ABSTRACT
Snake venom metalloproteases (SVMPs) are members of the a disintegrin and metalloprotease (ADAM) family of proteins, as they possess similar domains. SVMPs are known to elicit snake venom-induced haemorrhage; however, the target proteins and cleavage sites are not known. In this work, we identified a target protein of vascular apoptosis-inducing protein 1 (VAP1), an SVMP, relevant to its ability to induce haemorrhage. VAP1 disrupted cell-cell adhesions by relocating VE-cadherin and γ-catenin from the cell-cell junction to the cytosol, without inducing proteolysis of VE-cadherin. The Wnt receptors low-density lipoprotein receptor-related proteins 5 and 6 (LRP5/6) are known to promote catenin relocation, and are rendered constitutively active in Wnt signalling by truncation. Thus, we examined whether VAP1 cleaves LRP5/6 to induce catenin relocation. Indeed, we found that VAP1 cleaved the extracellular region of LRP6 and LRP5. This cleavage removes four inhibitory ß-propeller structures, resulting in activation of LRP5/6. Recombinant human ADAM8 and ADAM12 also cleaved LRP6 at the same site. An antibody against a peptide including the LRP6-cleavage site inhibited VAP1-induced VE-cadherin relocation and disruption of cell-cell adhesions in cultured cells, and blocked haemorrhage in mice in vivo. Intriguingly, animals resistant to the effects of haemorrhagic snake venom express variants of LRP5/6 that lack the VAP1-cleavage site, or low-density lipoprotein receptor domain class A domains involved in formation of the constitutively active form. The results validate LRP5/6 as physiological targets of ADAMs. Furthermore, they indicate that SVMP-induced cleavage of LRP5/6 causes disruption of cell-cell adhesion and haemorrhage, potentially opening new avenues for the treatment of snake bites.
