Melanoma differentiation associated gene-7/interleukin 24 (mda-7/IL-24) is a novel cytokine displaying selective apoptosis-inducing activity in transformed cells without harming normal cells. The present studies focused on defining the mechanism(s) by which a GST-MDA-7 fusion protein inhibits cell survival of primary human glioma cells in vitro. GST-MDA-7 killed glioma cells with diverse genetic characteristics that correlated with inactivation of ERK1/2 and activation of JNK1-3. Activation of JNK1-3 was dependent upon protein kinase R -like endoplasmic reticulum kinase (PERK) and GST-MDA-7 lethality was suppressed in PERK -/- cells. JNK1-3 signaling activated BAX, whereas inhibition of JNK1-3, deletion of BAX or expression of dominant negative caspase 9 suppressed lethality. GST-MDA-7 also promoted a PERK-, JNK- and cathepsin B- dependent cleavage of BID; loss of BID function promoted survival. GST-MDA-7 suppressed BAD and BIM phosphorylation and HSP70 expression. GST-MDA-7 caused PERK-dependent vacuolization of LC3 expressing endosomes whose formation was suppressed by incubation with 3-methyl adenine, expression of HSP70 or of BiP/GRP78, or by knock down of ATG5 or Beclin 1 expression, but not by inhibition of the JNK1-3 pathway. Knock down of ATG5 or Beclin 1 expression or over-expression of HSP70 reduced GST-MDA-7 lethality. Our data demonstrate that GST-MDA-7 induces an ER stress response that is causal in the activation of multiple pro-apoptotic pathways which converge on the mitochondrion and theyhighlight the complexity of signaling pathways altered by mda-7/IL-24 in glioma cells that ultimately culminate in decreased tumor-cell survival.
99th AACR Annual Meeting-- Apr 12-16, 2008; San Diego, CA