Regulated degradation of ornithine decarboxylase requires interaction with the polyamine-inducible protein antizyme
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1Department of Microbiology and Immunology, University of California, San Francisco 94143.
Abstract:
Intracellular degradation of vertebrate ornithine decarboxylase (ODC) is accelerated by polyamines, the products of the pathway controlled by ODC. Antizyme, a reversible, tightly binding protein inhibitor of ODC activity, is believed to be involved in this process. Mouse and Trypanosoma brucei ODCs are structurally similar, but the trypanosome enzyme, unlike that of the mouse, is not regulated by intracellular polyamines when expressed in hamster cells (L. Ghoda, D. Sidney, M. Macrae, and P. Coffino, Mol. Cell. Biol. 12:2178-2185, 1992). We found that mouse ODC interacts with antizyme in vitro but trypanosome ODC does not. To localize the region necessary for binding, we made a series of enzymatically active chimeric mouse-trypanosome ODCs and tested them for antizyme interaction. Replacing residues 117 to 140 within the 461-amino-acid mouse ODC sequence with the equivalent region of trypanosome ODC disrupted both antizyme binding and in vivo regulation. Formation of an antizyme-ODC complex is therefore required for regulated degradation.
Insights
Polyamines regulate ornithine decarboxylase (ODC) degradation via antizyme interaction. Mouse ODC binds antizyme, unlike trypanosome ODC, with a specific region (residues 117-140) crucial for this interaction and regulation.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Vertebrate ornithine decarboxylase (ODC) degradation is polyamine-accelerated.
- Antizyme, an ODC inhibitor, is implicated in this regulated degradation.
- Mouse and Trypanosoma brucei ODCs share structural similarity but differ in polyamine regulation.
Purpose of the Study:
- To identify the region of ODC responsible for antizyme interaction and polyamine-mediated regulation.
- To investigate the mechanism of intracellular degradation of ODC.
Main Methods:
- In vitro binding assays using mouse and T. brucei ODCs.
- Construction and testing of chimeric mouse-trypanosome ODC enzymes.
- Analysis of antizyme interaction and in vivo regulation of chimeric ODCs.
Main Results:
- Mouse ODC interacts with antizyme in vitro, while T. brucei ODC does not.
- A specific region (residues 117-140) in mouse ODC is essential for antizyme binding.
- Chimeric ODCs with T. brucei ODC residues 117-140 replacing mouse ODC residues 117-140 lost antizyme binding and in vivo regulation.
Conclusions:
- Formation of an antizyme-ODC complex is a prerequisite for regulated ODC degradation.
- The region between residues 117-140 of mouse ODC is critical for antizyme interaction and subsequent degradation.
- This study elucidates a key molecular mechanism in ODC post-translational regulation.