Abstract 4695: TGF-β enforces genomic instability in liver cancers

Background: Over 90% of liver cancers, from viral hepatitis to alcohol injury, occur against a background of chronic liver disease and cirrhosis. Genomic stability, G1/S cell cycle arrest through c-Myc and CDK suppression, have been some of the mechanisms proposed in tumor suppression by TGF-β. The Smad3/4 adaptor protein, β2SP, is emerging as potent regulator of tumor genesis by its ability to affect TGF-β tumor suppressor function. Deletion of β2SP results in a dramatic and spontaneous formation of liver cancer and gastrointestinal cancers. Moreover, β2SP+/− and β2SP+/− /Smad3+/− mutant mice phenocopy human Beckwith-Wiedemann syndrome (BWS), a hereditary human cancer stem cell syndrome imprinting disorder with loss of p57, increase in IGF2, and an association with 800 fold increase of cancers that include those of the liver. Delayed liver regeneration and extensive DNA damage was observed in β2SP heterozygote mice. In addition, spectrins have been observed to associate with FANC G and D, DNA interstrand cross links, and Smad3/4 to transcriptionally regulate FANC genes. Hypothesis: We therefore hypothesised that TGF-β is a crucial enforcer of genomic stability, and that β2SP and/or Smad3/4 are key mediators in suppressing liver injury and cancer through modulation of the DNA repair pathway. Materials & Methods: To determine the role of β2SP and Smad3 in the DNA damage response, and whether β2SP and β2SP/Smad3 loss plays a causal role in the downregulation of the Fanc/Brca pathway, we used our mouse models as well as the mouse embryonic fibroblasts. Oxidative DNA damage was induced by H2O2 treatment and assayed tail length analysis. Irradiation was induced by 8Gy IR and DNA was studied by immunofluorescence of DNA damage sensors H2AX, 532BP1, and pChk2. DNA repair was assayed by Mdc1, NBS1, and Rad51 foci formation at different time points after irradiation. Results: β2SP+/− and β2SP+/−/Smad3+/− mice exhibited an increased prevalence of HCC and GI cancer and many phenotypic characteristics observed in BWS patients. Loss of β2SP results in premature replicative senescence with spontaneous DNA damage. β2SP deficiency results in increased sensitivity to exogenous DNA damage and insufficient DNA repair. Depletion of TGF-β adaptor protein β2SP impairs the loading of repair proteins and repair of DNA double-strand breaks. Loss of FancD2 expression in HCC and GI cancer cell lines correlates with loss of β2SP. Moreover, β2SP−/− and β2SP+/−/Smad3+/− cell lines accumulate DNA damage that is further exacerbated by DNA cross-linking agents such as mitomycin C similar to P57 null cells and Fanconi anemia cell lines. Conclusions: TGF-β confers genomic stability through regulation of DNA impairment of the Fanc/Brca DNA damage response and interstrand link repair and inactivation of TGF- ≤ pathway results in alcohol toxicity, cirrhosis and liver cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 4695. doi:1538-7445.AM2012-4695