Accepted for publication in J Biol Chem, 2014 Jan 17. [Epub ahead of print]:
Functional crosstalk between Ras and Rho pathways: p120RasGAP competitively inhibits the RhoGAP activity of Deleted in Liver Cancer (DLC) tumor suppressors by masking its catalytic arginine finger.
Jaiswal M, Dvorsky R, Amin E, Risse SL, Fansa EK, Zhang SC, Taha MS, Gauhar AR, Nakhaei-Rad S, Kordes C, Koessmeier KT, Cirstea IC, Olayioye MA, Haeussinger D, Ahmadian MR.
The three Deleted in Liver Cancer genes (DLC1-3) encode Rho-specific GTPase-activating proteins (RhoGAPs). Their expression is frequently silenced in a variety of cancers. The RhoGAP activity, required for full DLC-dependent tumor suppressor activity, can be inhibited by the Src homology 3 (SH3) domain of a Ras-specific GAP (p120RasGAP). Here, we comprehensively investigated the molecular mechanism underlying crosstalk between two distinct regulators of small GTP-binding proteins using structural and biochemical methods. We demonstrate that only the SH3 domain of p120 specifically and selectively inhibits the RhoGAP activity of all three DLC isoforms as compared to a large set of other representative SH3 or RhoGAP proteins. Structural and mutational analyses provide new insights into the interaction mode of the p120 SH3 domain with the DLC1RhoGAP domain, which is unique and does not follow the classical PxxP-directed interaction. Hence, p120 associates with the DLC1 RhoGAP domain by targeting the catalytic arginine finger and thus by competitively and very potently inhibiting RhoGAP activity. The novel findings of this study shed light on the molecular mechanisms underlying the DLC inhibitory effects of p120 and suggest a functional crosstalk between Ras and Rho proteins at the level of regulatory proteins.