title: Sumoylation of p68 and p72 RNA helicases affects protein stability and transactivation potential.
abstract: The p68 (DDX5) and p72 (DDX17) proteins are members of the DEAD-box (DDX) family of RNA helicases. We show that both p68 and p72 are overexpressed in breast tumors. Bioinformatical analysis revealed that the SUMO pathway is upregulated in breast tumors and that both p68 and p72 contain one consensus sumoylation site, implicating that sumoylation of p68 and p72 increases during breast tumorigenesis and potentially contributes to their overexpression. We determined that p68 and p72 are indeed sumoylated at a single, homologous site. Importantly, sumoylation significantly increased the stability of p68 and p72. In contrast to p72 and consistent with an approximately 3-fold lesser half-life, p68 was found to be polyubiquitylated, and mutation of the sumoylation site increased polyubiquitylation, suggesting that sumoylation increases p68 half-life by reducing proteasomal degradation. Moreover, whereas p68 robustly coactivated transcription from an estrogen response element, its sumoylation mutant showed a drastically reduced coactivation potential. In contrast, the p68 sumoylation status did not affect the ability to enhance p53-mediated MDM2 transcription. On the contrary, preventing sumoylation of p72 caused an increase in its ability to transactivate both estrogen receptor and p53. Furthermore, sumoylation promoted the interaction of p68 and p72 with histone deacetylase 1 but had no effect on binding to histone deacetylases 2 and 3, the coactivator p300, or estrogen receptor and also did not affect homo/heterodimerization of p68/p72. In conclusion, sumoylation exerts pleiotropic effects on p68/p72, which may have important implications in breast cancer by modulating estrogen receptor and p53 activity.
authors.affiliation: Department of Biochemistry, Mayo Clinic, Rochester, Minnesota 55905, USA.
authors.forename: Steven M
authors.initials: SM
authors.lastname: Mooney
authors.forename: Joseph P
authors.initials: JP
authors.lastname: Grande
authors.forename: Jeffrey L
authors.initials: JL
authors.lastname: Salisbury
authors.forename: Ralf
authors.initials: R
authors.lastname: Janknecht
mesh_terms: D001665:Binding Sites; D001943:Breast Neoplasms / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D053487:DEAD-box RNA Helicases / Q000235:genetics / Q000378:metabolism*; D005260:Female; D006801:Humans; D055550:Protein Stability; D011960:Receptors, Estrogen / Q000378:metabolism; D025841:Small Ubiquitin-Related Modifier Proteins / Q000378:metabolism*; D015533:Transcriptional Activation / Q000235:genetics*; D014162:Transfection; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D011960:Receptors, Estrogen; D025841:Small Ubiquitin-Related Modifier Proteins; D016159:Tumor Suppressor Protein p53; C010140:estrophilin; D053487:DEAD-box RNA Helicases