July Newsletter: SUMO Wrestling: All About Balance

In mammalian cells, the small ubiquitin-like modifier (SUMO) family contains four isoforms (SUMO1, SUMO2, SUMO3, and SUMO4). SUMO2 and SUMO3 are almost identical, with only a difference in three amino acid residues. SUMO1 shares 48% identity with SUMO2/3¹. SUMO4 is about 85% identical to SUMO2/3, but it is unclear whether SUMO4 can be conjugated to substrates². Similar to ubiquitination, SUMOylation requires a three enzymes system (E1, E2, and E3) to conjugate SUMO covalently to target substrates. Briefly, SUMO is first activated by the SUMO E1 activating heterodimeric enzyme SAE1/SAE2 by adenylation in an ATP-dependent reaction. The activated SUMO is then transferred to the SUMO E2 conjugating enzyme UBC9 and finally conjugated to a target protein by a SUMO E3 ligase (e.g., PIAS family members, Ran binding protein 2). The covalently linked SUMO can be removed by sentrin-specific proteases (SENPs), a process known as deSUMOylation³ (Fig. 1). SUMOylation is an essential post-translational modification (PTM) that regulates the activity, subcellular localization, stability, and functions of target proteins and thereby modulates almost all major cellular pathways⁴. Therefore, it is not surprising that many diseases are associated with dysregulation of SUMOylation. In this newsletter, the roles of SUMOylation/deSUMOylation in cancer are discussed.