title: DNAJB6 chaperones PP2A mediated dephosphorylation of GSK3β to downregulate β-catenin transcription target, osteopontin.
abstract: Elevated levels of the oncoprotein, osteopontin (OPN), are associated with poor outcome of several types of cancers including melanoma. We have previously reported an important involvement of DNAJB6, a member of heat-shock protein 40 (HSP40) family, in negatively impacting tumor growth. The current study was prompted by our observations reported here which revealed a reciprocal relationship between DNAJB6 and OPN in melanoma specimens. The 'J domain' is the most conserved domain of HSP40 family of proteins. Hence, we assessed the functional role of the J domain in activities of DNAJB6. We report that the J domain of DNAJB6 is involved in mediating OPN suppression. Deletion of the J domain renders DNAJB6 incapable of impeding malignancy and suppressing OPN. Our mechanistic investigations reveal that DNAJB6 binds HSPA8 (heat-shock cognate protein, HSC70) and causes dephosphorylation of glycogen synthase kinase 3β (GSK3β) at Ser 9 by recruiting protein phosphatase, PP2A. This dephosphorylation activates GSK3β, leading to degradation of β-catenin and subsequent loss of TCF/LEF (T cell factor1/lymphoid enhancer factor1) activity. Deletion of the J domain abrogates assembly of this multiprotein complex and renders GSK3β inactive, thus, stabilizing β-catenin, a transcription co-activator for OPN expression. Our in-vitro and in-vivo functional analyses show that silencing OPN expression in the background of deletion of the J domain renders the resultant tumor cells less malignant despite the presence of stabilized β-catenin. Thus, we have uncovered a new mechanism for regulation of GSK3β activity leading to inhibition of Wnt/β-catenin signaling.
authors.affiliation: Department of Oncologic Sciences, Mitchell Cancer Institute, University of South Alabama, Mobile, AL 36604, USA.
authors.forename: A
authors.initials: A
authors.lastname: Mitra
authors.forename: M E
authors.initials: ME
authors.lastname: Menezes
authors.forename: L K
authors.initials: LK
authors.lastname: Pannell
authors.forename: M S
authors.initials: MS
authors.lastname: Mulekar
authors.forename: R E
authors.initials: RE
authors.lastname: Honkanen
authors.forename: L A
authors.initials: LA
authors.lastname: Shevde
authors.forename: R S
authors.initials: RS
authors.lastname: Samant
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D015536:Down-Regulation; D058750:Epithelial-Mesenchymal Transition; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D038362:Glycogen Synthase Kinase 3 / Q000378:metabolism*; D000071679:Glycogen Synthase Kinase 3 beta; D050883:HSC70 Heat-Shock Proteins / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D051821:Lymphoid Enhancer-Binding Factor 1 / Q000235:genetics / Q000378:metabolism; D008545:Melanoma / Q000378:metabolism / Q000556:secondary; D051379:Mice; D008819:Mice, Nude; D018832:Molecular Chaperones / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D009368:Neoplasm Transplantation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D019319:Okadaic Acid / Q000494:pharmacology; D020411:Oligonucleotide Array Sequence Analysis; D053495:Osteopontin / Q000235:genetics* / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D012878:Skin Neoplasms / Q000378:metabolism / Q000473:pathology; D051822:T Cell Transcription Factor 1 / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D059467:Transcriptome; D051176:beta Catenin / Q000378:metabolism*
chemical_list: C485565:DNAJB6 protein, human; D050883:HSC70 Heat-Shock Proteins; D050956:HSP40 Heat-Shock Proteins; C494371:HSPA8 protein, human; C497573:LEF1 protein, human; D051821:Lymphoid Enhancer-Binding Factor 1; D018832:Molecular Chaperones; D009419:Nerve Tissue Proteins; D051822:T Cell Transcription Factor 1; D051176:beta Catenin; D053495:Osteopontin; D019319:Okadaic Acid; C000605506:GSK3B protein, human; D000071679:Glycogen Synthase Kinase 3 beta; C000605507:Gsk3b protein, mouse; D038362:Glycogen Synthase Kinase 3; D054648:Protein Phosphatase 2