System-Wide Changes to SUMO Modifications in Response to Heat Shock

The small ubiquitin-like modifier protein SUMO is redistributed among many targets to mediate both short- and long-term signaling events. SUMO Status Revealed Posttranslational modification of proteins through their conjugation to small ubiquitin-like modifier (SUMO) proteins is important in the nucleus for the repair of damaged DNA and the maintenance of chromosome structure, as well as for a number of cytoplasmic processes. Although the machinery involved in attaching SUMO moieties to target proteins is well characterized, less is known about the upstream signals that trigger this modification. Golebiowski et al. designed a highly stringent, quantitative approach, involving protein purification and mass spectrometric techniques, to perform a system-wide analysis of the SUMOylation states of hundreds of proteins in HeLa cells in response to heat shock. The authors also analyzed the dynamic nature of SUMOylation in cells during the subsequent recovery phase. In addition to identifying many previously unknown substrates of SUMO-2, this proteome-wide analysis of SUMOylation revealed a rapid and dramatic redistribution of SUMO-2 among proteins involved in short- or long-term responses to heat stress. This new approach should also prove valuable in systems-wide analysis of other posttranslational modifications. Covalent conjugation of the small ubiquitin-like modifier (SUMO) proteins to target proteins regulates many important eukaryotic cellular mechanisms. Although the molecular consequences of the conjugation of SUMO proteins are relatively well understood, little is known about the cellular signals that regulate the modification of their substrates. Here, we show that SUMO-2 and SUMO-3 are required for cells to survive heat shock. Through quantitative labeling techniques, stringent purification of SUMOylated proteins, advanced mass spectrometric technology, and novel techniques of data analysis, we quantified heat shock–induced changes in the SUMOylation state of 766 putative substrates. In response to heat shock, SUMO was polymerized into polySUMO chains and redistributed among a wide range of proteins involved in cell cycle regulation; apoptosis; the trafficking, folding, and degradation of proteins; transcription; translation; and DNA replication, recombination, and repair. This comprehensive proteomic analysis of the substrates of a ubiquitin-like modifier (Ubl) identifies a pervasive role for SUMO proteins in the biologic response to hyperthermic stress.