p53 enhances BAK and CD95 expression in human malignant glioma cells but does not enhance CD95L-induced apoptosis.
The temperature-sensitive murine p53val135 mutant was introduced into 3 human malignant glioma cell lines to examine the effects of the p53 status on BCL-2 family protein expression, CD95 expression, and sensitivity to CD95 ligand (CD95L)-induced apoptosis. p53val135 behaves as a dominant negative mutant at 38.5 degrees C but assumes p53 wild-type properties. In order to dissect (i) specific effects of wild-type versus mutant p53, and (ii) transdominant-negative versus gain-of-function effects of mutant p53, we included glioma cell lines with functional wild-type (LN-229), mutant (LN-18) or deleted (LN-308) p53 genes. Wild-type, but not mutant, p53val135 promoted G2/M arrest and accumulation of BAK protein in all cell lines. The levels of other BCL-2 family members including BAX, BCL-2, BCL-X or MCL-1 were not consistently modulated by mutant or wild-type p53val135. Wild-type, but not mutant, p53val135 enhanced CD95 expression in all cell lines. CD95L-evoked caspase 3 activity was unaffected by wild-type p53 in all cell lines. Unexpectedly, mutant p53val135 differentially modulated caspase 3 activity in a gain-of-function fashion in that caspase 3 activity induced by CD95L was enhanced in LN-229 and LN-308 cells but reduced in LN-18 cells. Yet, mutant p53val135 enhanced the sensitivity to CD95L in LN-18 cells, had no effect in LN-229 cells, and decreased the sensitivity of LN-308 cells. Corresponding to the unaltered CD95L-evoked caspase 3 activity, wild-type p53val135 had no major effect on CD95L-induced apoptosis, except for a moderate sensitization of LN-229 cells but only when protein synthesis was inhibited. Thus, wild-type p53 induces BAK and CD95 expression in human glioma cells without enhancing their susceptibility to CD95-mediated apoptosis, and mutant p53 modulates CD95L-evoked apoptotic signalling in a gain-of-function fashion up-stream and down-stream of caspase 3 activation.
Pohl
U
U
Laboratory of Molecular Neuro-Oncology, Department of Neurology, University of Tübingen, Germany.
Wagenknecht
B
B
Naumann
U
U
Weller
M
M
D000818:Animals; D017209:Apoptosis / Q000502:physiology*; D001932:Brain Neoplasms; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D053222:Fas Ligand Protein; D015972:Gene Expression Regulation, Neoplastic; D016158:Genes, p53; D005910:Glioma; D006801:Humans; D020014:K562 Cells; D008562:Membrane Glycoproteins / Q000502:physiology*; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D050998:bcl-2 Homologous Antagonist-Killer Protein; D019014:fas Receptor / Q000235:genetics*
C494772:BAK1 protein, human; C494773:Bak1 protein, mouse; C505661:FASLG protein, human; D053222:Fas Ligand Protein; C505658:Fasl protein, mouse; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D011994:Recombinant Proteins; D016159:Tumor Suppressor Protein p53; D050998:bcl-2 Homologous Antagonist-Killer Protein; D019014:fas Receptor; C505407:CASP3 protein, human; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases