期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 100, 期 17, 页码 9867-9872出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1734038100
关键词
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资金
- NIDDK NIH HHS [5P30 DK 36836-15, P30 DK036836] Funding Source: Medline
- NIGMS NIH HHS [R01 GM041890, R01 GM036624, GM 36624] Funding Source: Medline
Phosphatidylinositol-5-phosphate (PI-5-P) is a newly identified phosphoinositide with characteristics of a signaling lipid but no known cellular function. PI-5-P levels are controlled by the type II PI-5-P 4-kinases (PIP4K Its), a family of kinases that converts PI-5-P into phosphatidylinositol-4,5-bisphosphate (PI-4,5-P-2). The PI-5-P pathway is an alternative route for PI-4,5-P-2 synthesis as the bulk of this lipid is generated by the canonical pathway in which phosphatidylinositol-4-phosphate (PI-4-P) is the intermediate. Here we examined the effect of activation of the PI-5-P pathway on phosphoinositide 3-kinase (PI3K) signaling by expressing PIP4K IIbeta in cells that lack this enzyme. Although PIP4K II generates PI-4,5-P-2, a substrate for PI3K, expression of this enzyme reduced rather than increased phosphatidylinositol-3,4,5-trisphosphate (PI-3,4,5-P-3) levels in cells stimulated with insulin or cells expressing activated PI3K. This reduction in PI-3,4,5-P-3 levels resulted in decreased activation of the downstream protein kinase, Akt/PKB. Consistent with these results, expression of IpgD, a bacterial phosphatase that converts PI-4,5-P-2 to PI-5-P, resulted in Akt activation, and this effect was partially reversed by PIP4K IIbeta. PIP4K IIbeta expression did not impair insulin-dependent association of PI3K with insulin receptor substrate 1 (IRS1) but abbreviated Akt activation, indicating that PIP4K II regulates PI-3,4,5-P-3 degradation rather than synthesis. These data support a model in which the PI-5-P pathway controls insulin signaling that leads to Akt activation by regulating a PI-3,4,5-P-3 phosphatase.
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