Abstract 2471: The tumor suppressor gene Rb1 controls telomeric length and genomic instability that predisposes to osteosarcoma development in irradiated mice

Abstract

Abstract Osteosarcomas are capable of exhibiting both alternative lengthening of telomeres (ALT) and genomic instability, and are commonly associated with inactivation of the Rb1 gene implicated in both, cell cycle checkpoint regulation and telomere maintainance. We demonstrate a functional relationship between the loss of Rb1, genomic instability and the shortening of telomeres in radiation-induced osteosarcoma. Conditional somatic deletion of a floxed-Rb1 allele in the osteoblastic lineage produces an increased sensitivity to the osteosarcomagenic effects of radiation (Gonzalez-Vasconcellos et al, 2010). In Rb1 +/- osteoblast cell lines established from non-irradiated Rb1fl/+ Col1a1-Cre mice we show that after irradiation there was the expected impaired cell cycle arrest accompanied by an increase in genomic instability and reduced radiation induced senescence. The DNAmicronucleus assay showed an increase of 1.53 fold in Rb +/- primary cells as compared to Rb+/+ after 2 Gy irradiation (p=0.0032). We could prove that the reduced Rb1 gene expression in primary osteoblasts leads to a reduction in telomeric length of up to 50% that increases in a passage dependent manner and was shown to be independent of radiation exposure. These mutant cells showed an inclination towards tetraploidy and radiation induced anaphase bridges formation was increased in 2.6 fold in the mutant cells after 2 Gy irradiation (p = 0.001). These studies suggest the tumor suppressor gene Rb1 functioning not only as a gatekeeper if not also as a caretaker of the genome controlling the telomere dynamics and genomic stability. This maintenance of the genome by Rb1 was proven to be driven by epigenetic changes on the Rb+/- primary osteoblasts involving histone methylation. Lower levels of 3metLys20-H4 fluorescence intensity (p = 0.0079) were detected in Rb1 mutant osteoblasts as compared to wt. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2471. doi:10.1158/1538-7445.AM2011-2471