title: Proteasome inhibition induces nuclear translocation of the dioxin receptor through an Sp1 and protein kinase C-dependent pathway.
abstract: The dioxin receptor (AhR), in addition to its role in xenobiotic-induced carcinogenesis, appears to participate in cell proliferation, differentiation and organ homeostasis. Understanding potential mechanisms of activation of this receptor in the absence of exogenous ligands is therefore important to study its contribution to endogenous cellular functions. Using mouse embryo primary fibroblasts, we have previously shown that proteasome inhibition increased AhR transcriptional activity in the absence of xenobiotics. We suggested that proteasome inhibition-dependent AhR activation could involve an increase in the expression of the partner protein dioxin receptor nuclear translocator (ARNT). Since ARNT over-expression induced nuclear translocation of the AhR, and ARNT-deficient cells were unable to translocate this receptor to the nucleus upon proteasome inhibition, we have analyzed the effect of proteasome inhibition on the expression of regulatory proteins controlling ARNT levels. Treatment with the proteasome inhibitor MG132 increased endogenous Sp1 phosphorylation and its DNA-binding activity to the ARNT promoter. Sp1 phosphorylation and binding to the ARNT promoter, ARNT over-expression and AhR nuclear translocation were inhibited by GF109203X, a protein kinase C-specific inhibitor. In addition, MG132 stimulated protein kinase C activity in MEF cells with a pattern similar to that observed for ARNT expression. These data suggest that cellular control of protein kinase C activity, through Sp1 and ARNT, could regulate AhR transcriptional activity in the absence of xenobiotics.
authors.affiliation: Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Extremadura, Avenida de Elvas s/n, 06071 Badajoz, Spain.
authors.forename: Belen
authors.initials: B
authors.lastname: Santiago-Josefat
authors.forename: Pedro M
authors.initials: PM
authors.lastname: Fernandez-Salguero
mesh_terms: D021581:Active Transport, Cell Nucleus; D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005347:Fibroblasts / Q000166:cytology / Q000378:metabolism; D015151:Immunoblotting; D007211:Indoles / Q000494:pharmacology; D007976:Leupeptins / Q000494:pharmacology; D008024:Ligands; D008301:Maleimides / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D011401:Promoter Regions, Genetic; D046988:Proteasome Endopeptidase Complex; D011493:Protein Kinase C / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D007211:Indoles; D007976:Leupeptins; D008024:Ligands; D008301:Maleimides; D009097:Multienzyme Complexes; D012333:RNA, Messenger; D018336:Receptors, Aryl Hydrocarbon; D016329:Sp1 Transcription Factor; D011493:Protein Kinase C; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C070515:bisindolylmaleimide I; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde