1
|
Gao H, Zhou Y, Jin PS, Wu DG, Wang YN, Zhao X, Zhao B. Molecular alteration of the proteasome contributes to AD-like pathology in the brain of HFD-STZ diabetic rats. Metab Brain Dis 2022; 38:1013-1024. [PMID: 36580191 DOI: 10.1007/s11011-022-01151-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/12/2022] [Accepted: 12/21/2022] [Indexed: 12/30/2022]
Abstract
Diabetes-related cognitive impairment has been shown in diverse epidemiological investigations and lab-based studies, although the underlying pathological mechanisms remain unclear. Unbalanced protein homeostasis may contribute to cognitive decline by inducing abnormal protein aggregation in the diabetic brain. This study aimed to determine possible changes in the proteasome, which is an important pathway involved in abnormal protein degradation. To this end, we examined potential alterations of proteasomal subunits and hydrolytic activity in the brain of diabetic rats fed with high-fat diet combined with small doses of streptozotocin (STZ). Furthermore, lactacystin were used to inhibit proteasomal activity in vivo and typical Alzheimer's disease (AD)-like pathologies were detected, including amyloid-beta, tau phosphorylation, and oxidative protein changes. Our results showed that proteasomal activity increased in the brains of diabetic rats compared to age-matched control rats. After proteasome inhibition, the levels of tau phosphorylation and protein oxidative modification significantly increased; however, no changes were detected in the pathway involved in amyloid production. These results indicated that changes in protein homeostasis balance in diabetes play a role in some typical AD-like changes, especially in oxidative protein degradation, providing evidence that prevention of diabetes-induced protein imbalance may be a potential therapeutic target.
Collapse
Affiliation(s)
- Han Gao
- School of Basic Medicine Sciences, Dali University, 6Th Xue-Ren Road, Dali, 671000, Yunnan Province, People's Republic of China
| | - Ye Zhou
- School of Basic Medicine Sciences, Dali University, 6Th Xue-Ren Road, Dali, 671000, Yunnan Province, People's Republic of China
| | - Peng-Shuai Jin
- School of Basic Medicine Sciences, Dali University, 6Th Xue-Ren Road, Dali, 671000, Yunnan Province, People's Republic of China
- Zhalantun Vocational College, 20Th Zhongyang Road, Hulunbuir, NeiMonggol Autonomous Region, People's Republic of China
| | - Dong-Gui Wu
- School of Basic Medicine Sciences, Dali University, 6Th Xue-Ren Road, Dali, 671000, Yunnan Province, People's Republic of China
- Zhuhai City People's Hospital, Zhuhai, Guangdong Province, People's Republic of China
| | - Yu-Na Wang
- School of Basic Medicine Sciences, Dali University, 6Th Xue-Ren Road, Dali, 671000, Yunnan Province, People's Republic of China
| | - Xi Zhao
- School of Basic Medicine Sciences, Dali University, 6Th Xue-Ren Road, Dali, 671000, Yunnan Province, People's Republic of China
| | - Bei Zhao
- School of Basic Medicine Sciences, Dali University, 6Th Xue-Ren Road, Dali, 671000, Yunnan Province, People's Republic of China.
- Li Yunqing Expert Workstation of Yunnan Province (No.202005AF150014), Dali University, 6Th Xue-Ren Road, Dali, Yunnan Province, People's Republic of China.
| |
Collapse
|
2
|
Gu Y, Barwick BG, Shanmugam M, Hofmeister CC, Kaufman J, Nooka A, Gupta V, Dhodapkar M, Boise LH, Lonial S. Downregulation of PA28α induces proteasome remodeling and results in resistance to proteasome inhibitors in multiple myeloma. Blood Cancer J 2020; 10:125. [PMID: 33318477 PMCID: PMC7736847 DOI: 10.1038/s41408-020-00393-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2020] [Revised: 10/14/2020] [Accepted: 10/28/2020] [Indexed: 01/05/2023] Open
Abstract
Protein homeostasis is critical for maintaining eukaryotic cell function as well as responses to intrinsic and extrinsic stress. The proteasome is a major portion of the proteolytic machinery in mammalian cells and plays an important role in protein homeostasis. Multiple myeloma (MM) is a plasma cell malignancy with high production of immunoglobulins and is especially sensitive to treatments that impact protein catabolism. Therapeutic agents such as proteasome inhibitors have demonstrated significant benefit for myeloma patients in all treatment phases. Here, we demonstrate that the 11S proteasome activator PA28α is upregulated in MM cells and is key for myeloma cell growth and proliferation. PA28α also regulates MM cell sensitivity to proteasome inhibitors. Downregulation of PA28α inhibits both proteasomal load and activity, resulting in a change in protein homeostasis less dependent on the proteasome and leads to cell resistance to proteasome inhibitors. Thus, our findings suggest an important role of PA28α in MM biology, and also provides a new approach for targeting the ubiquitin-proteasome system and ultimately sensitivity to proteasome inhibitors.
Collapse
Affiliation(s)
- Yanyan Gu
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Benjamin G Barwick
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Mala Shanmugam
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Craig C Hofmeister
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Jonathan Kaufman
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Ajay Nooka
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Vikas Gupta
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Madhav Dhodapkar
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Lawrence H Boise
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA.,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA
| | - Sagar Lonial
- Department of Hematology and Medical Oncology, Emory University School of Medicine, 1365 Clifton Road, Atlanta, GA, 30322, USA. .,Winship Cancer Institute, Emory University, 1365 Clifton Road, Atlanta, GA, 30322, USA.
| |
Collapse
|
3
|
The 20S immunoproteasome and constitutive proteasome bind with the same affinity to PA28αβ and equally degrade FAT10. Mol Immunol 2017; 113:22-30. [PMID: 29208314 DOI: 10.1016/j.molimm.2017.11.030] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2017] [Revised: 11/27/2017] [Accepted: 11/28/2017] [Indexed: 11/22/2022]
Abstract
The 20S immunoproteasome (IP) is an interferon(IFN)-γ - and tumor necrosis factor (TNF) -inducible variant of the 20S constitutive proteasome (CP) in which all its peptidolytically active subunits β1, β2, and β5 are replaced by their cytokine inducible homologues β1i (LMP2), β2i (MECL-1), and β5i (LMP7). These subunit replacements alter the cleavage specificity of the proteasome and the spectrum of proteasome-generated peptide ligands of MHC class I molecules. In addition to antigen processing, the IP has recently been shown to serve unique functions in the generation of pro-inflammatory T helper cell subtypes and cytokines as well as in the pathogenesis of autoimmune diseases, but the mechanistic involvement of the IP in these processes has remained elusive. In this study we investigated whether the IP differs from the CP in the interaction with two IFN-γ/TNF inducible factors: the 11S proteasome regulator PA28αβ and the ubiquitin-like modifier FAT10 (ubiquitin D). Using thermophoresis, we determined the affinity of PA28αβ for the CP and IP to be 12.2nM +/- 2.8nM and 15.3nM +/- 2.7nM, respectively, which is virtually identical. Also the activation of the peptidolytic activities of the IP and CP by PA28αβ did not differ. For FAT10 we determined the degradation kinetics in cycloheximide chase experiments in cells expressing almost exclusively IP or CP as well as in IFN-γ stimulated and unstimulated cells and found no differences between the degradation rates. Taken together, we conclude that neither differences in the binding strength to, nor activation by PA28αβ, nor a difference in the rate of FAT10-mediated degradation can account for distinct functional capabilities of the IP as compared to the CP.
Collapse
|
4
|
Huber EM, Groll M. The Mammalian Proteasome Activator PA28 Forms an Asymmetric α 4β 3 Complex. Structure 2017; 25:1473-1480.e3. [PMID: 28867616 DOI: 10.1016/j.str.2017.07.013] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2017] [Revised: 07/17/2017] [Accepted: 07/26/2017] [Indexed: 10/19/2022]
Abstract
The heptameric proteasome activator (PA) 28αβ is known to modulate class I antigen processing by docking onto 20S proteasome core particles (CPs). The exact stoichiometry and arrangement of its α and β subunits, however, is still controversial. Here we analyzed murine PA28 complexes regarding structure and assembly. Strikingly, PA28α, PA28β, and PA28αβ preparations form heptamers, but solely PA28α and PA28αβ associate with CPs. Co-expression of α and β yields one unique PA28αβ species with an unchangeable subunit composition. Structural data on PA28α, PA28β, and PA28αβ up to 2.9 Å resolution reveal a PA28α4β3 complex with an alternating subunit arrangement and a single α-α interface. Differential scanning fluorimetry experiments and activity assays classify PA28α4β3 as most stable and most active, indicating that this assembly might represent the physiologically relevant species. Together, our data resolve subunit composition and arrangement of PA28αβ and clarify how an asymmetric heptamer can be assembled from two highly homologous subunits.
Collapse
Affiliation(s)
- Eva M Huber
- Center for Integrated Protein Science, Department Chemie, Lehrstuhl für Biochemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
| | - Michael Groll
- Center for Integrated Protein Science, Department Chemie, Lehrstuhl für Biochemie, Technische Universität München, Lichtenbergstrasse 4, 85748 Garching, Germany.
| |
Collapse
|
5
|
Kloss A, Henklein P, Siele D, Schmolke M, Apcher S, Kuehn L, Sheppard PW, Dahlmann B. The cell-penetrating peptide octa-arginine is a potent inhibitor of proteasome activities. Eur J Pharm Biopharm 2008; 72:219-25. [PMID: 19027853 DOI: 10.1016/j.ejpb.2008.10.016] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Revised: 10/27/2008] [Accepted: 10/31/2008] [Indexed: 10/21/2022]
Abstract
Oligo-arginines are cell-penetrating peptides and find use as carriers for transportation of various membrane-impermeable biopharmaceuticals into target cells. We have found that oligo-arginines of a length of 4-10 amino acids, but especially (Arg)(8), are able to inhibit the major intracellular proteolytic system, the proteasome, with mixed-type inhibition characteristics. The IC(50) values of (Arg)(8) for the proteasomal chymotrypsin-like and caspase-like activities are approximately 100 and 200 nM, respectively. The inhibition of the trypsin-like activity never exceeds 50% even at micromolar concentrations. (Arg)(8) also inhibits 20S proteasome/PA28 complexes as well as 26S proteasomes, although with a decreased efficiency. Due to its cell membrane-penetrating capability, incubation of HeLa cells in the presence of (Arg)(8) resulted in an impaired activity of proteasomes going along with an accumulation of high-molecular mass ubiquitin-conjugated proteins, the preferred substrates of 26S proteasomes. The in vivo susceptibility of the three proteasome activities resembles that found in vitro with chymotrypsin-like>caspase-like>trypsin-like activities. Since inhibition of the proteasome system might affect fundamental basic cellular processes but on the other side might also prevent the degradation of a proteinacous cargo, we suggest that this proteasome inhibitory activity should be taken into account when oligo-arginines are being considered for use as vectors for the intracellular delivery of pharmaceuticals.
Collapse
Affiliation(s)
- Alexander Kloss
- Institut für Biochemie/CCM, Charité-Universitätsmedizin-Berlin, Berlin, Germany
| | | | | | | | | | | | | | | |
Collapse
|
6
|
Beedholm R, Clark BFC, Rattan SIS. Mild heat stress stimulates 20S proteasome and its 11S activator in human fibroblasts undergoing aging in vitro. Cell Stress Chaperones 2005; 9:49-57. [PMID: 15270077 PMCID: PMC1065306 DOI: 10.1379/475.1] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Repeated mild heat shock (RMHS) has been shown to have several beneficial hormetic effects on human skin fibroblast undergoing aging in vitro. Because an age-related decline in proteasome activity is 1 of the reasons for the accumulation of abnormal proteins during aging, we have investigated the effects of RMHS on the 20S proteasome, which is the major proteolytic system involved in the removal of abnormal and oxidatively damaged proteins. Serially passaged human skin fibroblasts exposed to RMHS at 41 degrees C for 60 minutes twice a week had increased 3 proteasomal activities by 40% to 95% in early- and midpassage cultures. RMHS-treated cells also contained a 2-fold higher amount of the proteasome activator 11S, and the extent of the bound activator was double in early- and midpassage cells only. Furthermore, there was no difference in the content of the 19S proteasome regulator in the stressed and the unstressed cells. Therefore, RMHS-induced proteasome stimulation in early- and midpassage fibroblasts appears to be due to an induction and enhanced binding of 11S proteasome activators. In contrast to this, the proteasomal system in late-passage senescent cells appears to be less responsive to the stimulatory effects of mild heat shock.
Collapse
Affiliation(s)
- Rasmus Beedholm
- Laboratory of Cellular Ageing, Danish Centre for Molecular Gerontology, Department of Molecular Biology, University of Aarhus, Gustav Wieds Vej 10-C, DK-8000 Aarhus-C, Denmark
| | | | | |
Collapse
|
7
|
Cascio P, Goldberg AL. Preparation of hybrid (19S-20S-PA28) proteasome complexes and analysis of peptides generated during protein degradation. Methods Enzymol 2005; 398:336-52. [PMID: 16275341 DOI: 10.1016/s0076-6879(05)98028-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
PA28 (also named REG or 11S) is a ring-shaped (180-kDa) interferon-gamma-induced complex that associates with the 20S proteasome and dramatically stimulates the breakdown of short peptides. Immunoprecipitation studies indicate that in vivo PA28 also exists in larger complexes that also contain the 19S particle, which is required for the ATP-ubiquitin-dependent degradation of proteins. However, because of its lability (e.g., it does not withstand exposure to high ionic strength buffers), this larger complex cannot be purified by standard biochemical protocols. Therefore, we developed a method to reconstitute in vitro such hybrid proteasomes (i.e., PA28-20S-19S) from highly purified components. This chapter describes conditions that allow the association of PA28 with "singly capped" 26S (i.e., 19S-20S) particles. In addition assays are described to measure absolute rates of degradation of several non-ubiquitinated proteins by 26S and 20S proteasomes and methods to analyze the pattern and size distribution of peptides generated during the degradation of these proteins.
Collapse
Affiliation(s)
- Paolo Cascio
- Department of Morphophysiology, School of Veterinary Medicine, University of Turin, 10095 Grugliasco, Turin, Italy
| | | |
Collapse
|
8
|
Beedholm R, Clark BF, Rattan SI. Mild heat stress stimulates 20S proteasome and its 11S activator in human fibroblasts undergoing aging in vitro. Cell Stress Chaperones 2004. [DOI: 10.1379/1466-1268(2004)009<0049:mhsssp>2.0.co;2] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
|
9
|
Rivett AJ, Bose S, Pemberton AJ, Brooks P, Onion D, Shirley D, Stratford FLL, Forti K. Assays of proteasome activity in relation to aging. Exp Gerontol 2002; 37:1217-22. [PMID: 12470834 DOI: 10.1016/s0531-5565(02)00127-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Proteasomes play a major role in intracellular protein turnover. They exist in cells in several different molecular forms including 20S proteasomes, 26S proteasomes and PA28-20S proteasome complexes. In this study we have compared the properties of these purified proteasome complexes to try to design assays that will distinguish between the different complexes (26S proteasome, 20S proteasome, PA28-20S proteasome) in cell extracts. Although the different purified complexes were found to have differences in stability, and in their sensitivity to low concentrations of SDS and salt, the results suggest that it is not straightforward to assay selectively for each type of complex in cell extracts. The relative contribution of different proteasome complexes varies in different cell types and there may be other proteases present which hydrolyse the chosen substrate. Proteasome assays carried out under defined conditions allow comparisons of activity in cell extracts as a function of age, but separation by gel filtration on a Superose 6 column was found to be a useful method for determining the level of different proteasome related complexes.
Collapse
Affiliation(s)
- A Jennifer Rivett
- Department of Biochemistry, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, UK.
| | | | | | | | | | | | | | | |
Collapse
|
10
|
Abstract
Although substantial progress has been made in understanding the biochemical properties of 11S regulators since their discovery in 1992, we still only have a rudimentary understanding of their biological role. As discussed above, we have proposed a model in which the alpha/beta complex promotes the production of antigenic peptides by opening the exit port of the 20S proteasome (Whitby et al. 2000). There are other possibilities, however, that are not exclusive of the exit port hypothesis. For example the alpha/beta complex may promote assembly of immunoproteasome as suggested by Preckel et al. 1999, or it may function as a docking module and conduit for the delivery of peptides to the ER lumen (Realini et al. 1994b). There are also unanswered structural and mechanistic questions. Higher resolution data are needed to discern important structural details of the PA26/20S proteasome complex. The models for binding and activation that are suggested from the structural data have to be tested by mutagenesis and biochemical analysis. What is the role of homolog-specific inserts? Will cognate regulator/proteasome complexes show conformational changes that are not apparent in the currently available crystal structures, including perhaps signs of allosteric communication between the regulator and the proteasome active sites?
Collapse
Affiliation(s)
- C P Hill
- Biochemistry Department, University of Utah Medical School, 50 N Medical Drive, Salt Lake City, UT 84132, USA
| | | | | |
Collapse
|
11
|
Kopp F, Dahlmann B, Kuehn L. Reconstitution of hybrid proteasomes from purified PA700-20 S complexes and PA28alphabeta activator: ultrastructure and peptidase activities. J Mol Biol 2001; 313:465-71. [PMID: 11676531 DOI: 10.1006/jmbi.2001.5063] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The activity of the proteasome, the major non-lysosomal proteinase in eukaryotes, is stimulated by two activator complexes, PA700 and PA28. PA700-20 S-PA700 proteasome complexes, generally designated as 26 S proteasomes, degrade proteins, whereas complexes of the type PA28-20 S-PA28 degrade only peptides. We report, for the first time, the in vitro reconstitution of previously identified hybrid proteasomes (PA700-20 S-PA28) from purified PA700-20 S proteasome complexes and PA28 activator. In electron micrographs, the hybrid appears as a corkscrew-shaped particle with a PA700 and a PA28 activator each bound to a terminal alpha-disk of the 20 S core proteasome. The multiple peptidase activities of hybrid proteasomes are not different from those of PA28-20 S-PA28 or PA700-20 S-PA700 complexes.
Collapse
Affiliation(s)
- F Kopp
- Department of Clinical Biochemistry, Deutsches Diabetes-Forschungsinstitut, Düsseldorf, Germany
| | | | | |
Collapse
|
12
|
Abstract
The proteasome activators known as 11S REG or PA28 were discovered about 10 years ago. They are homo- or heteroheptameric rings that bind to the ends of 20S proteasomes and activate cleavage of peptides but not folded proteins. In this article, we focus on structural features of three homologous REG subunits (termed alpha, beta, gamma) that contribute to their oligomerization, proteasome binding and proteasome activation. We review a number of published studies on the biochemical properties of REGs and present new results in which N-terminal sequences and sequences flanking REG activation loops have been exchanged between homologs. Characterization of these chimeras and previously constructed C-terminal chimeras reveal that N-terminal and loop flanking sequences affect oligomerization, whereas C-terminal sequences are essential for proteasome binding. None of these regions is responsible for the broad activation specificity of REGs alpha/beta versus the narrow specificity of REGgamma. Rather, mutation in a single residue lining the channel through the REGgamma heptamer changes the activation property of the gamma homolog to match that of REGs alpha and beta.
Collapse
Affiliation(s)
- J Li
- Department of Biochemistry, University of Utah School of Medicine, Salt Lake City 84132-0001, USA
| | | |
Collapse
|
13
|
Bose S, Brooks P, Mason GG, Rivett AJ. gamma-Interferon decreases the level of 26 S proteasomes and changes the pattern of phosphorylation. Biochem J 2001; 353:291-7. [PMID: 11139393 PMCID: PMC1221571 DOI: 10.1042/0264-6021:3530291] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
In mammalian cells proteasomes can be activated by two different types of regulatory complexes which bind to the ends of the proteasome cylinder. Addition of two 19 S (PA700; ATPase) complexes forms the 26 S proteasome, which is responsible for ATP-dependent non-lysosomal degradation of intracellular proteins, whereas 11 S complexes (PA28; REG) have been implicated in antigen processing. The PA28 complex is upregulated in response to gamma-interferon (gamma-IFN) as are three non-essential subunits of the 20 S proteasome. In the present study we have investigated the effects of gamma-IFN on the level of different proteasome complexes and on the phosphorylation of proteasome subunits. After treatment of cells with gamma-IFN, the level of 26 S proteasomes decreased and there was a concomitant increase in PA28-proteasome complexes. However, no free 19 S regulatory complexes were detected. The majority of the gamma-IFN-inducible proteasome subunits LMP2 and LMP7 were present in PA28-proteasome complexes, but these subunits were also found in 26 S proteasomes. The level of phosphorylation of both 20 S and 26 S proteasome subunits was found to decrease after gamma-IFN treatment of cells. The C8 alpha subunit showed more than a 50% decrease in phosphorylation, and the phosphorylation of C9 was only barely detectable after gamma-IFN treatment. These results suggest that association of regulatory components to 20 S proteasomes is regulated, and that phosphorylation of proteasome alpha subunits may be one mode of regulation.
Collapse
Affiliation(s)
- S Bose
- Department of Biochemistry, University of Bristol, School of Medical Sciences, Bristol BS8 1TD, U.K
| | | | | | | |
Collapse
|
14
|
Wilk S, Chen WE, Magnusson RP. Properties of the beta subunit of the proteasome activator PA28 (11S REG). Arch Biochem Biophys 2000; 384:174-80. [PMID: 11147828 DOI: 10.1006/abbi.2000.2112] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The proteasome activator PA28 (11S REG) is composed of two homologous subunits termed alpha and beta. The properties of the recombinant beta-subunit were explored and compared to the properties of the recombinant alpha-subunit. PA28beta produced in an Escherichia coli expression system migrates on a calibrated gel filtration column as an apparent heptamer (Mr = 250,000). Low concentrations of SDS (0.005%), dissociate the protein to a monomer (Mr = 33,000). PA28beta, has a complex effect on proteasome activity. At concentrations which favor oligomerization (> 2 microM), PA28beta is a strong proteasome activator although its affinity for the proteasome is about 10-fold less than recombinant PA28alpha. The catalytic properties of the PA28alpha and PA28beta-activated proteasome are similar. At low concentrations, PA28beta is a monomer and a potent allosteric proteasome inhibitor. These studies show that oligomerization of PA28beta is required for proteasome activation and that PA28beta monomers are potent proteasome inhibitors.
Collapse
Affiliation(s)
- S Wilk
- Department of Pharmacology, Mount Sinai School of Medicine, New York, New York 10029, USA.
| | | | | |
Collapse
|
15
|
Stohwasser R, Salzmann U, Giesebrecht J, Kloetzel PM, Holzhütter HG. Kinetic evidences for facilitation of peptide channelling by the proteasome activator PA28. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:6221-30. [PMID: 11012676 DOI: 10.1046/j.1432-1327.2000.01706.x] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The activation kinetics of constitutive and IFNgamma-stimulated 20S proteasomes obtained with homomeric (recPA28alpha, recPA28beta) and heteromeric (recPA28alphabeta) forms of recombinant 11S regulator PA28 was analysed by means of kinetic modelling. The activation curves obtained with increasing concentrations of the individual PA28 subunits (RecP28alpha/RecP28beta/RecP28alpha + RecP28beta) exhibit biphasic characteristics which can be attributed to a low-level activation by PA28 monomers and full proteasome activation by assembled activator complexes. The dissociation constants do not reveal significant differences between the constitutive and the immunoproteasome. Intriguingly, the affinity of the proteasome towards the recPA28alphabeta complex is about two orders of magnitude higher than towards the homomeric PA28alpha and PA28beta complexes. Striking similarities can been revealed in the way how PA28 mediates the kinetics of latent proteasomes with respect to three different fluorogenic peptides probing the chymotrypsin-like, trypsin-like and peptidylglutamyl-peptide hydrolyzing like activity: (a) positive cooperativity disappears as indicated by a lack of sigmoid initial parts of the kinetic curves, (b) substrate affinity is increased, whereby (c), the maximal activity remains virtually constant. As these kinetic features are independent of the peptide substrates, we conclude that PA28 exerts its activating influence on the proteasome by enhancing the uptake (and release) of shorter peptides.
Collapse
Affiliation(s)
- R Stohwasser
- Deutsches Institut für Ernährungsforschung, Abt. Präventiv-Medizinische Lebensmittelforschung, Bergholz-Rehbrücke, Bundesrepublik Deutschland.
| | | | | | | | | |
Collapse
|
16
|
Voges D, Zwickl P, Baumeister W. The 26S proteasome: a molecular machine designed for controlled proteolysis. Annu Rev Biochem 2000; 68:1015-68. [PMID: 10872471 DOI: 10.1146/annurev.biochem.68.1.1015] [Citation(s) in RCA: 1377] [Impact Index Per Article: 57.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
In eukaryotic cells, most proteins in the cytosol and nucleus are degraded via the ubiquitin-proteasome pathway. The 26S proteasome is a 2.5-MDa molecular machine built from approximately 31 different subunits, which catalyzes protein degradation. It contains a barrel-shaped proteolytic core complex (the 20S proteasome), capped at one or both ends by 19S regulatory complexes, which recognize ubiquitinated proteins. The regulatory complexes are also implicated in unfolding and translocation of ubiquitinated targets into the interior of the 20S complex, where they are degraded to oligopeptides. Structure, assembly and enzymatic mechanism of the 20S complex have been elucidated, but the functional organization of the 19S complex is less well understood. Most subunits of the 19S complex have been identified, however, specific functions have been assigned to only a few. A low-resolution structure of the 26S proteasome has been obtained by electron microscopy, but the precise arrangement of subunits in the 19S complex is unclear.
Collapse
Affiliation(s)
- D Voges
- Max-Planck-Institut für Biochemie, Martinsried, Germany
| | | | | |
Collapse
|
17
|
Abstract
There are two immune responses in vertebrates: humoral immunity is mediated by circulating antibodies, whereas cytotoxic T lymphocytes (CTL) confer cellular immunity. CTL lyse infected cells upon recognition of cell-surface MHC Class I molecules complexed with foreign peptides. The displayed peptides are produced in the cytosol by degradation of host proteins or proteins from intracellular pathogens that might be present. Proteasomes are cylindrical multisubunit proteases that generate many of the peptides eventually transferred to the cell surface for immune surveillance. In mammalian proteasomes, six active sites face a central chamber. As this chamber is sealed off from the enzyme's surface, there must be mechanisms to promote entry of substrates. Two protein complexes have been found to bind the ends of the proteasome and activate it. One of the activators is the 19 S regulatory complex of the 26 S proteasome; the other activator is '11 S REG' [Dubiel, Pratt, Ferrell and Rechsteiner (1992) J. Biol. Chem. 267, 22369-22377] or 'PA28' [Ma, Slaughter and DeMartino (1992) J. Biol. Chem. 267, 10515-10523]. During the past 7 years, our understanding of the structure of REG molecules has increased significantly, but much less is known about their biological functions. There are three REG subunits, namely alpha, beta and gamma. Recombinant REGalpha forms a ring-shaped heptamer of known crystal structure. 11 S REG is a heteroheptamer of alpha and beta subunits. REGgamma is also presumably a heptameric ring, and it is found in the nuclei of the nematode work Caenorhabditis elegans and higher organisms, where it may couple proteasomes to other nuclear components. REGalpha and REGbeta, which are abundant in vertebrate immune tissues, are located mostly in the cytoplasm. Synthesis of REG alpha and beta subunits is induced by interferon-gamma, and this has led to the prevalent hypothesis that REG alpha/beta hetero-oligomers play an important role in Class I antigen presentation. In the present review we focus on the structural properties of REG molecules and on the evidence that REGalpha/beta functions in the Class I immune response.
Collapse
|
18
|
Stohwasser R, Soza A, Eggers M, Koszinowski UH, Kloetzel PM. PA28alphabeta double and PA28beta single transfectant mouse B8 cell lines reveal enhanced presentation of a mouse cytomegalovirus (MCMV) pp89 MHC class I epitope. Mol Immunol 2000; 37:13-9. [PMID: 10781831 DOI: 10.1016/s0161-5890(00)00017-1] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
PA28 is an interferon-gamma inducible modulator of proteasome function composed of two subunits, i.e. PA28alpha and PA28beta. Previously we showed that stabile overexpression of the PA28alpha subunit alone supported MHC class I antigen presentation of two viral epitopes. However, no information was obtained on the consequences when PA28alpha and PA28beta function in concert or when PA28beta is overexpressed on its own. Here we demonstrate that overexpression of PA28alpha and beta together is similarly efficient in supporting MHC class I antigen presentation of the MCMV pp89 9mer epitope as PA28alpha alone, excluding a potentially potentiating role of PA28beta. Surprisingly, and despite the fact that PA28beta alone was thought to be inactive and to only stabilize PA28 activity, overexpression of PA28beta also resulted in improved antigen presentation. However, by northernblot and immunoprecipitation experiments we show that while PA28alpha is able to act alone the observed effect in the PA28beta and PA28alphabeta transfectant cell lines is due to increased levels of PA28alphabeta complexes.
Collapse
Affiliation(s)
- R Stohwasser
- Institute of Biochemistry, Medical Faculty - Charité, Humboldt University, Monbijoustrasse 2, 10117, Berlin, Germany.
| | | | | | | | | |
Collapse
|
19
|
Zwickl P, Voges D, Baumeister W. The proteasome: a macromolecular assembly designed for controlled proteolysis. Philos Trans R Soc Lond B Biol Sci 1999; 354:1501-11. [PMID: 10582236 PMCID: PMC1692663 DOI: 10.1098/rstb.1999.0494] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
In eukaryotic cells, the vast majority of proteins in the cytosol and nucleus are degraded via the proteasome-ubiquitin pathway. The 26S proteasome is a huge protein degradation machine of 2.5 MDa, built of approximately 35 different subunits. It contains a proteolytic core complex, the 20S proteasome and one or two 19S regulatory complexes which associate with the termini of the barrel-shaped 20S core. The 19S regulatory complex serves to recognize ubiquitylated target proteins and is implicated to have a role in their unfolding and translocation into the interior of the 20S complex where they are degraded into oligopeptides. While much progress has been made in recent years in elucidating the structure, assembly and enzymatic mechanism of the 20S complex, our knowledge of the functional organization of the 19S regulator is rather limited. Most of its subunits have been identified, but specific functions can be assigned to only a few of them.
Collapse
Affiliation(s)
- P Zwickl
- Max-Planck-Institute for Biochemistry, Martinsried, Germany
| | | | | |
Collapse
|
20
|
Rock KL, Goldberg AL. Degradation of cell proteins and the generation of MHC class I-presented peptides. Annu Rev Immunol 1999; 17:739-79. [PMID: 10358773 DOI: 10.1146/annurev.immunol.17.1.739] [Citation(s) in RCA: 675] [Impact Index Per Article: 27.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Major histocompatibility complex (MHC) class I molecules display on the cell surface 8- to 10-residue peptides derived from the spectrum of proteins expressed in the cells. By screening for non-self MHC-bound peptides, the immune system identifies and then can eliminate cells that are producing viral or mutant proteins. These antigenic peptides are generated as side products in the continual turnover of intracellular proteins, which occurs primarily by the ubiquitin-proteasome pathway. Most of the oligopeptides generated by the proteasome are further degraded by distinct endopeptidases and aminopeptidases into amino acids, which are used for new protein synthesis or energy production. However, a fraction of these peptides escape complete destruction and after transport into the endoplasmic reticulum are bound by MHC class I molecules and delivered to the cell surface. Herein we review recent discoveries about the proteolytic systems that degrade cell proteins, how the ubiquitin-proteasome pathway generates the peptides presented on MHC-class I molecules, and how this process is stimulated by immune modifiers to enhance antigen presentation.
Collapse
Affiliation(s)
- K L Rock
- Department of Pathology, University of Massachusetts Medical School, Worcester 01655, USA.
| | | |
Collapse
|
21
|
Kloetzel PM, Soza A, Stohwasser R. The role of the proteasome system and the proteasome activator PA28 complex in the cellular immune response. Biol Chem 1999; 380:293-7. [PMID: 10223331 DOI: 10.1515/bc.1999.040] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The generation of antigenic peptides bound and presented to the immune system by MHC class I molecules predominantly depends on the function of the proteasome system. Stimulation of cells with interferon gamma induces the incorporation of three active site bearing beta-subunits into the 20S proteasome and the formation of the PA28 proteasome modulator complex. PA28 alters the cleavage properties of the proteasome and enhances MHC class I antigen presentation. Thus, by cytokine induced change of the proteasome system cells may alter the proteolytic properties of the 20S proteasome and may render an organism more flexible in its peptide generation capacity.
Collapse
Affiliation(s)
- P M Kloetzel
- Institut für Biochemie-Charité, Humboldt-Universität zu Berlin, Germany
| | | | | |
Collapse
|
22
|
Abstract
Antigen processing by MHC class I molecules begins with the generation of peptides by proteolytic breakdown of proteins. IFN-gamma upregulates gene expression of several proteasomal subunits as well as the proteasome regulator PA28; this implicated their role in antigen degradation. Crystallographic, mutational and biochemical studies contributed to our understanding of the basic principles of proteasomal protein degradation and the consequences of IFN-gamma induction for proteasome function. In addition, nonproteasomal mechanisms seem to be involved in antigen degradation. Leucine aminopeptidase, which is also upregulated by IFN-gamma, was shown to collaborate with the proteasome for epitope production and unknown proteases seem to compensate for the loss of proteasomal degradation in the presence of proteasome inhibitors. Thus, a rather complex picture emerges for the rules governing peptide production in the presence or absence of IFN-gamma.
Collapse
Affiliation(s)
- K Früh
- The R. W. Johnson Pharmaceutical Research Institute, General Atomics Court, San Diego, CA 92121, USA.
| | | |
Collapse
|
23
|
Wilk S, Chen WE, Magnusson RP. Properties of the proteasome activator subunit PA28 alpha and its des-tyrosyl analog. Arch Biochem Biophys 1998; 359:283-90. [PMID: 9808770 DOI: 10.1006/abbi.1998.0918] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The proteasome activator protein PA28 or 11 S regulator may play an important role in facilitating the generation of peptides for presentation by the MHC class I system. PA28 is composed of two homologous subunits termed alpha and beta. Removal of the carboxyl terminal tyrosine of the alpha subunit of PA28 abolishes activity (X. Song et al., 1997, J. Biol. Chem. 272, 27994-28000). To explore the structural basis of this effect the des-tyrosyl analog of PA28alpha prepared by site-directed mutagenesis and PA28alpha were expressed at high levels in a baculovirus system and purified by FPLC. Des-tyrosyl-PA28alpha neither stimulated the proteasome nor competed with PA28alpha for binding to the proteasome. Hydrophobic interaction chromatography revealed that the hydrophobicity of the mutant protein was considerably greater than PA28alpha. When the mutant protein was chromatographed on a calibrated Superose 6 column a mixture of approximately 25% oligomer and 75% monomer was found. The oligomer weakly stimulated the proteasome but this molecule was labile. Very low concentrations of SDS (0.005%) dissociated PA28alpha and abolished its stimulatory activity. It is concluded that the lack of activity of des-tyrosyl-PA28alpha is due to conformational changes resulting in dissociation and that the oligomeric form of PA28alpha is required for activation.
Collapse
Affiliation(s)
- S Wilk
- Department of Pharmacology, Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, New York, 10029, USA.
| | | | | |
Collapse
|
24
|
Zhang Z, Clawson A, Rechsteiner M. The proteasome activator 11 S regulator or PA28. Contribution By both alpha and beta subunits to proteasome activation. J Biol Chem 1998; 273:30660-8. [PMID: 9804839 DOI: 10.1074/jbc.273.46.30660] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The proteasome 11 S regulator (REG) consists of two homologous subunits, REGalpha and REGbeta. Each subunit is capable of activating the proteasome, and when combined, they form superactive REGalpha/REGbeta complexes. We have previously shown that a highly conserved loop in the REGalpha crystal structure is critical for proteasome activation. We now show that hetero-oligomers formed from REGalpha activation loop mutants and wild-type REGbeta or vice versa are partially active. By contrast, hetero-oligomers bearing mutations in the activation loops of REGalpha and REGbeta subunits are inactive, demonstrating that both alpha and beta subunits contribute to proteasome activation. We have also characterized REG proteins with mutations near or at their C termini. Partially active REGalpha(Y249C) and REGalpha(M247V) and an inactive REGalpha subunit bearing five additional C-terminal amino acids formed active hetero-oligomers with REGbeta. REGbeta subunits lacking 1, 2, or 9 C-terminal amino acids did not bind or activate the proteasome, but each of these mutants formed partially active hetero-oligomers with the monomer REGalpha(N50Y). However, hetero-oligomers formed from REG subunits lacking the last 14 amino acids were unable to bind the proteasome. Thus, C-terminal regions of both alpha and beta subunits are required for hetero-oligomers to bind the proteasome.
Collapse
Affiliation(s)
- Z Zhang
- Department of Biochemistry, University of Utah, Salt Lake City, Utah 84132, USA
| | | | | |
Collapse
|
25
|
Mykles DL. Intracellular proteinases of invertebrates: calcium-dependent and proteasome/ubiquitin-dependent systems. INTERNATIONAL REVIEW OF CYTOLOGY 1998; 184:157-289. [PMID: 9697313 DOI: 10.1016/s0074-7696(08)62181-6] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Cytosolic proteinases carry out a variety of regulatory functions by controlling protein levels and/or activities within cells. Calcium-dependent and ubiquitin/proteasome-dependent pathways are common to all eukaryotes. The former pathway consists of a diverse group of Ca(2+)-dependent cysteine proteinases (CDPs; calpains in vertebrate tissues). The latter pathway is highly conserved and consists of ubiquitin, ubiquitin-conjugating enzymes, deubiquitinases, and the proteasome. This review summarizes the biochemical properties and genetics of invertebrate CDPs and proteasomes and their roles in programmed cell death, stress responses (heat shock and anoxia), skeletal muscle atrophy, gametogenesis and fertilization, development and pattern formation, cell-cell recognition, signal transduction and learning, and photoreceptor light adaptation. These pathways carry out bulk protein degradation in the programmed death of the intersegmental and flight muscles of insects and of individuals in a colonial ascidian; molt-induced atrophy of crustacean claw muscle; and responses of brine shrimp, mussels, and insects to environmental stress. Selective proteolysis occurs in response to specific signals, such as in modulating protein kinase A activity in sea hare and fruit fly associated with learning; gametogenesis, differentiation, and development in sponge, echinoderms, nematode, ascidian, and insects; and in light adaptation of photoreceptors in the eyes of squid, insects, and crustaceans. Proteolytic activities and specificities are regulated through proteinase gene expression (CDP isozymes and proteasomal subunits), allosteric regulators, and posttranslational modifications, as well as through specific targeting of protein substrates by a diverse assemblage of ubiquitin-conjugases and deubiquitinases. Thus, the regulation of intracellular proteolysis approaches the complexity and versatility of transcriptional and translational mechanisms.
Collapse
Affiliation(s)
- D L Mykles
- Department of Biology, Colorado State University, Fort Collins 80523, USA
| |
Collapse
|
26
|
Tanaka K, Kasahara M. The MHC class I ligand-generating system: roles of immunoproteasomes and the interferon-gamma-inducible proteasome activator PA28. Immunol Rev 1998; 163:161-76. [PMID: 9700509 DOI: 10.1111/j.1600-065x.1998.tb01195.x] [Citation(s) in RCA: 235] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Production of antigenic peptides that serve as MHC class I ligands is essential for initiation of cell-mediated immunity. Accumulating evidence indicates that the proteasome, a large multisubunit protein deg radative machine in eukaryotes, functions as a processing enzyme responsible for the generation of MHC class I ligands. This processing system is elaborately regulated by various immunomodulatory cytokines. In particular, interferon-gamma induces the formation of immunoproteasomes and a recently identified proteasomal regulatory factor. PA28, which in concert contribute to efficient production of MHC class I ligands. Many of the MHC-encoded genes including LMP appear to have emerged by an ancient chromosomal duplication, suggesting that modifications and renewal of pre-existing non-immune genes were instrumental in the emergence of adaptive immunity.
Collapse
Affiliation(s)
- K Tanaka
- Tokyo Metropolitan Institute of Medical Science, Bunkyo-ku, Japan.
| | | |
Collapse
|
27
|
Kohda K, Ishibashi T, Shimbara N, Tanaka K, Matsuda Y, Kasahara M. Characterization of the Mouse PA28 Activator Complex Gene Family: Complete Organizations of the Three Member Genes and a Physical Map of the ∼150-kb Region Containing the α- and β-Subunit Genes. THE JOURNAL OF IMMUNOLOGY 1998. [DOI: 10.4049/jimmunol.160.10.4923] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
The proteasome is a multisubunit protease responsible for the generation of peptides loaded onto MHC class I molecules. Recent evidence indicates that binding of an IFN-γ-inducible PA28 activator complex to the 20S proteasome enhances the generation of class I binding peptides. The α- and β-subunits, which constitute the PA28 activator complex in the form of an (αβ)3 heterohexamer, show significant amino acid sequence similarity to a protein, designated Ki or the γ-subunit, that is capable of binding to the 20S proteasome. In this study, we describe the complete nucleotide sequences of the mouse genes, Psme1, Psme2, and Psme3, coding for the α-, β-, and γ-subunits, respectively. The overall exon-intron organizations of the three Psme genes are virtually identical, thus providing evidence that they are descended from a single ancestral gene. The promoter regions of the Psme1 and Psme2 genes contain sequence motifs that qualify as IFN-stimulated response elements, consistent with the observation that their expression is induced strongly by IFN-γ. The Psme1 and Psme2 genes are located ∼6 kb apart with their 3′-ends pointing toward each other on bands C2 to D1 of mouse chromosome 14, supporting the idea that they emerged by tandem duplication.
Collapse
Affiliation(s)
- Keiko Kohda
- *Department of Biochemistry, Hokkaido University School of Medicine, Sapporo 060, Japan
| | - Teruo Ishibashi
- *Department of Biochemistry, Hokkaido University School of Medicine, Sapporo 060, Japan
| | - Naoki Shimbara
- †Biomedical R&D Department, Sumitomo Electric Industries, Yokohama 244, Japan
- ‡CREST (Core Research for Evolutional Science and Technology), Japan Science and Technology Corporation, Japan
| | - Keiji Tanaka
- ‡CREST (Core Research for Evolutional Science and Technology), Japan Science and Technology Corporation, Japan
- §Tokyo Metropolitan Institute of Medical Science, Tokyo 113, Japan; and
| | - Yoichi Matsuda
- ¶Laboratory of Animal Genetics, Nagoya University School of Agricultural Sciences, Nagoya 464-01, Japan
| | - Masanori Kasahara
- *Department of Biochemistry, Hokkaido University School of Medicine, Sapporo 060, Japan
- ‡CREST (Core Research for Evolutional Science and Technology), Japan Science and Technology Corporation, Japan
| |
Collapse
|
28
|
Song X, von Kampen J, Slaughter CA, DeMartino GN. Relative functions of the alpha and beta subunits of the proteasome activator, PA28. J Biol Chem 1997; 272:27994-8000. [PMID: 9346951 DOI: 10.1074/jbc.272.44.27994] [Citation(s) in RCA: 65] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
PA28 is a 180,000-dalton protein that activates hydrolysis of small nonubiquitinated peptides by the 20 S proteasome. PA28 is composed of two homologous subunits, alpha and beta, arranged in alternating positions in a ring-shaped oligomer with a likely stoichiometry of (alphabeta)3. Our previous work demonstrated that the carboxyl terminus of the alpha subunit was necessary for PA28 to bind to and activate the proteasome. The goals of this work were to define the exact structural basis for this effect and to determine the relative roles of the alpha and beta subunits in proteasome activation. Each subunit and various mutants of the alpha subunit were expressed in Escherichia coli and purified. PA28alpha stimulated the proteasome, but had a much greater Kact than native heteromeric PA28. In contrast, PA28beta was unable to stimulate the proteasome. Mutants of the alpha subunit in which the carboxyl-terminal tyrosine residue was deleted or substituted with charged amino acids could neither bind to nor activate the proteasome. However, substitution of the carboxyl-terminal tyrosine with other amino acids resulted in proteins which could stimulate the proteasome to various extents. Tryptophan mutants stimulated the proteasome as well as did native PA28, whereas serine or phenylalanine mutants stimulated the proteasome much poorer than did wild type PA28alpha. Deletion of the "KEKE" motif, a 28-amino acid domain near the amino terminus of PA28alpha, had no effect on proteasome stimulatory activity. Hetero-oligomeric PA28 proteins were reconstituted from isolated wild type and mutant subunits. PA28 reconstituted from wild type subunits had structural and functional properties that were indistinguishable from those of the native hetero-oligomeric protein. PA28 molecules reconstituted from inactive alpha subunits and wild type beta subunits remained inactive. However, PA28 molecules reconstituted from suboptimally active alpha mutants and wild type beta subunits had the same activity as native heteromeric PA28. These results indicate that the beta subunit modulates PA28 activity, perhaps by influencing the affinity of PA28 for the proteasome.
Collapse
Affiliation(s)
- X Song
- Department of Physiology, The University of Texas Southwestern Medical Center, Dallas, Texas 75235-9040, USA
| | | | | | | |
Collapse
|
29
|
Realini C, Jensen CC, Zhang Z, Johnston SC, Knowlton JR, Hill CP, Rechsteiner M. Characterization of recombinant REGalpha, REGbeta, and REGgamma proteasome activators. J Biol Chem 1997; 272:25483-92. [PMID: 9325261 DOI: 10.1074/jbc.272.41.25483] [Citation(s) in RCA: 142] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Full-length cDNAs for three human proteasome activator subunits, called REGalpha, REGbeta, and REGgamma, have been expressed in Escherichia coli, and the purified recombinant proteins have been characterized. Recombinant alpha or gamma subunits form heptameric species; recombinant beta subunits are found largely as monomers or small multimers. Each recombinant REG stimulates cleavage of fluorogenic peptides by human red cell proteasomes. The pattern of activated peptide hydrolysis is virtually identical for REGalpha and REGbeta. These two subunits, alone or in combination, stimulate cleavage after basic, acidic, and most hydrophobic residues in many peptides. Recombinant alpha and beta subunits bind each other with high affinity, and the REGalpha/beta heteromeric complex activates hydrolysis of LLVY-methylcoumaryl-7-amide (LLVY-MCA) and LLE-beta-nitroanilide (LLE-betaNA) more than REGalpha or REGbeta alone. Using filter binding and gel filtration assays, recombinant REGgamma subunits were shown to bind themselves but not alpha or beta subunits. REGgamma differs from REGalpha and REGbeta in that it markedly stimulates hydrolysis of peptides with basic residues in the P1 position but only modestly activates cleavage of LLVY-MCA or LLE-betaNA by the proteasome. REGgamma binds the proteasome with higher affinity than REGalpha or REGbeta yet with lower affinity than complexes containing both REGalpha and REGbeta. In summary, each of the three REG homologs is a proteasome activator with unique biochemical properties.
Collapse
Affiliation(s)
- C Realini
- Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah 84132, USA
| | | | | | | | | | | | | |
Collapse
|
30
|
Soza A, Knuehl C, Groettrup M, Henklein P, Tanaka K, Kloetzel PM. Expression and subcellular localization of mouse 20S proteasome activator complex PA28. FEBS Lett 1997; 413:27-34. [PMID: 9287111 DOI: 10.1016/s0014-5793(97)00864-8] [Citation(s) in RCA: 54] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
We have cloned the mouse PA28 proteasome activator cDNAs. Northern blot demonstrates high PA28 mRNA levels in liver, kidney and lung. mRNA levels are low in thymus, spleen and brain. In contrast, PA28 protein levels vary little between these tissues. Immunocytological analysis and cell fractionation experiments demonstrate that both subunits are almost equally distributed between the cytoplasm and the nucleus. Interestingly, PA28alpha spares nucleoli, while PA28beta is strongly enhanced in the nucleolus. This indicates for the first time that the PA28alpha and PA28beta subunits may serve nuclear functions which may be different from and independent of each other.
Collapse
Affiliation(s)
- A Soza
- Institute for Biochemistry, Center of Experimental Medicine (ZEM), Medical Faculty (Charité), Humboldt University, Berlin, FRG
| | | | | | | | | | | |
Collapse
|
31
|
Abstract
The proteasome activator PA28 or 11S regulator is a protein complex composed of two different but homologous polypeptides, termed PA28alpha and PA28beta. The purified activator protein (approximately 200 kDa) is a ring-shaped heteromultimer containing the two polypeptides, possibly with an (alpha3beta3 stoichiometry. The activator, which by itself shows no hydrolytic activity elicits activation of the proteasome's multiple peptidase activities by binding to the terminal rings of the proteinase. In vitro, active PA28 can be reconstituted from isolated alpha and beta subunits, yielding two different oligomers: with the single alpha subunit, PA28alpha homomultimers with moderate stimulatory activity toward 20S proteasomes are obtained whereas isolated beta-subunits are unable to form oligomers and are devoid of stimulatory activity. However, in the presence of both subunits, alphabeta heteromultimers form, concomitant with restoration of full stimulatory activity. The recent finding that PA28 modulates the proteasome-catalyzed production of antigenic peptides presented to the immune system on MHC class I molecules indicates a cellular function of the activator in antigen processing.
Collapse
Affiliation(s)
- L Kuehn
- Diabetes-Forschungsinstitut, Düsseldorf, Germany
| | | |
Collapse
|