Differential activation of the Fas/CD95 pathway by Ad-p53 in human gliomas

Int J Oncol. 2004 Feb;24(2):409-17.


Adenoviral p53 gene transfer (Ad-p53) induces apoptosis in glioma cells expressing mutant p53, but fails in cells with wild-type p53. Endogenously, gliomas express varied levels of Fas/CD95, yet constitutively high levels of Fas/CD95 ligand. Because the mechanism behind the differential apoptotic response to Ad-p53 infection remains elusive, we examined how the Fas/CD95 pathway is involved in U87MG (wt-p53), D54 (wt-p53), U251MG (mutant-p53), and U373MG (mutant-p53) glioma cell lines. Ad-p53 infection did not alter the levels of Fas/CD95 ligand in either wild-type or mutant p53-expressing cell lines. In contrast, Ad-p53 infection led to an approximately 3-fold increase in Fas/CD95 mRNA expression in mutant p53-bearing cell lines but not in their wild-type (wt) counterparts, as assessed in an RNase protection assay. Fas/CD95 mRNA induction appeared to be regulated at the transcriptional level because Ad-p53 infection resulted in up to a 4-fold increase in Fas/CD95 promoter reporter activity. Subsequently, flow cytometric analysis revealed a 2- to 4-fold increase in surface Fas/CD95 expression following Ad-p53 infection in mutant-p53-containing cell lines. Use of the protein transport inhibitor Brefeldin A significantly inhibited Ad-p53-induced surface Fas/CD95 expression, but only partially inhibited apoptosis in mutant-p53 cell lines. These results suggest that p53 regulates Fas/CD95 expression at the transcriptional level and through protein trafficking in mutant-p53 cell lines. Fluorogenic activity assays demonstrated that induction of caspase-8 activity following Ad-p53 infection correlated with increases in Fas/CD95 expression. Incubating cells with a caspase-8-specific inhibitor Ac-IETD-CHO prior to Ad-p53 infection inhibited caspase-8 activity and apoptosis. Together, our results suggest that regulation of the Fas/CD95 pathway is partly responsible for Ad-p53-induced apoptosis in glioma cells, which depends on the p53 status of the involved cells. Additionally, the inability of Ad-p53 to activate the Fas/CD95 pathway in wt-p53 glioma cells coincides with their apoptotic-resistant phenotype. Further elucidation of the nature of this resistance could ultimately augment the efficacy of Ad-p53 gene therapy.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adenoviridae / genetics*
  • Apoptosis
  • Brain Neoplasms / metabolism*
  • Brefeldin A / pharmacology
  • Caspase 8
  • Caspases / metabolism
  • Cell Line, Tumor
  • Cell Survival
  • Fas Ligand Protein
  • Flow Cytometry
  • Genes, Reporter
  • Genes, p53*
  • Glioma / metabolism*
  • Humans
  • Kinetics
  • Membrane Glycoproteins / metabolism
  • Mutation
  • Phenotype
  • Promoter Regions, Genetic
  • RNA, Messenger / metabolism
  • Ribonucleases / metabolism
  • Transfection
  • fas Receptor / biosynthesis*


  • FASLG protein, human
  • Fas Ligand Protein
  • Membrane Glycoproteins
  • RNA, Messenger
  • fas Receptor
  • Brefeldin A
  • Ribonucleases
  • CASP8 protein, human
  • Caspase 8
  • Caspases