A Rb1 promoter variant with reduced activity contributes to osteosarcoma susceptibility in irradiated mice

Abstract

BackgroundSyndromic forms of osteosarcoma (OS) account for less than 10% of all recorded cases of this malignancy. An individual OS predisposition is also possible by the inheritance of low penetrance alleles of tumor susceptibility genes, usually without evidence of a syndromic condition. Genetic variants involved in such a non-syndromic form of tumor predisposition are difficult to identify, given the low incidence of osteosarcoma cases and the genetic heterogeneity of patients. We recently mapped a major OS susceptibility QTL to mouse chromosome 14 by comparing alpha-radiation induced osteosarcoma in mouse strains which differ in their tumor susceptibility.MethodsTumor-specific allelic losses in murine osteosacoma were mapped along chromosome 14 using microsatellite markers and SNP allelotyping. Candidate gene search in the mapped interval was refined using PosMed data mining and mRNA expression analysis in normal osteoblasts. A strain-specific promoter variant in Rb1 was tested for its influence on mRNA expression using reporter assay.ResultsA common Rb1 allele derived from the BALB/cHeNhg strain was identified as the major determinant of radiation-induced OS risk at this locus. Increased OS-risk is linked with a hexanucleotide deletion in the promoter region which is predicted to change WT1 and SP1 transcription factor-binding sites. Both in-vitro reporter and in-vivo expression assays confirmed an approx. 1.5 fold reduced gene expression by this promoter variant. Concordantly, the 50% reduction in Rb1 expression in mice bearing a conditional hemizygous Rb1 deletion causes a significant rise of OS incidence following alpha-irradiation.ConclusionThis is the first experimental demonstration of a functional and genetic link between reduced Rb1 expression from a common promoter variant and increased tumor risk after radiation exposure. We propose that a reduced Rb1 expression by common variants in regulatory regions can modify the risk for a malignant transformation of bone cells after radiation exposure.

UHRF1 promotes human osteosarcoma cell invasion by downregulating the expression of E-cadherin in an Rb1-dependent manner

“…2). Homozygous deletion of the Rb1 gene has been A B C identified in Saos-2 cells (22,23), whereas MG-63 and U2OS cells exhibit normal expression levels of Rb1 (23,24). Therefore, the present study hypothesized that Rb1 may be involved in regulating the invasion of osteosarcoma cells by UHRF1.…”

“…The results of the present study demonstrated that UHRF1 promoted the invasion of osteosarcoma cells of the MG-63 and U2OS cell lines, but not of the Saos-2 cell line. Saos-2 cells undergo homozygous deletion of the Rb1 gene (22,23), therefore the present study hypothesized that Rb1 may be involved in the regulation of the invasion of osteosarcoma cells by UHRF1. Further investigations demonstrated that knockdown of the expression of Rb1 in the Rb1-positive cells eliminated the regulation of invasion by UHRF1.…”

Identification of key biomarkers involved in osteosarcoma using altered modules

“…Recent studies have mainly focused on individual gene-related analyses (Rosemann et al, 2014;Liu and Chen, 2015;Zeng and Xu, 2015;Li et al, 2016). However, these do not accurately reflect the interaction between integral genes under different conditions (Slonim, 2002).…”

Tumor Induction in Mice After Localized Single- or Fractionated-Dose Irradiation: Differences in Tumor Histotype and Genetic Susceptibility Based on Dose Scheduling

“…The risk of developing sarcomas is influenced by genetic susceptibility in humans and mice, however, only a few specific examples of a genetic susceptibility to radiation related sarcomas are present in the literature (13, 35, 36). Susceptibility to radiation induced osteosarcoma has been associated with a common promoter variant in Rb1 in mice (13).…”

“…The strain differences in susceptibilities are thought to be due to the differing genetic backgrounds of the strains and in some cases specific genetic polymorphisms have been identified that may be responsible (7,10–13). Most of these studies on strain differences involve single, acute, whole body exposures, although there are exceptions such as the use of internal emitters in the study of osteosarcoma and the use of dose fractionation to induce thymic lymphomas.…”