title: Evidence that inhibition of p44/42 mitogen-activated protein kinase signaling is a factor in proteasome inhibitor-mediated apoptosis.
abstract: The proteasome is emerging as a target for cancer therapy because small molecule inhibitors of its catalytic activity induce apoptosis in both in vitro and in vivo models of human malignancies and are proving to have efficacy in early clinical trials. To further elucidate the mechanism of action of these inhibitors, their impact on signaling through the p44/42 mitogen-activated protein kinase (MAPK) pathway was studied. Proteasome inhibition with either carbobenzoxy-leucyl-leucyl-phenylalaninal or lactacystin led to a loss of dually phosphorylated, activated p44/42 MAPK in A1N4-myc human mammary and MDA-MB-231 breast carcinoma cells in a dose- and time-dependent fashion. This correlated with an induction of the dual specificity MAPK phosphatases (MKP)-1 and -2, and blockade of MKP induction using either actinomycin D or Ro-31-8220 significantly decreased loss of activated p44/42 MAPK. Inhibition of p44/42 MAPK signaling by use of the MAPK kinase inhibitors PD 98059 or U0126, or by use of a dominant negative MAPK construct, enhanced proteasome inhibitor-mediated apoptosis. Conversely, activation of MAPK by epidermal growth factor, or use of a mutant MAPK resistant to MKP-mediated dephosphorylation, inhibited apoptosis. These studies support a role for inactivation of signaling through the p44/42 MAPK pathway in proteasome inhibitor-mediated apoptosis.
authors.affiliation: Lineberger Comprehensive Cancer Center and Department of Medicine, Division of Hematology/Oncology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7295, USA. r_orlowski@med.unc.edu
authors.forename: Robert Z
authors.initials: RZ
authors.lastname: Orlowski
authors.forename: George W
authors.initials: GW
authors.lastname: Small
authors.forename: Yue Y
authors.initials: YY
authors.lastname: Shi
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000502:physiology; D001943:Breast Neoplasms; D002070:Butadienes / Q000494:pharmacology; D002918:Chymotrypsin / Q000037:antagonists & inhibitors; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D003609:Dactinomycin / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D020935:MAP Kinase Signaling System / Q000502:physiology*; D019950:Mitogen-Activated Protein Kinase 1 / Q000037:antagonists & inhibitors*; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors*; D009097:Multienzyme Complexes / Q000378:metabolism*; D009570:Nitriles / Q000494:pharmacology; D009842:Oligopeptides / Q000138:chemical synthesis / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D014407:Tumor Cells, Cultured
chemical_list: D002070:Butadienes; D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009097:Multienzyme Complexes; D009570:Nitriles; D009842:Oligopeptides; C113580:U 0126; C077180:N-benzyloxycarbonyl-leucyl-leucyl-phenylalaninal; D003609:Dactinomycin; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D002918:Chymotrypsin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one