title: Proteasomal regulation of caspase-8 in cancer cell apoptosis.
abstract: Previous studies demonstrated that proteasome inhibition sensitizes TRAIL resistant prostate cancer cells to TRAIL-mediated apoptosis via stabilization of the active p18 subunit of caspase-8. The present study investigated the impact of proteasome inhibition on caspase-8 stability, ubiquitination, trafficking, and activation in cancer cells. Using caspase-8 deficient neuroblastoma (NB7) cells for reconstituting non-cleavable mutant forms of caspase-8, we demonstrated that the non-cleavable forms of caspase-8 are capable of inducing apoptosis comparably to wild-type caspase-8, in response to proteasome inhibitor and GST-TRAIL. Moreover in the LNCaP human prostate cancer cells, caspase-8 polyubiquitination occurs after TRAIL stimulation and caspase-8 processing. Subcellular fractionation analysis revealed caspase-8 activity in both cytosol and plasma membrane fractions in both NB7 reconstituted caspase-8 cell lines, as well the LNCaP prostate cancer cells. The present results suggest that caspase-8 stabilization through proteasome inhibition leads to reactivation of the extrinsic pathway of apoptosis and identify E3 ligase mediating caspase-8 polyubiquitination, as a novel molecular target. Inhibition of this E3 ligase in combination with TRAIL towards restoring apoptosis signaling activation may have potential therapeutic significance in resistant tumors.
authors: Department of Molecular and Cellular Biochemistry and the Markey Cancer Center, University of Kentucky College of Medicine, Combs Cancer Research Building, 306, 800 Rose Street, Lexington, KY 40536, USA.
authors: Michael V
authors: MV
authors: Fiandalo
authors: Steven R
authors: SR
authors: Schwarze
authors: Natasha
authors: N
authors: Kyprianou
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D053181:Caspase 8 / Q000235:genetics / Q000378:metabolism*; D045744:Cell Line, Tumor; D004789:Enzyme Activation; D006801:Humans; D008297:Male; D011471:Prostatic Neoplasms / Q000188:drug therapy; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism / Q000494:pharmacology; D054875:Ubiquitination
chemical_list: D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D053181:Caspase 8; D046988:Proteasome Endopeptidase Complex