Abstract
The small Rho GTPase RAC1 is an essential regulator of cellular signaling that controls actin rearrangements and cell motility. Here, we identify a novel CUL3 RING ubiquitin ligase complex, containing the substrate adaptors KBTBD6 and KBTBD7, that mediates ubiquitylation and proteasomal degradation of TIAM1, a RAC1-specific GEF. Increasing the abundance of TIAM1 by depletion of KBTBD6 and/or KBTBD7 leads to elevated RAC1 activity, changes in actin morphology, loss of focal adhesions, reduced proliferation, and enhanced invasion. KBTBD6 and KBTBD7 employ ATG8 family-interacting motifs to bind preferentially to GABARAP proteins. Surprisingly, ubiquitylation and degradation of TIAM1 by CUL3(KBTBD6/KBTBD7) depends on its binding to GABARAP proteins. Our study reveals that recruitment of CUL3(KBTBD6/KBTBD7) to GABARAP-containing vesicles regulates the abundance of membrane-associated TIAM1 and subsequently spatially restricted RAC1 signaling. Besides their role in autophagy and trafficking, we uncovered a previously unknown function of GABARAP proteins as membrane-localized signaling scaffolds.
Copyright © 2015 Elsevier Inc. All rights reserved.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing / chemistry
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Adaptor Proteins, Signal Transducing / genetics
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Adaptor Proteins, Signal Transducing / metabolism*
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Amino Acid Sequence
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Apoptosis Regulatory Proteins
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Autophagy-Related Protein 8 Family
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Cullin Proteins / genetics
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Cullin Proteins / metabolism*
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Guanine Nucleotide Exchange Factors / genetics
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Guanine Nucleotide Exchange Factors / metabolism*
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Humans
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Intracellular Signaling Peptides and Proteins
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Microfilament Proteins / metabolism
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Microtubule-Associated Proteins / chemistry
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Microtubule-Associated Proteins / genetics
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Microtubule-Associated Proteins / metabolism*
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Models, Molecular
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Molecular Sequence Data
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Multiprotein Complexes / genetics
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Multiprotein Complexes / metabolism
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Nuclear Magnetic Resonance, Biomolecular
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Protein Conformation
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Protein Multimerization
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Signal Transduction
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T-Lymphoma Invasion and Metastasis-inducing Protein 1
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Trans-Activators / genetics
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Trans-Activators / metabolism*
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Ubiquitination
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rac1 GTP-Binding Protein / genetics
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rac1 GTP-Binding Protein / metabolism*
Substances
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Adaptor Proteins, Signal Transducing
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Apoptosis Regulatory Proteins
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Autophagy-Related Protein 8 Family
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CUL3 protein, human
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Cullin Proteins
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GABARAP protein, human
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GABARAPL2 protein, human
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Guanine Nucleotide Exchange Factors
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Intracellular Signaling Peptides and Proteins
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KBTBD6 protein, human
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KBTBD7 protein, human
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Microfilament Proteins
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Microtubule-Associated Proteins
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Multiprotein Complexes
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RAC1 protein, human
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T-Lymphoma Invasion and Metastasis-inducing Protein 1
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TIAM1 protein, human
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Trans-Activators
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rac1 GTP-Binding Protein