Induction and intracellular regulation of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) mediated apotosis in human malignant gliomacells

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) preferentia lly triggers apoptosis in tumor cells versus normal cells, thus providing a therapeutic potential. In this study, we examined a large panel of human m alignant glioma cell lines and primary cultures of normal human astrocytes for their sensitivity to TRAIL. Of 13 glioma cell lines, 3 were sensitive ( 80-100% death), 4 were partially resistant (30-79% death), and 6 were resis tant (<30% death). Normal astrocytes were also resistant, TRAIL-induced cel l death was characterized by activation of caspase-8 and -3, poly(ADP-ribos e) polymerase cleavage, and DNA fragmentation. Decoy receptor (DcR1 and DcR 2) expression was limited in the glioma cell lines and did not correlate wi th TRAIL sensitivity. Both sensitive and resistant cell lines expressed TRA IL death receptor (DR5), adapter protein Fas-associated death domain (FADD) , and caspase-8; but resistant cell lines expressed 2-fold higher levels of the apoptosis inhibitor phosphoprotein enriched in diabetes/phosphoprotein enriched in astrocytes-15 kDa (PED/PEA-15), In contrast, cellular FADD-lik e IL-1<beta>-converting enzyme-like inhibitory protein (cFLIP) expression w as similar in sensitive and resistant cells. Transfection of sense PED/PEA- 15 cDNA in sensitive cells resulted in cell resistance, whereas transfectio n of antisense in resistant cells rendered them sensitive, Inhibition of pr otein kinase C (PKC) activity restored TRAIL sensitivity in resistant cells , suggesting that PED/PEA-15 function might be dependent on PKC-mediated ph osphorylation, In summary, TRAIL induces apoptosis in >50% of glioma cell l ines, and this killing occurs through activation of the DR pathway. This ca spase-8-induced apoptotic cascade is regulated by intracellular PED/PEA-15, but not by cFLIP or decoy receptors, This pathway may be exploitable for g lioma and possibly for other cancer therapies.