Constitutively active Akt is an important regulator of TRAIL sensitivity in prostate cancer.
TRAIL/Apo-2L is a member of the tumor necrosis factor superfamily and has recently been shown to induce apoptosis in cancer cells, but not in normal cells. In nude mice injected with human tumors, TRAIL reduces the size of these tumors without side effects. Akt promotes cell survival and block apoptosis. Some prostate cancer cells express high levels of Akt due to lack of active lipid phosphatase PTEN, a negative regulator of PI-3 kinase pathway, which may be responsible for drug resistance. The objective of this paper is to investigate the intracellular molecules that regulate TRAIL resistance. We have examined caspase-8 activity, BID cleavage, Akt activity, mitochondrial membrane potential (DeltaPsi(m)) and apoptosis in prostate cancer (LNCap, PC-3, PC-3M and DU145) cells treated with or without TRAIL. PC-3, PC-3M and DU145 cells are sensitive to TRAIL, whereas LNCap cells are resistant. LNCap cells express the highest level of constitutively active Akt, which is directly correlated with TRAIL resistance. TRAIL activates caspase-8 in all the cell lines. Downregulation of constitutively active Akt by PI-3 kinase inhibitors (wortmannin and LY-294002), dominant negative Akt or PTEN, renders LNCap cells sensitive to TRAIL. Inhibition of TRAIL sensitivity occurs at the level of BID cleavage. Inhibition of protein synthesis by cycloheximide also causes LNCap cells sensitive to TRAIL. Overexpression of Bcl-2 or Bcl-X(L) inhibits TRAIL-induced DeltaPsi(m) and apoptosis. Overexpression of constitutively active Akt in PC-3M cells (express very low levels of constitutively active Akt) restores TRAIL resistance. These data suggest that elevated Akt activity protects LNCap cells from TRAIL-induced apoptosis, and the PI-3 kinase/Akt pathway may inhibit apoptotic signals by inhibiting processing of BID. Thus, constitutively active Akt is an important regulator of TRAIL sensitivity in prostate cancer.
Chen
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X
Department of Pharmaceutical Sciences, University of Maryland-School of Pharmacy, Greenebaum Cancer Center, 20 N Pine Street, Baltimore, MD 21201-1180, USA.
Thakkar
H
H
Tyan
F
F
Gim
S
S
Robinson
H
H
Lee
C
C
Pandey
S K
SK
Nwokorie
C
C
Onwudiwe
N
N
Srivastava
R K
RK
D000730:Androstadienes / Q000494:pharmacology; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002470:Cell Survival; D002867:Chromones / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D008297:Male; D008562:Membrane Glycoproteins / Q000494:pharmacology*; D008928:Mitochondria / Q000502:physiology; D009025:Morpholines / Q000494:pharmacology; D009154:Mutation; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011471:Prostatic Neoplasms / Q000201:enzymology* / Q000473:pathology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D051057:Proto-Oncogene Proteins c-akt; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000502:physiology; D053221:TNF-Related Apoptosis-Inducing Ligand; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D000077191:Wortmannin; D051020:bcl-X Protein
D000730:Androstadienes; D051017:Apoptosis Regulatory Proteins; C494811:BCL2L1 protein, human; D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D002867:Chromones; D004791:Enzyme Inhibitors; D008562:Membrane Glycoproteins; D009025:Morpholines; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D053221:TNF-Related Apoptosis-Inducing Ligand; C505653:TNFSF10 protein, human; D014409:Tumor Necrosis Factor-alpha; D051020:bcl-X Protein; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D000077191:Wortmannin