Tiazofurin decreases Ras-GTP complex in K562 cells
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Updated: Oct 9, 2026
Spatio-Temporal Manipulation of Small GTPase Activity at Subcellular Level and on Timescale of Seconds in Living Cells
Published on: March 9, 2012
1Laboratory for Experimental Oncology, Indiana University School of Medicine, Indianapolis 46202-5200.
Abstract:
The ras oncogene product (p21ras, Ras) is a GTP-binding protein and is thought to transduce signals regulating cellular proliferation and differentiation. The active form Ras-GTP is inactivated by hydrolyzing bound GTP to GDP. Tiazofurin, a specific inhibitor of IMP dehydrogenase, decreased cellular GTP pools and downregulated c-ras gene expression, leading to differentiation (Olah, E. et al., Proc. Natl. Acad. Sci. USA 85: 6533-6537, 1988; Weber et al., Cancer Commun. 3:61-66, 1991). To clarify the link between the action of tiazofurin on metabolic alterations and the induction of differentiation, we examined the effect of tiazofurin on the ratio of active Ras-GTP to total Ras in K562 cells in culture. Cells were labeled for 6 h with [32P]Pi in phosphate-free RPMI 1640. Tiazofurin (100 or 200 microM) was added to cells, and samples were taken at 0, 2, 4, 6 and 12 h of incubation. Cell lysates were immunoprecipitated with monoclonal anti-p21 antibody (Y13-259), then developed on thin layer chromatography. GTP and GDP bound to Ras were visualized by autoradiography. Tiazofurin treatment decreased Ras-GTP concentration in a time- and dose-dependent fashion. In the untreated K562 cells the Ras-GTP concentration was 26.3 +/- 1.4, and tiazofurin (200 microM) decreased it at 6 h to 16.6 +/- 2.9 and at 12 h to 10.6 +/- 2.1%. Inhibition of the GTP salvage pathway with hypoxanthine (100 or 200 microM) enhanced the tiazofurin-induced decrease of Ras-GTP, whereas addition of guanosine (100 microM) prevented the Ras-GTP decrease.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Tiazofurin reduces active Ras-GTP levels, promoting cell differentiation. This effect is dose-dependent and can be modulated by interfering with GTP metabolism, highlighting a link between metabolic alterations and Ras signaling.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Ras proteins are key regulators of cellular proliferation and differentiation, cycling between active GTP-bound and inactive GDP-bound states.
- Tiazofurin, an IMP dehydrogenase inhibitor, depletes cellular GTP and has been shown to induce differentiation by downregulating c-ras gene expression.
- The precise mechanism linking tiazofurin's metabolic effects to Ras signaling and differentiation remains to be fully elucidated.
Purpose of the Study:
- To investigate the effect of tiazofurin on the ratio of active Ras-GTP to total Ras in K562 cells.
- To clarify the relationship between tiazofurin-induced metabolic alterations and the induction of cell differentiation.
- To determine the influence of modulating GTP pools on tiazofurin's effect on Ras-GTP levels.
Main Methods:
- K562 cells were treated with tiazofurin (100 or 200 microM) and labeled with [32P]Pi.
- Ras-GTP and Ras-GDP levels were quantified using immunoprecipitation with anti-p21 antibody followed by thin-layer chromatography and autoradiography.
- The impact of hypoxanthine and guanosine on tiazofurin's effect was assessed.
Main Results:
- Tiazofurin treatment led to a time- and dose-dependent decrease in Ras-GTP concentration.
- In untreated cells, Ras-GTP was 26.3 +/- 1.4%, decreasing to 16.6 +/- 2.9% at 6 hours and 10.6 +/- 2.1% at 12 hours with 200 microM tiazofurin.
- Inhibition of GTP salvage pathway with hypoxanthine enhanced the decrease in Ras-GTP, while guanosine addition prevented it.
Conclusions:
- Tiazofurin effectively reduces the concentration of active Ras-GTP in K562 cells, supporting its role in modulating Ras signaling.
- The findings suggest a direct link between tiazofurin's impact on cellular GTP pools and the downregulation of active Ras.
- Modulating GTP availability influences tiazofurin's effect on Ras-GTP, providing insights into the mechanism of tiazofurin-induced differentiation.
