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Feedback activation of neurofibromin terminates growth factor-induced Ras activation.


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Authors

Hennig, Anne 
Markwart, Robby 
Wolff, Katharina 
Schubert, Katja 
Cui, Yan 

Abstract

BACKGROUND: Growth factors induce a characteristically short-lived Ras activation in cells emerging from quiescence. Extensive work has shown that transient as opposed to sustained Ras activation is critical for the induction of mitogenic programs. Mitogen-induced accumulation of active Ras-GTP results from increased nucleotide exchange driven by the nucleotide exchange factor Sos. In contrast, the mechanism accounting for signal termination and prompt restoration of basal Ras-GTP levels is unclear, but has been inferred to involve feedback inhibition of Sos. Remarkably, how GTP-hydrolase activating proteins (GAPs) participate in controlling the rise and fall of Ras-GTP levels is unknown. RESULTS: Monitoring nucleotide exchange of Ras in permeabilized cells we find, unexpectedly, that the decline of growth factor-induced Ras-GTP levels proceeds in the presence of unabated high nucleotide exchange, pointing to GAP activation as a major mechanism of signal termination. Experiments with non-hydrolysable GTP analogues and mathematical modeling confirmed and rationalized the presence of high GAP activity as Ras-GTP levels decline in a background of high nucleotide exchange. Using pharmacological and genetic approaches we document a raised activity of the neurofibromatosis type I tumor suppressor Ras-GAP neurofibromin and an involvement of Rsk1 and Rsk2 in the down-regulation of Ras-GTP levels. CONCLUSIONS: Our findings show that, in addition to feedback inhibition of Sos, feedback stimulation of the RasGAP neurofibromin enforces termination of the Ras signal in the context of growth-factor signaling. These findings ascribe a precise role to neurofibromin in growth factor-dependent control of Ras activity and illustrate how, by engaging Ras-GAP activity, mitogen-challenged cells play safe to ensure a timely termination of the Ras signal irrespectively of the reigning rate of nucleotide exchange.

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Keywords

Animals, Cell Line, Enzyme Activation, Epidermal Growth Factor, Guanosine Triphosphate, HEK293 Cells, HeLa Cells, Humans, MAP Kinase Signaling System, Mice, Neurofibromin 1, Phosphorylation, Ribosomal Protein S6 Kinases, 90-kDa, Signal Transduction, Son of Sevenless Protein, Drosophila, ras Proteins

Journal Title

Cell Commun Signal

Conference Name

Journal ISSN

1478-811X
1478-811X

Volume Title

14

Publisher

Springer Science and Business Media LLC
Sponsorship
Biotechnology and Biological Sciences Research Council (BB/M00015X/2)
Biotechnology and Biological Sciences Research Council (BB/M00015X/1)
Biotechnology and Biological Sciences Research Council (BB/G01227X/1)
We acknowledge funding by the German research council (DFG), grant # RU 860/4-1 (AH), by the Federal Ministry of Education and Research (BMBF), Germany, FKZ: 01EO1002 (I.R., R.M.), by the BBSRC and through the BBSRC Midlands Interdisciplinary BioSciences Training Partnership (MAE-F) (GL - BB/G01227X/1 and BB/M00015X/1) and the National Council on Science and Technology of Mexico (CONACYT) (MAE-F).