Functional heterogeneity of small ubiquitin-related protein modifiers SUMO-1 versus SUMO-2/3.
Post-translational modification marked by the covalent attachment of the ubiquitin-like protein SUMO-1/SMT3C has been implicated in a wide variety of cellular processes. Recently, two cDNAs encoding proteins related to SUMO-1 have been identified in human and mouse. The functions and regulation of these proteins, known as SUMO-2/SMT3A and SUMO-3/SMT3B, remain largely uncharacterized. We describe herein quantitative and qualitative distinctions between SUMO-1 and SUMO-2/3 in vertebrate cells. Much of this was accomplished through the application of an antibody that recognizes SUMO-2 and -3, but not SUMO-1. This antibody detected multiple SUMO-2/3-modified proteins and revealed that, together, SUMO-2 and -3 constitute a greater percentage of total cellular protein modification than does SUMO-1. Intriguingly, we found that there was a large pool of free, non-conjugated SUMO-2/3 and that the conjugation of SUMO-2/3 to high molecular mass proteins was induced when the cells were subjected to protein-damaging stimuli such as acute temperature fluctuation. In addition, we demonstrated that SUMO-2/3 conjugated poorly, if at all, to a major SUMO-1 substrate, the Ran GTPase-activating protein RanGAP1. Together, these results support the concept of important distinctions between the SUMO-2/3 and SUMO-1 conjugation pathways and suggest a role for SUMO-2/3 in the cellular responses to environmental stress.
Saitoh
H
H
The Picower Institute for Medical Research, Manhasset, New York 11030, USA. hisaitoh@picower.edu
Hinchey
J
J
D000818:Animals; D019556:COS Cells; D005455:Fluorescent Antibody Technique; D020690:GTPase-Activating Proteins / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D009994:Osmolar Concentration; D011499:Protein Processing, Post-Translational; D025842:SUMO-1 Protein; D025841:Small Ubiquitin-Related Modifier Proteins; D013696:Temperature; D014162:Transfection; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*
D020690:GTPase-Activating Proteins; C092317:RANGAP1 protein, human; D025842:SUMO-1 Protein; C117909:SUMO2 protein, human; C492189:SUMO3 protein, human; D025841:Small Ubiquitin-Related Modifier Proteins; D014452:Ubiquitins