Coleman CS, Pegg AE. Polyamine analogues inhibit the ubiquitination of spermidine/spermine N1-acetyltransferase and prevent its targeting to the proteasome for degradation.
Biochem J 2001;
358:137-45. [PMID:
11485561 PMCID:
PMC1222041 DOI:
10.1042/0264-6021:3580137]
[Citation(s) in RCA: 21] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Spermidine/spermine N(1)-acetyltransferase (SSAT), a key enzyme in mammalian polyamine catabolism, undergoes rapid turnover (half-life approx. 30 min) and is highly inducible in response to polyamine analogues such as bis(ethyl)spermine (BE-3-4-3), which greatly stabilize the enzyme. Rapid degradation of SSAT in reticulocyte lysates was preceded by formation of a ladder of ubiquitinated forms, and required the production of high-molecular-mass complexes with ubiquitin (HMM-SSAT-Ubs). Mutation of all 11 lysines in SSAT separately to arginine demonstrated that no single lysine residue is critical for its degradation in vitro, but mutant K87R had a significantly longer half-life, suggesting that lysine-87 may be the preferred site for ubiquitination. Mutations at the C-terminus of SSAT, such as E171Q, resulted in marked stabilization of the protein, due to the lack of formation of the HMM-SSAT-Ubs. Addition of BE-3-4-3 prevented the accumulation of ubiquitin conjugates and the proteasomal degradation of wild-type SSAT. These results indicate that conformational changes brought about by the binding of polyamine analogues prevent the efficient polyubiquitination of SSAT, leading to a major increase in the amount of SSAT protein, and that alteration of the C-terminal end of the protein has a similar effect in preventing the productive interaction with an E2 or E3 component of the ubiquitin pathway.
Collapse