The Differentiation Stage of p53-Rb-deficient Bone Marrow Mesenchymal Stem Cells imposes the phenotype of in vivo sarcoma development

Abstract

Increasing evidence suggests that mesenchymal stem/stromal cells (MSCs) carrying specific mutations are at the origin of some sarcomas. We have reported that the deficiency of p53 alone or in combination with Rb (Rb-/- p53-/-) in adipose-derived MSCs (ASCs) promotes leiomyosarcoma-like tumors in vivo. Here, we hypothesized that the source of MSCs and/or the cell differentiation stage could determine the phenotype of sarcoma development. To investigate whether there is a link between the source of MSCs and sarcoma phenotype, we generated p53-/- and Rb-/-p53-/- MSCs from bone marrow (BM-MSCs). Both genotypes of BM-MSCs initiated leiomyosarcoma formation similar to p53-/- and Rb-/-p53-/- ASCs. In addition, gene expression profiling revealed transcriptome similarities between p53- or Rb-p53-deficient BM-MSCs/ASCs and muscle-associated sarcomagenesis. These data suggest that the tissue source of MSC does not seem to determine the development of a particular sarcoma phenotype. To analyze whether the differentiation stage defines the sarcoma phenotype, BM-MSCs and ASCs were induced to differentiate towards the osteogenic lineage, and both p53 and Rb were excised using Creexpressing adenovectors at different stages along osteogenic differentiation. Regardless the level of osteogenic commitment, the inactivation of Rb and p53 in BM-MSC-derived, but not in ASCderived, osteogenic progenitors gave rise to osteosarcoma-like tumors which could be serially transplanted. This indicates that the osteogenic differentiation stage of BM-MSCs imposes the phenotype of in vivo sarcoma development, and that BM-MSC-derived osteogenic progenitors rather than undifferentiated BM-MSCs, undifferentiated ASCs or ASC-derived osteogenic progenitors, represent the cell of origin for osteosarcoma development.