Novel regulation of Ras proteins by direct tyrosine phosphorylation and dephosphorylation

Somatic mutations in the RAS genes are frequent in human tumors, especially in pancreatic, colorectal, and non-small-cell lung cancers. Such mutations generally decrease the ability of Ras to hydrolyze GTP, maintaining the protein in a constitutively active GTP-bound form that drives uncontrolled cell proliferation. Efforts to develop drugs that target Ras oncoproteins have been unsuccessful. Recent emerging data suggest that Ras regulation is more complex than the scientific community has believed for decades. In this review, we summarize advances in the "textbook" view of Ras activation. We also discuss a novel type of Ras regulation that involves direct phosphorylation and dephosphorylation of Ras tyrosine residues. The discovery that pharmacological inhibition of the tyrosine phosphoprotein phosphatase SHP2 maintains mutant Ras in an inactive state suggests that SHP2 could be a novel drug target for the treatment of Ras-driven human cancers

A Gain-of-Function Germline Mutation in Drosophila ras1 Affects Apoptosis and Cell Fate during Development

The RAS/MAPK signal transduction pathway is an intracellular signaling cascade that transmits environmental signals from activated receptor tyrosine kinases (RTKs) on the cell surface and other endomembranes to transcription factors in the nucleus, thereby linking extracellular stimuli to changes in gene expression. Largely as a consequence of its role in oncogenesis, RAS signaling has been the subject of intense research efforts for many years. More recently, it has been shown that milder perturbations in Ras signaling during embryogenesis also contribute to the etiology of a group of human diseases. Here we report the identification and characterization of the first gain-of-function germline mutation in Drosophila ras1 (ras85D), the Drosophila homolog of human K-ras, N-ras and H-ras. A single amino acid substitution (R68Q) in the highly conserved switch II region of Ras causes a defective protein with reduced intrinsic GTPase activity, but with normal sensitivity to GAP stimulation. The ras1R68Q mutant is homozygous viable but causes various developmental defects associated with elevated Ras signaling, including cell fate changes and ectopic survival of cells in the nervous system. These biochemical and functional properties are reminiscent of germline Ras mutants found in patients afflicted with Noonan, Costello or cardio-facio-cutaneous syndromes. Finally, we used ras1R68Q to identify novel genes that interact with Ras and suppress cell death

GTPase activity of Di-Ras proteins is stimulated by Rap1GAP proteins

The Ras family is the largest and most diverse sub-group of Ras-like G proteins. This complexity is further increased by the high number of regulatory Guanine nucleotide Exchange Factors (GEFs) and GTPase Activating Proteins (GAPs) that target specific members of this subfamily. Di-Ras1 and Di-Ras2 are little characterized members of the Ras-like sub-group with still unidentified regulatory and effector proteins. Here we determined the nucleotide binding properties of Di-Ras1/Di-Ras2. The above nanomolar affinity and the inability to react with members of the Cdc25 RasGEF family might suggest that activation does not require a GEF. We identified Rap1GAP1 and Rap1GAP2 as specific GTPase activating proteins of the Di-Ras family. Dual-specificity GAPs of the GAP1m family could not activate Di-Ras proteins, despite the presence of the required catalytic residue. Although Di-Ras proteins share GAPs with Rap G proteins, no common effectors could be identified in vitro

Structure of human guanylate-binding protein 1 representing a unique class of GTP-binding proteins

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