title: Solamargine induces apoptosis associated with p53 transcription-dependent and transcription-independent pathways in human osteosarcoma U2OS cells.
abstract: OBJECTIVE
  Solamargine, a steroidal glycoalkaloid isolated from S. incanum, has been shown to induce apoptosis in several cancer cell lines. In this study, the involvement of p53 in the pro-apoptotic action of solamargine was investigated in human osteosarcoma U2OS cells.
  
  
  METHODS
  The cytotoxicity of solamargine was evaluated by MTT assay. Solamargine-induced apoptosis was evidenced by chromatin condensation, formation of apoptotic bodies and exposure of phosphatidylserine on the extracellular surface as revealed by DAPI nuclear staining, transmission electron microscopy and flow cytometry, respectively. mRNA expressions of p53 and Bax were investigated using real time-PCR. Western blot was used to examine the changes in the expression levels of p53, Bax, Bcl-2, caspase-3, caspase-9 and cytochrome c. Subcellular localization of p53 was verified by immunofluorescence staining and cell fractionation.
  
  
  RESULTS
  Solamargine substantially reduced cell viability and induced apoptosis in osteosarcoma U2OS cells. In this connection, solamargine increased the mRNA and protein expressions of p53 and Bax (a pro-apoptotic protein downstream to p53). The expression of Bcl-2 (an anti-apoptotic protein) was also reduced. Furthermore, solamargine induced mitochondrial translocation of p53, loss of mitochondrial membrane potential, cytochrome c release and activation of caspase-9 and -3. p53-specific transcriptional inhibitor pifithrin-α or mitochondrial translocation inhibitor pifithrin-μ partially reversed solamargine-induced apoptosis.
  
  
  CONCLUSIONS
  Solamargine activates the mitochondria-mediated apoptotic pathway in U2OS cells via both p53 transcription-dependent and -independent mechanisms. This compound may merit further investigation as a potential therapeutic agent for the treatment of cancer.
authors.affiliation: School of Pharmaceutical Sciences, Shandong University, Jinan 250012, PR China.
authors.forename: Xia
authors.initials: X
authors.lastname: Li
authors.forename: Ying
authors.initials: Y
authors.lastname: Zhao
authors.forename: William K K
authors.initials: WK
authors.lastname: Wu
authors.forename: Shanshan
authors.initials: S
authors.lastname: Liu
authors.forename: Min
authors.initials: M
authors.lastname: Cui
authors.forename: Hongxiang
authors.initials: H
authors.lastname: Lou
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001859:Bone Neoplasms / Q000188:drug therapy*; D053148:Caspase 3 / Q000096:biosynthesis; D053453:Caspase 9 / Q000096:biosynthesis; D045744:Cell Line, Tumor; D045304:Cytochromes c / Q000096:biosynthesis; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects / Q000235:genetics; D006801:Humans; D012516:Osteosarcoma / Q000188:drug therapy*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis; D012991:Solanaceous Alkaloids / Q000494:pharmacology* / Q000627:therapeutic use; D014158:Transcription, Genetic / Q000187:drug effects; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis* / Q000187:drug effects / Q000235:genetics; D051028:bcl-2-Associated X Protein / Q000096:biosynthesis
chemical_list: D000970:Antineoplastic Agents; D019253:Proto-Oncogene Proteins c-bcl-2; D012991:Solanaceous Alkaloids; D016159:Tumor Suppressor Protein p53; D051028:bcl-2-Associated X Protein; C026609:beta-solamarine; D045304:Cytochromes c; D053148:Caspase 3; D053453:Caspase 9