SUMO-1 modification required for transformation by adenovirus type 5 earlyregion 1B 55-kDa oncoprotein

SUMO-1 is a small ubiquitin-related modifier protein that is covalently lin ked to many cellular and viral protein targets. Modification by SUMO-1 is p roposed to play a role in protein targeting and/or stability. We show here that adenovirus type 5 early region 1B 55-kDa (E1B-55kDa) oncoprotein can b e covalently modified by SUMO-1 in vivo through a major attachment site com prising a single lysine residue at amino acid position 104. The sequence su rrounding this lysine matches the proposed psi KxE consensus motif required for SUMO-1 conjugation. A single mutation (K104R) that abolishes SUMOylati on of E1B-55kDa dramatically reduces the ability of the adenovirus type 5 p rotein to transform primary baby rat kidney cells in cooperation with E1A a nd to inhibit p53-mediated transactivation. Overexpression of SUMO-1 in ade novirus type 5E1A/E1B-55kDa-transformed baby rat kidney cells causes the re localization of E1B-55kDa from the cytoplasm to the nucleus, where it accum ulates with SUMO-1 in dot- or track-like structures. Significantly, when SU MO-1 is ectopically expressed in transformed rat cells no effect on the cyt oplasmic localization of the E1B-K104R mutant protein is observed. Our resu lts demonstrate that SUMO-1 modification is required for transformation by adenovirus type 5E1B-55kDa and provide further evidence for the idea that t his posttranslational modification plays a role in protein targeting to spe cific subcellular sites.