title: Elevated inorganic phosphate stimulates Akt-ERK1/2-Mnk1 signaling in human lung cells.
abstract: Inorganic phosphate (Pi) plays a critical role in diverse cellular functions. Among three classes of sodium/phosphate co-transporters (NPTs), two types have been identified in mammalian lung. The potential importance of Pi as a novel signaling molecule and pulmonary expression of NPTs with poor prognosis of diverse lung diseases including cancer have prompted us to begin to define the pathways by which Pi regulates nontumorigenic human bronchial epithelial cells. Pi activates Akt phosphorylation on Thr308 specifically, and activated signal transmits on the Raf/MEK/ERK signaling. Here, we report that Pi controls cell growth by activating ERK cascades and by facilitating the translocation of Mnk1 from cytosol into nucleus through an Akt-mediated MEK pathway. Sequentially, translocated Mnk1 increases eIF4E-BP1 phosphorylation. As a result, Pi stimulates cap-dependent protein translation. Such Akt-mediated signaling of inorganic phosphate may provide critical clues for treatment as well as prevention of diverse lung diseases.
authors.affiliation: Laboratory of Toxicology, College of Veterinary Medicine, Seoul National University, 56-1, Sillim-dong, Seoul 151-742, Korea.
authors.forename: Seung-Hee
authors.initials: SH
authors.lastname: Chang
authors.forename: Kyeong Nam
authors.initials: KN
authors.lastname: Yu
authors.forename: Yeon-Sook
authors.initials: YS
authors.lastname: Lee
authors.forename: Gil-Hwan
authors.initials: GH
authors.lastname: An
authors.forename: George R
authors.initials: GR
authors.lastname: Beck
authors.forename: Nancy H
authors.initials: NH
authors.lastname: Colburn
authors.forename: Kee-Ho
authors.initials: KH
authors.lastname: Lee
authors.forename: Myung-Haing
authors.initials: MH
authors.lastname: Cho
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D018797:Cell Cycle Proteins; D002458:Cell Fractionation; D002478:Cells, Cultured; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D017245:Foscarnet / Q000378:metabolism; D005786:Gene Expression Regulation; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008969:Molecular Sequence Data; D010710:Phosphates / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D021381:Protein Transport; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D020545:Respiratory Mucosa / Q000166:cytology*; D015398:Signal Transduction / Q000502:physiology; D013912:Threonine / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D018797:Cell Cycle Proteins; C087000:EIF4EBP1 protein, human; D004791:Enzyme Inhibitors; D047908:Intracellular Signaling Peptides and Proteins; D010710:Phosphates; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D013912:Threonine; D017245:Foscarnet; C491395:MKNK1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3