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PubMed2005

Preponderance of the oncogenic V599E and V599K mutations in the B-raf kinase domain is enhanced in melanoma lymph node metastases.

Downstream of Ras, the serine/threonine kinase B-raf has been reported to be mutated, amongst other carcinomas, in a substantial subset of primary melanomas, with a preponderance of mutations within the kinase domain, including the activating V599E and V599K transitions. We investigated a representative series of 54 resection specimens of melanoma lymph node metastases for the presence of mutations within the activation segment (exon 15) of the B-raf kinase domain by polymerase chain reaction (PCR) and single-strand conformational polymorphism (SSCP) gel electrophoresis. Sequencing of cloned PCR-SSCP amplicons resulted in 24 (44%) samples harbouring somatic mutations, which is not significantly different from the mutation frequency found in recently investigated primary cutaneous melanomas (Deichmann M, Thome M, Benner A, Näher H. B-raf exon 15 mutations are common in primary melanoma resection specimens but not associated with clinical outcome. Oncology 2004; 66:411-419). The activating mutation T1796A was present in 20 (83%) of these resection specimens, followed in frequency by the oncogenic g1795A mutation in five (21%) cases. With regard to the B-raf protein sequence, the acidic amino acid transitions V599E and V599K were predicted in 15 (62%) and five (21%) of the 24 positive metastases, respectively. The detection of mutations at this hot spot codon was significantly associated with subsequent visceral metastasis (P=0.03; Fisher's exact test). During the transition from primary melanomas (see reference above) to lymph node metastases, the spectrum of B-raf mutations narrows significantly (P=0.00047). The oncogenic B-raf mutations V599E and V599K, as early events in melanocyte transformation, persist throughout metastasis with important prognostic implications.

Exons↗
PubMed1998

A role for c-Raf kinase and Ha-Ras in cytokine-mediated induction of cell adhesion molecules.

Cytokines such as tumor necrosis factor (TNFalpha) play fundamental roles in the pathophysiology of inflammation and immunity-related diseases. Despite rapid advances in our understanding of cytokine biology in recent years, definitive knowledge of the cytokine cell signaling pathways remains elusive due to the enormous complexity of these pathways and the lack of specific biological tools and reagents. Using highly specific antisense oligonucleotides that target the mRNA encoding c-Raf kinase and Ha-Ras, we show here that inhibition of c-raf and Ha-ras expression blocks the up-regulation of E-selectin and vascular adhesion molecule-1 induced by TNFalpha in endothelial cells. Induction of intercellular adhesion molecule-1 was also reduced, although to a much lesser extent, by treatment with antisense oligonucleotides. We also show that inhibition of c-raf kinase expression decreased extracellular signal-regulated kinase and c-Jun N-terminal kinase (JNK) kinase stimulation by TNFalpha. Furthermore, antisense inhibition of JNK2 also blocked TNFalpha-mediated induction of E-selectin, whereas PD98059 (mitogen-activated protein kinase kinase 1 and 2 inhibitor) had no effect on this process. These results indicate that TNFalpha induction of E-selectin and vascular adhesion molecule-1 in endothelial cells occurs through signaling pathways that are, at least in part, dependent on c-Raf kinase, Ha-Ras, and JNK2.

Base Sequence↗
PubMed2005

Preponderance of the oncogenic V599E and V599K mutations in B-raf kinase domain is enhanced in melanoma cutaneous/subcutaneous metastases.

BACKGROUND: Downstream of Ras, the serine/threonine kinase B-raf has been reported to be mutated, among other carcinomas, in a substantial subset of primary melanomas with a preponderance of mutations within the kinase domain including the activating V599E and V599K transitions. METHODS: We here investigated a representative series of 60 resection specimens of cutaneous and subcutaneous melanoma metastases for the presence of mutations within the activation segment (exon 15) of the B-raf kinase domain by polymerase chain reaction (PCR) and single-strand conformation polymorphism (SSCP) gel electrophoresis. RESULTS: Sequencing of cloned PCR-SSCP amplicons resulted in 24 (40%) samples harbouring somatic mutations which is not exceeding the mutation frequency in recently investigated primary melanomas. The activating mutation T1796A was present in 24/60 (40%) resection specimens, followed in frequency by the oncogenic g1795A mutation in 8/60 (13%) cases. As to the B-raf protein sequence, the acidic amino acid transitions V599E and V599K were predicted in 19/60 (32%) and 6/60 (10%) cases, respectively, but were not associated with enhanced risk for subsequent metastasis in patients' follow up. In comparison to the primary melanomas that we recently investigated, the spectrum of predicted B-raf protein mutations narrowed significantly in the cutaneous/subcutaneous metastases. Unexpectedly, V599 and V599E mutations were absent in cutaneous/subcutaneous metastases derived from acrolentiginous melanomas as preceding primary tumours. CONCLUSION: During transition from primary melanomas towards cutaneous/subcutaneous metastases, the spectrum of predicted B-raf mutations narrows significantly. Focusing on the V599E and V599K, these oncogenic mutations are likely to affect melanocyte-specific pathways controlling proliferation and differentiation.

Cell Differentiation↗
PubMed1999

Selection of phage-displayed fab antibodies on the active conformation of ras yields a high affinity conformation-specific antibody preventing the binding of c-Raf kinase to Ras.

The Ras proteins cycle in the cell between an inactive state and an active state. In the active state, Ras signals via the switch I region to effectors like c-Raf kinase, leading to cell growth. Since Ras mutations in cancer are often associated with the presence of permanently active Ras, molecules that prevent downstream signaling may be of interest. Here, we show that by selection on the active conformation of Ras, using a recently described large phage antibody repertoire [de Haard et al. (1999) J. Biol. Chem. 274, 18218-18230], a Fab antibody (Fab H2) was identified that exclusively binds to active Ras, and not to inactive Ras. Using surface plasmon resonance (SPR) analysis, the interaction was demonstrated to be of high affinity (7.2 nM). In addition, the interaction with Ras is specific, since binding to the homologous Rap1A protein in BIAcore analysis is at least three orders of magnitude lower, and undetectable in an enzyme-linked immunosorbent assay. The antibody fragment prevents the binding of active Ras to the immobilized Ras-binding domain of c-Raf kinase (Raf-RBD) at an IC(50) value of 135 nM. This value compares well to the K(D) of active Ras-binding to immobilized Raf-RBD using SPR, suggesting identical binding sites. Like the IgG Y13-259, which does not demonstrate preferential binding to either inactive or active Ras, Fab H2 inhibits intrinsic GTPase activity of Ras in vitro. Mapping studies using SPR analysis demonstrate that the binding sites for the antibodies are non-identical. This antibody could be used for dissecting functional differences between Ras effectors. Due to its specificity for active Ras, Fab H2 may well be more selective than previously used anti-Ras antibodies, and thus could be used for gene therapy of cancer with intracellular antibodies.

Antibodies↗
PubMed2004

Regulation of B-Raf kinase activity by tuberin and Rheb is mammalian target of rapamycin (mTOR)-independent.

Tuberous sclerosis complex (TSC) is a tumor suppressor gene syndrome with manifestations that can include seizures, mental retardation, autism, and tumors in the brain, retina, kidney, heart, and skin. The products of the TSC1 and TSC2 genes, hamartin and tuberin, respectively, heterodimerize and inhibit the mammalian target of rapamycin (mTOR). We found that tuberin expression increases p42/44 MAPK phosphorylation and B-Raf kinase activity. Short interfering RNA down-regulation of tuberin decreased the p42/44 MAPK phosphorylation and B-Raf activity. Expression of Rheb, the target of the GTPase-activating domain of tuberin, inhibited wild-type B-Raf kinase but not activated forms of B-Raf. The interaction of endogenous Rheb with B-Raf was enhanced by serum and by Ras overexpression. A farnesylation-defective mutant of Rheb co-immunoprecipitated with and inhibited B-Raf but did not activate ribosomal protein S6 kinase, indicating that farnesylation is not required for B-Raf inhibition by Rheb and that B-Raf inhibition and S6 kinase activation are separable activities of Rheb. Consistent with this, inhibition of B-Raf and p42/44 MAPK by Rheb was resistant to rapamycin in contrast to Rheb activation of S6 kinase, which is rapamycin-sensitive. Taken together these data demonstrate that inhibition of B-Raf kinase via Rheb is an mTOR-independent function of tuberin.

Cell Differentiation↗
PubMed2006

Loss of Raf kinase inhibitor protein promotes cell proliferation and migration of human hepatoma cells.

BACKGROUND & AIMS: The Raf kinase inhibitor protein (RKIP) has been identified as a suppressor of the mitogen-activated protein kinase (MAPK) pathway. Loss of RKIP function promotes tumor metastasis in prostate cancer and melanoma. The insulin-like growth factor I (IGF-I)-mediated MAPK cascade is often activated in hepatocellular carcinoma (HCC), but the role of RKIP in the molecular pathogenesis of these tumors is unknown. This study was performed to evaluate the role of RKIP in the development of HCC. METHODS: The levels of RKIP expression in HCC tumor and corresponding peritumoral tissues were determined by immunohistochemistry and Western blot analysis. The underlying mechanisms of RKIP were assessed with immunoblot analysis, Raf kinase activity assay, cell proliferation, and migration assays after either overexpression or knockdown of RKIP expression in HCC cell lines. RESULTS: RKIP expression is down-regulated in human HCC compared with adjacent peritumoral tissues. Low RKIP levels were correlated with enhanced extracellular signal-regulated-kinase (ERK)/MAPK pathway activation. Reconstitution experiments antagonized IGF-I-mediated MAPK pathway activation, resulting in reduced nuclear accumulation of phospho-ERK. In contrast, knockdown of RKIP expression using small interfering RNA induced activation of the ERK/MAPK pathway. Ectopic expression of RKIP altered HCC cell proliferation and migration. CONCLUSIONS: Our findings indicate that down-regulation of RKIP expression is a major factor in activation of the IGF-I/ERK/MAPK pathway during human hepatocarcinogenesis.

Carcinoma, Hepatocellular↗
PubMed1994

Binding of 14-3-3 proteins to the protein kinase Raf and effects on its activation.

To identify proteins that may participate in the activation of the protein kinase Raf, proteins that interact with Raf were selected in a two-hybrid screen. Two members of the 14-3-3 protein family were isolated that interacted with both the amino terminal regulatory regions of Raf and the kinase domain of Raf, but did not compete with the guanine nucleotide-binding protein Ras for binding to Raf. 14-3-3 proteins associated with Raf in mammalian cells and accompanied Raf to the membrane in the presence of activated Ras. In yeast cells expressing Raf and MEK, mammalian 14-3-3 beta or 14-3-3 zeta activated Raf to a similar extent as did expression of Ras. Therefore, 14-3-3 proteins may participate in or be required for the regulation of Raf function. These findings suggest a role for 14-3-3 proteins in Raf-mediated signal transduction.

14-3-3 Proteins↗
PubMed2001

Positive and negative regulation of Raf kinase activity and function by phosphorylation.

Activating and inhibitory phosphorylation mechanisms play an essential role in regulating Raf kinase activity. Here we demonstrate that phosphorylation of C-Raf in the kinase activation loop (residues T491 and S494) is necessary, but not sufficient, for activation. C-Raf has additional activating phosphorylation sites at S338 and Y341. Mutating all four of these residues to acidic residues, S338D/Y341D/T491E/S494D (DDED), in C-Raf results in constitutive activity. However, acidic residue substitutions at the corresponding activation loop sites in B-Raf are sufficient to confer constitutive activity. B-Raf and C-Raf also utilize similar inhibitory phosphorylation mechanisms to regulate kinase activity. B-Raf has multiple inhibitory phosphorylation sites necessary for full kinase inhibition where C-Raf requires only one. We examined the functional significance of these inhibitory and activating phosphorylations in Caenorhabditis elegans lin-45 Raf. Eliminating the inhibitory phosphorylation or mimicking activating phosphorylation sites is sufficient to confer constitutive activity upon lin-45 Raf and induce multi-vulva phenotypes in C.elegans. Our results demonstrate that different members of the Raf family kinases have both common and distinct phosphorylation mechanisms to regulate kinase activity and biological function.

Amino Acid Sequence↗
PubMed1998

Preclinical evaluation of the effects of a novel antisense compound targeting C-raf kinase in mice and monkeys.

CGP 69846A (ISIS 5132) is an antisense phosphorothioate oligodeoxynucleotide which targets human C-raf kinase and is currently being developed as an antineoplastic agent. The toxicity of this compound was evaluated in mice and monkeys following repeated i.v. injections or infusions for 4 weeks at doses up to 100 mg/kg. Because CGP 69846A is inactive in the mouse, ISIS 11061, the murine-specific homologue targeting C-raf kinase mRNA was evaluated concurrently with CGP 69846A to assess the potential toxicity associated with reduced C-raf expression. There were no toxicities that differentiated ISIS 11061 from CGP 69846A in mice. Effects in mice included hepatomegaly and hepatocellular degeneration at the high dose of 100 mg/kg CGP 69846A that potentially resulted in lethality. Other effects which were observed at 20 and 100 mg/kg included mononuclear cell infiltrates in multiple organs, extramedullary hematopoiesis in the spleen and liver, an increase in bone marrow cellularity, an increase in white blood cells, a decrease in platelet counts, and Kupffer cell hyperplasia. These alterations were reversible following a recovery period. No adverse effects in mice were observed with doses < or = 10 mg/kg. In monkeys, administration of 10 mg/kg of CGP 69846A was associated with effects observed with other P = S ODNs, namely, prolongation of activated partial thromboplastin time (APTT) and activation of complement. These effects were transient and correlated with plasma concentrations of CGP 69846A. Below a concentration of 35 micrograms/ml of intact CGP 69846A the prolongation of APTT was less than 50% and levels of complement split products were not increased. All monkeys tolerated complement activation with no evidence of treatment-related clinical signs. Complement and coagulation were not affected by the lower doses of 1 and 3 mg/kg. No histopathology or alteration in hematology or serum chemistry was induced by doses up to 10 mg/kg in monkeys. The plasma and tissue deposition of CGP 69846A were characterized in mice and monkeys and toxicity was dependent on dose of CGP 69846A. In the present preclinical evaluation of toxicity in mice and monkeys, CGP 69846A is well tolerated at doses targeted for clinical trials. Toxicities induced by CGP 69846A in monkeys and mice occurred at doses of 10 mg/kg and greater. Effects induced by CGP 69846A were not unique and have been observed previously with other phosphorothioate oligodeoxynucleotides.

Animals↗
PubMed1996

PKC epsilon functions as an oncogene by enhancing activation of the Raf kinase.

Previous studies have indicated that PKCepsilon behaves as an oncogene when overproduced in rodent fibroblasts (Cacace et al., 1993; Mishak et al., 1993). In the present study, Western blot analysis revealed that the hyperphosphorylated form of Raf kinase was present at a high level in PKCepsilon overproducing R6 rat fibroblasts but not in R6 fibroblasts overproducing PKCalpha or beta1. Extracts from the PKCepsilon overproducing cells also exhibited a marked increase in Raf-1 kinase and MAP-kinase activity. To investigate the significance of these findings, dominant negative mutants of ras (N17) or raf (301-1) were stably expressed in early passage control and PKCepsilon-transformed R6 fibroblasts, by transduction using retrovirus-derived constructs. Dominant negative raf expressing clones exhibited a flat morphology, a decreased saturation density, and decreased growth in soft agar. In addition, these reverted clones exhibited decreased Raf kinase activity. In contrast, dominant negative ras expressing clones remained highly transformed. In addition, PKCepsilon was detected in Raf-1 immunoprecipitates indicating that PKCepsilon forms a complex with Raf-1 in vivo. Taken together, these results suggest that PKCepsilon functions as an oncogene in R6 cells by enhancing activation of the Raf-1 kinase.

Animals↗
PubMed2004

Raf kinase activation of adenylyl cyclases: isoform-selective regulation.

Adenylyl cyclases (AC), a family of enzymes that catalyze the synthesis of cyclic AMP, are critical regulators of cellular functions. The activity of adenylyl cyclase is stimulated by a range of hormone receptors, primarily via interactions with G-proteins; however, recently we identified an alternate mechanism by which growth factors sensitize adenylyl cyclase activation. We suggested that this mechanism might involve a Raf kinase-mediated serine phosphorylation of adenylyl cyclase. However, the direct involvement of a specific form of Raf kinase is yet to be demonstrated. Furthermore, whether this mechanism is generalized to other isoforms of adenylyl cyclase is unknown. In human embryonic kidney 293 cells, we now demonstrate that in reconstitution studies, c-Raf kinase can mediate phosphorylation of AC VI. Furthermore, AC VI coimmunoprecipitates with c-Raf. Raf kinase-dependent regulation of adenylyl cyclase VI is dependent on the integrity of Ser750 in the fourth intracellular loop of the enzyme and Ser603/Ser608 in the C1b region of the molecule. To examine how generalized this effect is, we studied representative isoforms of the major subfamilies of adenylyl cyclase viz., AC I, AC II, and AC V. Raf kinase-dependent sensitization/ phosphorylation of adenylyl cyclases is common to AC VI, AC V, and AC II isoforms but not AC I. In aggregate, these studies indicate that Raf kinase associates with adenylyl cyclases. Furthermore, Raf kinase regulation of adenylyl cyclase is isoform-selective. These functional interactions (as well as the physical association) between adenylyl cyclases and Raf kinases suggest an important but previously unrecognized interaction between these two key regulatory enzymes.

Adenylyl Cyclases↗
PubMed1999

Potentiation of cell migration by adhesion-dependent cooperative signals from the GTPase Rac and Raf kinase.

The small GTPase Rac is thought to regulate cell movement by influencing actin cytoskeletal organization and membrane ruffling. However, cell migration also depends on the activation of mitogen-activated protein kinase (MAPK), which can regulate myosin motor function, an event critical for cell contraction. Evidence is provided that, during active cell adhesion to the extracellular matrix, Rac potentiates the MAPK pathway and influences cell migration by selectively synergizing with Raf kinase but not with Ras or MAPK kinase. In fact, the synergy between Rac and Raf kinase increases the chemotactic sensitivity of cells to epidermal growth factor by 1000-fold. Therefore, the role of Rac in cell migration not only depends on its ability to regulate actin cytoskeletal organization but also on its capacity to potentiate chemokine activation of MAPK in a manner that depends on active cell adhesion to the extracellular matrix.

3T3 Cells↗
PubMed1999

Strict regulation of c-Raf kinase levels is required for early organogenesis of the vertebrate inner ear.

Regulation of organogenesis involves a dynamic balance of the mechanisms regulating cell division, differentiation and death. Here we have investigated the pattern of expression of c-Raf kinase in the inner ear during early developmental stages and the consequences of manipulating c-Raf levels by misexpression of c-raf viral vectors in organotypic cultures of otic vesicle explants. We found that otic vesicles expressed c-Raf and its level remained constant during embryonic days 2 and 3 (E2-E3). c-Raf activity was increased in response to insulin like growth factor-I (IGF-I) and the activation by IGF-I of the c-Raf kinase pathway was a requirement to turn on cell proliferation in the otic vesicle. Overexpression of c-raf in E2.5 explants increased the proliferative response to low serum and IGF-I and blocked differentiation induced by retinoic acid. The increase in c-Raf levels also prevented nerve growth factor (NGF)-dependent induction of programmed cell death. Consistent with these results, the expression of a dominant negative c-Raf mutant potentiated retinoic acid action and decreased the rate of cell proliferation. We conclude that a strict control of c-Raf levels is essential for the co-ordination of the biological processes that operate simultaneously during early inner ear development.

Animals↗
PubMed2003

Effects of raf kinase inhibitor protein expression on suppression of prostate cancer metastasis.

BACKGROUND: Raf kinase inhibitor protein (RKIP), an inhibitor of Raf-mediated activation of mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK), is expressed at lower levels in human C4-2B metastatic prostate cancer cells than in the parental non-metastatic LNCaP prostate cancer cells from which they were derived. We examined whether RKIP functions as a suppressor of metastasis. METHODS: Immunohistochemistry was used to detect RKIP expression in clinical samples of primary prostate cancer and prostate cancer metastases. LNCaP and C4-2B cells were stably transfected with plasmids that constitutively expressed antisense and sense RKIP cDNA, respectively, or with empty vector. Assays of cell proliferation, soft-agar colony formation, and in vitro cell invasion were used to examine the malignant phenotypes of the transfected cells. An orthotopic murine model was used to examine the effect of expressing RKIP in C4-2B cells on the development of spontaneous metastasis. RESULTS: Clinical samples of primary prostate cancer had detectable RKIP expression, whereas clinical samples of prostate cancer metastases did not. There were no differences in the in vitro proliferation rate or colony-forming ability between the control vector-transfected and sense RKIP vector-transfected C4-2B cells or between the control vector-transfected and the antisense RKIP vector-transfected LNCaP cells. Overexpression of RKIP in C4-2B cells was associated with decreased in vitro cell invasion, decreased development of lung metastases in vivo, and decreased vascular invasion in the primary tumor but did not affect primary tumor growth in mice. CONCLUSIONS: RKIP does not influence the tumorigenic properties of human prostate cancer cells. It appears to be a novel and clinically relevant suppressor of metastasis that may function by decreasing vascular invasion.

Aged↗
PubMed2005

Ran binding protein 9 interacts with Raf kinase but does not contribute to downstream ERK1/2 activation in skeletal myoblasts.

Raf kinase is the upstream activator of MEK1/2 leading to phosphorylation and activation of ERK1/2. Sustained activation of Raf represses skeletal muscle-specific reporter gene transcription and formation of multinucleated myofibers. Inhibition of myogenesis by activated Raf involves downstream ERK1/2 as well as undefined mediators. To identify Raf-interacting proteins that may influence repression of muscle formation, a yeast two-hybrid screen was performed using a MEK1-binding defective Raf (RafBXB-T481A) as bait. Twenty cDNAs coding for Raf-interacting proteins were identified including Ran binding protein 9 (RanBP9), a protein previously reported to interact with receptor tyrosine kinases. Forced expression of RanBP9 in myogenic cells did not alter myogenesis. Co-expression of RanBP9 with constitutively active RafBXB, but not RafBXB-T481A, synergistically inhibited MyoD-directed muscle reporter gene transcription. Knockdown of RanBP9 expression did not restore the differentiation program to Raf-expressing myoblasts. Thus, RanBP9 physically associates with Raf but does not substantially contribute to the inhibitory actions of the kinase.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Activation of B-Raf kinase requires phosphorylation of the conserved residues Thr598 and Ser601.

The Raf kinase family serves as a central intermediate to relay signals from Ras to ERK. The precise molecular mechanism for Raf activation is still not fully understood. Here we report that phosphorylation of Thr598 and Ser601, which lie between kinase subdomains VII and VIII, is essential for B-Raf activation by Ras. Substitution of these residues by alanine (B-RafAA) abolished Ras-induced B-Raf activation without altering the association of B-Raf with other signaling proteins. Phosphopeptide mapping and immunoblotting with phospho-specific antibodies confirmed that Thr598 and Ser601 are in vivo phosphorylation sites induced by Ras. Furthermore, replacement of these two sites by acidic residues (B-RafED) renders B-Raf constitutively active. Con sistent with these data, B-RafAA and B-RafED exhibited diminished and enhanced ability, respectively, to stimulate ERK activation and Elk-dependent transcription. Moreover, functional studies revealed that B-RafED was able to promote NIH 3T3 cell transformation and PC12 cell differentiation. Since Thr598 and Ser601 are conserved in all Raf family members from Caenorhabditis elegans to mammals, we propose that phosphorylation of these two residues may be a general mechanism for Raf activation.

14-3-3 Proteins↗
PubMed2005

RKIP downregulates B-Raf kinase activity in melanoma cancer cells.

The Raf-MEK-ERK protein kinase cascade is a highly conserved signaling pathway that is pivotal in relaying environmental cues from the cell surface to the nucleus. Three Raf isoforms, which share great sequence and structure similarities, have been identified in mammalian cells. We have previously identified Raf kinase inhibitor protein (RKIP) as a negative regulator of the Raf-MEK-ERK signaling pathway by specifically binding to the Raf-1 isoform. We show here that RKIP also antagonizes kinase activity of the B-Raf isoform. Yeast two-hybrid and coimmunoprecipitation experiments indicated that RKIP specifically interacted with B-Raf. Ectopic expression of RKIP antagonized the kinase activity of B-Raf. We showed that the effects of RKIP on B-Raf functions were independent of its known inhibitory action on Raf-1. The expression levels of RKIP in melanoma cancer cell lines are low relative to primary melanocytes. Forced expression of RKIP partially reverted the oncogenic B-Raf kinase-transformed melanoma cancer cell line SK-Mel-28. The low expression of RKIP and its antagonistic action on B-Raf suggests that RKIP may play an important role in melanoma turmorgenesis.

Androgen-Binding Protein↗
PubMed2001

Discovery of heterocyclic ureas as a new class of raf kinase inhibitors: identification of a second generation lead by a combinatorial chemistry approach.

Heterocyclic ureas, such as N-3-thienyl N'-aryl ureas, have been identified as novel inhibitors of raf kinase, a key mediator in the ras signal transduction pathway. Structure-activity relationships were established, and the potency of the screening hit was improved 10-fold to IC(50)=1.7 microM. A combinatorial synthesis approach enabled the identification of a breakthrough lead (IC(50)=0.54 microM) for a second generation series of heterocyclic urea raf kinase inhibitors.

Proto-Oncogene Proteins c-raf↗