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Reduced tyrosine phosphorylation in polyamine-starved cells
C Oetken1, T Pessa-Morikawa, M Autero
1Department of Pathology, University of Helsinki, Finland.
Experimental Cell Research
|October 1, 1992
Summary
Polyamines, essential for cell proliferation, regulate tyrosine phosphorylation by inhibiting protein tyrosine phosphatases. Inhibiting ornithine decarboxylase (ODC) with DFMO reduces phosphotyrosine levels, a effect reversed by adding putrescine.
Area of Science:
- Biochemistry
- Cell Biology
- Molecular Oncology
Background:
- Cell proliferation involves increased polyamine turnover, particularly putrescine, spermidine, and spermine.
- The precise physiological roles of polyamines in cell signaling remain largely undefined.
- Ornithine decarboxylase (ODC) activity, the rate-limiting step in polyamine synthesis, significantly increases during cell proliferation.
Purpose of the Study:
- To elucidate the physiological functions of polyamines in cellular processes.
- To investigate the impact of inhibiting polyamine synthesis on protein tyrosine phosphorylation.
- To determine the mechanism by which polyamines influence tyrosine kinase signaling pathways.
Main Methods:
- Treatment of LSTRA cells with alpha-difluoromethylornithine (DFMO), an irreversible ODC inhibitor.
- Assessment of phosphotyrosine levels in cellular substrates, including p56lck.
- In vitro and in vivo enzymatic activity assays for p56lck and protein tyrosine phosphatases.
- Reversal studies using putrescine, the product of ODC.
Main Results:
- DFMO treatment decreased phosphotyrosine levels in substrates like p56lck without affecting cell viability or overall protein/DNA synthesis initially.
- DFMO did not alter the intrinsic catalytic activity of p56lck.
- Putrescine addition fully reversed the DFMO-induced reduction in tyrosine phosphorylation.
- Polyamines were found to inhibit the activity of cellular protein tyrosine phosphatases.
Conclusions:
- Polyamines play a crucial role in regulating tyrosine phosphorylation.
- The mechanism involves the modulation of protein tyrosine phosphatase activity.
- These findings suggest polyamines influence cell proliferation and malignant transformation by controlling phosphotyrosine levels on key substrates.