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Mol Cell Biol
1999 Jan 01;191:229-40. doi: 10.1128/MCB.19.1.229.
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Identification of constitutive and ras-inducible phosphorylation sites of KSR: implications for 14-3-3 binding, mitogen-activated protein kinase binding, and KSR overexpression.
Cacace AM
,
Michaud NR
,
Therrien M
,
Mathes K
,
Copeland T
,
Rubin GM
,
Morrison DK
.
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Genetic and biochemical studies have identified kinase suppressor of Ras (KSR) to be a conserved component of Ras-dependent signaling pathways. To better understand the role of KSR in signal transduction, we have initiated studies investigating the effect of phosphorylation and protein interactions on KSR function. Here, we report the identification of five in vivo phosphorylation sites of KSR. In serum-starved cells, KSR contains two constitutive sites of phosphorylation (Ser297 and Ser392), which mediate the binding of KSR to the 14-3-3 family of proteins. In the presence of activated Ras, KSR contains three additional sites of phosphorylation (Thr260, Thr274, and Ser443), all of which match the consensus motif (Px[S/T]P) for phosphorylation by mitogen-activated protein kinase (MAPK). Further, we find that treatment of cells with the MEK inhibitor PD98059 blocks phosphorylation of the Ras-inducible sites and that activated MAPK associates with KSR in a Ras-dependent manner. Together, these findings indicate that KSR is an in vivo substrate of MAPK. Mutation of the identified phosphorylation sites did not alter the ability of KSR to facilitate Ras signaling in Xenopus oocytes, suggesting that phosphorylation at these sites may serve other functional roles, such as regulating catalytic activity. Interestingly, during the course of this study, we found that the biological effect of KSR varied dramatically with the level of KSR protein expressed. In Xenopus oocytes, KSR functioned as a positive regulator of Ras signaling when expressed at low levels, whereas at high levels of expression, KSR blocked Ras-dependent signal transduction. Likewise, overexpression of Drosophila KSR blocked R7 photoreceptor formation in the Drosophila eye. Therefore, the biological function of KSR as a positive effector of Ras-dependent signaling appears to be dependent on maintaining KSR protein expression at low or near-physiological levels.
Aitken,
14-3-3 and its possible role in co-ordinating multiple signalling pathways.
1996, Pubmed
Aitken,
14-3-3 and its possible role in co-ordinating multiple signalling pathways.
1996,
Pubmed
Alessi,
Identification of the sites in MAP kinase kinase-1 phosphorylated by p74raf-1.
1994,
Pubmed
Alvarez,
Pro-Leu-Ser/Thr-Pro is a consensus primary sequence for substrate protein phosphorylation. Characterization of the phosphorylation of c-myc and c-jun proteins by an epidermal growth factor receptor threonine 669 protein kinase.
1991,
Pubmed
Barbacid,
ras genes.
1987,
Pubmed
Choi,
Ste5 tethers multiple protein kinases in the MAP kinase cascade required for mating in S. cerevisiae.
1994,
Pubmed
Clark,
C. elegans cell-signalling gene sem-5 encodes a protein with SH2 and SH3 domains.
1992,
Pubmed
Clark-Lewis,
Definition of a consensus sequence for peptide substrate recognition by p44mpk, the meiosis-activated myelin basic protein kinase.
1991,
Pubmed
Denouel-Galy,
Murine Ksr interacts with MEK and inhibits Ras-induced transformation.
1998,
Pubmed
Dickson,
Raf functions downstream of Ras1 in the Sevenless signal transduction pathway.
1992,
Pubmed
Duffy,
Recent advances in understanding signal transduction pathways in worms and flies.
1996,
Pubmed
Fabian,
Critical tyrosine residues regulate the enzymatic and biological activity of Raf-1 kinase.
1993,
Pubmed
,
Xenbase
Gonzalez,
Identification of substrate recognition determinants for human ERK1 and ERK2 protein kinases.
1991,
Pubmed
Han,
C. elegans lin-45 raf gene participates in let-60 ras-stimulated vulval differentiation.
1993,
Pubmed
Herskowitz,
MAP kinase pathways in yeast: for mating and more.
1995,
Pubmed
Hunter,
Protein kinase classification.
1991,
Pubmed
Joneson,
Kinase suppressor of Ras inhibits the activation of extracellular ligand-regulated (ERK) mitogen-activated protein (MAP) kinase by growth factors, activated Ras, and Ras effectors.
1998,
Pubmed
Karim,
A screen for genes that function downstream of Ras1 during Drosophila eye development.
1996,
Pubmed
Kornfeld,
The ksr-1 gene encodes a novel protein kinase involved in Ras-mediated signaling in C. elegans.
1995,
Pubmed
Kranz,
The MAP kinase Fus3 associates with and phosphorylates the upstream signaling component Ste5.
1994,
Pubmed
Lew,
Regulatory roles of cyclin dependent kinase phosphorylation in cell cycle control.
1996,
Pubmed
Liu,
Crystal structure of the zeta isoform of the 14-3-3 protein.
1995,
Pubmed
,
Xenbase
Marshall,
Specificity of receptor tyrosine kinase signaling: transient versus sustained extracellular signal-regulated kinase activation.
1995,
Pubmed
Marshall,
Ras effectors.
1996,
Pubmed
Marshall,
MAP kinase kinase kinase, MAP kinase kinase and MAP kinase.
1994,
Pubmed
Marshall,
Signal transduction. Hot lips and phosphorylation of protein kinases.
1994,
Pubmed
McCormick,
ras GTPase activating protein: signal transmitter and signal terminator.
1989,
Pubmed
McCormick,
Activators and effectors of ras p21 proteins.
1994,
Pubmed
Michaud,
KSR stimulates Raf-1 activity in a kinase-independent manner.
1997,
Pubmed
Moodie,
The 3Rs of life: Ras, Raf and growth regulation.
1994,
Pubmed
Morrison,
The complexity of Raf-1 regulation.
1997,
Pubmed
Morrison,
Identification of the major phosphorylation sites of the Raf-1 kinase.
1993,
Pubmed
Muslin,
Interaction of 14-3-3 with signaling proteins is mediated by the recognition of phosphoserine.
1996,
Pubmed
,
Xenbase
Pawson,
Signaling through scaffold, anchoring, and adaptor proteins.
1997,
Pubmed
Peng,
Mitotic and G2 checkpoint control: regulation of 14-3-3 protein binding by phosphorylation of Cdc25C on serine-216.
1997,
Pubmed
Posas,
Osmotic activation of the HOG MAPK pathway via Ste11p MAPKKK: scaffold role of Pbs2p MAPKK.
1997,
Pubmed
Simon,
Ras1 and a putative guanine nucleotide exchange factor perform crucial steps in signaling by the sevenless protein tyrosine kinase.
1991,
Pubmed
Spradling,
Transposition of cloned P elements into Drosophila germ line chromosomes.
1982,
Pubmed
Sundaram,
The C. elegans ksr-1 gene encodes a novel Raf-related kinase involved in Ras-mediated signal transduction.
1995,
Pubmed
Therrien,
KSR, a novel protein kinase required for RAS signal transduction.
1995,
Pubmed
Therrien,
KSR modulates signal propagation within the MAPK cascade.
1996,
Pubmed
,
Xenbase
Tomlinson,
Cell fate in the Drosophila ommatidium.
1987,
Pubmed
Wassarman,
The Ras signaling pathway in Drosophila.
1995,
Pubmed
Wigler,
Biochemical transfer of single-copy eucaryotic genes using total cellular DNA as donor.
1978,
Pubmed
Xiao,
Structure of a 14-3-3 protein and implications for coordination of multiple signalling pathways.
1995,
Pubmed
Xing,
The protein kinase KSR interacts with 14-3-3 protein and Raf.
1997,
Pubmed
,
Xenbase
Yaffe,
The structural basis for 14-3-3:phosphopeptide binding specificity.
1997,
Pubmed
Yan,
Identification of 2 serine residues of MEK-1 that are differentially phosphorylated during activation by raf and MEK kinase.
1994,
Pubmed
Yu,
Regulation of the MAP kinase pathway by mammalian Ksr through direct interaction with MEK and ERK.
1998,
Pubmed
Zha,
Serine phosphorylation of death agonist BAD in response to survival factor results in binding to 14-3-3 not BCL-X(L).
1996,
Pubmed
