ERK and Beyond: Insights from B-Raf and Raf-1 Conditional Knockouts

Galabova-Kovacs, Gergana; Kolbus, Andrea; Matzen, Dana; Meissl, Katrin; Piazzolla, Daniela; Rubiolo, Cristina; Steinitz, Katharina Nora; Baccarini, Manuela

doi:10.4161/cc.5.14.2981

Cited by 83 publications

(81 citation statements)

References 40 publications

(66 reference statements)

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“…Knockout of C-Raf in mice or in C-Raf-deficient cells can cause Fas-induced apoptosis (43,60). We observed that transfection of ODN-Raf led to a significant detachment of transfected cells and loss of viability as determined by an MTS assay.…”

Section: Discussionmentioning

confidence: 75%

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A Short Hairpin DNA Analogous to miR-125b Inhibits C-Raf Expression, Proliferation, and Survival of Breast Cancer Cells

Hofmann

Heinrich

Radziwil

et al. 2009

Molecular Cancer Research

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The noncoding RNA miR-125b has been described to reduce ErbB2 protein expression as well as proliferation and migration of cancer cell lines. As additional target of miR-125b, we identified the c-raf-1 mRNA by sequence analysis. We designed a short hairpin-looped oligodeoxynucleotide (ODN) targeted to the same 3′ untranslated region of c-raf-1 mRNA as miR-125b. The fully complementary ODN antisense strand is linked to a second strand constituting a partially double-stranded structure of the ODN. Transfection of the c-raf-1-specific ODN (ODN-Raf) in a breast cancer cell line reduced the protein levels of C-Raf, ErbB2, and their downstream effector cyclin D1 similar to miR-125b. MiR-125b as well as ODN-Raf showed no effect on the c-raf-1 mRNA level in contrast to small interfering RNA. Unlike miR-125b, ODN-Raf induced a cytopathic effect. This may be explained by the structural properties of ODN-Raf, which can form G-tetrads. Thus, the short hairpin-looped ODN-Raf, targeting the same region of c-raf-1 as miR-125b, is a multifunctional molecule reducing the expression of oncoproteins and stimulating cell death. Both features may be useful to interfere with tumor growth. (Mol Cancer Res 2009;7(10):1635-44)

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Section: Discussionmentioning

confidence: 75%

“…C-Raf is a survival factor, and downregulation of C-Raf or knockout of c-raf-1 can induce cell death (43). We investigated the effect of ODN-Raf on cell survival by performing an MTS assay.…”

Section: Effect Of Odn-raf On Survivalmentioning

confidence: 99%

A Short Hairpin DNA Analogous to miR-125b Inhibits C-Raf Expression, Proliferation, and Survival of Breast Cancer Cells

Hofmann

Heinrich

Radziwil

et al. 2009

Molecular Cancer Research

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“…33 Further complications are brought by cell type specificity, for example in wild-type erythroblasts the downregulation of C-Raf, but not of B-Raf, correlates with the decay of ERK phosphorylation associated with differentiation. 31 Is it only due to the observation that C-Raf is more expressed than B-Raf in these cells? Therefore although Raf isoforms elicit different strength of MEK activation, the in-vivo situation is blurred by the expression levels of isoforms and by crossactivations among isoforms.…”

Section: Do Isoforms Of the Ras/raf/mek/erk Pathway Gather To Constitmentioning

confidence: 99%

“…30 For all these reasons it is assumed that B-Raf is the main MEK1/2 activator. 31 However, in some cancer cells, B-Raf catalytically inactivated by mutations can still signal and activate MEK, it does so by dimerizing with C-Raf and stimulating its kinase activity. 32 Some reports even indicate that heterodimers B-Raf/C-Raf are more efficient to phosphorylate MEK than homodimers or monomers.…”

Section: Do Isoforms Of the Ras/raf/mek/erk Pathway Gather To Constitmentioning

confidence: 99%

Total ERK1/2 activity regulates cell proliferation

LeFloch¹,

Pouysségur²,

Lenormand³

2009

Cell Cycle

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Regulating ERK activity is essential for normal cell proliferation to occur. In mammals and most vertebrates ERK activity is provided by ERK1 and ERK2 that are highly similar, ubiquitously expressed and share activators and substrates. By combining single and double silencings of ERK1 and ERK2 we recently demonstrated that the apparent dominant role of ERK2 to regulate cell proliferation was due to its markedly higher expression level than ERK1. The contribution of ERK1 was revealed when ERK2 activation was clamped to avoid compensating over-activation of ERK2. We found no evidences in the literature for insulated isoform-specific modules in the Ras/Raf/MEK signaling cascade that could activate specifically ERK1 or ERK2. Obviously in frogs all signal integration and fine modulation provided by three Ras and three Raf isoforms is conducted by only one MEK and one ERK isoform. In mammals, ERK1 and ERK2 display similar specific activities and are activated respectively to their expression levels. After integrating signals from Ras, Raf and MEK isoforms, ERK1 and ERK2 regulate positively cell proliferation according to their expression levels.

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“…B-Raf is most similar to the Rafs of lower organisms, it interacts best with both Ras and MEK, has the highest basal kinase activity (Emuss et al, 2005) and is most readily activated by extracellular stimuli (Wellbrock et al, 2004). In contrast to c-Raf-1 (Galabova- Kovacs et al, 2006a), B-Raf is indispensable for MEK/ERK activation in cultured mouse fibroblasts and in the placenta, but not in the embryo proper, during development. Intriguingly, B-Raf sustains placental development not by mediating cell proliferation or survival, but rather by regulating the production of vascular endothelial growth factor A (VEGF-A, Galabova-Kovacs et al, 2006b), a prototype angiogenic factor with a prominent role in tumor-induced neovascularization (Ferrara et al, 2003).…”

Section: Introductionmentioning

confidence: 99%

B-Raf is required for ERK activation and tumor progression in a mouse model of pancreatic β-cell carcinogenesis

et al. 2008

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Activation of the Raf/MEK/ERK pathway, often by gainof-function mutations of RAS or RAF, is observed in many human cancers. The extracellular signal-regulated kinase (ERK) pathway is required for the proliferation of cancer cell lines harboring activating BRAF or, to a lesser extent, activating RAS mutations. It is still unclear, however, whether the pathway is required in vivo for tumor development, particularly in tumors in which B-Raf is not mutationally activated. During embryonic development, B-Raf is essential for angiogenesis in the placenta. To address the question of whether B-Raf contributed to tumor angiogenesis in vivo we conditionally ablated B-Raf in a model of pancreatic islet carcinoma driven by the functional inactivation of tumor suppressors (RIP1Tag2), which critically depends on angiogenesis for growth. We find that B-Raf is dispensable for the proliferation of tumor cells in culture, but necessary for ERK activation and for the expression of angiogenic factors by tumor cells in vivo and in vitro. In vivo, these defects result in the formation of hollow tumors with decreased vessel density and strongly reduced proliferation. The progression from adenoma to carcinoma is also significantly impaired. Thus, endogenous B-Raf contributes to the development of RIP1Tag2 tumors by supporting the stromal response and tumor progression.

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ERK and Beyond: Insights from B-Raf and Raf-1 Conditional Knockouts

Cited by 83 publications

References 40 publications

A Short Hairpin DNA Analogous to miR-125b Inhibits C-Raf Expression, Proliferation, and Survival of Breast Cancer Cells

A Short Hairpin DNA Analogous to miR-125b Inhibits C-Raf Expression, Proliferation, and Survival of Breast Cancer Cells

Total ERK1/2 activity regulates cell proliferation

B-Raf is required for ERK activation and tumor progression in a mouse model of pancreatic β-cell carcinogenesis

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