Cerebral cavernous malformation protein CCM1 inhibits sprouting angiogenesis by activating DELTA-NOTCH signaling

Abstract

Cerebral cavernous malformations (CCM) are frequent vascular abnormalities caused by mutations in one of the CCM genes. CCM1 (also known as KRIT1) stabilizes endothelial junctions and is essential for vascular morphogenesis in mouse embryos. However, cellular functions of CCM1 during the early steps of the CCM pathogenesis remain unknown. We show here that CCM1 represents an antiangiogenic protein to keep the human endothelium quiescent. CCM1 inhibits endothelial proliferation, apoptosis, migration, lumen formation, and sprouting angiogenesis in primary human endothelial cells. CCM1 strongly induces DLL4-NOTCH signaling, which promotes AKT phosphorylation but reduces phosphorylation of the mitogen-activated protein kinase ERK. Consistently, blocking of NOTCH activity alleviates CCM1 effects. ERK phosphorylation is increased in human CCM lesions. Transplantation of CCM1-silenced human endothelial cells into SCID mice recapitulates hallmarks of the CCM pathology and serves as a unique CCM model system. In this setting, the multikinase inhibitor Sorafenib can ameliorate loss of CCM1-induced excessive microvascular growth, reducing the microvessel density to levels of normal wild-type endothelial cells. Collectively, our data suggest that the origin of CCM lesions is caused by perturbed Notch signaling-induced excessive capillary sprouting, which can be therapeutically targeted.endothelial cells | vascular malformations | CCM | KRIT1

Nuclear Localization of Integrin Cytoplasmic Domain-associated Protein-1 (ICAP1) Influences β1 Integrin Activation and Recruits Krev/Interaction Trapped-1 (KRIT1) to the Nucleus

“…In endothelial cells, KRIT1 also appears to stabilize the ICAP1 protein, so KRIT1 loss leads to decreased ICAP1 levels and consequently increased ␤1 integrin activation (20). In addition to its role with ICAP1, KRIT1 has also been linked to several other important signaling pathways, including Rho/ROCK (21)(22)(23), Notch/PI3K (24), reactive oxygen species/ SOD2/AKT (25), and ␤-catenin (26).…”

CCM1 and the second life of proteins in adhesion complexes

“…Phosphorylation of FOXO by PKB results in ubiquitination and degradation of FOXOs, 141,142 which contradicts the conclusions of the authors. Also, others have shown increased PKB phosphorylation upon CCM1 overexpression in HUVEC cells, 92 whereas this is not shown for CCM3. 94 Based on these data, it is unclear what effect CCM1 could have on FOXO function and if this involves the nuclear localization of either FOXO or CCM1.…”

“…[88][89][90][91] Interestingly, loss of CCM1, CCM3, or ICAP1 impairs DLL4-Notch signaling, resulting in excessive angiogenesis. [92][93][94] Furthermore, induction of DLL4-NOTCH signaling by CCM1 results in increased PKB signaling and inhibition of ERK. Also, protein lysates from human CCM1 lesions show increased phospho-ERK levels, 92 indicating that CCM1 suppresses ERK activation.…”

“…[92][93][94] Furthermore, induction of DLL4-NOTCH signaling by CCM1 results in increased PKB signaling and inhibition of ERK. Also, protein lysates from human CCM1 lesions show increased phospho-ERK levels, 92 indicating that CCM1 suppresses ERK activation. Altogether, this suggests that CCM proteins activate DLL4-Notch signaling, and thereby, inhibit excessive angiogenesis, but also here molecular details are lacking on how CCM proteins activate DDL4-Notch signaling.…”

Molecular and Genetic Basis of Cerebral Cavernous Malformations

“…Notch-DLL4 ilişkisinin endotelyal tomurcuklanmayı kontrol altında tuttuğu ve tümör anjiyogenezinde endotelyal hücrelerin tomurcuklanmasını inhibe ettiği gösterilmiştir (22,25). CCM1 veya ICAP1α'dan herhangi birinin hücrede yokluğu üzerine yapılan çalışmalarda, DLL4-Notch sinyal iletim yapısının bozulduğu ve anjiyogenezin aşırı miktarda arttığını göstermektedir (26,27).…”