Regulation and Function of SUMO Protein Modification

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PROJECT SUMMARY Small ubiquitin related modifiers (SUMOs) function as posttranslational protein modifications and thereby regulate nearly all essential cell functions. As such, sumoylation is linked to a variety of human diseases, including cancer and neurodegenerative disorders, and there is great interest in targeting the SUMO pathway for therapeutic purposes. Notably, the first phase I clinical trial of a SUMO inhibitor was recently approved for cancer therapy. A more detailed understanding of basic molecular mechanisms regulating sumoylation and its consequences on cell function, however, is needed to achieve the full potential of these efforts. In particular, an ability to target specific branches of the SUMO pathway could allow for more precise therapies. Vertebrates express multiple SUMO paralogs which could allow for such precision targeting. However, the unique properties and functions of SUMO paralogs remain poorly understood. To address this gap in knowledge, we are taking advantage of recently developed SUMO1 and SUMO2 knockout cell lines to define and characterize the specific functions and molecular mechanisms of action of these two paralogs. Aims of our proposal include: (1) We will obtain support for the hypothesis that SUMO1 and SUMO2 function as unique signals specifying unique fates upon conjugation to proteins. This will be achieved through characterization of paralog-specific phenotypes we have identified in SUMO1 and SUMO2 knockout cell lines, including changes in cell morphology, defects in proteostasis and hypersensitivities to cell stress. (2) We will test multiple hypotheses to reveal the molecular basis for non-redundant functions of SUMO1 and SUMO2. Hypotheses concerning the function of chain formation and selective non-covalent interactions with effector proteins will be explored through rescue of knockout cell phenotypes using a panel of SUMO1 and SUMO2 mutant proteins. (3) We will test the hypothesis that phenotypic changes observed in SUMO1 and SUMO2 knockout cell lines are due in part to paralog-specific effects on gene expression. Results from our studies will provide unequivocal evidence for SUMO1 and SUMO2 paralog-specific functions and vital insights required to target specific branches of the SUMO pathway for therapeutic purposes.