RNA-dependent protein kinase is essential for 2-methoxyestradiol-induced autophagy in osteosarcoma cells

PLoS One. 2013;8(3):e59406. doi: 10.1371/journal.pone.0059406. Epub 2013 Mar 19.

Abstract

Osteosarcoma is the most common primary malignant bone tumor in children and young adults. Surgical resection and adjunctive chemotherapy are the only widely available options of treatment for this disease. Anti-tumor compound 2-Methoxyestradiol (2-ME) triggers cell death through the induction of apoptosis in osteosarcoma cells, but not in normal osteoblasts. In this report, we have investigated whether autophagy plays a role in 2-ME actions on osteosarcoma cells. Transmission electron microscopy imaging shows that 2-ME treatment leads to the accumulation of autophagosomes in human osteosarcoma cells. 2-ME induces the conversion of the microtubule-associated protein LC3-I to LC3-II, a biochemical marker of autophagy that is correlated with the formation of autophagosomes. Conversion to LC3-II is accompanied by protein degradation in 2-ME-treated cells. 2-ME does not induce autophagosome formation in normal primary human osteoblasts. In addition, 2-ME-dependent autophagosome formation in osteosarcoma cells requires ATG7 expression. Furthermore, 2-ME does not induce accumulation of autophagosomes in osteosarcoma cells that express dominant negative mutant RNA-dependent protein kinase (PKR) and are resistant to anti-proliferative and anti-tumor effects of 2-ME. Taken together, our study shows that 2-ME treatment induces PKR-dependent autophagy in osteosarcoma cells, and that autophagy could play an important role in 2-ME-mediated anti-tumor actions and in the control of osteosarcoma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 2-Methoxyestradiol
  • Analysis of Variance
  • Autophagy / drug effects*
  • Autophagy-Related Protein 7
  • Blotting, Western
  • Cell Line, Tumor
  • Estradiol / analogs & derivatives*
  • Estradiol / metabolism
  • Estradiol / pharmacology
  • Humans
  • Immunoprecipitation
  • Microscopy, Electron, Transmission
  • Microtubule-Associated Proteins / genetics
  • Microtubule-Associated Proteins / metabolism
  • Osteosarcoma / physiopathology*
  • Osteosarcoma / ultrastructure
  • RNA, Small Interfering / genetics
  • Ubiquitin-Activating Enzymes / metabolism
  • eIF-2 Kinase / metabolism*

Substances

  • MAP1LC3A protein, human
  • Microtubule-Associated Proteins
  • RNA, Small Interfering
  • Estradiol
  • 2-Methoxyestradiol
  • eIF-2 Kinase
  • ATG7 protein, human
  • Autophagy-Related Protein 7
  • Ubiquitin-Activating Enzymes

Grants and funding

This work was supported by Mayo Clinic Cancer Center Bridging to Success Award (Fraternal order of Eagles) to AM and the Mayo Clinic. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.