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What does insulin do to Ras?
1Department of Medicine, Denver Veterans Affairs Medical Center, University of Colorado Health Sciences Center, 80220, USA.
Abstract:
The Ras pathway lies in the center of signalling cascades of numerous growth-promoting factors. The Ras pathway appears to connect signalling events that begin at the plasma membrane with nuclear events. Insulin is one of the major stimulants of the Ras signalling pathway. The influence of insulin on this pathway consists of five important events: (1) p21Ras activation is promoted by insulin stimulation of the guanine nucleotide exchange factor, Sos, resulting in increased GTP-loading of p21Ras; (2) p21Ras deactivation involves the hyperphosphorylation of Sos; (3) insulin increases farnesyltransferase (FTase) activity that farnesylates p21Ras; (4) increased amounts of farnesylated p21Ras translocate to the plasma membrane where they can be activated by other growth-promoting agents; and (5) cellular responses to other growth factors are potentiated by insulin-stimulated pre-loading of the plasma membrane with farnesylated p21Ras.
Insights
Insulin activates the Ras pathway by promoting p21Ras activation and membrane translocation. This insulin-mediated pre-loading potentiates cellular responses to other growth factors.
Area of Science:
- Cellular signaling
- Molecular biology
- Endocrinology
Background:
- The Ras pathway is central to growth factor signaling, linking plasma membrane events to nuclear responses.
- Insulin is a key stimulant of the Ras signaling pathway, influencing multiple steps.
Purpose of the Study:
- To elucidate the specific mechanisms by which insulin influences the Ras signaling pathway.
- To understand how insulin primes the Ras pathway for enhanced responses to other growth factors.
Main Methods:
- The study investigated insulin's effects on p21Ras activation, guanine nucleotide exchange factor Sos, and farnesyltransferase (FTase) activity.
- Mechanisms of p21Ras translocation and its impact on plasma membrane signaling were examined.
Main Results:
- Insulin stimulates Sos, increasing GTP-loading and activation of p21Ras.
- Insulin enhances FTase activity, leading to farnesylation and plasma membrane translocation of p21Ras.
- Insulin-stimulated p21Ras pre-loading potentiates cellular responses to other growth factors.
Conclusions:
- Insulin plays a critical role in modulating Ras pathway activity through direct activation and enhanced membrane localization of p21Ras.
- Insulin primes the cellular machinery for amplified signaling in response to subsequent growth factor stimulation.