SUMO-1 modification of the Wilms' tumor suppressor WT1.
SUMO-1 conjugation modulates numerous cellular functions, including the subnuclear localization of its target proteins. The WT1 tumor suppressor encodes a four-zinc finger protein with distinct splicing isoforms. WT1(-KTS), encoding uninterrupted zinc fingers, functions as a transcription factor and has a diffusely nuclear distribution; WT1(+KTS), with an insertion of three amino acids (KTS) between zinc fingers three and four, localizes to discrete nuclear speckles, the function of which is unknown. Because the SUMO-1 E2-conjugating enzyme, Ubc9, interacts with WT1, we tested whether sumoylation modulates the cellular localization of WT1. We find here that both WT1 isoforms are directly sumoylated on lysine residues 73 and 177. Although RNA interference-mediated Ubc9 depletion effectively suppresses WT1 nuclear speckles, a SUMO-1-deficient WT1(+KTS)(K73, 177R) double mutant retains localization to speckles. Thus, direct sumoylation of WT1 is not responsible for its cellular localization, and other sumoylated proteins may target WT1 to these nuclear structures. Identification of other components of WT1-associated speckles is likely to provide clues to their function.
Smolen
Gromoslaw A
GA
Massachusetts General Hospital Cancer Center and Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Vassileva
Maria T
MT
Wells
Julie
J
Matunis
Michael J
MJ
Haber
Daniel A
DA
D021581:Active Transport, Cell Nucleus; D045744:Cell Line, Tumor; D006801:Humans; D009363:Neoplasm Proteins / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D000071156:Promyelocytic Leukemia Protein; D025842:SUMO-1 Protein / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D025521:Tumor Suppressor Proteins; D044763:Ubiquitin-Conjugating Enzymes / Q000502:physiology; D025721:WT1 Proteins / Q000378:metabolism*; D000098843:Ubiquitin-Conjugating Enzyme UBC9
D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000071156:Promyelocytic Leukemia Protein; D025842:SUMO-1 Protein; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D025721:WT1 Proteins; C070576:PML protein, human; D044763:Ubiquitin-Conjugating Enzymes; D000098843:Ubiquitin-Conjugating Enzyme UBC9