The Ubiquitin-like Protein LC3 Regulates the Rho-GEF Activity of AKAP-Lbc

• Published in: The Journal of biological chemistry Vol. 284; no. 41; pp. 28232 - 28242
• Main Authors: Baisamy, Laurent, Cavin, Sabrina, Jurisch, Nathalie, Diviani, Dario
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 09.10.2009; American Society for Biochemistry and Molecular Biology
• Subjects: A Kinase Anchor Proteins - genetics; A Kinase Anchor Proteins - metabolism; Animals; Cell Line; Guanine Nucleotide Exchange Factors - genetics; Guanine Nucleotide Exchange Factors - metabolism; Humans; Mechanisms of Signal Transduction; Mice; Microtubule-Associated Proteins - genetics; Microtubule-Associated Proteins - metabolism; Minor Histocompatibility Antigens; Models, Molecular; NIH 3T3 Cells; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - metabolism; Recombinant Fusion Proteins - genetics; Recombinant Fusion Proteins - metabolism; Rho Guanine Nucleotide Exchange Factors; Signal Transduction - physiology; Two-Hybrid System Techniques
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M109.054668

AKAP-Lbc is a member of the A-kinase anchoring protein (AKAP) family that has been recently associated with the development of pathologies, such as cardiac hypertrophy and cancer. We have previously demonstrated that, at the molecular level, AKAP-Lbc functions as a guanine nucleotide exchange factor (GEF) that promotes the specific activation of RhoA. In the present study, we identified the ubiquitin-like protein LC3 as a novel regulatory protein interacting with AKAP-Lbc. Mutagenesis studies revealed that LC3, through its NH2-terminal α-helical domain, interacts with two binding sites located within the NH2-terminal regulatory region of AKAP-Lbc. Interestingly, LC3 overexpression strongly reduced the ability of AKAP-Lbc to interact with RhoA, profoundly impairing the Rho-GEF activity of the anchoring protein and, as a consequence, its ability to promote cytoskeletal rearrangements associated with the formation of actin stress fibers. Moreover, AKAP-Lbc mutants that fail to interact with LC3 show a higher basal Rho-GEF activity as compared with the wild type protein and become refractory to the inhibitory effect of LC3. This suggests that LC3 binding maintains AKAP-Lbc in an inactive state that displays a reduced ability to promote downstream signaling. Collectively, these findings provide evidence for a previously uncharacterized role of LC3 in the regulation of Rho signaling and in the reorganization of the actin cytoskeleton.