title: Autophagy and 3-Phosphoinositide-Dependent Kinase 1 (PDK1)-Related Kinome in Pagetic Osteoclasts.
abstract: In Paget's disease of bone (PDB), a major contributory factor are osteoclasts (OCs) that are larger, more numerous, resistant to apoptosis, and hyperactive. The aim of this human in vitro study was to identify kinase cascades involved in the OC phenotype and to determine their impact on downstream processes. Basal phosphorylation levels of Akt and ERK were found to be elevated in PDB OCs. Given our previous findings that 3-phosphoinositide-dependent protein kinase 1 (PDK1) associates with the crucial adaptor p62 in OCs, we hypothesized that PDK1 may play an important role in OC-related kinome regulation. The increased phosphorylation of Akt and its substrate GSK3β observed in PDB OCs was reduced significantly upon PDK1 inhibition, as well as that of 4EBP1 and Raptor. This suggests a PDK1/Akt-dependent activation of mammalian target of rapamycin complex 1 (mTORC1) in PDB OCs. The resistance to apoptosis and the bone resorption were also overcome upon PDK1 inhibition. Studying autophagy by LC3B expression, we found a less inducible autophagy compared with control cells, which was reversed by PDK1 inhibition. In addition, PBD OCs exhibited higher LC3B-II/LC3B-I ratios and numbers of p62 and LC3B puncta per OC area, which did not further increase in the presence of lysosomal protease inhibitors, suggesting an accumulation of non-degradative autophagosomes. Together these results indicate a strong potential regulatory role for PDK1 in OC stimulatory pathways (Akt, ERK) and autophagy induction (via mTORC1), which may contribute to the OC phenotype in PDB. We also identified defects in late autophagosome maturation in these cells, the mechanism of which remains to be determined. © 2016 American Society for Bone and Mineral Research.
authors: Division of Rheumatology, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada.
authors: Stephen
authors: S
authors: McManus
authors: Division of Rheumatology, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada.
authors: Martine
authors: M
authors: Bisson
authors: Division of Rheumatology, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada.
authors: Richard
authors: R
authors: Chamberland
authors: Division of Rheumatology, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada.
authors: Michèle
authors: M
authors: Roy
authors: Division of Rheumatology, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada.
authors: Shekeba
authors: S
authors: Nazari
authors: Division of Rheumatology, Faculty of Medicine, University of Sherbrooke, Sherbrooke, Canada.
authors: Sophie
authors: S
authors: Roux
mesh_terms: D064413:3-Phosphoinositide-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D000368:Aged; D000369:Aged, 80 and over; D001343:Autophagy; D048049:Extracellular Signal-Regulated MAP Kinases / Q000235:genetics / Q000378:metabolism; D005260:Female; D006801:Humans; D020935:MAP Kinase Signaling System; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1 / Q000235:genetics / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism; D010001:Osteitis Deformans / Q000201:enzymology* / Q000235:genetics / Q000473:pathology; D010010:Osteoclasts / Q000201:enzymology* / Q000473:pathology; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: C502070:MAP1LC3B protein, human; D008869:Microtubule-Associated Proteins; C118585:P62 protein, human; D016601:RNA-Binding Proteins; D064413:3-Phosphoinositide-Dependent Protein Kinases; D000076222:Mechanistic Target of Rapamycin Complex 1; C578562:PDPK1 protein, human; D051057:Proto-Oncogene Proteins c-akt; D048049:Extracellular Signal-Regulated MAP Kinases
keywords: CELL SIGNALING; OSTEOCLAST; PAGET'S DISEASE OF BONE