Mechanisms of regulation of the guanine nucleotide exchange factor C3G
Speaker: Arturo Carabias del Rey
Centro de Investigación del Cáncer (CIC-IBMCC), Salamanca
Salón de actos del Centro de Investigación del Cáncer
C3G (also known as RapGEF1), is a guanine nucleotide exchange factor (GEF) for the small GTPases of the Ras family Rap1, Rap2, R-Ras, TC21 and for the Rho GTPase TC10. GEFs interact with GTPases and favor the switch from the inactive GDP-bound state to the active GTP-bound form. C3G participates in a large repertoire of cell functions and plays a prominent role in the control of cell adhesion and migration through the activation of Rap1. The GEFs of the Ras family are frequently regulated by intramolecular interactions, and the loss of these mechanisms cause the spurious activation of the GTPases, leading to pathological states
C3G has a tripartite structure. (i) The N-terminal domain binds to E-cadherin. (ii) The central region (SH3b), interacts with SH3-containing proteins such as Crk proteins, p130Cas, Grb2, Hck, c-Abl, and the onco-protein Bcr-Abl. Among all of them, Crk proteins bind to C3G with high affinity and mediate the adaptor functions for C3G in the majority of the scenarios. The SH3b region is also phosphorylated in Tyr residues, and pY504 cause the activation of the protein in COS1 cells. (iii) The C-terminal region is composed of the REM and Cdc25H domains that harbor the catalytic activity.
The overall scope of this work was to understand the mechanisms of autoregulation and activation of C3G and to explore potential alterations linked to diseases. In this talk I will present data showing that the activity of the protein is fine-tuned by intramolecular interactions. We also show that the two main stimuli that activate the GEF activity: Crk binding and phosphorylation of C3G, modulate the autoregulatory interactions. Additionally, single nucleotide variants (SNVs) in the RAPGEF1 gene, found in lymphoma patients, affect residues that are essential for the autoinhibitory mechanism, causing constitutive activation of C3G in vitro and in the HEK293T cell line. Our results help to understand the regulation of C3G during both physiological and pathological signaling events.