular mechanisms involved in the formation of a vascular lumen of appropriate size, or tubulogenesis, are still only partially understood. Src homology 2 domain containing E (She) protein was previously identified in a screen for proteins that interact with Abelson (Abl)-kinase. However, its biological role has remained unknown. Here we demonstrate that She and Abl signaling regulate vessel size in zebrafish embryos and human endothelial cell culture. Zebrafish she mutants displayed increased endothelial cell number and enlarged lumen size of the dorsal aorta (DA) and defects in blood flow, eventually leading to the DA collapse. Vascular endothelial specific overexpression of she resulted in a reduced diameter of the DA, which correlated with the reduced arterial cell number and lower endothelial cell proliferation. Chemical inhibition of Abl signaling in zebrafish embryos caused a similar reduction in the DA diameter and alleviated the she mutant phenotype, suggesting that She acts as a negative regulator of Abl signaling. Enlargement of the DA size in she mutants correlated with an increased endothelial expression of claudin 5a (cldn5a), which encodes a protein enriched in tight junctions. Inhibition of cldn5a expression partially rescued the enlarged DA in she mutants, suggesting that She regulates DA size, in part, by promoting cldn5a expression. SHE knockdown in human endothelial umbilical vein cells resulted in a similar increase in the diameter of vascular tubes, and also increased phosphorylation of a known ABL downstream effector CRKL. These results argue that SHE functions as an evolutionarily conserved inhibitor of ABL signaling and regulates vessel and lumen size during vascular tubulogenesis. Blood vessels in different vascular beds vary in their size. Formation of the proper vessel size is critical for vascular function. However, mechanisms regulating blood vessel size are not well understood. Here we identified a gene of unknown function, called SH2 domain protein E (abbreviated as She), as one of regulators in blood vessel size. Zebrafish embryos, deficient in She function, form enlarged dorsal aorta. In contrast, embryos with increased She amounts form dorsal aorta of a reduced size. We show that She affects vessel size by regulating cell proliferation. Our results suggest that She functions by modulating signaling activity of Abelson kinase (ABL), which is commonly hyperactivated in human tumors. Human vascular endothelial cells, deficient in SHE function, formed enlarged tubes, suggesting that She function is conserved between different organisms. These results will help to identify the mechanisms that control blood vessel and lumen size and may promote therapeutic developments for vascular malformations, which often show greatly enlarged vessels.