An EWS-FLI1-Induced Osteosarcoma Model Unveiled a Crucial Role of Impaired Osteogenic Differentiation on Osteosarcoma Development

摘要

class="head no_bottom_margin" id="sec1title">IntroductionCancer cells often exhibit similar properties to somatic stem/progenitor cells of the tissue of origin (, ). Considering that progenitor cells at the developmental stage and somatic stem/progenitor cells in some adult tissues have the ability for self-renewal and/or active proliferation, it has been proposed that maintenance of the stem/progenitor cell state could be a driving force for tumor development (). Osteosarcoma is a representative cancer that exhibits shared features with normal stem/progenitor cells (, ). The late markers of osteogenic differentiation are silenced while the early markers are modestly expressed in osteosarcomas (, ). Moreover, more aggressive phenotypes of osteosarcomas are correlated with features of early osteogenic progenitors (, ), suggesting that defects in the osteogenic differentiation program may play a role in osteosarcoma development and progression. However, the causative aberrations that confer stem/progenitor cell properties on osteosarcoma cells are not fully understood.EWS-FLI1, a widely recognized fusion oncogene for Ewing sarcomas, is generated by the chromosomal translocation of t(11;22) (q24;q12), which consists of the N-terminal transactivator domain of the EWS gene and the C-terminal ETS DNA binding domain of the FLI1 gene. The resulting EWS-FLI1 fusion protein harbors multiple functions, acting as a transcriptional activator, transcriptional repressor, chromatin modulator, and splicing modulator (, , , ). Despite the variety of oncogenic functions of EWS-FLI1, a number of previous studies implied that EWS-FLI1 expression itself is not sufficient to induce Ewing sarcoma (, , href="#bib28" rid="bib28" class=" bibr popnode">Riggi et al., 2008, href="#bib39" rid="bib39" class=" bibr popnode">Tanaka et al., 2015) and that other aberrations may be necessary. Indeed, genetic variants near EGR2 and TARDBP are associated with susceptibility to Ewing sarcoma (href="#bib7" rid="bib7" class=" bibr popnode">Grunewald et al., 2015, href="#bib24" rid="bib24" class=" bibr popnode">Postel-Vinay et al., 2012). Moreover, additional genetic mutations, such as TP53, CDKN2A, and STAG2, have been identified in a subset of Ewing sarcomas (href="#bib5" rid="bib5" class=" bibr popnode">Crompton et al., 2014, href="#bib42" rid="bib42" class=" bibr popnode">Tirode et al., 2014). However, it remains unclear whether these mutations are additional driver mutations or passenger mutations and how they contribute to the sarcoma development.The derivation of induced pluripotent stem cells (iPSCs) demonstrated that mammalian somatic cells can be reprogrammed into pluripotent stem cells (href="#bib37" rid="bib37" class=" bibr popnode">Takahashi and Yamanaka, 2006). It is noteworthy that the reprogramming process does not require any particular alterations to the genetic information, which makes iPSC technology suitable to study the genotype-phenotype relationship in various diseases (href="#bib36" rid="bib36" class=" bibr popnode">Soldner et al., 2009, href="#bib45" rid="bib45" class=" bibr popnode">Yamashita et al., 2014). Considering that cancer is a genetic disease involving genetic mutations, single nucleotide variants, and structural abnormalities of the chromosome, iPSCs derived from cancer cells are expected to harbor shared genetic abnormalities with the parental cancer cells and therefore should be a powerful tool for dissecting the role of the cancer genome on the phenotype (href="#bib33" rid="bib33" class=" bibr popnode">Semi and Yamada, 2015).Here, we established a murine EWS-FLI1-induced osteosarcoma model from adult bone marrow stromal cells using a doxycycline (Dox)-inducible-EWS-FLI1 expression system. We revealed that EWS-FLI1 expression inhibits the osteogenic differentiation of sarcoma cells in vitro and in vivo. Moreover, we found that iPSCs derived from the EWS-FLI1-induced osteosarcoma cells exhibit impaired osteogenic differentiation and give rise to sarcoma cells after osteogenic differentiation in vitro in conjunction with EWS-FLI1 expression.