title: Ectopic expression of cancer/testis antigen SSX2 induces DNA damage and promotes genomic instability.
abstract: SSX cancer/testis antigens are frequently expressed in melanoma tumors and represent attractive targets for immunotherapy, but their role in melanoma tumorigenesis has remained elusive. Here, we investigated the cellular effects of SSX2 expression. In A375 melanoma cells, SSX2 expression resulted in an increased DNA content and enlargement of cell nuclei, suggestive of replication aberrations. The cells further displayed signs of DNA damage and genomic instability, associated with p53-mediated G1 cell cycle arrest and a late apoptotic response. These results suggest a model wherein SSX2-mediated replication stress translates into mitotic defects and genomic instability. Arrest of cell growth and induction of DNA double-strand breaks was also observed in MCF7 breast cancer cells in response to SSX2 expression. Additionally, MCF7 cells with ectopic SSX2 expression demonstrated typical signs of senescence (i.e. an irregular and enlarged cell shape, enhanced β-galactosidase activity and DNA double-strand breaks). Since replication defects, DNA damage and senescence are interconnected and well-documented effects of oncogene expression, we tested the oncogenic potential of SSX2. Importantly, knockdown of SSX2 expression in melanoma cell lines demonstrated that SSX2 supports the growth of melanoma cells. Our results reveal two important phenotypes of ectopic SSX2 expression that may drive/support tumorigenesis: First, immediate induction of genomic instability, and second, long-term support of tumor cell growth.
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Katrine B V
authors.initials: KB
authors.lastname: Greve
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Jonas N
authors.initials: JN
authors.lastname: Lindgreen
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark; The Lundbeckfonden Center of Excellence NanoCAN, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Mikkel G
authors.initials: MG
authors.lastname: Terp
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Christina B
authors.initials: CB
authors.lastname: Pedersen
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark; The Lundbeckfonden Center of Excellence NanoCAN, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Steffen
authors.initials: S
authors.lastname: Schmidt
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark; The Lundbeckfonden Center of Excellence NanoCAN, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Jan
authors.initials: J
authors.lastname: Mollenhauer
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Stine B
authors.initials: SB
authors.lastname: Kristensen
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Rikke S
authors.initials: RS
authors.lastname: Andersen
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark.
authors.forename: Mette M
authors.initials: MM
authors.lastname: Relster
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark; The Lundbeckfonden Center of Excellence NanoCAN, University of Southern Denmark, DK-5000 Odense, Denmark; Department of Oncology, Odense University Hospital, DK-5230 Odense, Denmark. Electronic address: hditzel@health.sdu.dk.
authors.forename: Henrik J
authors.initials: HJ
authors.lastname: Ditzel
authors.affiliation: Department of Cancer and Inflammation Research, Institute for Molecular Medicine, University of Southern Denmark, DK-5000 Odense, Denmark. Electronic address: mgjerstorff@health.sdu.dk.
authors.forename: Morten F
authors.initials: MF
authors.lastname: Gjerstorff
mesh_terms: D045744:Cell Line, Tumor; D016922:Cellular Senescence / Q000235:genetics; D053903:DNA Breaks, Double-Stranded; D059585:G1 Phase Cell Cycle Checkpoints; D015972:Gene Expression Regulation, Neoplastic; D042822:Genomic Instability; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009363:Neoplasm Proteins / Q000096:biosynthesis* / Q000235:genetics; D012097:Repressor Proteins / Q000096:biosynthesis* / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D009363:Neoplasm Proteins; D012097:Repressor Proteins; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; C093962:synovial sarcoma X breakpoint proteins
keywords: Cancer/testis antigen; Genomic instability; Oncogene; SSX2; Senescence