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.
► Raf dimerization is required for normal Ras-dependent Raf activation ► Function of Raf mutants with all but high catalytic activity requires dimerization ► A dimerization inhibitor peptide blocks Raf signaling and induces apoptosis
Cancer often arises when normal cellular growth goes awry due to defects in critical signal transduction pathways. A growing number of inhibitors that target specific components of these pathways are ...in clinical use, but the success of these agents has been limited by the resistance to inhibitor therapy that ultimately develops. Studies have now shown that cancer cells respond to chronic drug treatment by adapting their signaling circuitry, taking advantage of pathway redundancy and routes of feedback and cross-talk to maintain their function. This review focuses on the compensatory signaling mechanisms highlighted by the use of targeted inhibitors in cancer therapy.
► Function and regulation of 14-3-3 binding interactions in RTK/Ras signaling. ► New regulators of 14-3-3 binding interactions in the Hippo pathway. ► 14-3-3 and cell migration: role in regulating ...the actin cytoskeleton. ► 14-3-3 and EMT: implications for cancer progression. ► 14-3-3 proteins: clinical significance in human cancer.
The 14-3-3 proteins were the first phosphoserine/phosphothreonine-binding proteins to be discovered, a finding that provided the foundation for their prominent role in cell signaling. 14-3-3 family members interact with a wide spectrum of proteins including transcription factors, biosynthetic enzymes, cytoskeletal proteins, signaling molecules, apoptosis factors, and tumor suppressors. The interaction with 14-3-3 can have a profound effect on a target protein, altering its localization, stability, conformation, phosphorylation state, activity, and/or molecular interactions. Thus, by modulating the function of a diverse array of binding partners, 14-3-3 proteins have become key regulatory components in many vital cellular processes – processes that are crucial for normal growth and development and that often become dysregulated in human cancer. This review will examine the recent advances that further elucidate the role of 14-3-3 proteins in normal growth and cancer signaling with a particular emphasis on the signaling pathways that impact cell proliferation, cell migration, and epithelial-to-mesenchymal transition.
RAF kinases are essential effectors of RAS, but how RAS binding initiates the conformational changes needed for autoinhibited RAF monomers to form active dimers has remained unclear. Here, we present ...cryo-electron microscopy structures of full-length BRAF complexes derived from mammalian cells: autoinhibited, monomeric BRAF:14-3-3
:MEK and BRAF:14-3-3
complexes, and an inhibitor-bound, dimeric BRAF
:14-3-3
complex, at 3.7, 4.1, and 3.9 Å resolution, respectively. In both autoinhibited, monomeric structures, the RAS binding domain (RBD) of BRAF is resolved, revealing that the RBD forms an extensive contact interface with the 14-3-3 protomer bound to the BRAF C-terminal site and that key basic residues required for RBD-RAS binding are exposed. Moreover, through structure-guided mutational studies, our findings indicate that RAS-RAF binding is a dynamic process and that RBD residues at the center of the RBD:14-3-3 interface have a dual function, first contributing to RAF autoinhibition and then to the full spectrum of RAS-RBD interactions.
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.
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•C-Raf binds all Ras proteins equivalently, but B-Raf exhibits selectivity for K-Ras•Raf N-terminal segments and Ras HVR sequences determine binding preferences•C-Raf is critical for downstream transmission of H-Ras-driven signaling•Events that increase B-Raf/C-Raf dimerization augment the B-Raf/H-Ras interaction
The Raf kinases bind to active Ras proteins and function to transmit signals that control cell growth and tumorigenesis. The study by Terrell et al. reveals distinct binding preferences between individual Ras and Raf family members and identifies events that can alter these interactions to upregulate Ras-driven cancer signaling.
The highly conserved 14-3-3 protein family has risen to a position of importance in cell biology owing to its involvement in vital cellular processes, such as metabolism, protein trafficking, signal ...transduction, apoptosis and cell-cycle regulation. The 14-3-3 proteins are phospho-serine/phospho-threonine binding proteins that interact with a diverse array of binding partners. Because many 14-3-3 interactions are phosphorylation-dependent, 14-3-3 has been tightly integrated into the core phospho-regulatory pathways that are crucial for normal growth and development and that often become dysregulated in human disease states such as cancer. This review examines the recent advances that further elucidate the role of 14-3-3 proteins as integrators of diverse signaling cues that influence cell fate decisions and tumorigenesis.
MAP kinase pathways Morrison, Deborah K
Cold Spring Harbor perspectives in biology,
2012-Nov-01, 2012-11-01, 20121101, Letnik:
4, Številka:
11
Journal Article
Recenzirano
Odprti dostop
MAP kinases are activated within protein kinase cascades that regulate cell proliferation, differentiation, and death. In mammals, MAP kinases are grouped into three families: ERKs, JNKs, and ...p38/SAPKs.
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.
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•Route for the phospho-inhibition of Ras pathway signaling mediated by JNK cascade•Stress-induced S/TP phosphorylation inhibits the function of Sos1 and the Rafs•S/TP phospho-regulatory circuit may act as a stress-induced signaling checkpoint•S/TP circuit engaged by cancer drugs that activate JNK via mitotic/oxidative stress
The Ras pathway is an important cellular signal transduction pathway frequently activated in human cancer. Ritt et al. identify a route for the phospho-inhibition of key Ras pathway components, Sos1 and the Rafs, that is mediated by JNK cascade activation and may function as a stress-induced signaling checkpoint.
The mitogen-activated protein kinase (MAPK) group of serine/threonine
protein kinases mediates the response of cells to many extracellular stimuli
such as cytokines and growth factors. These protein ...kinases include the
extracellular signal-regulated protein kinases (ERK) and two stress-activated
protein kinases (SAPK), the c-Jun N-terminal kinases (JNK), and the p38 MAPK.
The enzymes are evolutionarily conserved and are activated by a common
mechanism that involves a protein kinase cascade. Scaffold proteins have been
proposed to interact with MAPK pathway components to create a functional
signaling module and to control the specificity of signal transduction. Here we
critically evaluate the evidence that supports a physiologically relevant role
of MAPK scaffold proteins in mammals.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
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