Acquisition of unprecedented phosphatidylinositol 3,5-bisphosphate rise in hyperosmotically stressed 3T3-L1 adipocytes, mediated by ArPIKfyve-PIKfyve pathway.
Unlike yeast, where hyperosmotic stress induces a dramatic increase in phosphatidylinositol 3,5-bisphosphate (PtdIns 3,5-P(2)) synthesis, in mammalian cells, although activating a complex array of signaling events, hyperosmotic stress fails to up-regulate PtdIns 3,5-P(2), indicating the PtdIns 3,5-P(2) pathway is not involved in mammalian osmo-protective responses. Here we report an unexpected and marked PtdIns 3,5-P(2) increase in response to hyperosmotic stress in differentiated 3T3-L1 adipocytes. Because this effect was not observed in the precursor preadipocytes, a specific role during acquisition of the adipocyte phenotype and transition into insulin-responsive cells could be suggested. However, acute insulin action did not result in a measurable PtdIns 3,5-P(2) rise, indicating the PtdIns 3,5-P(2) pathway is a specific hyperosmotically activated signaling cascade selectively operating in differentiated 3T3-L1 adipocytes. Hyperosmolarity activates different components of several kinase cascades, including p38 mitogen-activated protein and tyrosine kinases, but these appear to be separate from the activated PtdIns 3,5-P(2) pathway. Because PtdIns 3,5-P(2) is primarily produced by PIKfyve-catalyzed synthesis and requires the upstream activator hVac14 (called herein ArPIKfyve) that physically associates with and activates PIKfyve, we examined the contribution of ArPIKfyve-PIKfyve for the hyperosmotic stress-induced rise in PtdIns 3,5-P(2). Small interfering RNA-directed gene silencing to selectively deplete ArPIKfyve or PIKfyve in 3T3-L1 adipocytes determined the ArPIKfyve-PIKfyve axis fully accountable for the hyperosmotically activated PtdIns 3,5-P(2). Together these results reveal a previously uncharacterized PtdIns 3,5-P(2) pathway activated selectively in hyperosmotically stressed 3T3-L1 adipocytes and suggest a plausible role for PtdIns 3,5-P(2) in the osmo-protective response mechanism in this cell type.
Sbrissa
Diego
D
Department of Physiology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
Shisheva
Assia
A
D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism; D000818:Animals; D002384:Catalysis; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism; D050356:Lipid Metabolism; D051379:Mice; D009995:Osmosis; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000737:chemistry; D018129:Phosphatidylinositol Phosphates / Q000737:chemistry* / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D015398:Signal Transduction; D013997:Time Factors; D015854:Up-Regulation
D007328:Insulin; D018129:Phosphatidylinositol Phosphates; D034741:RNA, Small Interfering; C106336:phosphatidylinositol 3,5-diphosphate; D019869:Phosphatidylinositol 3-Kinases; C492139:PIKFYVE protein, human; C116930:Pikfyve protein, mouse