Understanding the Role of SUMOylation in the Function of Aac11/Api5

Abstract

Api5 and Aac11 are orthologous anti-apoptotic proteins in humans and flies respectively. Api5 is gaining prominence as a target in therapy due to its ability to confer cancer cells with resistance to apoptosis. Api5 also confers stemcell like properties to cancer cells through interactions with E2f1 and Fgf2. Posttranslational modification of Api5 by way of acetylation has been demonstrated to be crucial to its function. In this study, I explore the regulation of Api5 and Aac11 function by SUMOylation. Bioinformatics tools predict that Api5 and Aac11 are SUMOylated at several putative target lysines, some of which are conserved between the two proteins. I demonstrate that both proteins are SUMOylated in vitro, and have generated reagents to test the same in vivo. I have also carried out extensive mutagenesis of the predicted lysine target sites for SUMO, but until date have not been able to abolish SUMOylation. This may indicate either that I have not targeted the correct SUMO site, or that Api5/Aac11 are promiscuous in terms of their SUMOylation. Additionally, I explore the possibility of rescuing Aac11 null flies with Api5. If the rescue is successful, known Api5 variants can be tested in Drosophila to uncover biological function.