Effects Of NEDD4 Family Ubiquitin Ligases On Ras Superfamily Protein Levels And Ubiquitination Of Arl3 Mediated By Ubiquitin Ligase Smurf1

Ras superfamily is a class of small GTPases that regulate a variety of key introcellular processes by functioning as GDP/GTP-regulated molecular switches.It has been demonstrated that these GTPases,along with their GEFs,GAPs and GDIs,undergo ubiquitination leading to varieties of fates such as re-localization or degradation.It has been clear for us that the NEDD4 family E3s are also important regulators for some Ras superfamily members.This superfamily comprises more than 160 proteins,but the ubiquitin ligases(E3s)for most of these GTPases have not been discovered,and their regulatory mechanisms are also much less clear.In this study,We systematically examed the effects of NEDD4 family E3s on the total protein levels of these GTPases.Our results demonstrated that the protein levels of many small GTPases can be decreased when certain ubiquitin ligases of NEDD4 family were co-expressed intracellularly with them.In order to further confirm these screening results,We studied the phenomenon of Smurfl-mediated down-regulation of Arl3 total protein level.We demonstrated that Smurfl can specifically downregulate the protein level of Arl3 and degrade Arl3 through the lysosomal pathway.In addition,Smurfl can interact with Arl3 and promote its Monoubiquitination in vivo and in vitro.The extensive screenings of the possible ubiquitin ligases of these small GTPases and the further systematic and comprehensive studies of their regulatory mechanisms by ubiquitination are of great significance.The ubiquitination of Ras-family proteins by the NEDD4 family ubiquitin ligases reveals their potential as new targets for cancer treatments.