title: TSSC3 overexpression reduces stemness and induces apoptosis of osteosarcoma tumor-initiating cells.
abstract: Osteosarcoma (OS) is the most common primary bone tumor in children and adolescents, typically presenting with poor prognosis. Recent studies suggested that tumor initiating cells (T-ICs) drive tumor formation and relapse or metastasis and are relatively resistant to cell death induced by conventional chemo- and radiotherapies. Therefore, the poor prognosis of OS appears to be associated with T-ICs. Here, we enriched T-ICs in OS cell lines and evaluated whether the imprinted gene TSSC3 (tumor-suppressing STF cDNA 3) associated with apoptosis could affect T-ICs in OS. Sarcosphere selection and serial clone-forming unit assays were successfully used to enrich T-ICs from OS cell lines. Enrichment of T-ICs from a malignantly transformed hFOB1.19 osteoblast cell line (MThFOB1.19) indicated that OS T-ICs could originate from differentiated cells, and most of these MThFOB1.19 cells showed stem-like features. TSSC3 was expressed at a low level in T-ICs, while overexpression of TSSC3 could efficiently downregulate the expression of stem cell markers Nanog, Oct4 and Sox2 in T-ICs and decrease the clone formation rate, as well as downregulate tumorigenesis in MThFOB1.19 cells, supporting a suppressive role for TSSC3 in OS T-ICs. Furthermore, overexpression of TSSC3 was found to induce apoptosis of OS T-ICs through increasing cleaved caspase-3 (active form), increasing the release of Cyt c and decreasing pro-caspase-9 (pro-enzyme form), as well as disruption of the mitochondrial membrane potential (ΔΨ). Taken together, our findings provide preliminary evidence that TSSC3 inhibits OS tumorigenicity through reducing stemness and promoting apoptosis of T-ICs. Thus, targeting TSSC3 may be a promising approach to suppressing tumorigenicity in OS.
authors.affiliation: Institute of Pathology and Southwest Cancer Center, Southwest Hospital, Third Military Medical University, 400038, Chongqing, China.
authors.forename: Yusheng
authors.initials: Y
authors.lastname: Huang
authors.forename: Huanzi
authors.initials: H
authors.lastname: Dai
authors.forename: Qiao-Nan
authors.initials: QN
authors.lastname: Guo
mesh_terms: D000818:Animals; D017209:Apoptosis; D001859:Bone Neoplasms / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000378:metabolism; D005260:Female; D015870:Gene Expression; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D053078:Membrane Potential, Mitochondrial; D051379:Mice; D008819:Mice, Nude; D000071317:Nanog Homeobox Protein; D009368:Neoplasm Transplantation; D014411:Neoplastic Stem Cells / Q000378:metabolism* / Q000502:physiology; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D050814:Octamer Transcription Factor-3 / Q000235:genetics / Q000378:metabolism; D012516:Osteosarcoma / Q000378:metabolism* / Q000473:pathology; D055748:SOXB1 Transcription Factors / Q000235:genetics / Q000378:metabolism; D018874:Spheroids, Cellular / Q000378:metabolism; D047368:Tumor Burden
chemical_list: D018398:Homeodomain Proteins; C486780:NANOG protein, human; D000071317:Nanog Homeobox Protein; D009687:Nuclear Proteins; D050814:Octamer Transcription Factor-3; C494173:POU5F1 protein, human; C527782:SOX2 protein, human; D055748:SOXB1 Transcription Factors; C109277:TSSC3 protein