Functional analysis of the E3 ubiquitin ligase HECTD1, and its relationship with the TRABID deubiquitinase

HECTD1 is a conserved ubiquitin ligase essential for cellular migration and development of the vertebrate neural tube. Here I show that HECTD1 accumulates along cell-cell contacts and mitotic spindle, and localizes to the centrosome in a dynein-independent manner. Likewise, I reveal that TRABID, a deubiquitinase and suspected HECTD1 interaction partner, enriches along spindle microtubules during cytokinesis, and at the centrosome. Previously documented knock-down phenotypes of HECTD1 and TRABID suggest that the proteins may participate in cytoskeletal dynamics. Interestingly, HECTD1 and TRABID were also shown to interact with the Adenomatous polyposis coli (APC) protein, modulating its K63 polyubiquitination. Redistribution of APC occurs in HECTD1 and TRABID knock-down cells, leading me to hypothesize that the ligase-deubiquitinase system controls cytoskeletal organization through APC trafficking. Given the importance of HECTD1 in mammalian development, I generated a hectd1 knock-out cell line using TALENs that will permit further detailed analysis of the microtubule-associated roles of HECTD1.