title: Mammalian target of rapamycin complex 1 (mTORC1) plays a role in Pasteurella multocida toxin (PMT)-induced protein synthesis and proliferation in Swiss 3T3 cells.
abstract: Pasteurella multocida toxin (PMT) is a potent mitogen known to activate several signaling pathways via deamidation of a conserved glutamine residue in the α subunit of heterotrimeric G-proteins. However, the detailed mechanism behind mitogenic properties of PMT is unknown. Herein, we show that PMT induces protein synthesis, cell migration, and proliferation in serum-starved Swiss 3T3 cells. Concomitantly PMT induces phosphorylation of ribosomal S6 kinase (S6K1) and its substrate, ribosomal S6 protein (rpS6), in quiescent 3T3 cells. The extent of the phosphorylation is time and PMT concentration dependent, and is inhibited by rapamycin and Torin1, the two specific inhibitors of the mammalian target of rapamycin complex 1 (mTORC1). Interestingly, PMT-mediated mTOR signaling activation was observed in MEF WT but not in Gα(q/11) knock-out cells. These observations are consistent with the data indicating that PMT-induced mTORC1 activation proceeds via the deamidation of Gα(q/11), which leads to the activation of PLCβ to generate diacylglycerol and inositol trisphosphate, two known activators of the PKC pathway. Exogenously added diacylglycerol or phorbol 12-myristate 13-acetate, known activators of PKC, leads to rpS6 phosphorylation in a rapamycin-dependent manner. Furthermore, PMT-induced rpS6 phosphorylation is inhibited by PKC inhibitor, Gö6976. Although PMT induces epidermal growth factor receptor activation, it exerts no effect on PMT-induced rpS6 phosphorylation. Together, our findings reveal for the first time that PMT activates mTORC1 through the Gα(q/11)/PLCβ/PKC pathway. The fact that PMT-induced protein synthesis and cell migration is partially inhibited by rapamycin indicates that these processes are in part mediated by the mTORC1 pathway.
authors.affiliation: Laboratory of Biochemistry, NHLBI, National Institutes of Health, Bethesda, Maryland 20892-8012, USA. oubrahih@nhlbi.nih.gov
authors.forename: Hammou
authors.initials: H
authors.lastname: Oubrahim
authors.forename: Allison
authors.initials: A
authors.lastname: Wong
authors.forename: Brenda A
authors.initials: BA
authors.lastname: Wilson
authors.forename: P Boon
authors.initials: PB
authors.lastname: Chock
mesh_terms: D016475:3T3 Cells; D000255:Adenosine Triphosphate / Q000737:chemistry; D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism*; D001427:Bacterial Toxins / Q000378:metabolism*; D002227:Carbazoles / Q000494:pharmacology; D002465:Cell Movement; D043802:GTP-Binding Protein alpha Subunits, Gq-G11 / Q000378:metabolism; D000076222:Mechanistic Target of Rapamycin Complex 1; D008715:Methionine / Q000737:chemistry; D051379:Mice; D008954:Models, Biological; D046912:Multiprotein Complexes / Q000378:metabolism / Q000502:physiology*; D054799:Phospholipase C beta / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D038601:Ribosomal Protein S6 / Q000378:metabolism; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism / Q000502:physiology*; D013755:Tetradecanoylphorbol Acetate / Q000737:chemistry; D014945:Wound Healing
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D002227:Carbazoles; D046912:Multiprotein Complexes; C062258:Pasteurella multocida toxin; D038601:Ribosomal Protein S6; C081021:Go 6976; D000255:Adenosine Triphosphate; D008715:Methionine; D020794:Receptor Protein-Tyrosine Kinases; D000076222:Mechanistic Target of Rapamycin Complex 1; D058570:TOR Serine-Threonine Kinases; D011493:Protein Kinase C; D054799:Phospholipase C beta; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D013755:Tetradecanoylphorbol Acetate