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Polyamine administration reduces ornithine decarboxylase activity without affecting its mRNA content
Abstract:
Ornithine decarboxylase, the first enzyme in the polyamine biosynthetic pathway, is induced by androgens in the mouse kidney. Enzyme activity, as well as enzyme protein levels are increased 100-400 fold. Utilizing a specific cDNA probe to ODC, mRNA levels in these cells were found to increase 7-25 fold as measured by densitometric scanning. Treatment of the mice for 5 hours with 2 mmol/kg doses of putrescine or 1,3-diaminopropane after androgen stimulation reduced enzyme activity to control levels, while mRNA levels remained elevated 18-30 fold above control. In a different system, serum starved SV-3T3 cells showed low ODC activity and amounts of ODC mRNA. Serum stimulation increased the 2.2 kilobase mRNA levels 6 fold and enzyme activity 13 fold in a coordinate fashion within 5 hours. While the rise in activity was blocked by the simultaneous addition of serum and 1 mM putrescine, ODC mRNA levels appeared unchanged. The addition of 50 microM spermidine or 100 microM spermine also had no effect on ODC mRNA levels, while at the same time reducing enzyme activity amounts. These results suggest that the mechanism by which polyamines regulate ODC activity in the mouse is primarily translational.
Insights
Polyamines regulate ornithine decarboxylase (ODC) activity in mice mainly at the translational level. This finding is crucial for understanding polyamine biosynthesis and its control mechanisms.
Area of Science:
- Biochemistry
- Molecular Biology
- Cellular Regulation
Background:
- Ornithine decarboxylase (ODC) is the initial enzyme in polyamine synthesis.
- Androgens induce ODC in mouse kidneys, significantly increasing enzyme and protein levels.
- Polyamines are essential for cell growth and proliferation.
Purpose of the Study:
- To investigate the regulatory mechanisms of ornithine decarboxylase (ODC) activity by polyamines.
- To determine whether polyamine regulation of ODC occurs at the mRNA or translational level.
- To elucidate the role of ODC in androgen-stimulated kidney growth and serum-stimulated cell growth.
Main Methods:
- Quantitative analysis of ODC enzyme activity and protein levels.
- Measurement of ODC mRNA levels using a specific cDNA probe and densitometric scanning.
- Experimental manipulation using androgens, putrescine, 1,3-diaminopropane, spermidine, spermine, and serum stimulation in mouse kidney and SV-3T3 cells.
Main Results:
- Androgen stimulation increased mouse kidney ODC activity (100-400 fold) and mRNA levels (7-25 fold).
- Putrescine and 1,3-diaminopropane reduced ODC activity but not mRNA levels in androgen-stimulated mice.
- Serum stimulation in SV-3T3 cells coordinately increased ODC mRNA (6 fold) and activity (13 fold), but putrescine blocked activity increase without affecting mRNA.
- Spermidine and spermine reduced ODC activity but not mRNA levels in SV-3T3 cells.
Conclusions:
- Polyamines primarily regulate ornithine decarboxylase (ODC) activity at the translational level in mouse systems.
- The findings suggest post-transcriptional control of ODC by polyamines.
- This translational regulation is key to managing polyamine homeostasis and cellular processes.