SUMOylation of the Lens Epithelium-derived Growth Factor/p75 attenuates its transcriptional activity on the Heat Shock Protein 27 promoter

摘要

Lens epithelium-derived growth factor (LEDGF) proteins, p75 and p52, are transcriptional co-activators that connect sequence-specific activators to the basal transcription machinery. We have found that these proteins are post translationally modified by the Small Ubiquitin-like Modifier (SUMO)-1 and SUMO-3. Three SUMOylation sites, K75, K250 and K254, were mapped in the shared N-terminal region of these molecules, while a fourth site, K364, was identified in the C-terminal part exclusive of LEDGF/p75. The N-terminal SUMO targets are located in evolutionarily conserved charge-rich regions that lack resemblance to the described consensus SUMOylation motif, whereas the C-terminal SUMO target is solvent-exposed and situated in a typical consensus motif. SUMOylation did not affect the cellular localization of LEDGF proteins and was not necessary for their chromatin-binding ability, nor did it affect this activity. However, lysine to arginine mutations of the identified SUMO acceptor sites drastically inhibited LEDGF SUMOylation, extended the half-life of LEDGF/p75 and significantly increased its transcriptional activity on the Heat shock protein 27 (Hsp27) promoter, indicating a negative effect of SUMOylation on the transcriptional activity of LEDGF/p75. Considering that SUMOylation is known to negatively affect the transcriptional activity of all transcription factors known to transactivate Hsp27 expression, these findings support the paradigm establishing SUMOylation as a global neutralizer of cellular processes upregulated upon cellular stress.