SV40 Oncoproteins Enhance Asbestos-Induced DNA Double-Strand Breaks and Abrogate Senescence in Murine Mesothelial Cells

Department of Pathology and Laboratory Medicine, Brown University, Providence, Rhode Island, United States
Cancer Research (Impact Factor: 9.33). 05/2007; 67(8):3637-45. DOI: 10.1158/0008-5472.CAN-05-3727
Source: PubMed


SV40 virus has emerged as a potential cofactor with asbestos in the development of diffuse malignant mesothelioma, but its precise role in the pathogenesis of this tumor is unclear. SV40 large T antigen is known to inactivate cellular proteins involved in DNA damage and senescence, including p53 and pRb. We hypothesize that SV40 oncoproteins will sensitize mesothelial cells to DNA damage induced by asbestos or chemotherapeutic agents. SV40 oncoprotein expression in murine mesothelial cell lines enhanced spontaneous and asbestos-induced double-strand breaks, indicated by gamma-H2AX foci, and potentiated micronucleus formation. Mesothelial cells exposed to asbestos or bleomycin for 96 h acquired senescent-like morphology and displayed elevated senescence-associated beta-galactosidase activity, reduced bromodeoxyuridine (BrdUrd) incorporation, and reduced colony formation. SV40 oncoprotein expression abrogated the senescent phenotype, and transfected cell lines showed an increase in both BrdUrd incorporation and colony formation after prolonged DNA damage. Murine mesothelial cell lines lacking wild-type p53 due to a point mutation or gene rearrangement also failed to senesce in response to asbestos or chemotherapeutic agents. In addition, stress-induced senescence in human mesothelial cell lines was impaired by SV40 oncoprotein expression (MeT-5A), p53 small interfering RNA, or spontaneous p53 mutation (REN). These studies suggest that exposure to DNA-damaging agents can induce senescence in both murine and human mesothelioma cell lines and suggest a major, although not exclusive, role for p53 in this response. SV40 virus may contribute to mesothelioma progression by impairing stress-induced senescence, in part through p53 inactivation, thereby favoring survival and proliferation of mesothelial cells that have sustained DNA damage.

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Available from: Jodie Pietruska, Dec 11, 2014
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    • "It is possible that this is a byproduct of sequestering DDR proteins to viral replication centers, which could physically prevent recognition of host DNA damage. Supporting this, SV40 infected murine mesothelial cells showed enhanced susceptibility to asbestos-induced DSBs (Pietruska and Kane, 2007). MPyV infection sensitizes host cells to DNA damaging agents—possibly through TAg binding to RPA (Banerjee et al., 2013). "
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    • "Indeed, although Nf2-deficient murine cell lines are available (Jongsma et al. 2008), they are, in addition, also deficient for cyclin-dependent kinase inhibitor 2A (Cdkn2a) and, moreover, are on a mixed genetic background. Mesothelial lines immortalized with SV40 T antigens have allowed highlighting the importance of p53 in maintaining genomic stability (Levresse et al. 2000; Pietruska and Kane 2007). We confirmed that SV40 T antigen expression, although accelerating the rate of the cell cycle, consistent with previous data (reviewed in An et al. 2012), is not sufficient to transform mesothelial cells (Cleaver et al. 2014). "
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    ABSTRACT: Mesothelial cells are susceptible to asbestos fiber-induced cytotoxicity and on longer time scales to transformation; the resulting mesothelioma is a highly aggressive neoplasm that is considered as incurable at the present time Zucali et al. (Cancer Treatment Reviews 37:543-558, 2011). Only few murine cell culture models of immortalized mesothelial cells and mesothelioma cell lines exist to date. We generated SV40-immortalized cell lines derived from wild-type (WT) and neurofibromatosis 2 (merlin) heterozygote (Nf2+/-) mice, both on a commonly used genetic background, C57Bl/6J. All immortalized mesothelial clones consistently grow in DMEM supplemented with fetal bovine serum. Cells can be passaged for more than 40 times without any signs of morphological changes or a decrease in proliferation rate. The tumor suppressor gene NF2 is one of the most frequently mutated genes in human mesothelioma, but its detailed function is still unknown. Thus, these genotypically distinct cell lines likely relevant for malignant mesothelioma formation are expected to serve as useful in vitro models, in particular to compare with in vivo studies in mice of the same genotype. Furthermore, we generated a novel murine mesothelioma cell line RN5 originating from an Nf2+/- mouse subjected to repeated crocidolite exposure. RN5 cells are highly tumorigenic.
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    • "As shown in Figure 6, Noxa overexpression occurs in REN cells upon treatment with bortezomib. The transcriptional mechanism involved in REN cells must be p53-independent because REN cells are known to contain a rearranged p53 gene and lack expression of p53 protein [40]. We thus suggest the c-Myc is the only driver of Noxa expression in this contest. "
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