RETRACTED: Autoimmunity as the Consequence of a Spontaneous Mutation in Rasgrp1

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the Authors.The authors have agreed to retract the paper because of the falsification of the Western blot in Figure 6A. The figure shows a defect in Ras activation, labeled as RasGTP, following TCR engagement, in thymocytes isolated from a RasGRP1 lag mutant mouse strain. This data set is one of several that show signaling and functional deficiencies identified for cells with lost of function of RasGRP. The authors stand by the validity of the other figures, results and interpretation in this paper. This matter was investigated by the Massachusetts Institute of Technology and the Office of Research Integrity at the United States Department of Health & Human Services, which found the figure was falsified by Luk Van Parijs, who is solely responsible. The authors deeply regret any inconvenience resulting from the publication of this data

Mutations in conserved regions 1, 2, and 3 of Raf-1 that activate transforming activity

To investigate the role of Raf-1 in v-Ha-ras transformation, we have isolated and characterized a number of Raf-1 mutants that display increased transforming activity in Rat2 fibroblasts. A dipeptide deletion (Delta144-145) in the cysteine-rich domain (CRD) of conserved region (CR) 1 increased the interaction between Raf-1 and v-Ha-ras effector loop mutants in the yeast two-hybrid system, supporting the proposal that the CRD serves as a secondary ras-binding domain. Many activating mutations were located in CR2. Two representative CR2 mutants (Delta250-258 and S257L) displayed increased interaction with v-Ha-ras effector loop mutants and with mitogen-activated protein kinase/extracellular signal-regulated kinase (ERK) kinase (MEK) 1 in the two-hybrid system. One novel mutation in CR3 was recovered; G361S affected the third glycine of the GXGXXG protein kinase motif involved in ATP binding. Expression of G361S Raf-1 in Rat2 fibroblasts activated MEK and ERK. The CR1, CR2, and CR3 activating mutations, when combined in cis, cooperated in transforming Rat2 fibroblasts. Conversely, Raf-1 transforming activity was decreased when the S257L or G361S mutation was combined in cis with the R89E substitution, which disrupts ras-Raf interaction. This mutant analysis provides additional information about the distinct functions of individual Raf-1 regions and documents a novel genetic mechanism for activating an oncogenic kinase

Hypothermic stress leads to activation of Ras-Erk signaling

The small GTPase Ras is converted to the active, GTP-bound state during exposure of vertebrate cells to hypothermic stress. This activation occurs more rapidly than can be accounted for by spontaneous nucleotide exchange. Ras–guanyl nucleotide exchange factors and Ras GTPase–activating proteins have significant activity at 0°C in vitro, leading to the hypothesis that normal Ras regulators influence the relative amounts of Ras-GTP and Ras-GDP at low temperatures in vivo. When hypothermic cells are warmed to 37°C, the Raf-Mek-Erk protein kinase cascade is activated. After prolonged hypothermic stress, followed by warming to physiologic temperature, cultured fibroblasts assume a rounded morphology, detach from the substratum, and die. All of these biologic responses are attenuated by pharmacologic inhibition of Mek. Previously, it had been found that low temperature blocks acute growth factor signaling to Erk. In the present study, we found that this block occurs at the level of Raf activation. Temperature regulation of Ras signaling could help animal cells respond appropriately to hypothermic stress, and Ras-Erk signaling can be manipulated to improve the survival of cells in cold storage