BACKGROUND: Genetic screens in Drosophila melanogaster and Caenorhabditis elegans identified the kinase suppressor of Ras, Ksr, as a new component in the Ras intracellular signaling pathway. In these organisms, mutations in Ksr resulted in attenuation of Ras-mediated signaling. Homologs of Ksr have also been isolated from mice and humans; their precise role in Ras signaling is not well defined. Here, we present data showing interactions between the murine form of Ksr (mKsr-1) and other components of the Ras pathway. RESULTS: To gain insight into the biological function of Ksr, we used a yeast two-hybrid screen and found an interaction between the carboxy-terminal region of mKsr-1 and mitogen-activated protein (MAP) kinase kinase 1 (MAPKK-1 or MEK-1). An interaction was also detected between MAP kinase (also called extracellular signal-regulated kinase; ERK), and the amino-terminal region of mKsr-1. These interactions were recapitulated in COS-7 cells. Further, when COS-7 cells were transfected with either full-length mKsr-1 or only its carboxy-terminal region, an inhibition of serum-stimulated MAP kinase activation was observed. Microinjection of full-length mKsr-1 or its carboxy-terminal, but not its amino-terminal region, blocked serum-induced DNA synthesis in rat embryo fibroblasts. Co-injection of mKsr-1 with MEK-1 reversed the blockade. CONCLUSIONS: Together with the data from genetic analyses, our findings lead us to propose that mKsr-1 may control MAP kinase signaling by serving as a scaffold protein that links MEK and its substrate ERK.
BACKGROUND: Genetic screens in Drosophila melanogaster and Caenorhabditis elegans identified the kinase suppressor of Ras, Ksr, as a new component in the Ras intracellular signaling pathway. In these organisms, mutations in Ksr resulted in attenuation of Ras-mediated signaling. Homologs of Ksr have also been isolated from mice and humans; their precise role in Ras signaling is not well defined. Here, we present data showing interactions between the murine form of Ksr (mKsr-1) and other components of the Ras pathway. RESULTS: To gain insight into the biological function of Ksr, we used a yeast two-hybrid screen and found an interaction between the carboxy-terminal region of mKsr-1 and mitogen-activated protein (MAP) kinase kinase 1 (MAPKK-1 or MEK-1). An interaction was also detected between MAP kinase (also called extracellular signal-regulated kinase; ERK), and the amino-terminal region of mKsr-1. These interactions were recapitulated in COS-7 cells. Further, when COS-7 cells were transfected with either full-length mKsr-1 or only its carboxy-terminal region, an inhibition of serum-stimulated MAP kinase activation was observed. Microinjection of full-length mKsr-1 or its carboxy-terminal, but not its amino-terminal region, blocked serum-induced DNA synthesis in rat embryo fibroblasts. Co-injection of mKsr-1 with MEK-1 reversed the blockade. CONCLUSIONS: Together with the data from genetic analyses, our findings lead us to propose that mKsr-1 may control MAP kinase signaling by serving as a scaffold protein that links MEK and its substrate ERK.
Authors: Christian E Rocheleau; Robyn M Howard; Alissa P Goldman; Mandy L Volk; Laura J Girard; Meera V Sundaram Journal: Genetics Date: 2002-05 Impact factor: 4.562
Authors: Gina L Razidlo; Heidi J Johnson; Scott M Stoeger; Kenneth H Cowan; Tadayoshi Bessho; Robert E Lewis Journal: J Biol Chem Date: 2009-01-15 Impact factor: 5.157