KSR stimulates Raf-1 activity in a kinase-independent manner

Michaud, Neil R.; Therrien, Marc; Cacace, Angela; Edsall, Lisa C.; Spiegel, Sarah; Rubin, Gerald M.; Morrison, Deborah K.

doi:10.1073/pnas.94.24.12792

Cited by 155 publications

(176 citation statements)

References 44 publications

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“…Although the kinase domains of mouse and human KSR1 lack evolutionarily conserved sequences that are typically required for catalytic activity (21), KSR1 has been reported to be an active kinase (39 -42). However, other evidence demonstrates that KSR1 function is independent of the kinase domain (26,29,32). Autophosphorylation on Thr 274 is unlikely since KSR1 constructs that lack the entire KSR1 kinase domain are still phosphorylated on Thr 274 in immune complex kinase assays (31).…”

Section: Discussionmentioning

confidence: 99%

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Phosphorylation Regulates KSR1 Stability, ERK Activation, and Cell Proliferation

Razidlo

Kortum

Haferbier³

et al. 2004

Journal of Biological Chemistry

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Kinase suppressor of Ras (KSR) is a molecular scaffold that interacts with the components of the Raf/MEK/ERK kinase cascade and positively regulates ERK signaling. Phosphorylation of KSR1, particularly at Ser 392 , is a critical regulator of KSR1 subcellular localization and ERK activation. We examined the role of phosphorylation of both Ser 392 and Thr 274 in regulating ERK activation and cell proliferation. We hypothesized that KSR1 phosphorylation is involved in generating signaling specificity through the Raf/MEK/ERK kinase cascade in response to stimulation by different growth factors. In fibroblasts, platelet-derived growth factor stimulation induces sustained ERK activation and promotes S-phase entry. Treatment with epidermal growth factor induces transient ERK activation but fails to drive cells into S phase. Mutation of Ser 392 and Thr 274 (KSR1.TVSA) promotes sustained ERK activation and cell cycle progression with either platelet-derived growth factor or epidermal growth factor treatment. KSR1 ؊/؊ mouse embryo fibroblasts expressing KSR1.TVSA proliferate two times faster and grow to a higher density than cells expressing the same level of wild-type KSR1. In addition, KSR1.TVSA is more stable than wild-type KSR1. These data demonstrate that phosphorylation and stability of the molecular scaffold KSR1 are critical regulators of growth factor-specific responses that promote cell proliferation.

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Section: Discussionmentioning

confidence: 99%

“…KSR1 was originally identified in Caenorhabditis elegans and Drosophila melanogaster as a modifier of activated Ras (19 -21). KSR1 associates with Raf, MEK, and ERK (22)(23)(24)(25)(26)(27)(28) and positively regulates ERK activation (16,18,22,23,29). KSR1 is phosphorylated on multiple sites by associated kinases (30,31).…”

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confidence: 99%

Phosphorylation Regulates KSR1 Stability, ERK Activation, and Cell Proliferation

Razidlo

Kortum

Haferbier³

et al. 2004

Journal of Biological Chemistry

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“…In fact, the KSR kinase domain alone inhibited all these effects [111]. Further, KSR associated with Raf-1 at the cell membrane in a Ras-dependent manner and could enhance Raf-1 activation, a trait that was again traced to CA3, a cysteine-rich domain resembling the Raf CRD [112]. The CA3 region was also implicated in mediating the translocation of KSR to the cell membrane in an independent study, probably via an interaction with the β subunit of heterotrimeric G-proteins [113].…”

Section: Holding It Together : Scaffolds and Adapters Ksr And Cnk (Comentioning

confidence: 98%

“…In all cases the kinase activity of KSR was dispensable, and the mutation of essential catalytic residues did not affect KSR function. To date no bona fide substrate for KSR has been found, and reports that KSR corresponds to ceramide-activated kinase [119] and phosphorylates Raf-1 [120] are disputed [49,112] and have not been widely accepted. It could well be that KSR is genuinely devoid of catalytic activity, and we are witnessing the transition from a kinase to a dedicated scaffolding protein.…”

Section: Holding It Together : Scaffolds and Adapters Ksr And Cnk (Comentioning

confidence: 99%

Meaningful relationships: the regulation of the Ras/Raf/MEK/ERK pathway by protein interactions

Kölch

2000

Biochemical Journal

1,057

118

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The Ras\Raf\MEK (mitogen-activated protein kinase\ERK kinase)\ERK (extracellular-signal-regulated kinase) pathway is at the heart of signalling networks that govern proliferation, differentiation and cell survival. Although the basic regulatory steps have been elucidated, many features of this pathway are only beginning to emerge. This review focuses on the role of protein-protein interactions in the regulation of this pathway, INTRODUCTIONThe mitogen-activated protein kinase (MAPK) pathway is one of the primordial signalling systems that Nature has used in several permutations to accomplish an amazing variety of tasks. It exists in all eukaryotes, and controls such fundamental cellular processes as proliferation, differentiation, survival and apoptosis. The basic arrangement includes a G-protein working upstream of a core module consisting of three kinases : a MAPK kinase kinase (MAPKKK) that phosphorylates and activates a MAPK kinase (MAPKK), which in turn activates MAPK ( Figure 1). This set-up provides not only for signal amplification, but, maybe even more importantly, for additional regulatory interfaces that allow the kinetics, duration and amplitude of the activity to be precisely tuned. At present we can distinguish six MAPK modules, which share structurally related components, but seem to mediate specific biological responses. For recent reviews on MAPK pathways, the reader is referred to references [1][2][3]. Here we will focus on the regulation of the ERK (extracellular-signal-regulated kinase) pathway, which features Ras as G-protein, Raf as MAPKKK, MEK (MAPK\ERK kinase) as MAPKK and ERK as MAPK.Despite enjoying a decade in the limelight of scientific interest and revealing a plethora of new insights into the circuitry of signalling pathways in general, this pathway still holds many secrets. These pertain mainly to the regulation of Raf, and to a deeper understanding of how specific biological responses are encoded by spatial and temporal changes in the activity and subcellular distribution of the pathway components, and how these fluctuations are orchestrated at the molecular level. Work from many laboratories has highlighted protein-protein interactions as powerful means of co-ordinating signalling processes, most strikingly exemplified by the assembly of multi-protein signalling complexes on activated receptors, or of transcriptionfactor complexes on gene promoters. However, it is becoming Abbreviations used : Bcr, Breakpoint cluster region ; BXB, isolated Raf-1 kinase domain ; CNK, connector-enhancer of KSR ; CK2, casein kinase 2 ; CRD, cysteine-rich domain ; DEF, docking site for ERK, FxFP ; DLK, dual leucine-zipper-bearing kinase ; ERK, extracellular-signal-regulated kinase ; Hsp, heat-shock protein ; KIM, kinase interaction motif ; IκB, inhibitor of NF-κB ; JNK, c-Jun N-terminal kinase ; KSR, kinase suppressor of Ras ; MAPK, mitogen-activated protein kinase ; MAPKK, MAPK kinase ; MAPKKK, MAPK kinase kinase ; MEK, MAPK/ERK kinase ; MEKK, MEK kinase ; MP1, MEK partner 1 ; MUK, MAPK upstream kin...

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“…KSR constitutively associates with MEK and appears to transiently associate with Raf and ERK upon signaling (10). KSR links Raf to its substrate MEK but could play an additional role in Raf activation (11)(12)(13)(14). C. elegans sur-6 encodes a B-regulatory subunit of the protein phosphatase 2A (PP2A) holoenzyme, thought to function with KSR (15)(16)(17), and sur-8 encodes a leucine-rich repeat protein that binds Ras and may facilitate interactions between Ras and Raf (18)(19)(20).…”

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confidence: 99%

Caenorhabditis elegans CNK-1 promotes Raf activation but is not essential for Ras/Raf signaling

Rocheleau

Rönnlund²,

Tuck³

et al. 2005

Proc. Natl. Acad. Sci. U.S.A.

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Connector enhancer of Ksr (CNK) is a conserved multidomain protein essential for Ras signaling in Drosophila melanogaster and thought to be involved in Raf kinase activation. However, the precise role of CNK in Ras signaling is not known, and mammalian CNKs are proposed to have distinct functions. Caenorhabditis elegans has a single CNK homologue, cnk-1. Here, we describe the role of cnk-1 in C. elegans Ras signaling and its requirements for LIN-45 Raf activation. We find that cnk-1 positively regulates multiple Ras signaling events during development, but, unlike Drosophila CNK, cnk-1 does not appear to be essential for signaling. cnk-1 mutants appear to be normal but show cell-type-specific genetic interactions with mutations in two other Ras pathway scaffolds͞adaptors ksr-1 and sur-8. Genetic epistasis using various activated LIN-45 Raf transgenes shows that CNK-1 promotes LIN-45 Raf activation at a step between the dephosphorylation of inhibitory sites in the regulatory domain and activating phosphorylation in the kinase domain. Our data are consistent with a model in which CNK promotes Raf phosphorylation͞activation through membrane localization, oligomerization, or association with an activating kinase.scaffold ͉ vulva ͉ lin-45

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KSR stimulates Raf-1 activity in a kinase-independent manner

Cited by 155 publications

References 44 publications

Phosphorylation Regulates KSR1 Stability, ERK Activation, and Cell Proliferation

Phosphorylation Regulates KSR1 Stability, ERK Activation, and Cell Proliferation

Meaningful relationships: the regulation of the Ras/Raf/MEK/ERK pathway by protein interactions

Caenorhabditis elegans CNK-1 promotes Raf activation but is not essential for Ras/Raf signaling

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