title: BAG3 down-modulation reduces anaplastic thyroid tumor growth by enhancing proteasome-mediated degradation of BRAF protein.
abstract: BACKGROUND
  Anaplastic thyroid tumors (ATC) express high levels of BAG3, a member of the BAG family of cochaperone proteins that is involved in regulating cell apoptosis through multiple mechanisms.
  
  
  OBJECTIVE
  The objective of the study was the investigation of the influence of B-cell lymphoma-2-associated athanogene 3 (BAG3) on ATC growth.
  
  
  METHODS
  We investigated the effects of BAG3 down-modulation, obtained by using a specific small interfering RNA, on in vitro and in vivo growth of the human ATC cell line 8505C. Because BRAF protein plays an important role in ATC cell growth, we analyzed the effects of BAG3 down-modulation on BRAF protein levels. Furthermore, by using a proteasome inhibitor, we verified whether BAG3-mediated regulation of BRAF levels involved a proteasome-dependent mechanism.
  
  
  RESULTS
  BAG3 down-modulation significantly inhibits ATC growth in vitro and in vivo. BAG3 coimmunoprecipitates with BRAF protein, and its down-modulation results in a significant reduction of BRAF protein levels, which can be reverted by incubation with the proteasome inhibitor MG132.
  
  
  CONCLUSIONS
  BAG3 protein sustains ATC growth in vitro and in vivo. The underlying molecular mechanism appears to rely on BAG3 binding to BRAF, thus protecting it from proteasome-dependent degradation. These results are in line with the reported ability of BAG3 to interfere with the proteasomal delivery of a number of other client proteins.
authors.affiliation: Functional Genomic Unit, National Cancer Institute, Fondazione G. Pascale, via M. Semmola, 80131 Naples, Italy. chiappetta.gennaro@gmail.com
authors.forename: Gennaro
authors.initials: G
authors.lastname: Chiappetta
authors.forename: Anna
authors.initials: A
authors.lastname: Basile
authors.forename: Claudio
authors.initials: C
authors.lastname: Arra
authors.forename: Daniela
authors.initials: D
authors.lastname: Califano
authors.forename: Rosa
authors.initials: R
authors.lastname: Pasquinelli
authors.forename: Antonio
authors.initials: A
authors.lastname: Barbieri
authors.forename: Veronica
authors.initials: V
authors.lastname: De Simone
authors.forename: Domenica
authors.initials: D
authors.lastname: Rea
authors.forename: Aldo
authors.initials: A
authors.lastname: Giudice
authors.forename: Luciano
authors.initials: L
authors.lastname: Pezzullo
authors.forename: Vincenzo
authors.initials: V
authors.lastname: De Laurenzi
authors.forename: Gerardo
authors.initials: G
authors.lastname: Botti
authors.forename: Simona
authors.initials: S
authors.lastname: Losito
authors.forename: Daniela
authors.initials: D
authors.lastname: Conforti
authors.forename: Maria Caterina
authors.initials: MC
authors.lastname: Turco
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D048708:Cell Growth Processes / Q000235:genetics; D045744:Cell Line, Tumor; D015536:Down-Regulation / Q000235:genetics; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D051379:Mice; D008819:Mice, Nude; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding / Q000187:drug effects; D059748:Proteolysis / Q000187:drug effects; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D065646:Thyroid Carcinoma, Anaplastic; D013964:Thyroid Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D015854:Up-Regulation / Q000187:drug effects / Q000235:genetics; D023041:Xenograft Model Antitumor Assays
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C414431:BAG3 protein, human; D034741:RNA, Small Interfering; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D046988:Proteasome Endopeptidase Complex