Hybrid Proteasomes
INDUCTION BY INTERFERON-γ AND CONTRIBUTION TO ATP-DEPENDENT PROTEOLYSIS*
- Nobuyuki Tanahashi‡,
- Yasuko Murakami§,
- Yasufumi Minami¶,
- Naoki Shimbara‖,
- Klavs B. Hendil** and
- Keiji Tanaka‡‡
- From the ‡Tokyo Metropolitan Institute of Medical Science and Core Rsearch for Evolutional Science and Technology, Japan Science and Technology Corporation, 3-18-22 Honkomagome, Bunkyo-ku, Tokyo 113-8613, Japan, the §Department of Biochemistry 2, Jikei University School of Medicine, Minato-ku, Tokyo 105-8461, Japan, the ¶Department of Biochemistry, Oita Medical University, 1-1 Idaigaoka, Hasama-machi, Oita 879-5593, Japan, the ‖Department of Research, UP Science, Inc., 1, Taya-cho, Sakae-ku, Yokohama 244-8588, Japan, and the **August Krogh Institute, University of Copenhagen, 13 Universitetsparken, DK 2100 Copenhagen, Denmark
Abstract
Eukaryotic cells contain various types of proteasomes. Core 20 S proteasomes (abbreviated 20 S below) have two binding sites for the regulatory particles, PA700 and PA28. PA700–20 S-PA700 complexes are known as 26 S proteasomes and are ATP-dependent machines that degrade cell proteins. PA28 is found both in previously described complexes of the type PA28–20 S-PA28 and in complexes that also contain PA700, as PA700–20 S-PA28. We refer to the latter as “hybrid proteasomes.” The relative amounts of the various types of proteasomes in HeLa extracts were determined by a combination of immunoprecipitation and immunoblotting. Hybrid proteasomes accounted for about a fourth of all proteasomes in the extracts. Association of PA28 and proteasomes proved to be ATP-dependent. Hybrid proteasomes catalyzed ATP-dependent degradation of ornithine decarboxylase (ODC) without ubiquitinylation, as do 26 S proteasomes. In contrast, the homo-PA28 complex (PA28–20 S-PA28) was incapable of degrading ODC. Intriguingly, a major immunomodulatory cytokine, interferon-γ, appreciably enhanced the ODC degradation in HeLa and SW620 cells through induction of the hybrid proteasome, which may also be responsible for the immunological processing of intracellular antigens. Taken together, we report here for the first time the existence of two types of ATP-dependent proteases, the 26 S proteasome and the hybrid proteasome, which appear to share the ATP-dependent proteolytic pathway in mammalian cells.
Footnotes
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↵* This work was supported in part by Grants-in-aid for Scientific Research on Priority Areas (Intracellular Proteolysis) from the Ministry of Education, Science, Sports, and Culture of Japan and by grants from the Human Frontier Science Promotion Organization.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
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↵‡ To whom correspondence should be addressed. Fax: 81-3-3823-2237; E-mail: tanakak@rinshoken.or.jp.
- Abbreviations:
- Ub
-
ubiquitin
- ODC
-
ornithine decarboxylase
- AZ
-
antizyme
- IFN-γ
-
interferon-γ
- Suc-LLVY-AMC
-
succinyl-Leu-Leu-Val-Tyr-7-amino-4-methylcoumarin
- PAGE
-
polyacrylamide gel electrophoresis
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- Received September 15, 1999.
- Revision received January 5, 2000.
- The American Society for Biochemistry and Molecular Biology, Inc.
