STRUCTURE, FUNCTION AND MECHANISM OF ACTION OF ISM1

Abstract

Isthmin 1 (ISM1) is a secreted angiogenesis inhibitor protein. Bacterial produced recombinant ISM1 induced endothelial cell (EC) apoptosis via two cell surface receptors namely Integrin αvβ5 and cell surface GRP78. How ISM1 interacts with its two receptors and the domains of ISM1 that mediate its receptor interaction remain unknown. In this study, I set out to answer these questions. The structure-function relationships of ISM1 was investigated using both bacteria and mammalian cell produced recombinant ISM1 protein and its various truncates. Through co-immunoprecipitation assays as well as apoptosis assays, I demonstrated that the AMOP domain of ISM1 mediates its binding to both receptors as well as its pro-apoptotic activity. Taken together, these studies have advanced our understanding of the structure, function and mechanism of action of ISM1, and generated useful knowledge to help future structural determination of ISM-Receptor complex and development of ISM1-based therapeutic agents.