title: Delayed and sustained activation of p42/p44 mitogen-activated protein kinase induced by proteasome inhibitors through p21(ras) in PC12 cells.
abstract: Proteolysis by the ubiquitin/proteasome pathway regulates the intracellular level of several proteins, some of which control cell proliferation and cell cycle progression. To determine what kinds of signaling cascades are activated or inhibited by proteasome inhibition, we treated PC12 cells with specific proteasome inhibitors and subsequently performed in-gel kinase assays. N-Acetyl-Leu-Leu-norleucinal and lactacystin, which inhibit the activity of the proteasome, induced the activation of p42/p44 mitogen-activated protein (MAP) kinases [extracellular signal-regulated kinases (ERKs) 1 and 2]. In contrast, N-acetyl-Leu-Leu-methional, which inhibits the activity of calpains, but not of the proteasome, failed to induce ERK activation. Uniquely, the kinetics of MAP kinase activation induced by proteasome inhibitors are very slow compared with those resulting from activation by nerve growth factor; ERK activation is detectable only after a 5-h treatment with the inhibitors, and its activity remained unchanged for at least until 27 h. Proteasome inhibitor-initiated ERK activation is inhibited by pretreatment with the ERK kinase inhibitor PD 98059, as well as by overexpression of a dominant-negative form of Ras. Thus, proteasome inhibitors induce sustained ERK activation in a Ras-dependent manner. Proteasome inhibitor-induced neurite outgrowth, however, is not inhibited by PD 98059, indicating that sustained activation of ERKs is not the factor responsible for proteasome inhibitor-induced morphological differentiation. Our data suggest the presence of a novel mechanism for activation of the MAP kinase cascade that involves proteasome activity.
authors.affiliation: Section on Growth Factors, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
authors.forename: K
authors.initials: K
authors.lastname: Hashimoto
authors.forename: G
authors.initials: G
authors.lastname: Guroff
authors.forename: Y
authors.initials: Y
authors.lastname: Katagiri
mesh_terms: D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D019898:Autocrine Communication / Q000502:physiology; D003546:Cysteine Endopeptidases / Q000187:drug effects*; D004268:DNA-Binding Proteins; D004789:Enzyme Activation; D007976:Leupeptins / Q000494:pharmacology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000502:physiology; D009097:Multienzyme Complexes / Q000187:drug effects*; D016501:Neurites / Q000187:drug effects / Q000502:physiology; D016716:PC12 Cells / Q000187:drug effects / Q000201:enzymology*; D010766:Phosphorylation; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology*; D051381:Rats; D013997:Time Factors; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1
chemical_list: D004268:DNA-Binding Proteins; C494114:Elk1 protein, rat; D007976:Leupeptins; D009097:Multienzyme Complexes; D011480:Protease Inhibitors; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; C089487:acetyl-leucinyl-leucinyl-methional; D050807:ets-Domain Protein Elk-1; C067713:lactacystin; D019950:Mitogen-Activated Protein Kinase 1; D020929:Mitogen-Activated Protein Kinase Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D016283:Proto-Oncogene Proteins p21(ras); D000111:Acetylcysteine