p53 enhances BAK and CD95 expression in human malignant glioma cells but does not enhance CD95L-induced apoptosis

The temperature-sensitive murine p53val(135) mutant was introduced into 3 h uman malignant glioma cell lines to examine the effects of the p53 status o n BCL-2 family protein expression, CD95 expression, and sensitivity to CD95 ligand (CD95L)-induced apoptosis. p53val(135) behaves as a dominant negati ve 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) tr ansdominant-negative versus gain-of-function effects of mutant p53, we incl uded glioma cell lines with functional wild-type (LN-229), mutant (LN-18) o r deleted (LN-308) p53 genes. Wild-type, but not mutant, p53val(135) promot ed G2/M arrest and accumulation of BAK protein in all cell lines. The level s of other BCL-2 family members including BAX, BCL-2, BCL-X or MCL-1 were n ot consistently modulated by mutant or wildtype p53val135. Wild-type, but n ot mutant, p53val135 enhanced CD95 expression in all cell lines. CD95L-evok ed caspase 3 activity was unaffected by wild-type p53 in all cell lines. Un expectedly, mutant p53val135 differentially modulated caspase 3 activity in a gain-of-function fash ion in that caspase 3 activity induced by CD95L wa s enhanced in LN-229 and LN-308 cells but reduced in LN-18 cells. Yet, muta nt p53val135 enhanced the sensitivity to CD95L in LN-18 cells, had no effec t in LN-229 cells, and decreased the sensitivity of LN-308 cells. Correspon ding to the unaltered CD95L-evoked caspase 3 activity, wild-type p53val(135 ) had no major effect on CD95L-induced apoptosis, except for a moderate sen sitization of LN-229 cells but only when protein synthesis was inhibited. T hus, wild-type p53 induces BAK and CD95 expression in human glioma cells wi thout enhancing their susceptibility to CD95-mediated apoptosis, and mutant p53 modulates CD95L-evoked apoptotic signalling in a gain-of-function fash ion up-stream and downstream of caspase 3 activation.