The role of angiomotin in endothelial cell motility and cell-cell junction formation

Sammanfattning: Clinical as well as pre-clinical data show that tumor growth can be restrained by inhibiting angiogenesis. We have been investigating the mechanism of action of angiostatin, an inhibitor of angiogenesis, in order to design novel therapies against cancer. In line with this we have previously identified angiomotin as an angiostatin-binding protein that controls endothelial migration and tube formation. Angiomotin mediates the effect of angiostatin in vitro. In this study, we first show that angiomotin belongs to a novel protein family with two additional members in human; angiomotin like 1 and angiomotin like 2. The protein family is characterized by a highly conserved coiled-coil motif, a C-terminal putative PDZ binding motif and an N-terminal glutamine rich domain. Database searches show that family members are present in the genomes of metazoa such as mouse and zebra fish. Previous data show that angiomotin expression promotes cell motility. Here we report that angiomotin promotes endothelial cell invasion of matrigel and collagen in vitro, and hemangioendothelioma growth and invasion in a mouse model. Cells expressing angiomotin with a truncation of the PDZ binding motif, however, invaded less than control cells, and tumors formed by these cells remained dormant and were non-invasive. Cell migration, but not cell proliferation or protease activity, accounted for the invasive property of angiomotin-expressing cells. We also present data that suggest that the effects of angiomotin and angiostatin in mouse aortic endothelial cells are mediated by the Rho effector Rho kinase (ROCK). We show that angiostatin binds angiomotin on the cell surface which provides the rationale for future attempts to design antibodies that are targeted against angiomotin. Furthermore, p80 and p130 isoforms of angiomotin localize to cell-cell junctions in vivo and in vitro. p130, but not p80 angiomotin, interacts with the tight junction protein MAGI-1. Both angiomotin isoforms reduced paracellular permeability when stably expressed in Chinese hamster ovary cells. Angiostatin reduced angiomotin-mediated migration but not angiomotin-mediated control of permeability. This suggests dual roles for angiomotin in angiogenesis and suggests a therapeutic window for interfering with angiomotin. In conclusion, this work provides insight into the molecular and cellular biology of angiomotin, which may be important for designing new compounds that interfere with angiogenesis.