uPAR and cathepsin B inhibition enhanced radiation-induced apoptosis in gliomainitiating cells

Neuro Oncol. 2012 Jun;14(6):745-60. doi: 10.1093/neuonc/nos088. Epub 2012 May 9.

Abstract

Glioblastomas present as diffuse tumors with invasion into normal brain tissue and frequently recur or progress after radiation as focal masses because of glioma-initiating cells. The role of the urokinase-type plasminogen activator receptor (uPAR) and cathepsin B in stem-like phenotype has been extensively studied in several solid tumors. In the present study, we demonstrated that selection of glioma-initiating cells using CD133 expression leads to a specific enrichment of CD133(+) cells in both U87 and 4910 cells. In addition, CD133(+) cells exhibited a considerable amount of other stem cell markers, such as Nestin and Sox-2. Radiation treatment significantly enhanced uPAR and cathepsin B levels in glioma-initiating cells. To downregulate radiation-induced uPAR and cathepsin B expression, we used a bicistronic shRNA construct that simultaneously targets both uPAR and cathepsin B (pCU). Downregulation of uPAR and cathepsin B using pCU decreased radiation-enhanced uPAR and cathepsin B levels and caused DNA damage-induced apoptosis in glioma cell lines and glioma-initiating cells. The most striking finding of this study is that knockdown of uPAR and cathepsin B inhibited ongoing transcription by suppressing BrUTP incorporation at γH2AX foci. In addition, uPAR and cathepsin B gene silencing inversely regulated survivin and H2AX expression in both glioma cells and glioma-initiating cells. Pretreatment with pCU reduced radiation-enhanced expression of uPAR, cathepsin B, and survivin and enhanced DNA damage in pre-established glioma in nude mice. Taken together, our in vitro and in vivo findings suggest that uPAR and cathepsin B inhibition might serve as an adjunct to radiation therapy to target glioma-initiating cells and, therefore, for the treatment of glioma.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Apoptosis / radiation effects*
  • Blotting, Western
  • Cathepsin B / antagonists & inhibitors*
  • Cathepsin B / genetics
  • Cathepsin B / metabolism
  • Cell Cycle / radiation effects
  • Cell Line, Tumor
  • Down-Regulation
  • Fluorescent Antibody Technique
  • Glioma / metabolism
  • Glioma / pathology*
  • Glioma / radiotherapy
  • Humans
  • Immunoenzyme Techniques
  • Immunoprecipitation
  • In Situ Nick-End Labeling
  • Inhibitor of Apoptosis Proteins / genetics
  • Inhibitor of Apoptosis Proteins / metabolism
  • Mice
  • Mice, Nude
  • Neoplastic Stem Cells / metabolism*
  • Neoplastic Stem Cells / radiation effects*
  • RNA, Messenger / genetics
  • RNA, Small Interfering / genetics
  • Real-Time Polymerase Chain Reaction
  • Receptors, Urokinase Plasminogen Activator / antagonists & inhibitors*
  • Receptors, Urokinase Plasminogen Activator / genetics
  • Receptors, Urokinase Plasminogen Activator / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Survivin
  • Transcription, Genetic

Substances

  • BIRC5 protein, human
  • Inhibitor of Apoptosis Proteins
  • RNA, Messenger
  • RNA, Small Interfering
  • Receptors, Urokinase Plasminogen Activator
  • Survivin
  • Cathepsin B