RESUMO
BRAF is frequently mutated in human cancer and the RASopathy syndromes, with RASopathy mutations often observed in the cysteine-rich domain (CRD). Although the CRD participates in phosphatidylserine (PS) binding, the RAS-RAF interaction, and RAF autoinhibition, the impact of these activities on RAF function in normal and disease states is not well characterized. Here, we analyze a panel of CRD mutations and show that they increase BRAF activity by relieving autoinhibition and/or enhancing PS binding, with relief of autoinhibition being the major factor determining mutation severity. Further, we show that CRD-mediated autoinhibition prevents the constitutive plasma membrane localization of BRAF that causes increased RAS-dependent and RAS-independent function. Comparison of the BRAF- and CRAF-CRDs also indicates that the BRAF-CRD is a stronger mediator of autoinhibition and PS binding, and given the increased catalytic activity of BRAF, our studies reveal a more critical role for CRD-mediated autoinhibition in BRAF regulation.
Assuntos
Cisteína , Proteínas Proto-Oncogênicas B-raf , Humanos , Cisteína/genética , Proteínas Proto-Oncogênicas B-raf/genética , Domínios Proteicos , Mutação , SíndromeRESUMO
Lung squamous cell carcinoma (LSCC) is the second most prevalent type of lung cancer. Despite extensive genomic characterization, no targeted therapies are approved for the treatment of LSCC. Distal amplification of the 3q chromosome is the most frequent genomic alteration in LSCC, and there is an urgent need to identify efficacious druggable targets within this amplicon. We identify the protein kinase TNIK as a therapeutic target in LSCC. TNIK is amplified in approximately 50% of LSCC cases. TNIK genetic depletion or pharmacologic inhibition reduces the growth of LSCC cells in vitro and in vivo. In addition, TNIK inhibition showed antitumor activity and increased apoptosis in established LSCC patient-derived xenografts. Mechanistically, we identified the tumor suppressor Merlin/NF2 as a novel TNIK substrate and showed that TNIK and Merlin are required for the activation of focal adhesion kinase. In conclusion, our data identify targeting TNIK as a potential therapeutic strategy in LSCC. SIGNIFICANCE: Targeted therapies have not yet been approved for the treatment of LSCC, due to lack of identification of actionable cancer drivers. We define TNIK catalytic activity as essential for maintaining LSCC viability and validate the antitumor efficacy of TNIK inhibition in preclinical models of LSCC.This article is highlighted in the In This Issue feature, p. 1307.
Assuntos
Antineoplásicos/uso terapêutico , Carcinoma de Células Escamosas/tratamento farmacológico , Neoplasias Pulmonares/tratamento farmacológico , Inibidores de Proteínas Quinases/uso terapêutico , Proteínas Serina-Treonina Quinases/antagonistas & inibidores , Animais , Antineoplásicos/farmacologia , Carcinoma de Células Escamosas/genética , Linhagem Celular Tumoral/efeitos dos fármacos , Células Epiteliais/efeitos dos fármacos , Regulação Neoplásica da Expressão Gênica , Humanos , Neoplasias Pulmonares/genética , Camundongos , Terapia de Alvo Molecular , Inibidores de Proteínas Quinases/farmacologia , Proteínas Serina-Treonina Quinases/genéticaRESUMO
The Ras GTPases are frequently mutated in human cancer, and, although the Raf kinases are essential effectors of Ras signaling, the tumorigenic properties of specific Ras-Raf complexes are not well characterized. Here, we examine the ability of individual Ras and Raf proteins to interact in live cells using bioluminescence resonance energy transfer (BRET) technology. We find that C-Raf binds all mutant Ras proteins with high affinity, whereas B-Raf exhibits a striking preference for mutant K-Ras. This selectivity is mediated by the acidic, N-terminal segment of B-Raf and requires the K-Ras polybasic region for high-affinity binding. In addition, we find that C-Raf is critical for mutant H-Ras-driven signaling and that events stabilizing B-Raf/C-Raf dimerization, such as Raf inhibitor treatment or certain B-Raf mutations, can allow mutant H-Ras to engage B-Raf with increased affinity to promote tumorigenesis, thus revealing a previously unappreciated role for C-Raf in potentiating B-Raf function.
Assuntos
Proliferação de Células , Transformação Celular Neoplásica/metabolismo , Neoplasias/enzimologia , Quinases raf/metabolismo , Proteínas ras/metabolismo , Animais , Transformação Celular Neoplásica/genética , Transformação Celular Neoplásica/patologia , Feminino , Regulação Neoplásica da Expressão Gênica , Células HEK293 , Células HeLa , Humanos , Masculino , Camundongos , Mutação , Células NIH 3T3 , Neoplasias/genética , Neoplasias/patologia , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Multimerização Proteica , Proteínas Proto-Oncogênicas B-raf/genética , Proteínas Proto-Oncogênicas B-raf/metabolismo , Proteínas Proto-Oncogênicas c-raf/genética , Proteínas Proto-Oncogênicas c-raf/metabolismo , Proteínas Proto-Oncogênicas p21(ras)/genética , Proteínas Proto-Oncogênicas p21(ras)/metabolismo , Transdução de Sinais/genética , Esferoides Celulares , Quinases raf/genética , Proteínas ras/genéticaRESUMO
Serum starvation stimulates cilia growth in cultured cells, yet serum factors associated with ciliogenesis are unknown. Previously, we showed that starvation induces rapid Rab11-dependent vesicular trafficking of Rabin8, a Rab8 guanine-nucleotide exchange factor (GEF), to the mother centriole, leading to Rab8 activation and cilium growth. Here, we demonstrate that through the LPA receptor 1 (LPAR1), serum lysophosphatidic acid (LPA) inhibits Rab11a-Rabin8 interaction and ciliogenesis. LPA/LPAR1 regulates ciliogenesis initiation via downstream PI3K/Akt activation, independent of effects on cell cycle. Akt stabilizes Rab11a binding to its effector, WDR44, and a WDR44-pAkt-phosphomimetic mutant blocks ciliogenesis. WDR44 depletion promotes Rabin8 preciliary trafficking and ciliogenesis-initiating events at the mother centriole. Our work suggests disruption of Akt signaling causes a switch from Rab11-WDR44 to the ciliogenic Rab11-FIP3-Rabin8 complex. Finally, we demonstrate that Akt regulates downstream ciliogenesis processes associated with Rab8-dependent cilia growth. Together, this study uncovers a mechanism whereby serum mitogen signaling regulates Rabin8 preciliary trafficking and ciliogenesis initiation.
Assuntos
Cílios/fisiologia , Regulação da Expressão Gênica , Quinase I-kappa B/metabolismo , Fosfatidilinositol 3-Quinases/metabolismo , Proteínas Proto-Oncogênicas c-akt/metabolismo , Proteínas rab de Ligação ao GTP/metabolismo , Animais , Humanos , Quinase I-kappa B/genética , Fosfatidilinositol 3-Quinases/genética , Transporte Proteico , Proteínas Proto-Oncogênicas c-akt/genética , Peixe-Zebra , Proteínas rab de Ligação ao GTP/genéticaRESUMO
Collective cell migration is required for normal embryonic development and contributes to various biological processes, including wound healing and cancer cell invasion. The M-Ras GTPase and its effector, the Shoc2 scaffold, are proteins mutated in the developmental RASopathy Noonan syndrome, and, here, we report that activated M-Ras recruits Shoc2 to cell surface junctions where M-Ras/Shoc2 signaling contributes to the dynamic regulation of cell-cell junction turnover required for collective cell migration. MCF10A cells expressing the dominant-inhibitory M-RasS27N variant or those lacking Shoc2 exhibited reduced junction turnover and were unable to migrate effectively as a group. Through further depletion/reconstitution studies, we found that M-Ras/Shoc2 signaling contributes to junction turnover by modulating the E-cadherin/p120-catenin interaction and, in turn, the junctional expression of E-cadherin. The regulatory effect of the M-Ras/Shoc2 complex was mediated at least in part through the phosphoregulation of p120-catenin and required downstream ERK cascade activation. Strikingly, cells rescued with the Noonan-associated, myristoylated-Shoc2 mutant (Myr-Shoc2) displayed a gain-of-function (GOF) phenotype, with the cells exhibiting increased junction turnover and reduced E-cadherin/p120-catenin binding and migrating as a faster but less cohesive group. Consistent with these results, Noonan-associated C-Raf mutants that bypass the need for M-Ras/Shoc2 signaling exhibited a similar GOF phenotype when expressed in Shoc2-depleted MCF10A cells. Finally, expression of the Noonan-associated Myr-Shoc2 or C-Raf mutants, but not their WT counterparts, induced gastrulation defects indicative of aberrant cell migration in zebrafish embryos, further demonstrating the function of the M-Ras/Shoc2/ERK cascade signaling axis in the dynamic control of coordinated cell movement.
Assuntos
Adesão Celular/genética , Movimento Celular/genética , Desenvolvimento Embrionário/genética , Peptídeos e Proteínas de Sinalização Intracelular/genética , Proteínas Monoméricas de Ligação ao GTP/genética , Animais , Caderinas/genética , Mutação com Ganho de Função/genética , Gastrulação/genética , Humanos , Sistema de Sinalização das MAP Quinases/genética , Síndrome de Noonan/genética , Síndrome de Noonan/fisiopatologia , Ligação Proteica , Peixe-Zebra/genéticaRESUMO
In the present study, a series of novel madecassic acid derivatives was synthesized and screened against the National Cancer Institute's 60 human cancer cell line panel. Among them, compounds 5, 12, and 17 displayed potent and highly differential antiproliferative activity against 80% of the tumor cells harboring the B-RafV600E mutation within the nanomolar range. Structure-activity analysis revealed that a 5-membered A ring containing an α,ß-unsaturated aldehyde substituted at C-23 with a 2-furoyl group seems to be crucial to produce this particular growth inhibition signature. In silico analysis of the cytotoxicity pattern of these compounds identified two highly correlated clinically approved drugs with known B-RafV600E inhibitory activity. Follow-up analysis revealed inhibition of the ERK signaling pathway through the reduction of cellular Raf protein levels is a key mechanism of action of these compounds. In particular, 17 was the most potent compound in suppressing tumor growth of B-RafV600E-mutant cell lines and displayed the highest reduction of Raf protein levels among the tested compounds. Taken together, this study revealed that modifications of madecassic acid structure can provide molecules with potent anticancer activity against cell lines harboring the clinically relevant B-RafV600E mutation, with compound 17 identified as a promising lead for the development of new anticancer drugs.
RESUMO
Six new macrophilone-type pyrroloiminoquines were isolated and identified from an extract of the marine hydroid Macrorhynchia philippina. The proton-deficient and heteroatom-rich structures of macrophilones B-G (2-7) were elucidated by spectroscopic analysis and comparison of their data with those of the previously reported metabolite macrophilone A (1). Compounds 1-7 are the first pyrroloiminoquines to be reported from a hydroid. The macrophilones were shown to inhibit the enzymatic conjugation of SUMO to peptide substrates, and macrophilones A (1) and C (3) exhibit potent and selective cytotoxic properties in the NCI-60 anticancer screen. Bioinformatic analysis revealed a close association of the cytotoxicity profiles of 1 and 3 with two known B-Raf kinase inhibitory drugs. While compounds 1 and 3 showed no kinase inhibitory activity, they resulted in a dramatic decrease in cellular protein levels of selected components of the ERK signal cascade. As such, the chemical scaffold of the macrophilones could provide small-molecule therapeutic leads that target the ERK signal transduction pathway.
Assuntos
Hidrozoários/química , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Pirroliminoquinonas/isolamento & purificação , Animais , Antineoplásicos/isolamento & purificação , Antineoplásicos/farmacologia , Linhagem Celular Tumoral , Ensaios de Seleção de Medicamentos Antitumorais , Humanos , Estrutura Molecular , Pirroliminoquinonas/farmacologia , Sumoilação/efeitos dos fármacosRESUMO
BRCA2 loss-of-heterozygosity (LOH) is frequently observed in BRCA2-mutated tumors, but its biallelic loss causes embryonic lethality in mice and inhibits proliferation of normal somatic cells. Therefore, it remains unclear how loss of BRCA2 contributes to tumorigenesis. One possibility is that mutation in potential genetic interactors of BRCA2, such as TRP53, is required for cell survival/proliferation in the absence of BRCA2. In this study, using an insertional mutagenesis screen in mouse embryonic stem cells (mESC), we have identified GIPC3 (GAIP-interacting protein C-terminus 3) as a BRCA2 genetic interactor that contributes to survival of Brca2-null mESC. GIPC3 does not compensate for BRCA2 loss in the repair of double-strand breaks. Mass-spectrometric analysis resulted in the identification of G-protein signaling transducers, APPL1 and APPL2, as potential GIPC3-binding proteins. A mutant GIPC3 (His155Ala) that does not bind to APPL1/2 failed to rescue the lethality of Brca2-null mESC, suggesting that the cell viability by GIPC3 is mediated via APPL1/2. Finally, the physiological significance of GIPC3 as a genetic interactor of BRCA2 is supported by the observation that Brca2-null embryos with Gipc3 overexpression are developmentally more advanced than their control littermates. Taken together, we have uncovered a novel role for GIPC3 as a BRCA2 genetic interactor.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/genética , Proteína BRCA2/genética , Neoplasias da Mama/genética , Carcinogênese/genética , Animais , Proteína BRCA2/deficiência , Neoplasias da Mama/patologia , Proteínas de Transporte/genética , Feminino , Regulação Neoplásica da Expressão Gênica , Humanos , Perda de Heterozigosidade/genética , Camundongos , Células-Tronco Embrionárias Murinas/metabolismo , Mutagênese Insercional , MutaçãoRESUMO
Ras pathway signaling plays a critical role in cell growth control and is often upregulated in human cancer. The Raf kinases selectively interact with GTP-bound Ras and are important effectors of Ras signaling, functioning as the initiating kinases in the ERK cascade. Here, we identify a route for the phospho-inhibition of Ras/Raf/MEK/ERK pathway signaling that is mediated by the stress-activated JNK cascade. We find that key Ras pathway components, the RasGEF Sos1 and the Rafs, are phosphorylated on multiple S/TP sites in response to JNK activation and that the hyperphosphorylation of these sites renders the Rafs and Sos1 unresponsive to upstream signals. This phospho-regulatory circuit is engaged by cancer therapeutics, such as rigosertib and paclitaxel/Taxol, that activate JNK through mitotic and oxidative stress as well as by physiological regulators of the JNK cascade and may function as a signaling checkpoint to suppress the Ras pathway during conditions of cellular stress.
Assuntos
Glicina/análogos & derivados , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Paclitaxel , Proteínas Proto-Oncogênicas B-raf/metabolismo , Proteínas Proto-Oncogênicas c-raf/metabolismo , Sulfonas , Ativação Enzimática/efeitos dos fármacos , Glicina/farmacocinética , Glicina/farmacologia , Células HeLa , Humanos , Estresse Oxidativo , Paclitaxel/farmacocinética , Paclitaxel/farmacologia , Fosforilação , Sulfonas/farmacocinética , Sulfonas/farmacologia , Proteínas ras/metabolismoRESUMO
The protein kinase casein kinase 2 (CK2) is a pleiotropic and constitutively active kinase that plays crucial roles in cellular proliferation and survival. Overexpression of CK2, particularly the α catalytic subunit (CK2α, CSNK2A1), has been implicated in a wide variety of cancers and is associated with poorer survival and resistance to both conventional and targeted anticancer therapies. Here, we found that CK2α protein is elevated in melanoma cell lines compared with normal human melanocytes. We then tested the involvement of CK2α in drug resistance to Food and Drug Administration-approved single agent targeted therapies for melanoma. In BRAF mutant melanoma cells, ectopic CK2α decreased sensitivity to vemurafenib (BRAF inhibitor), dabrafenib (BRAF inhibitor), and trametinib (MEK inhibitor) by a mechanism distinct from that of mutant NRAS. Conversely, knockdown of CK2α sensitized cells to inhibitor treatment. CK2α-mediated RAF-MEK kinase inhibitor resistance was tightly linked to its maintenance of ERK phosphorylation. We found that CK2α post-translationally regulates the ERK-specific phosphatase dual specificity phosphatase 6 (DUSP6) in a kinase dependent-manner, decreasing its abundance. However, we unexpectedly showed, by using a kinase-inactive mutant of CK2α, that RAF-MEK inhibitor resistance did not rely on CK2α kinase catalytic function, and both wild-type and kinase-inactive CK2α maintained ERK phosphorylation upon inhibition of BRAF or MEK. That both wild-type and kinase-inactive CK2α bound equally well to the RAF-MEK-ERK scaffold kinase suppressor of Ras 1 (KSR1) suggested that CK2α increases KSR facilitation of ERK phosphorylation. Accordingly, CK2α did not cause resistance to direct inhibition of ERK by the ERK1/2-selective inhibitor SCH772984. Our findings support a kinase-independent scaffolding function of CK2α that promotes resistance to RAF- and MEK-targeted therapies.
Assuntos
Antineoplásicos/farmacologia , Resistencia a Medicamentos Antineoplásicos , MAP Quinases Reguladas por Sinal Extracelular , Sistema de Sinalização das MAP Quinases , Melanoma , Mutação , Inibidores de Proteínas Quinases/farmacologia , Proteínas Proto-Oncogênicas B-raf , Caseína Quinase II/antagonistas & inibidores , Caseína Quinase II/genética , Caseína Quinase II/metabolismo , Linhagem Celular Tumoral , Resistencia a Medicamentos Antineoplásicos/efeitos dos fármacos , Resistencia a Medicamentos Antineoplásicos/genética , Fosfatase 6 de Especificidade Dupla/genética , Fosfatase 6 de Especificidade Dupla/metabolismo , MAP Quinases Reguladas por Sinal Extracelular/antagonistas & inibidores , MAP Quinases Reguladas por Sinal Extracelular/genética , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Humanos , Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Sistema de Sinalização das MAP Quinases/genética , Melanoma/tratamento farmacológico , Melanoma/enzimologia , Melanoma/genética , Melanoma/patologia , Fosforilação/efeitos dos fármacos , Proteínas Proto-Oncogênicas B-raf/antagonistas & inibidores , Proteínas Proto-Oncogênicas B-raf/genética , Proteínas Proto-Oncogênicas B-raf/metabolismoRESUMO
UNLABELLED: Somatic mutations in the EGFR kinase domain drive lung adenocarcinoma. We have previously identified MIG6, an inhibitor of ERBB signaling and a potential tumor suppressor, as a target for phosphorylation by mutant EGFRs. Here, we demonstrate that MIG6 is a tumor suppressor for the initiation and progression of mutant EGFR-driven lung adenocarcinoma in mouse models. Mutant EGFR-induced lung tumor formation was accelerated in Mig6-deficient mice, even with Mig6 haploinsufficiency. We demonstrate that constitutive phosphorylation of MIG6 at Y394/Y395 in EGFR-mutant human lung adenocarcinoma cell lines is associated with an increased interaction of MIG6 with mutant EGFR, which may stabilize EGFR protein. MIG6 also fails to promote mutant EGFR degradation. We propose a model whereby increased tyrosine phosphorylation of MIG6 decreases its capacity to inhibit mutant EGFR. Nonetheless, the residual inhibition is sufficient for MIG6 to delay mutant EGFR-driven tumor initiation and progression in mouse models. SIGNIFICANCE: This study demonstrates that MIG6 is a potent tumor suppressor for mutant EGFR-driven lung tumor initiation and progression in mice and provides a possible mechanism by which mutant EGFR can partially circumvent this tumor suppressor in human lung adenocarcinoma.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/deficiência , Adenocarcinoma/genética , Adenocarcinoma/patologia , Transformação Celular Neoplásica/genética , Receptores ErbB/genética , Neoplasias Pulmonares/genética , Neoplasias Pulmonares/patologia , Mutação , Proteínas Supressoras de Tumor/deficiência , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Adenocarcinoma/mortalidade , Adenocarcinoma de Pulmão , Animais , Linhagem Celular Tumoral , Progressão da Doença , Receptores ErbB/metabolismo , Deleção de Genes , Expressão Gênica , Humanos , Neoplasias Pulmonares/mortalidade , Camundongos , Camundongos Knockout , Camundongos Transgênicos , Proteínas Quinases Ativadas por Mitógeno/metabolismo , Fosforilação , Inibidores de Proteínas Quinases/farmacologia , Proteômica , Transdução de Sinais/efeitos dos fármacos , Proteínas Supressoras de Tumor/genética , Proteínas Supressoras de Tumor/metabolismoRESUMO
Protein scaffolds play an important role in signal transduction, functioning to facilitate protein interactions and localize key pathway components to specific signaling sites. Connector enhancer of KSR-2 (CNK2) is a neuronally expressed scaffold recently implicated in nonsyndromic, X-linked intellectual disability (NS-XLID) [1-3]. NS-XLID patients have deficits in cognitive function and their neurons often exhibit dendritic spine abnormalities [4], suggesting a role for CNK2 in synaptic signaling and/or spine formation. To gain insight regarding how CNK2 might contribute to these processes, we used mass spectrometry to identify proteins that interact with the endogenous CNK2 scaffold. Here, we report that the major binding partner of CNK2 is Vilse/ARHGAP39 and that CNK2 complexes are enriched for proteins involved in Rac/Cdc42 signaling, including Rac1 itself, α-PIX and ß-PIX, GIT1 and GIT2, PAK3 and PAK4, and members of the cytohesin family. Binding between CNK2 and Vilse was found to be constitutive, mediated by the WW domains of Vilse and a proline motif in CNK2. Through mutant analysis, protein depletion and rescue experiments, we identify CNK2 as a spatial modulator of Rac cycling during spine morphogenesis and find that the interaction with Vilse is critical for maintaining RacGDP/GTP levels at a balance required for spine formation.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/fisiologia , Espinhas Dendríticas/metabolismo , Proteínas rac de Ligação ao GTP/metabolismo , Proteínas Adaptadoras de Transdução de Sinal/química , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Motivos de Aminoácidos , Espinhas Dendríticas/ultraestrutura , Hipocampo/citologia , Hipocampo/metabolismo , Humanos , Morfogênese , Transdução de SinaisRESUMO
The Raf family of protein kinases are key signaling intermediates, acting as a central link between the membrane-bound Ras GTPases and the downstream kinases MEK and ERK. Raf kinase regulation is well-known for its complexity but only recently has it been realized that many of the mechanisms involved in Raf regulation also modulate Raf dimerization, now acknowledged to be a required step for Raf signaling in multiple cellular contexts. Recent studies have shown that Raf dimerization is necessary for normal Ras-dependent Raf kinase activation and contributes to the pathogenic function of disease-associated mutant Raf proteins with all but high intrinsic kinase activity. Raf dimerization has also been found to alter therapeutic responses and disease progression in patients treated with ATP-competitive Raf inhibitors as well as certain other kinase-targeted drugs. This demonstration of clinical significance has stimulated the recent development of biosensor assays that can monitor inhibitor-induced Raf dimerization as well as studies demonstrating the therapeutic potential of blocking Raf dimerization.
Assuntos
Transdução de Sinais , Quinases raf/metabolismo , Dimerização , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Humanos , MAP Quinase Quinase Quinases/metabolismo , Mutação , Neoplasias/tratamento farmacológico , Inibidores de Proteínas Quinases/farmacologia , Inibidores de Proteínas Quinases/uso terapêutico , Transdução de Sinais/efeitos dos fármacos , Quinases raf/antagonistas & inibidores , Quinases raf/genética , Proteínas ras/metabolismoRESUMO
Raf kinases are essential for normal Ras-Raf-MEK-ERK pathway signaling, and activating mutations in components of this pathway are associated with a variety of human cancers, as well as the related developmental disorders Noonan, LEOPARD, and cardiofaciocutaneous syndromes. Although the Raf kinases are known to dimerize during normal and disease-associated Raf signaling, the functional significance of Raf dimerization has not been fully elucidated. Here, using mutational analysis and a peptide inhibitor, we show that dimerization is required for normal Ras-dependent Raf activation and for the biological function of disease-associated Raf mutants with moderate, low, or impaired kinase activity. However, dimerization is not needed for the function of B-Raf mutants with high catalytic activity, such as V600E-B-Raf. Importantly, we find that a dimer interface peptide can effectively block Raf dimerization and inhibit Raf signaling when dimerization is required for Raf function, thus identifying the Raf dimer interface as a therapeutic target.
Assuntos
Sistema de Sinalização das MAP Quinases , Quinases raf/metabolismo , Substituição de Aminoácidos , Animais , Linhagem Celular , Ativação Enzimática , Fator de Crescimento Epidérmico/fisiologia , Humanos , Camundongos , Mutagênese Sítio-Dirigida , Mutação de Sentido Incorreto , Neoplasias/enzimologia , Fragmentos de Peptídeos/farmacologia , Fator de Crescimento Derivado de Plaquetas/fisiologia , Domínios e Motivos de Interação entre Proteínas , Inibidores de Proteínas Quinases/farmacologia , Multimerização Proteica , Quinases raf/antagonistas & inibidores , Quinases raf/química , Quinases raf/genética , Proteínas ras/metabolismoRESUMO
Kinase suppressor of Ras-1 (KSR-1) is an essential scaffolding protein that coordinates the assembly of the mitogen-activated protein kinase (MAPK) module, consisting of the MAPK kinase kinase Raf, the MAPK kinase MEK (mitogen-activated or extracellular signal-regulated protein kinase kinase), and the MAPK ERK (extracellular signal-regulated kinase) to facilitate activation of MEK and thus ERK. Although KSR-1 is targeted to the cell membrane in part by its atypical C1 domain, which binds to phospholipids, other domains may be involved. We identified another domain in KSR-1 that we termed CC-SAM, which is composed of a coiled coil (CC) and a sterile α motif (SAM). The CC-SAM domain targeted KSR-1 to specific signaling sites at the plasma membrane in growth factor-treated cells, and it bound directly to various micelles and bicelles in vitro, indicating that the CC-SAM functioned as a membrane-binding module. By combining nuclear magnetic resonance spectroscopy and experiments in cultured cells, we found that membrane binding was mediated by helix α3 of the CC motif and that mutating residues in α3 abolished targeting of KSR-1 to the plasma membrane. Thus, in addition to the atypical C1 domain, the CC-SAM domain is required to target KSR-1 to the plasma membrane.
Assuntos
Membrana Celular , Fosfolipídeos , Proteínas Quinases , Motivos de Aminoácidos , Substituição de Aminoácidos , Animais , Membrana Celular/química , Membrana Celular/genética , Membrana Celular/metabolismo , Células Cultivadas , Drosophila melanogaster , MAP Quinases Reguladas por Sinal Extracelular/química , MAP Quinases Reguladas por Sinal Extracelular/genética , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Humanos , Camundongos , Camundongos Knockout , Mutação de Sentido Incorreto , Ressonância Magnética Nuclear Biomolecular , Fosfolipídeos/química , Fosfolipídeos/genética , Fosfolipídeos/metabolismo , Ligação Proteica/fisiologia , Proteínas Quinases/química , Proteínas Quinases/genética , Proteínas Quinases/metabolismo , Estrutura Terciária de Proteína , Quinases raf/química , Quinases raf/genética , Quinases raf/metabolismoRESUMO
RAF kinase inhibitors can induce ERK cascade signaling by promoting dimerization of RAF family members in the presence of oncogenic or normally activated RAS. This interaction is mediated by a dimer interface region in the RAF kinase domain that is conserved in members of the ERK cascade scaffold family, kinase suppressor of RAS (KSR). In this study, we find that most RAF inhibitors also induce the binding of KSR1 to wild-type and oncogenic B-RAF proteins, including V600E B-RAF, but promote little complex formation between KSR1 and C-RAF. The inhibitor-induced KSR1/B-RAF interaction requires direct binding of the drug to B-RAF and is dependent on conserved dimer interface residues in each protein, but, unexpectedly, is not dependent on binding of B-RAF to activated RAS. Inhibitor-induced KSR/B-RAF complex formation can occur in the cytosol and is observed in normal mouse fibroblasts, as well as a variety of human cancer cell lines. Strikingly, we find that KSR1 competes with C-RAF for inhibitor-induced binding to B-RAF and, as a result, alters the effect of the inhibitors on ERK cascade signaling.
Assuntos
Sistema de Sinalização das MAP Quinases/efeitos dos fármacos , Inibidores de Proteínas Quinases/farmacologia , Proteínas Quinases/metabolismo , Proteínas Proto-Oncogênicas B-raf/metabolismo , Quinases raf/antagonistas & inibidores , Animais , Carcinoma Pulmonar de Células não Pequenas , Linhagem Celular Tumoral , Dimerização , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Humanos , Melanoma , Camundongos , Ligação Proteica , Inibidores de Proteínas Quinases/metabolismo , Proteínas Quinases/genética , Proteínas Proto-Oncogênicas B-raf/genética , Piridinas/metabolismo , Piridinas/farmacologia , Quinases raf/metabolismoRESUMO
Maintenance of genomic integrity is an essential cellular function. We previously reported that the transcription factor and tumor suppressor CCAAT/enhancer binding protein δ (C/EBPδ, CEBPD; also known as "NFIL-6ß") promotes genomic stability. However, the molecular mechanism was not known. Here, we show that C/EBPδ is a DNA damage-induced gene, which supports survival of mouse bone marrow cells, mouse embryo fibroblasts (MEF), human fibroblasts, and breast tumor cells in response to the DNA cross-linking agent mitomycin C (MMC). Using gene knockout, protein depletion, and overexpression studies, we found that C/EBPδ promotes monoubiquitination of the Fanconi anemia complementation group D2 protein (FANCD2), which is necessary for its function in replication-associated DNA repair. C/EBPδ interacts with FANCD2 and importin 4 (IPO4, also known as "Imp4" and "RanBP4") via separate domains, mediating FANCD2-IPO4 association and augmenting nuclear import of FANCD2, a prerequisite for its monoubiquitination. This study identifies a transcription-independent activity of C/EBPδ in the DNA damage response that may in part underlie its tumor suppressor function. Furthermore, we report a function of IPO4 and nuclear import in the Fanconi anemia pathway of DNA repair.
Assuntos
Proteína delta de Ligação ao Facilitador CCAAT/metabolismo , Dano ao DNA , Proteína do Grupo de Complementação D2 da Anemia de Fanconi/metabolismo , Carioferinas/metabolismo , Proteínas de Membrana Transportadoras/metabolismo , Transporte Ativo do Núcleo Celular , Animais , Proteína delta de Ligação ao Facilitador CCAAT/deficiência , Proteína delta de Ligação ao Facilitador CCAAT/genética , Linhagem Celular , Sobrevivência Celular , Humanos , Camundongos , Camundongos Knockout , Ligação Proteica , UbiquitinaçãoRESUMO
The B-Raf kinase is a Ras pathway effector activated by mutation in numerous human cancers and certain developmental disorders. Here we report that normal and oncogenic B-Raf proteins are subject to a regulatory cycle of extracellular signal-regulated kinase (ERK)-dependent feedback phosphorylation, followed by PP2A- and Pin1-dependent dephosphorylation/recycling. We identify four S/TP sites of B-Raf phosphorylated by activated ERK and find that feedback phosphorylation of B-Raf inhibits binding to activated Ras and disrupts heterodimerization with C-Raf, which is dependent on the B-Raf pS729/14-3-3 binding site. Moreover, we find that events influencing Raf heterodimerization can alter the transforming potential of oncogenic B-Raf proteins possessing intermediate or impaired kinase activity but have no significant effect on proteins with high kinase activity, such as V600E B-Raf. Mutation of the feedback sites or overexpression of the Pin1 prolyl-isomerase, which facilitates B-Raf dephosphorylation/recycling, resulted in increased transformation, whereas mutation of the S729/14-3-3 binding site or expression of dominant negative Pin1 reduced transformation. Mutation of each feedback site caused increased transformation and correlated with enhanced heterodimerization and activation of C-Raf. Finally, we find that B-Raf and C-Raf proteins containing mutations identified in certain developmental disorders constitutively heterodimerize and that their signaling activity can also be modulated by feedback phosphorylation.
Assuntos
MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Retroalimentação Fisiológica , Proteínas Proto-Oncogênicas B-raf/metabolismo , Proteínas Proto-Oncogênicas c-raf/metabolismo , Animais , Butadienos/farmacologia , Inibidores Enzimáticos/farmacologia , Humanos , MAP Quinase Quinase Quinases/antagonistas & inibidores , MAP Quinase Quinase Quinases/metabolismo , Camundongos , Mutação , Células NIH 3T3 , Peptidilprolil Isomerase de Interação com NIMA , Nitrilas/farmacologia , Peptidilprolil Isomerase/genética , Fosforilação , Fator de Crescimento Derivado de Plaquetas/farmacologia , Multimerização Proteica , Proteína Fosfatase 2/metabolismo , Proteínas Proto-Oncogênicas B-raf/genética , Proteínas Proto-Oncogênicas c-raf/genética , Transdução de SinaisRESUMO
Scaffold proteins contribute to the spatiotemporal control of MAPK signaling and KSR1 is an ERK cascade scaffold that localizes to the plasma membrane in response to growth factor treatment. To better understand the molecular mechanisms of KSR1 function, we examined the interaction of KSR1 with each of the ERK cascade components, Raf, MEK, and ERK. Here, we identify a hydrophobic motif within the proline-rich sequence (PRS) of MEK1 and MEK2 that is required for constitutive binding to KSR1 and find that MEK binding and residues in the KSR1 CA1 region enable KSR1 to form a ternary complex with B-Raf and MEK following growth factor treatment that enhances MEK activation. We also find that docking of active ERK to the KSR1 scaffold allows ERK to phosphorylate KSR1 and B-Raf on feedback S/TP sites. Strikingly, feedback phosphorylation of KSR1 and B-Raf promote their dissociation and result in the release of KSR1 from the plasma membrane. Together, these findings provide unique insight into the signaling dynamics of the KSR1 scaffold and reveal that through regulated interactions with Raf and ERK, KSR1 acts to both potentiate and attenuate ERK cascade activation, thus regulating the intensity and duration of ERK cascade signaling emanating from the plasma membrane during growth factor signaling.
Assuntos
Complexos Multiproteicos/metabolismo , Proteínas Quinases/metabolismo , Transdução de Sinais , Motivos de Aminoácidos , Sequência de Aminoácidos , Animais , Linhagem Celular , Ativação Enzimática , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Retroalimentação Fisiológica , Humanos , Camundongos , Quinases de Proteína Quinase Ativadas por Mitógeno/química , Quinases de Proteína Quinase Ativadas por Mitógeno/metabolismo , Dados de Sequência Molecular , Fosforilação , Domínios Proteicos Ricos em Prolina , Ligação Proteica , Proteínas Proto-Oncogênicas B-raf/metabolismoRESUMO
Protein scaffolds have emerged as important regulators of MAPK cascades, facilitating kinase activation and providing crucial spatio/temporal control to their signaling outputs. Using a proteomics approach to compare the binding partners of the two mammalian KSR scaffolds, we find that both KSR1 and KSR2 interact with the kinase components of the ERK cascade and have a common function in promoting RTK-mediated ERK signaling. Strikingly, we find that the protein phosphatase calcineurin selectively interacts with KSR2 and that KSR2 uniquely contributes to Ca2+-mediated ERK signaling. Calcineurin dephosphorylates KSR2 on specific sites in response to Ca2+ signals, thus regulating KSR2 localization and activity. Moreover, we find that depletion of endogenous KSR2 impairs Ca2+-mediated ERK activation and ERK-dependent signaling responses in INS1 pancreatic beta-cells and NG108 neuroblastoma cells. These findings identify KSR2 as a Ca2+-regulated ERK scaffold and reveal a new mechanism whereby Ca2+ impacts Ras to ERK pathway signaling.