title: A Phosphatidic Acid (PA) conveyor system of continuous intracellular transport from cell membrane to nucleus maintains EGF receptor homeostasis.
abstract: The intracellular concentration of the mitogen phosphatidic acid (PA) must be maintained at low levels until the need arises for cell proliferation. How temporal and spatial trafficking of PA affects its target proteins in the different cellular compartments is not fully understood. We report that in cancer cells, PA cycles back and forth from the cellular membrane to the nucleus, affecting the function of epidermal growth factor (EGF), in a process that involves PPARα/LXRα signaling. Upon binding to its ligand, EGF receptor (EGFR)-initiated activation of phospholipase D (PLD) causes a spike in intracellular PA production that forms vesicles transporting EGFR from early endosomes (EEA1 marker) and prolonged internalization in late endosomes and Golgi (RCAS marker). Cells incubated with fluorescent-labeled PA (NBD-PA) show PA in "diffuse" locations throughout the cytoplasm, punctae (small, <0.1 μm) vesicles) and large (>0.5 μm) vesicles that co-localize with EGFR. We also report that PPARα/LXRα form heterodimers that bind to new Responsive Elements (RE) in the EGFR promoter. Nuclear PA enhances EGFR expression, a role compatible with the mitogenic ability of the phospholipid. Newly made EGFR is packaged into PA recycling vesicles (Rab11 marker) and transported back to the cytoplasm and plasma membrane. However, a PLD+PA combination impedes binding of PPARα/LXRα to the EGFR promoter. Thus, if PA levels inside the nucleus reach a certain threshold (>100 nM) PA outcompetes the nuclear receptors and transcription is inhibited. This new signaling function of PLD-PA targeting EGFR trafficking and biphasically modulating its transcription, could explain cell proliferation initiation and its maintenance in cancer cells.
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University Boonshoft School of Medicine, Dayton, OH, USA.
authors.forename: Karen M
authors.initials: KM
authors.lastname: Henkels
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University Boonshoft School of Medicine, Dayton, OH, USA.
authors.forename: Taylor E
authors.initials: TE
authors.lastname: Miller
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University Boonshoft School of Medicine, Dayton, OH, USA.
authors.forename: Ramya
authors.initials: R
authors.lastname: Ganesan
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University Boonshoft School of Medicine, Dayton, OH, USA.
authors.forename: Brandon A
authors.initials: BA
authors.lastname: Wilkins
authors.affiliation: Department of Biochemistry and Molecular Biology, Wright State University Boonshoft School of Medicine, Dayton, OH, USA.
authors.forename: Kristen
authors.initials: K
authors.lastname: Fite
authors.affiliation: Center for Experimental Therapeutics and Reperfusion Injury, Brigham and Women Hospital and Harvard Medical School, Boston, MA, USA.|Department of Biochemistry and Molecular Biology, Wright State University Boonshoft School of Medicine, Dayton, OH, USA.
authors.forename: Julian
authors.initials: J
authors.lastname: Gomez-Cambronero
mesh_terms: D009327:4-Chloro-7-nitrobenzofurazan / Q000031:analogs & derivatives; D000818:Animals; D019556:COS Cells; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism*; D002522:Chlorocebus aethiops; D011992:Endosomes / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000378:metabolism; D066246:ErbB Receptors / Q000378:metabolism*; D006801:Humans; D000071518:Liver X Receptors / Q000378:metabolism; D047493:PPAR alpha / Q000378:metabolism; D010712:Phosphatidic Acids / Q000378:metabolism*; D010739:Phospholipase D / Q000378:metabolism; D011401:Promoter Regions, Genetic; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*
chemical_list: C086969:1-oleoyl-2-((N-(7-(nitro)-2,1,3-benzoxadiazol-4-yl)amino)hexanoyl)glycero-3-phosphate; D000071518:Liver X Receptors; D047493:PPAR alpha; D010712:Phosphatidic Acids; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D010739:Phospholipase D; D009327:4-Chloro-7-nitrobenzofurazan
keywords: breast cancer; cell signaling; gene expression; mammalian cells; phospholipids