Inhibition of clonogenic tumor growth: a novel function of Smac contributing to its antitumor activity

Oncogene. 2005 Nov 3;24(48):7190-202. doi: 10.1038/sj.onc.1208876.


While second mitochondria derived activator of caspase (Smac) has been described to sensitize for apoptosis, its effect on cell viability in the absence of apoptotic stimuli has remained unclear. Here, we report that Smac inhibits clonogenic tumor growth by blocking random migration and proliferation and by enhancing apoptosis in a cell density and cell type dependent manner in SH-EP neuroblastoma cells. Inhibition of clonogenic survival by overexpression of full-length or processed Smac strictly depended on low cell density, and was reversible by replatement at high density. We discovered that Smac inhibits cell motility and random migration at low cell density. In addition, Smac enhanced apoptosis and inhibited protein, but not mRNA expression of XIAP, survivin and other short-lived proteins (FLIP, p21), indicating that Smac may globally inhibit protein expression. Also, Smac inhibited proliferation and increased polynucleation with no evidence for polyploidy, cell cycle arrest or senescence indicating that Smac impaired cell division. Interestingly, inhibition of clonogenic capacity by Smac occurred independent of its apoptosis promoting activity. By demonstrating that Smac restrains clonogenic tumor growth, our findings may have important implications for control of tumor growth and/or its metastatic spread. Thus, Smac agonists may be useful in cancer therapy, for example, for tumor control in minimal residual disease. Oncogene (2005) 24, 7190-7202. doi:10.1038/sj.onc.1208876; published online 8 August 2005.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibiotics, Antineoplastic / pharmacology
  • Apoptosis / drug effects*
  • Apoptosis Regulatory Proteins
  • Blotting, Western
  • Carcinoma / metabolism
  • Carcinoma / pathology
  • Caspases / metabolism
  • Cell Count
  • Cell Cycle
  • Cell Division / drug effects
  • Cell Line, Tumor
  • Cell Movement / drug effects
  • Cell Proliferation / drug effects*
  • Cell Survival / drug effects*
  • Colonic Neoplasms / metabolism
  • Colonic Neoplasms / pathology
  • Cytosol / metabolism
  • Doxorubicin / pharmacology
  • Gene Expression Regulation, Neoplastic / drug effects*
  • Glioblastoma / metabolism
  • Glioblastoma / pathology
  • Humans
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Intracellular Signaling Peptides and Proteins / pharmacology
  • Mitochondria / metabolism
  • Mitochondrial Proteins / genetics
  • Mitochondrial Proteins / metabolism*
  • Mitochondrial Proteins / pharmacology
  • Neuroblastoma / metabolism
  • Neuroblastoma / pathology
  • Pancreatic Neoplasms / metabolism
  • Pancreatic Neoplasms / pathology
  • Proteins / antagonists & inhibitors
  • X-Linked Inhibitor of Apoptosis Protein / antagonists & inhibitors
  • beta-Galactosidase / metabolism


  • Antibiotics, Antineoplastic
  • Apoptosis Regulatory Proteins
  • DIABLO protein, human
  • Intracellular Signaling Peptides and Proteins
  • Mitochondrial Proteins
  • Proteins
  • X-Linked Inhibitor of Apoptosis Protein
  • Doxorubicin
  • beta-Galactosidase
  • Caspases