title: Sensitivity of proteasome to its inhibitors increases during cAMP-induced differentiation of neuroblastoma cells in culture and causes decreased viability.
abstract: Inhibition of proteasome activity is associated with a reduction in proliferation and apoptosis in cancer cells, depending upon the extent of inhibition. We have reported that a minimal inhibition of proteasome activity prevented adenosine 3'5'-cyclic monophosphate (cAMP)-induced differentiation and caused apoptosis in murine neuroblastoma (NB) cells in culture. In order to establish whether an elevated cAMP level increases the sensitivity of proteasome to its inhibitors, MG-132 and lactacystin (proteasome inhibitors) were added concomitantly with a stimulator of adenylate cyclase (prostaglandin A1) and an inhibitor of cyclic nucleotide phosphodiesterase (RO20-1724). Results showed that concentrations of MG-132 that did not reduce or that minimally inhibited proteasome activity also did not affect the proliferation of undifferentiated NB cells. However, these concentrations of MG-132 in the presence of an elevated cAMP level markedly inhibited proteasome activity and caused extensive cell death. Similar results were obtained with lactacystin. In normal murine fibroblasts, cAMP-induced reduction in proliferation was not affected by any concentration of MG-132 used in this study. These results suggest that proteasome exhibits increased sensitivity to its inhibitors following an elevation of cAMP level in NB cells, but not in normal fibroblasts, and that this may account for the enhanced cell death in NB cells. Thus, the strategy of using low doses of a proteasome inhibitor in combination with a cAMP-stimulating agent may be useful in pre-clinical and clinical studies on NB tumor because of the selectivity of the effect on cancer cells.
authors.affiliation: Center for Vitamins and Cancer Research, Department of Radiology, School of Medicine, University of Colorado Health Sciences Center, Denver, CO 80262, USA.
authors.forename: Bipin
authors.initials: B
authors.lastname: Kumar
authors.forename: Amy J
authors.initials: AJ
authors.lastname: Hanson
authors.forename: Kedar N
authors.initials: KN
authors.lastname: Prasad
mesh_terms: D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone / Q000494:pharmacology; D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism*; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism*; D009447:Neuroblastoma / Q000201:enzymology / Q000473:pathology*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D014407:Tumor Cells, Cultured
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D009097:Multienzyme Complexes; D010726:Phosphodiesterase Inhibitors; C067713:lactacystin; D012368:4-(3-Butoxy-4-methoxybenzyl)-2-imidazolidinone; D000242:Cyclic AMP; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; D000111:Acetylcysteine