title: The oncoprotein SS18-SSX1 promotes p53 ubiquitination and degradation by enhancing HDM2 stability.
abstract: Mutations of the p53 gene are uncommon in synovial sarcoma, a high-grade tumor genetically characterized by the chromosomal translocation t:(X;18), which results in the fusion of SS18 with members of SSX gene family. Although implicated in tumorigenesis, the mechanisms by which SS18-SSX promotes tumor growth and cell survival are poorly defined. Here, we show that SS18-SSX1 negatively regulates the stability of the tumor suppressor p53 under basal conditions. Overexpression of SS18-SSX1 enhanced p53 ubiquitination and degradation in a manner dependent on the ubiquitin ligase activity of HDM2. The negative effect of SS18-SSX1 expression on p53 was mediated by its ability to promote HDM2 stabilization through inhibition of HDM2 autoubiquitination. Furthermore, SS18-SSX1 expression altered the induction of p53-regulated genes in response to cellular stress by abrogating the transactivation of HDM2, PUMA, and NOXA but not p21. Our data uncover a novel mechanism whereby SS18-SSX1 can negatively regulate p53 tumor-suppressive function by increasing the stability of its negative regulator HDM2 and suggest that chemical compounds that target the p53-HDM2 regulatory axis may be of therapeutic benefit for the treatment of synovial sarcoma.
authors.affiliation: Department of Oncology-Pathology, Cancer Center Karolinska R8:04, Karolinska Institute, Stockholm, Sweden.
authors.forename: Pádraig
authors.initials: P
authors.lastname: D'Arcy
authors.forename: Wessen
authors.initials: W
authors.lastname: Maruwge
authors.forename: Bríd Ann
authors.initials: BA
authors.lastname: Ryan
authors.forename: Bertha
authors.initials: B
authors.lastname: Brodin
mesh_terms: D021581:Active Transport, Cell Nucleus; D017209:Apoptosis; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002470:Cell Survival; D004249:DNA Damage; D015972:Gene Expression Regulation, Neoplastic; D006207:Half-Life; D006801:Humans; D015514:Oncogene Proteins, Fusion / Q000235:genetics / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D051736:Proto-Oncogene Proteins c-mdm2 / Q000378:metabolism*; D013816:Thermodynamics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D015514:Oncogene Proteins, Fusion; C116512:SYT-SSX fusion protein; D016159:Tumor Suppressor Protein p53; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2