title: Sequential transformation of mesenchymal stem cells is associated with increased radiosensitivity and reduced DNA repair capacity.
abstract: We used sequentially transformed mesenchymal stem cells to investigate how the events that lead to tumorigenicity influence the cellular response to radiation. Bone marrow derived SH2(+), SH4(+), Stro-1(+) mesenchymal stem cells (MSC) were transformed stepwise by retroviral transfection of hTERT, HPV-16 E6 and E7, SV40 small T antigen and oncogenic H-ras. Cells at three different stages of transformation were irradiated and compared using assays for cytotoxicity, apoptosis, DNA double-strand break (DSB) repair and checkpoint signaling. The effects of inhibition of cell cycle checkpoint signaling on radiosensitivity were investigated using RNA interference. During stepwise transformation, specifically after HPV-16 E6 and E7 transduction, MSCs became more sensitive to radiation. This was associated with increased residual DNA DSB at 24 h and increased apoptosis. Enhanced checkpoint signaling occurred during transformation and there was a differential effect of checkpoint targeting in cells at different stages; Chk1 knockdown enhanced radiosensitivity in all cells while Chk2 knockdown only affected non-transformed cells. These data show that transformation of MSC is associated with a reduction in DNA DSB repair capacity and increased radiosensitivity. Up-regulation of checkpoint signaling does not overcome this and the effect of checkpoint inhibition may change with transformation status.
authors: UCL Cancer Institute, London, United Kingdom.
authors: M
authors: M
authors: Worku
authors: N
authors: N
authors: Fersht
authors: C
authors: C
authors: Martindale
authors: J M
authors: JM
authors: Funes
authors: S C
authors: SC
authors: Short
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D059447:Cell Cycle Checkpoints / Q000528:radiation effects; D002460:Cell Line; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000528:radiation effects*; D004249:DNA Damage; D004260:DNA Repair / Q000528:radiation effects*; D006801:Humans; D059630:Mesenchymal Stem Cells / Q000166:cytology* / Q000378:metabolism / Q000528:radiation effects*; D011836:Radiation Tolerance / Q000528:radiation effects*; D015398:Signal Transduction / Q000528:radiation effects; D013997:Time Factors