title: Concomitant differentiation and partial proteasome inhibition trigger apoptosis in neuroblastoma cells.
abstract: Proteasome activity is essential during cAMP-induced terminal differentiation of a murine neuroblastoma cell line (NBP2). However, the mechanisms through which proteasome affects NBP2 differentiation have not been characterized. We hypothesized that proteasome is required to implement the differentiation-mediated effects on cell cycle, and its partial inhibition during differentiation may have adverse consequences. Here we show that partial inhibition of proteasome during cAMP-induced differentiation of NBP2 cells causes apoptosis. Whereas differentiation induced growth arrest at G1 phase, partial proteasome inhibition during differentiation resulted in the accumulation of cells at G2M phase. Cell cycle data correlated with the level of cyclin-dependent kinase inhibitors p21WAF and p27Kip1, and cyclin A. While the level of p21 and p27 increased, the level of cyclin A decreased upon differentiation. In contrast, cells treated with proteasome inhibitor in the presence of cAMP-inducing agents showed increased levels of p21 and cyclin A early in the course of differentiation. However, the level of p21 and p27, but not cyclin A, decreased later during concomitant differentiation and partial proteasome inhibition when cells were undergoing apoptosis. Our data suggest that differentiation-mediated growth arrest is dependent on the temporal activity of cell cycle proteins. Partial inhibition of proteasome interferes with differentiation events partly by stabilizing cell cycle proteins and this triggers apoptosis. Thus, differentiating drugs combined with partial proteasome inhibition may impart higher therapeutic efficacy than differentiating agents alone for the treatment of neuroblastoma tumors.
authors.affiliation: Department of Radiology, Center for Vitamins and Cancer Research, School of Medicine, University of Colorado Health Sciences Center, Denver, CO 80262, USA. piruz.nahreini@uchsc.edu
authors.forename: Piruz
authors.initials: P
authors.lastname: Nahreini
authors.forename: Cynthia
authors.initials: C
authors.lastname: Andreatta
authors.forename: Amy
authors.initials: A
authors.lastname: Hanson
authors.forename: Kedar N
authors.initials: KN
authors.lastname: Prasad
mesh_terms: D000818:Animals; D017209:Apoptosis; D053148:Caspase 3; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects*; D000242:Cyclic AMP / Q000494:pharmacology*; D019925:Cyclin A / Q000378:metabolism; D050759:Cyclin-Dependent Kinase Inhibitor p21; D050760:Cyclin-Dependent Kinase Inhibitor p27; D016213:Cyclins / Q000378:metabolism; D003546:Cysteine Endopeptidases; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D009447:Neuroblastoma / Q000201:enzymology / Q000473:pathology*; D046988:Proteasome Endopeptidase Complex; D012190:Retroviridae / Q000235:genetics; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins / Q000378:metabolism
chemical_list: D061945:Caspase Inhibitors; C493957:Cdkn1a protein, mouse; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D019925:Cyclin A; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D007976:Leupeptins; D009097:Multienzyme Complexes; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D000242:Cyclic AMP; C505409:Casp3 protein, mouse; D053148:Caspase 3; D020169:Caspases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde