Article

Role for a novel signaling intermediate, phosphatidylinositol 5-phosphate, in insulin-regulated F-actin stress fiber breakdown and GLUT4 translocation

Wayne State University, Detroit, Michigan, United States
Endocrinology (Impact Factor: 4.64). 12/2004; 145(11):4853-65. DOI: 10.1210/en.2004-0489
Source: PubMed

ABSTRACT The cellular functions and regulation of phosphatidylinositol (PtdIns) 5-phosphate (5-P), the newest addition to the family of phosphoinositides (PIs), are still elusive. Here we have examined a plausible role of PtdIns 5-P as a signaling intermediate in acute insulin action. A wortmannin-insensitive transient increase of PtdIns 5-P mass levels that peaked at 10 min, and declined 20-30 min after insulin stimulation, was observed in both Chinese hamster ovary (CHO)-T cells stably expressing the insulin receptor and 3T3-L1 adipocytes. Similarly to insulin, found to induce a rapid disassembly of Texas-Red phalloidin-labeled actin stress fibers in CHO-T cells, microinjected PtdIns 5-P, but not other PIs, decreased the number and length of F-actin stress fibers in this cell type to a magnitude seen in response to insulin. Likewise, increases of PtdIns 5-P by ectopic expression of the PtdIns 5-P-producing enzyme PIKfyve yielded a similar effect. As with insulin, the PtdIns 5-P-induced loss of actin stress fibers was independent of PI 3-kinase activation. Furthermore, sequestration of functional PtdIns 5-P, either by ectopic expression of 3xPHD domains that bind selectively PtdIns 5-P or by microinjecting the GST-3xPHD fusion peptide, abrogated insulin-induced F-actin stress fiber disassembly in CHO-T cells. In 3T3-L1 adipocytes, microinjected PtdIns 5-P, but not other PIs, partially mimicked insulin's effect of translocating enhanced green fluorescent protein-GLUT4 to the cell surface. Conversely, insulin-induced myc-GLUT4 vesicle dynamics was arrested in the presence of coexpressed enhanced green fluorescent protein-3xPHD. Involvement of PIKfyve membrane recruitment, but not activation, and/or a decrease in PtdIns 4,5-bisphosphate levels are likely to be among the mechanisms underlying the insulin-induced PtdIns 5-P increase. Together, these results identify PtdIns 5-P as a novel key intermediate for insulin signaling in F-actin remodeling and GLUT4 translocation.

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    • "This implies that the relative level of the PIP5K2B substrate, phosphatidylinositol-5-phosphate (PtdIns(5)P), seems to impact on PtdIns(3,4,5)P3 levels and Akt/ PKB phosphorylation. In support of this hypothesis, levels of PtdIns(5)P have been reported to be induced by insulin stimulation and that injection of PtdIns(5)P into cells could mimic insulin stimulation at the level of Akt/PKB phosphorylation, Glut4 translocation as well as F-Actin stress fiber breakdown in different cell systems [3] [4]. Genetic ablation of PIP5K2B in mice resulted in increased insulin sensitivity, improved weight and lipid profiles. "
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