A novel oncogene related to c-mil is transduced in chicken neuroretina cells induced to proliferate by infection with an avian lymphomatosis virus.

Marx, Maria; Eychène, Alain; Laugier, D; Béchade, Catherine; Crisanti, Patricia; Dezélée, Philippe; Pessac, Bernard; Calothy, Georges

doi:10.1002/j.1460-2075.1988.tb03209.x

Cited by 39 publications

(45 citation statements)

References 33 publications

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“…We next investigated whether these differences in intramolecular interactions could modulate B-Raf biological activity. B-Raf was initially identified thanks to the ability of its isolated kinase domain to transform primary cultures of chicken embryonic NR cells upon retroviral transduction (35). Indeed, the NR cell system represents a sensitive indicator for the detection of mitogenic properties, even in the absence of gross morphological alterations (13,41,43).…”

Section: B-raf Isoforms Are Differentially Regulated By Intramoleculamentioning

confidence: 99%

“…These primary cultures can be maintained in a nondividing state for several weeks in the presence of serum growth factors. Constitutive expression of activated oncogenes, such as Ras and Raf, promotes sustained NR cell division that results in the formation of foci of dividing cells (11,35,43). Therefore, we used this system to compare the abilities of the different myc-Nter constructs to inhibit the transforming potential of Flag-Cter B-Raf.…”

Section: B-raf Isoforms Are Differentially Regulated By Intramoleculamentioning

confidence: 99%

“…The BRAF oncogene encodes a MEK1/2 kinase that was initially identified due to its transduction into the genome of IC10, an acute mitogenic retrovirus able to transform primary cultures of chicken embryonic neuroretina cells (35). Its human ortholog was simultaneously identified in NIH 3T3 cells transfected with Ewing sarcoma DNA (25).…”

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confidence: 99%

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Differential Regulation of B-Raf Isoforms by Phosphorylation and AutoinhibitoryMechanisms

Hmitou

Druillennec

Valluet

et al. 2007

Molecular and Cellular Biology

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The B-Raf proto-oncogene encodes several isoforms resulting from alternative splicing in the hinge region upstream of the kinase domain. The presence of exon 8b in the B2-Raf 8b isoform and exon 9b in the B3-Raf 9b isoform differentially regulates B-Raf by decreasing and increasing MEK activating and oncogenic activities, respectively. Using different cell systems, we investigated here the molecular basis of this regulation. We show that exons 8b and 9b interfere with the ability of the B-Raf N-terminal region to interact with and inhibit the C-terminal kinase domain, thus modulating the autoinhibition mechanism in an opposite manner. Exons 8b and 9b are flanked by two residues reported to down-regulate B-Raf activity upon phosphorylation. The S365A mutation increased the activity of all B-Raf isoforms, but the effect on B2-Raf 8b was more pronounced. This was correlated to the high level of S365 phosphorylation in this isoform, whereas the B3-Raf 9b isoform was poorly phosphorylated on this residue. In contrast, S429 was equally phosphorylated in all B-Raf isoforms, but the S429A mutation activated B2-Raf 8b , whereas it inhibited B3-Raf 9b . These results indicate that phosphorylation on both S365 and S429 participate in the differential regulation of B-Raf isoforms through distinct mechanisms. Finally, we show that autoinhibition and phosphorylation represent independent but convergent mechanisms accounting for B-Raf regulation by alternative splicing.

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Section: B-raf Isoforms Are Differentially Regulated By Intramoleculamentioning

confidence: 99%

Section: B-raf Isoforms Are Differentially Regulated By Intramoleculamentioning

confidence: 99%

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Differential Regulation of B-Raf Isoforms by Phosphorylation and AutoinhibitoryMechanisms

Hmitou

Druillennec

Valluet

et al. 2007

Molecular and Cellular Biology

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“…DISCUSSION BRAF was first identified as an oncogene by its ability to induce proliferation of avian primary cell cultures upon retroviral transduction and to transform NIH3T3 cells upon transfection with Ewing sarcoma DNA (31,32). Although its role as a major activator of the MEK/ERK pathway has been demonstrated in a large number of physiological processes (2, 8 -11, 18), its role in cell transformation has been poorly documented until 2002, when activating mutations were identified in the BRAF gene in human cancers, with the highest frequencies found in cutaneous melanomas (6) and papillary thyroid carcinoma (33,34).…”

Section: Fig 5 Effects Of Mek1/2 Inhibition On Erk1/2 Phosphorylatimentioning

confidence: 99%

Mutation of B-Raf in Human Choroidal Melanoma Cells Mediates Cell Proliferation and Transformation through the MEK/ERK Pathway

Calipel

Lefèvre

Pouponnot

et al. 2003

Journal of Biological Chemistry

111

112

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The BRAF gene, encoding a mitogen-activated protein kinase kinase kinase, is mutated in several human cancers, with the highest incidence occurring in cutaneous melanoma. The activating V599E mutation accounted for 80% of all mutations detected in cutaneous melanoma cell lines. Reconstitution experiments have shown that this mutation increases ectopically expressed B-Raf kinase activity and induces NIH3T3 cell transformation. Here we used tumor-derived cell lines to characterize the activity of endogenous mutated B-Raf protein and assess its specific role in transformation. We show that three cell lines (OCM-1, MKT-BR, and SP-6.5) derived from human choroidal melanoma, the most frequent primary ocular neoplasm in humans, express B-Raf containing the V599E mutation. These melanoma cells showed a 10-fold increase in endogenous B-Raf One of the main hallmarks of cancer is the acquisition by transformed cells of self-sufficiency in growth signals. In contrast, normal cells require mitogenic growth signals transmitted by transmembrane receptors to enter the cell cycle (1). The Raf/MEK 1 (MAPK or ERK kinase)/ERK (extracellular signalregulated kinase) module of the mitogen-activated protein kinase cascade is a major intracellular mediator of mitogenic signaling that regulates numerous biological processes (2, 3). Activation of this cascade downstream of membrane-bound receptors occurs through the interaction of Raf proteins with the small GTPase Ras upon its conversion to the GTP loaded, activated form. Mutations in genes encoding components of the Ras/Raf/MEK/ERK signaling pathway contribute to the development of many human cancers. Point mutations in HRAS, KRAS, and NRAS that lead to the constitutive activation of their protein products are found in ϳ30% of all human cancers (4), suggesting that the deregulation of downstream effectors of Ras is involved in oncogenesis. Although constitutive activation of ERK1/2 was detected in 36% of 50 studied human tumor cell lines (5), no mutations have been found in either ERK1/2 or MEK1/2 in human tumors. However, mutations in the BRAF gene were detected recently in ϳ20% of 530 human tumoral cell lines (6). B-Raf, the major MEK activator, has a higher affinity for and is a more efficient activator of MEK1 and MEK2 than Raf-1 (7-11). Two classes of BRAF gene mutation have been detected in the kinase domain of B-Raf; both of them lead to a constitutive increase in its kinase activity (6). One consists of single amino acid substitutions within the glycine-rich loop located in exon 11 of BRAF. These mutations are frequently associated with a RAS gene mutation. The other consists of single amino acid substitutions within the activation loop (exon 15 of BRAF). This class is never associated with a RAS gene mutation (6). B-Raf is more strongly activated by the second class of mutations, which may explain why the first class is always found associated with a RAS mutation. The highest incidence of BRAF mutations was found in cutaneous melanomas. Sixty-six percent of malignant cutaneous ...

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“…The CR1 region encodes the Ras binding domain of the protein and a`cysteine ®nger' Finney et al, 1993;Koide et al, 1993;Moodie et al, 1993;Papin et al, 1996;Van Aelst et al, 1993;Vojtek et al, 1993;Warne et al, 1993;Zhang et al, 1993). Although CR1 and CR2 contain regulatory sites of phosphorylation, it appears that the CR2 region is the major negative regulator of protein kinase activity as a deletion encompassing this region in Raf-1 is constitutively activated and capable of promoting oncogenic transformation of several cell types (Beck et al, 1987;Ikawa et al, 1988;Marx et al, 1988;Stanton et al, 1989).…”

Section: Introductionmentioning

confidence: 99%

Mutations of critical amino acids affect the biological and biochemical properties of oncogenic A-Raf and Raf-1

et al. 1997

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The catalytic domains of the Raf family of protein kinases (DRaf) dier in their ability to activate MEK in vitro and in vivo and in their ability to oncogenically transform mammalian cells. The kinase domain of B-Raf is more active than the equivalent portion of Raf-1 which in turn is more active than A-Raf. In Raf-1 the phosphorylation or mutation to aspartic acid of two key tyrosine residues upstream of the ATP binding site has been demonstrated to signi®cantly potentiate catalytic activity. In A-Raf the analogous amino acids are also tyrosine whereas in B-Raf they are aspartic acid. To determine if these dierences in amino acid sequence in¯uence the relative catalytic activity of the Raf kinase domains we constructed forms of DA-Raf, DB-Raf and DRaf-1 that encode either aspartic acid forms of the DRaf-1:ER and DA-Raf:ER proteins were the most potently oncogenic which correlated with their ability to elicit activation of the MAP kinase pathway. Consistent with the transformation data, the catalytic activity of the [DD] forms of DA-Raf:ER and DRaf-1:ER was about ten times greater than the cognate [FF] and [YY] forms of the proteins. By contrast all of the DB-Raf:ER proteins were highly transforming and DBRaf catalytic activity was largely unaected by mutation of the aforementioned aspartic acids to either tyrosine or phenylalanine. Similar results were obtained with epitope-tagged forms of DA-Raf, DB-Raf and DRaf-1 expressed in Sf9 cells. These data provide support for the model that key tyrosine residues in the protein kinase domains of A-Raf and Raf-1 are important in the regulation of catalytic activity. In addition they demonstrate that the higher intrinsic activity of B-Raf cannot be explained simply by the presence of aspartic acids at the analogous positions.

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A novel oncogene related to c-mil is transduced in chicken neuroretina cells induced to proliferate by infection with an avian lymphomatosis virus.

Cited by 39 publications

References 33 publications

Differential Regulation of B-Raf Isoforms by Phosphorylation and AutoinhibitoryMechanisms

Differential Regulation of B-Raf Isoforms by Phosphorylation and AutoinhibitoryMechanisms

Mutation of B-Raf in Human Choroidal Melanoma Cells Mediates Cell Proliferation and Transformation through the MEK/ERK Pathway

Mutations of critical amino acids affect the biological and biochemical properties of oncogenic A-Raf and Raf-1

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