CUL3-KBTBD6/KBTBD7 ubiquitin ligase cooperates with GABARAP proteins to spatially restrict TIAM1-RAC1 signaling

  • Mol Cell. 2015 Mar 19;57(6):995-1010. doi: 10.1016/j.molcel.2014.12.040.
Heide Marika Genau  1 ,  Jessica Huber  2 ,  Francesco Baschieri  3 ,  Masato Akutsu  4 ,  Volker Dötsch  2 ,  Hesso Farhan  3 ,  Vladimir Rogov  2 ,  Christian Behrends  5
Affiliations
  • 1. Institute of Biochemistry II, Goethe University School of Medicine, 60590 Frankfurt am Main, Germany.
  • 2. Institute of Biophysical Chemistry and Center for Biomolecular Magnetic Resonance, Goethe University, 60438 Frankfurt am Main, Germany.
  • 3. Department of Biology, University of Konstanz, 78464 Konstanz, Germany; Biotechnology Institute Thurgau, 8280 Kreuzlingen, Switzerland.
  • 4. Buchmann Institute for Molecular Life Sciences, Goethe University, 60438 Frankfurt am Main, Germany.
  • 5. Institute of Biochemistry II, Goethe University School of Medicine, 60590 Frankfurt am Main, Germany. Electronic address: [email protected].
PMID: 25684205 DOI: 10.1016/j.molcel.2014.12.040
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.