title: Temozolomide sensitizes stem-like cells of glioma spheres to TRAIL-induced apoptosis via upregulation of casitas B-lineage lymphoma (c-Cbl) protein.
abstract: Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has potent antitumor effects in glioma cell lines but has shown little clinical benefit for patients. We investigated whether the widely used chemotherapeutic agent temozolomide (TMZ) can sensitize glioma stem-like cells (GSCs) from human glioblastoma multiforme (GBM) to TRAIL-induced apoptosis. GSCs were isolated from GBM, and stem cell properties were confirmed by immunocytochemistry and in vivo tumorigenicity. Primary GSCs (PGCs) were produced by serum treatment of GBM-derived cells. Changes in expression levels of various TRAIL-related signaling factors before and after TRAIL or TRAIL + TMZ treatment were measured by Western blotting. Overexpression vectors and siRNAs were used to investigate mechanism of TRAIL sensitivity. GSCs showed greater resistance to TRAIL-induced apoptosis than PGCs and had lower basal caspase activity. Caspase knockdown in PGCs reduced TRAIL sensitivity. Expression levels of c-Fas-associated death domain-like interleukin 1-converting enzyme-like inhibitory protein long and short isoforms (c-FLIPL and c-FLIPS) were significantly higher in GSCs than PGCs, and siRNA-mediated c-FLIP knockdown in GSCs enhanced TRAIL-induced apoptosis. TMZ enhanced TRAIL-induced apoptosis in GSCs and downregulated c-FLIP expression. Add of TMZ also upregulated the expression of the E3 ubiquitin ligase casitas B-lineage lymphoma (c-Cbl). Moreover, overexpression of c-Cbl alone reduced c-FLIP expression, and c-Cbl knockdown both enhanced c-FLIP expression and reduced the potentiating effect of TMZ on TRAIL-induced apoptosis. The result indicated that TMZ may overcome TRAIL resistance in GSCs by suppressing c-FLIP expression through c-Cbl-mediated ubiquitination and degradation.
authors.affiliation: Department of Neurosurgery, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Zhitao
authors.affiliation: Department of Neurosurgery, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China.
authors.forename: Li
authors.initials: L
authors.lastname: Long
authors.affiliation: Department of Neurosurgery, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China.
authors.forename: Liu
authors.initials: L
authors.lastname: Jia
authors.affiliation: Department of Neurosurgery, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China.
authors.forename: Ban
authors.initials: B
authors.lastname: Yunchao
authors.affiliation: Department of Neurosurgery, The First Affiliated Hospital of China Medical University, Shenyang, Liaoning, China. wuanhua@yahoo.com.
authors.forename: Wu
authors.initials: W
authors.lastname: Anhua
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000096:biosynthesis / Q000235:genetics*; D020169:Caspases / Q000235:genetics; D003606:Dacarbazine / Q000008:administration & dosage / Q000031:analogs & derivatives; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D005909:Glioblastoma / Q000188:drug therapy / Q000235:genetics* / Q000473:pathology; D005910:Glioma / Q000188:drug therapy / Q000235:genetics / Q000473:pathology; D006801:Humans; D014411:Neoplastic Stem Cells; D050721:Proto-Oncogene Proteins c-cbl / Q000096:biosynthesis* / Q000235:genetics; D015398:Signal Transduction; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics*; D000077204:Temozolomide
chemical_list: D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D003606:Dacarbazine; D050721:Proto-Oncogene Proteins c-cbl; D020169:Caspases; C067419:CBL protein, human; D000077204:Temozolomide
keywords: Apoptosis; Glioma sphere; TRAIL; Temozolomide; c-Cbl