Expression of an Exogenous Human Oct-4 Promoter Identifies Tumor-Initiating Cells in Osteosarcoma

Abstract

We explored the nature of the tumor-initiating cell in osteosarcoma, a bone malignancy that predominately occurs in children. Previously, we observed expression of Oct-4, an embryonal transcriptional regulator, in osteosarcoma cell cultures and tissues. To examine the relationship between Oct-4 and tumorigenesis, cells from an osteosarcoma biopsy (OS521) were stably transfected with a plasmid containing the human Oct-4 promoter driving a green fluorescent protein (GFP) reporter to generate the transgenic line OS521Oct-4p. In culture, only f24% of the OS521Oct-4p cells were capable of activating the transgenic Oct-4 promoter; yet, xenograft tumors generated in NOD/SCID mice contained f67% GFP + cells, which selectively expressed the mesenchymal stem cellassociated surface antigens CD105 and ICAM-1. Comparison of the tumor-forming capacity of GFP-enriched and GFPdepleted cell fractions revealed that the GFP-enriched fractions were at least 100-fold more tumorigenic, capable of forming tumors at doses of <300 cells, and formed metastases in the lung. Clonal populations derived from a single Oct-4/GFP + cell were capable of forming tumors heterogeneous for Oct-4/GFP expression. These data are consistent with the cancer stem cell model of tumorigenesis in osteosarcoma and implicate a functional link between the capacity to activate an exogenous Oct-4 promoter and tumor formation. This osteosarcoma tumor-initiating cell appears highly prolific and constitutes a majority of the cell population in a primary xenograft tumor, which may provide a biological basis for the particular virulence of this type of cancer.

An integrated computational and experimental study uncovers FUT 9 as a metabolic driver of colorectal cancer

“…On a molecular level, this was accompanied by the reduced expression of OCT4 transcription factor in FUT9‐silenced cells (Appendix Fig S4). Since OCT4 has been shown to support TIC formation (Levings et al , 2009; Chiou et al , 2010), this observation provides a mechanistic explanation for FUT9 effect in supporting TIC activity. These results show that, in contrast to the anti‐proliferative effects of FUT9 activity in the bulk of colon cancer cells (Fig 3A–D), FUT9 activity may actually be required for the efficient expansion of TIC populations.…”

Modeling sarcomagenesis using multipotent mesenchymal stem cells

“…CSCs that display tumor re-initiating properties have been recently identified in osteosarcoma [81][82][83], chondrosarcoma [82], Ewing's sarcoma [61] and synovial sarcoma [79]. The identification of these sarcoma-initiating cells was based on both their ability to form spherical, clonal expanding colonies (called sarcospheres) in anchorage-independent and serum-starved conditions and the expression of stem cell markers [61,79,[81][82][83][84].…”

“…All of these CSCs are characterized by the expression of the pluripotent stem cell markers OCT3/4, NANOG and SOX2 and are able to self-renew and to sustain the tumor in serial transplantation experiments. More importantly, many of these sarcoma-initiating cells express MSC markers [79,[81][82][83] and retain MSC in vitro differentiation properties, giving rise to adipogenic, chondrogenic and osteogenic lineages [61,79,82]. In addition, these MSC-like CSCs are associated with drug resistance and metastasis [81,84] and therefore, they may be responsible for the frequent relapses observed in sarcomas [85].…”

The MET oncogene transforms human primary bone-derived cells into osteosarcomas by targeting committed osteo-progenitors

“…Both CD117 (15) and OCT3/4 have already been identified as potential markers of osteosarcoma-initiating cells. (13) Because we show that MET overexpression transforms osteoblast precursors rather than MSCs, the data presented here suggest that METdriven osteo-progenitor amplification favors acquisition of either RB1 or p53 mutations in the progression of human osteosarcomas. Alternatively, MET overexpression in cells carrying RB1 or p53 mutations might sustain their ''freezing'' in a state of committed osteo-progenitors.…”

“…(12) Despite recent advances in osteosarcoma treatments, the patient prognosis for advanced disease remains poor. (8) Several studies have provided evidence of the identification of osteosarcoma-initiating cells, (13)(14)(15)(16) the definition of which is crucial in the search for novel and more effective therapies and to characterize the genetic events that occur before the full-blown clinical manifestation. It is widely accepted that osteosarcomas derive from the mesenchymal stem cell lineage, as Ewing sarcomas do, although for the latter, the origin has been better defined.…”