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.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Cell Line, Tumor
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Down-Regulation
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Epithelial-Mesenchymal Transition
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Female
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Gene Expression Regulation, Neoplastic
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Glycogen Synthase Kinase 3 / metabolism*
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Glycogen Synthase Kinase 3 beta
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HSC70 Heat-Shock Proteins / metabolism
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HSP40 Heat-Shock Proteins / genetics
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HSP40 Heat-Shock Proteins / metabolism
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HSP40 Heat-Shock Proteins / physiology*
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Humans
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Lymphoid Enhancer-Binding Factor 1 / genetics
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Lymphoid Enhancer-Binding Factor 1 / metabolism
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Melanoma / metabolism
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Melanoma / secondary
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Mice
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Mice, Nude
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Molecular Chaperones / genetics
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Molecular Chaperones / metabolism
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Molecular Chaperones / physiology*
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Neoplasm Transplantation
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Nerve Tissue Proteins / genetics
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Nerve Tissue Proteins / metabolism
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Nerve Tissue Proteins / physiology*
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Okadaic Acid / pharmacology
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Oligonucleotide Array Sequence Analysis
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Osteopontin / genetics*
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Osteopontin / metabolism
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Phosphorylation
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Protein Binding
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Protein Interaction Domains and Motifs
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Protein Phosphatase 2 / antagonists & inhibitors
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Protein Phosphatase 2 / metabolism*
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Protein Processing, Post-Translational
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Protein Structure, Tertiary
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Skin Neoplasms / metabolism
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Skin Neoplasms / pathology
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T Cell Transcription Factor 1 / genetics
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T Cell Transcription Factor 1 / metabolism
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Transcription, Genetic
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Transcriptome
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beta Catenin / metabolism*
Substances
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DNAJB6 protein, human
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HSC70 Heat-Shock Proteins
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HSP40 Heat-Shock Proteins
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HSPA8 protein, human
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LEF1 protein, human
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Lymphoid Enhancer-Binding Factor 1
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Molecular Chaperones
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Nerve Tissue Proteins
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T Cell Transcription Factor 1
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beta Catenin
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Osteopontin
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Okadaic Acid
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GSK3B protein, human
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Glycogen Synthase Kinase 3 beta
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Gsk3b protein, mouse
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Glycogen Synthase Kinase 3
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Protein Phosphatase 2