Insulin-stimulated interaction with 14-3-3 promotes cytoplasmic localization of lipin-1 in adipocytes.
Lipin-1 is a bifunctional protein involved in lipid metabolism and adipogenesis. Lipin-1 plays a role in the biosynthesis of triacylglycerol through its phosphatidate phosphatase activity and also acts as a transcriptional co-activator of genes involved in oxidative metabolism. Lipin-1 resides in the cytoplasm and translocates to the endoplasmic reticulum membrane to catalyze the phosphatidate phosphatase reaction. It also possesses a nuclear localization signal, which is required for its translocation to the nucleus and may therefore be important for lipin-1 co-activator function. Thus, subcellular localization may be an important factor in the regulation of this protein. Here, we show that the nuclear localization signal alone is not sufficient for lipin-1 nuclear localization, and identify lipin-1 interaction with 14-3-3 as a determinant of its subcellular localization. We demonstrate that lipin-1 interacts with 14-3-3 proteins and that overexpression of 14-3-3 promotes the cytoplasmic localization of lipin-1 in 3T3-L1 adipocytes. The effect of 14-3-3 is mediated through a serine-rich domain in lipin-1. Functional mapping of the 14-3-3-interacting region within the serine-rich domain indicates redundancy and cooperativity among several sites, including five phosphorylated serine and threonine residues. Insulin stimulation of 3T3-L1 adipocytes results in increased lipin-1 phosphorylation, enhanced interaction with 14-3-3, and predominantly cytoplasmic localization. In summary, our studies suggest that insulin may modulate the cellular function of lipin-1 by regulating its subcellular localization through interactions with 14-3-3 proteins.
Péterfy
Miklós
M
From the Departments of Medicine, University of California, Los Angeles, California 90095; the Veterans Affairs Greater Los Angeles Healthcare System, Los Angeles, California 90073; the Medical Genetics Institute, Cedars-Sinai Medical Center, Los Angeles, California 90048.
Harris
Thurl E
TE
the Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, and.
Fujita
Naoya
N
the Cancer Chemotherapy Center, Japanese Foundation for Cancer Research, Tokyo 135-8550, Japan.
Reue
Karen
K
From the Departments of Medicine, University of California, Los Angeles, California 90095; Departments of Human Genetics, David Geffen School of Medicine, University of California, Los Angeles, California 90095. Electronic address: reuek@ucla.edu.
D048948:14-3-3 Proteins / Q000235:genetics / Q000378:metabolism*; D041721:3T3-L1 Cells; D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D018613:Microscopy, Confocal; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010711:Phosphatidate Phosphatase; D010766:Phosphorylation / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D012694:Serine / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000494:pharmacology
D048948:14-3-3 Proteins; D007328:Insulin; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D012694:Serine; C418978:Lpin1 protein, mouse; D010711:Phosphatidate Phosphatase; D020123:Sirolimus