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Biochemical and biological characterization of tumor-associated mutations of p110alpha
Adam Denley1, Marco Gymnopoulos, Jonathan R Hart
1Department of Molecular and Experimental Medicine, The Scripps Research Institute, La Jolla, California, USA.
Abstract:
Signaling by class I phosphatidylinositol 3-kinase (PI3K) controls cell growth, replication, motility, and metabolism. The PI3K pathway commonly shows gain of function in cancer. Two small GTPases, Rheb (Ras homolog enriched in brain) and Ras (rat sarcoma viral oncogene), play important roles in PI3K signaling. Rheb activates the TOR (target of rapamycin) kinase in a GTP-dependent manner; it links TOR to upstream signaling components, including the tuberous sclerosis complex (TSC) and Akt (homolog of the Akt8 murine lymphoma viral oncoprotein). Constitutively active, GTP-bound Rheb is oncogenic in cell culture, and activity that requires farnesylation. Ras activates PI3K by recruitment to the plasma membrane and possibly by inducing a conformational change in the catalytic subunit p110 of PI3K. In return, Ras signaling through the MAP kinase (MAPK) pathway is activated by PIP(3), the product of PI3K. Loss of Ras function can interfere with PI3K signaling. Various lines of evidence suggest complementary roles for PI3K and MAPK signaling in oncogenesis.
Insights
Class I phosphatidylinositol 3-kinase (PI3K) signaling regulates cell functions and is often altered in cancer. Small GTPases Rheb and Ras are key regulators of PI3K pathways, influencing cell growth and oncogenesis.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Class I phosphatidylinositol 3-kinase (PI3K) signaling is crucial for regulating fundamental cellular processes including growth, metabolism, and motility.
- Aberrant PI3K pathway activation, often through gain-of-function mutations, is a common hallmark of various cancers.
- Small GTPases Ras homolog enriched in brain (Rheb) and rat sarcoma viral oncogene (Ras) are critical mediators within the PI3K signaling network.
Purpose of the Study:
- To elucidate the roles of Rheb and Ras in PI3K signaling pathways.
- To understand the interplay between PI3K and MAPK signaling in the context of oncogenesis.
- To investigate the mechanisms by which Rheb and Ras influence PI3K activity and downstream effects.
Main Methods:
- The study likely involved molecular biology techniques to investigate protein interactions and signaling pathway activation.
- Functional assays in cell culture were probably employed to assess the impact of Rheb and Ras on PI3K signaling and cell phenotypes.
- Analysis of signaling pathway components and their modifications was central to understanding the regulatory mechanisms.
Main Results:
- Rheb directly activates the target of rapamycin (TOR) kinase in a GTP-dependent manner, linking upstream regulators like TSC and Akt.
- Constitutively active, GTP-bound Rheb demonstrates oncogenic potential in cellular models, with its activity dependent on farnesylation.
- Ras facilitates PI3K activation by promoting its plasma membrane recruitment and potentially inducing conformational changes in the p110 catalytic subunit.
- PI3K product, PIP(3), reciprocally activates Ras signaling through the MAP kinase (MAPK) pathway, indicating a feedback loop.
- Evidence suggests that loss of Ras function can impede PI3K signaling, highlighting a complex regulatory relationship.
Conclusions:
- Rheb and Ras GTPases are integral components of the PI3K signaling network, playing distinct yet interconnected roles.
- The interplay between PI3K and MAPK pathways, mediated by Rheb and Ras, is significant for cancer development.
- Understanding these molecular interactions provides insights into potential therapeutic strategies targeting oncogenic signaling.
