title: MEKK3 interacts with the PA28 gamma regulatory subunit of the proteasome.
abstract: The proteasome is a multisubunit proteolytic enzyme comprising activator complexes bound to the 20 S catalytic core. The functions of the proteasomal activator (PA) 700 in ubiquitin/ATP-dependent protein degradation and of the PA28 alpha/beta activators in antigen presentation are well defined. However, the function of a third PA, PA28 gamma, remains elusive. We now show that mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) kinase kinase 3 (MEKK3), a MAPK kinase kinase (MAPKKK) involved in MAPK kinase 7 (MKK7)-c-Jun N-terminal kinase ('JNK') and MKK6-p38 signalling, can bind PA28 gamma but not PA28 alpha. In contrast, B-Raf, a MAPKKK specific for the MAPK/ERK kinase ('MEK')-ERK module, binds PA28 gamma and alpha. The PA28 gamma-binding domain of MEKK3 is located within its N-terminal regulatory domain (amino acids 1-178). Expression of MEKK3 in Cos-7 cells led to an increase in endogenous and co-expressed PA28 gamma protein levels, whereas kinase-deficient MEKK3 had no effect on PA28 gamma expression. Furthermore, in vitro assays indicated that PA28 gamma was a MEKK3 substrate. MEKK3 represents the first protein kinase capable of binding and phosphorylating a PA, and provides a potential mechanism to link stress-activated protein kinase signalling with the PA28 gamma-dependent proteasome.
authors.affiliation: Department of Cell Physiology and Pharmacology, University of Leicester, Medical Sciences Building, University Road, Leicester LE1 9HN, UK.
authors.forename: Carsten
authors.initials: C
authors.lastname: Hagemann
authors.forename: Rajnikant
authors.initials: R
authors.lastname: Patel
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Blank
mesh_terms: D000818:Animals; D001324:Autoantigens; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000737:chemistry / Q000378:metabolism; D048748:MAP Kinase Kinase Kinase 3; D020930:MAP Kinase Kinase Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008938:Mitosis; D009097:Multienzyme Complexes / Q000737:chemistry / Q000378:metabolism; D016296:Mutagenesis; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016716:PC12 Cells; D010766:Phosphorylation; D016133:Polymerase Chain Reaction; D046988:Proteasome Endopeptidase Complex; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D051381:Rats; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D014162:Transfection
chemical_list: D001324:Autoantigens; C099558:Ki antigen; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D021122:Protein Subunits; D011994:Recombinant Proteins; D048748:MAP Kinase Kinase Kinase 3; D020930:MAP Kinase Kinase Kinases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex