Binding of 14-3-3 Proteins to the Protein Kinase Raf and Effects on Its Activation

Freed, Ellen; Symons, Marc; Macdonald, Susan G.; McCormick, Frank; Ruggieri, Rosamaria

doi:10.1126/science.8085158

Cited by 400 publications

(277 citation statements)

References 41 publications

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“…For example, 14-3-3 was identi®ed as a molecule that activates Raf-1 in a Ras-dependent manner using a genetic screen with Saccharomyces cerevisiae (Irie et al, 1994) and as a Raf-1 binding protein using yeast twohybrid system (Fantl et al, 1994;Freed et al, 1994). Furthermore, 14-3-3 has been shown to increase the kinase activity of Raf-1 when introduced into Xenopus oocytes or yeast cells (Fantl et al, 1994;Freed et al, 1994) or in the cell-free system derived from yeast (Irie et al, 1994). However, since Raf-1 constitutively binds to 14-3-3, regardless of its activated state (Freed et al, 1994), it is likely that 14-3-3 functions as a structural component of a complex involving Raf-1.…”

Section: Discussionmentioning

confidence: 99%

“…Furthermore, 14-3-3 has been shown to increase the kinase activity of Raf-1 when introduced into Xenopus oocytes or yeast cells (Fantl et al, 1994;Freed et al, 1994) or in the cell-free system derived from yeast (Irie et al, 1994). However, since Raf-1 constitutively binds to 14-3-3, regardless of its activated state (Freed et al, 1994), it is likely that 14-3-3 functions as a structural component of a complex involving Raf-1. PKC is also reported to be a Raf-1 activator, because treatment of cells with phorbol ester leads to activation of Raf-1.…”

Section: Discussionmentioning

confidence: 99%

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Isolation of a new protein factor required for activation of Raf-1 by Ha-Ras: partial purification from rat brain cytosols

1998

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Ras-mediated signaling pathways play a critical role in cellular proliferation and di erentiation. Although it has been demonstrated that Ras interacts with Raf-1 to stimulate the serine/threonine kinase activity of Raf-1, the precise mechanism by which Ras activates Raf-1 remains obscure. To address this question, we developed a cell-free system in which the activated form of H-Ras can induce Raf-1 activation. Using this system, we found the presence of a new protein factor, in cytosolic fractions of both human embryonic kidney 293 cells and rat brain tissues, that is required for Ras-dependent activation of Raf-1. The factor was puri®ed from rat brain cytosols through successive column chromatographies on DEAE Sephacel, SP Sepharose and Sephacryl S-300. The approximate molecular weight of the activator was estimated as 400 000 by gel ®ltration. Its activity was sensitive to heat and trypsin treatments. The puri®ed activator did not contain Src, 14-3-3, protein kinase C, JAK2 or Ksr-1, as judged by immunoblotting. Further characterization of the activator is underway.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Isolation of a new protein factor required for activation of Raf-1 by Ha-Ras: partial purification from rat brain cytosols

1998

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“…This family of ubiquitously expressed, highly conserved proteins can exist as dimers and are known to complex with a variety of proteins (BCR, cdc25, A20, PKC) suggesting that they may act as an adaptor proteins (Braselmann and McCormick, 1995;Conklin et al, 1995;Vincenz and Dixit, 1996). The role of 14-3-3 in Raf-1 regulation remains controversial (Michaud et al, 1995;Suen et al, 1995;Li et al, 1995;Irie et al, 1994;Freed et al, 1994;Fantl et al, 1994;Chang and Rubin, 1997;Luo et al, 1996;Braselmann and McCormick, 1995;Shimizu et al, 1994). This may be due, at least in part, to the complex nature of the Raf-1/14-3-3 interaction which involves multiple binding sites, including the Raf-1 CRD and two sites containing a phospho-serine consensus sequence for 14-3-3 at positions 259 and 621 of Raf-1 (Clark et al, 1997b;Li et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

Increasing complexity of Ras signaling

et al. 1998

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The initial discovery that ras genes endowed retroviruses with potent carcinogenic properties and the subsequent determination that mutated ras genes were present in a wide variety of human cancers, prompted a strong suspicion that the growth-promoting actions of mutated Ras proteins contribute to their aberrant regulation of growth stimulatory signaling pathways. In 1993, a remarkable convergence of experimental observations from genetic analyses of Drosophila, S. cerevisiae and C. elegans as well as biochemical and biological studies in mammalian cells came together to de®ne a clear role for Ras in signal transduction. What emerged was an elegant linear signaling pathway where Ras functions as a relay switch that is positioned downstream of cell surface receptor tyrosine kinases and upstream of a cytoplasmic cascade of kinases that included the mitogen-activated protein kinases (MAPKs). Activated MAPKs in turn regulated the activities of nuclear transcription factors. Thus, a signaling cascade where every component between the cell surface and the nucleus was de®ned and conserved in worms,¯ies and man. This was a remarkable achievement in our e orts to appreciate how the aberrant function of Ras proteins may contribute to the malignant growth properties of the cancer cell. However, the identi®cation of this pathway has proven to be just the beginning, rather than the culmination, of our understanding of Ras in signal transduction. Instead, we now appreciate that this simple linear pathway represents but a minor component of a very complex signaling circuitry. Ras signaling has emerged to involve a complex array of signaling pathways, where cross-talk, feedback loops, branch points and multi-component signaling complexes are recurring themes. The simplest concept of a signaling cascade, where each component simply relays the same message to the next, is clearly not the case. In this review, we summarize our current understanding of Ras signal transduction with an emphasis on new complexities associated with the recognition and/or activation of cellular e ectors, and the diverse array of signaling pathways mediated by interaction between Ras and Ras-subfamily proteins with multiple e ectors.

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“…The e ect of 14-3-3 proteins on the kinase activity of Raf-1 is contentious, since in vitro they have been reported to either have no e ect on Raf-1 kinase activity (Fu et al, 1994;Michaud et al, 1995;Suen et al, 1995) or to activate Raf-1 (Fantl et al, 1994;Freed et al, 1994;Irie et al, 1994;Li et al, 1995). Genetic studies have identi®ed dominant negative 14-3-3 mutants that can inhibit signalling downstream of Ras and Raf-1 (Chang and Rubin, 1997) and have con®rmed that 14-3-3 proteins are required for Rasmediated Raf-1 activation (Kockel et al, 1997).…”

Section: Introductionmentioning

confidence: 99%