title: Calcineurin-independent inhibition of 3T3-L1 adipogenesis by Pasteurella multocida toxin: suppression of Notch1, stabilization of beta-catenin and pre-adipocyte factor 1.
abstract: Pasteurella multocida toxin (PMT) is a potent mitogen and a specific activator of Gq-dependent signalling pathways. PMT impairs osteoblast differentiation and causes bone loss and fat reduction in vivo. We examined the effect of PMT on cell signalling pathways involved in 3T3-L1 adipocyte differentiation. We demonstrate that PMT treatment before or together with differentiation induction factors inhibits adipogenesis and prevents upregulation of important adipocyte markers - peroxisome-proliferator-activated receptor gamma (PPARgamma) and CAATT enhancer-binding protein alpha (C/EBPalpha). Moreover, PMT completely downregulates PPARgamma and C/EBPalpha expression in mature adipocytes. Differentiation of pre-adipocytes into adipocytes requires the suppression of pre-adipocyte factor 1 (Pref1) and Wnt signalling, along with the degradation of beta-catenin. PMT prevents downregulation of Pref1 and beta-catenin under differentiation-inducing conditions. In addition, PMT treatment downregulates expression of Notch1, a protein responsible for cell fate decision and implicated in regulation of adipogenesis in 3T3-L1 cells. PMT action on adipogenesis was not reversed by cyclosporin A, an inhibitor of Galphaq-PLC-calcium-dependent calcineurin activation. Our results reveal new pathways involved in PMT action on cellular physiology and differentiation. Our study further demonstrates that the effect of PMT on Pref1/PPARgamma/C/EBPalpha expression and adipogenesis does not occur just through activation of the Galphaq-calcium-calcineurin pathway, but involves Wnt/beta-catenin and Notch1 signalling pathways, two signalling pathways strongly linked to cancer predisposition, neurological and immunological dysfunctions, and fat and bone development.
authors.affiliation: Department of Microbiology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
authors.forename: Leila R
authors.initials: LR
authors.lastname: Aminova
authors.forename: Brenda A
authors.initials: BA
authors.lastname: Wilson
mesh_terms: D041721:3T3-L1 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D050156:Adipogenesis; D000818:Animals; D001426:Bacterial Proteins / Q000494:pharmacology / Q000502:physiology*; D001427:Bacterial Toxins / Q000494:pharmacology; D019703:Calcineurin / Q000378:metabolism*; D065095:Calcineurin Inhibitors; D002135:Calcium-Binding Proteins; D002454:Cell Differentiation; D016572:Cyclosporine / Q000494:pharmacology; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism*; D051379:Mice; D016979:Pasteurella multocida / Q000378:metabolism*; D051881:Receptor, Notch1 / Q000378:metabolism*; D015398:Signal Transduction; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D001427:Bacterial Toxins; D065095:Calcineurin Inhibitors; D002135:Calcium-Binding Proteins; C512925:Dlk1 protein, mouse; D036341:Intercellular Signaling Peptides and Proteins; C497762:Notch1 protein, mouse; C062258:Pasteurella multocida toxin; D051881:Receptor, Notch1; D051176:beta Catenin; D016572:Cyclosporine; D019703:Calcineurin