Raf-1 is a potential substrate for mitogen-activated protein kinase in vivo.
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ABSTRACT:
SUBMITTER: Anderson NG
PROVIDER: S-EPMC1151274 | biostudies-other | 1991 Jul
REPOSITORIES: biostudies-other
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Project description:Kinases are pivotal regulators of cellular physiology. The human genome contains more than 500 putative kinases, which exert their action via the phosphorylation of specific substrates. The determinants of this specificity are still only partly understood and as a consequence it is difficult to predict kinase substrate preferences from the primary structure, hampering the understanding of kinase function in physiology and prompting the development of technologies that allow easy assessment of kinase substrate consensus sequences. Hence, we decided to explore the usefulness of phosphorylation of peptide arrays comprising of 1176 different peptide substrates with recombinant kinases for determining kinase substrate preferences, based on the contribution of individual amino acids to total array phosphorylation. Employing this technology, we were able to determine the consensus peptide sequences for substrates of both c-Raf and Mitogen Activated Protein Kinase Kinase Kinase 8, two highly homologous kinases with distinct signalling roles in cellular physiology. The results show that although consensus sequences for these two kinases identified through our analysis share important chemical similarities, there is still some sequence specificity that could explain the different biological action of the two enzymes. Thus peptide arrays are a useful instrument for deducing substrate consensus sequences and highly homologous kinases can differ in their requirement for phosphorylation events.
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Project description:The kinase p38? MAPK (p38?) plays a pivotal role in many biological processes. p38? is activated by canonical upstream kinases that phosphorylate the activation region. The purpose of our study was to determine whether such activation may depend on redox-sensing cysteines within p38?. p38? was activated and formed a disulfide-bound heterodimer with MAP2K3 (MKK3) in rat cardiomyocytes and isolated hearts exposed to H2O2 This disulfide heterodimer was sensitive to reduction by mercaptoethanol and was enhanced by the thioredoxin-reductase inhibitor auranofin. We predicted that Cys-119 or Cys-162 of p38?, close to the known MKK3 docking domain, were relevant for these redox characteristics. The C119S mutation decreased whereas the C162S mutation increased the dimer formation, suggesting that these two Cys residues act as vicinal thiols, consistent with C119S/C162S being incapable of sensing H2O2 Similarly, disulfide heterodimer formation was abolished in H9C2 cells expressing both MKK3 and p38? C119S/C162S and subjected to simulated ischemia and reperfusion. However, the p38? C119S/C162S mutants did not exhibit appreciable alteration in activating dual phosphorylation. In contrast, the anti-inflammatory agent 10-nitro-oleic acid (NO2-OA), a component of the Mediterranean diet, reduced p38? activation and covalently modified Cys-119/Cys-162, probably obstructing MKK3 access. Moreover, NO2-OA reduced the dephosphorylation of p38? by hematopoietic tyrosine phosphatase (HePTP). Furthermore, steric obstruction of Cys-119/Cys-162 by NO2-OA pretreatment in Langendorff-perfused murine hearts prevented the p38-MKK3 disulfide dimer formation and attenuated H2O2-induced contractile dysfunction. Our findings suggest that cysteine residues within p38? act as redox sensors that can dynamically regulate the association between p38 and MKK3.
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Project description:Aldosterone in some tissues increases expression of the mRNA encoding the small monomeric G protein Ki-RasA. Renal A6 epithelial cells were used to determine whether induction of Ki-ras leads to concomitant increases in the total as well as active levels of Ki-RasA and whether this then leads to subsequent activation of its effector mitogen-activated protein kinase (MAPK/extracellular signal-regulated kinase) cascade. The molecular basis and cellular consequences of this action were specifically investigated. We identified the intron 1-exon 1 region (rasI/E1) of the mouse Ki-ras gene as sufficient to reconstitute aldosterone responsiveness to a heterologous promotor. Aldosterone increased reporter gene activity containing rasI/E1 threefold. Aldosterone increased the absolute and GTP-bound levels of Ki-RasA by a similar extent, suggesting that activation resulted from mass action and not effects on GTP binding/hydrolysis rates. Aldosterone significantly increased Ki-RasA and MAPK activity as early as 15 min with activation peaking by 2 h and waning after 4 h. Inhibitors of transcription, translation, and a glucocorticoid receptor antagonist attenuated MAPK signaling. Similarly, rasI/E1-driven luciferase expression was sensitive to glucocorticoid receptor blockade. Overexpression of dominant-negative RasN17, addition of antisense Ki-rasA and inhibition of mitogen-activated protein kinase kinase also attenuated steroid-dependent increases in MAPK signaling. Thus, activation of MAPK by aldosterone is dependent, in part, on a genomic mechanism involving induction of Ki-ras transcription and subsequent activation of its downstream effectors. This genomic mechanism has a distinct time course from activation by traditional mitogens, such as serum, which affect the GTP-binding state and not absolute levels of Ras. The result of such a genomic mechanism is that peak activation of the MAPK cascade by adrenal corticosteroids is delayed but prolonged.
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Project description:The substrate specificity of mitogen-activated protein (MAP) kinase-activated protein kinase-2 (MAPKAP kinase-2) was investigated by using synthetic peptides related to the N-terminus of glycogen synthase. The minimum sequence required for efficient phosphorylation was found to be Xaa-Xaa-Hyd-Xaa-Arg-Xaa-Xaa-Ser-Xaa-Xaa, where Hyd is a bulky hydrophobic residue (Phe > Leu > Val >> Ala), and the peptide Lys-Lys-Phe-Asn-Arg-Thr-Leu-Ser-Val-Ala was phosphorylated with a Km of 9.3 microM and Vmax. of 10 mumol/min per mg. MAPKAP kinase-1 (a homologue of ribosomal protein S6 kinase) also requires an arginine three residues N-terminal to the serine (position n-3), but not a hydrophobic residue at position n-5. Neither MAPKAP kinase-1 nor MAPKAP kinase-2 could tolerate a proline residue at position n + 1, indicating that their specificities do not overlap with that of MAP kinase. The specificity of calmodulin-dependent protein kinase-II resembled that of MAPKAP kinase-2, except that it could tolerate replacement of the arginine by a lysine and the phosphorylation-site serine by a threonine residue. Partial cDNAs encoding MAPKAP kinase-2 were isolated from rabbit and human skeletal muscle and human teratocarcinoma libraries, and Northern-blotting experiments revealed a single 3.3 kb mRNA transcript present at similar levels in six human tissues examined. The catalytic domain was most similar (35-40% identity) to calmodulin-dependent protein kinases II and IV, phosphorylase kinase, putative serine kinase H1 and the C-terminal domain of MAPKAP kinase-1, which form one branch of the protein kinase phylogenetic tree. The sequence N-terminal to the catalytic domain is proline-rich and contains two putative SH3-binding sites. The threonine residue phosphorylated by MAP kinase lies immediately C-terminal to the catalytic domain and is followed by a nuclear localization signal, Lys-Lys-(Xaa)10-Lys-Arg-Arg-Lys-Lys, near the C-terminus.
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Project description:Adventitial fibroblasts (AFs) are key determinants of arterial function and critical mediators of arterial disease progression. The effects of altered stiffness, particularly those observed across individuals during normal vascular function, and the mechanisms by which AFs respond to altered stiffness, are not well understood. To study the effects of matrix stiffness on AF phenotype, cytokine production, and the regulatory pathways utilized to interpret basic cell-matrix interactions, human aortic AFs were grown in 5%, 7.5%, and 10% (w/v%) PEG-based hydrogels with Young's moduli of 1.2, 3.3, and 9.6 kPa, respectively. In 5% gels, AFs had higher proliferation rates, elevated monocyte chemoattractant protein-1 secretion, and enhanced monocyte recruitment. Significantly more AFs were ?-smooth muscle actin positive in 7.5% gels, indicating myofibroblast development. AFs in 10% gels had low proliferation rates but produced high levels of interleukin-6 and vascular endothelial growth factor-A. Importantly, these modulus-dependent changes in AF phenotype were accompanied by alterations in the mitogen-activated protein kinase (MAPK) pathways contributing to the production of cytokines. These data indicate that complex cell regulatory changes occur with altered tissue stiffness and suggest that therapeutics affecting MAPK pathways may have altered effects on AFs depending on substrate stiffness.
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Project description:Mitogen-activated protein kinase (MPK) cascades are important to cellular signaling in eukaryotes. They regulate growth, development and the response to environmental challenges. MPK cascades function via reversible phosphorylation of cascade components, MEKK, MEK, and MPK, but also by MPK substrate phosphorylation. Using mass spectrometry, we previously identified many in vivo MPK3 and MPK6 substrates in Arabidopsis thaliana, and we disclosed their phosphorylation sites.We verified phosphorylation of several of our previously identified MPK3/6 substrates using a nonradioactive in vitro labeling assay. We engineered MPK3, MPK4, and MPK6 to accept bio-orthogonal ATP?S analogs for thiophosphorylating their appropriate substrate proteins. Subsequent alkylation of the thiophosphorylated amino acid residue(s) allows immunodetection using thiophosphate ester-specific antibodies. Site-directed mutagenesis of amino acids confirmed the protein substrates' site-specific phosphorylation by MPK3 and MPK6. A combined assay with MPK3, MPK6, and MPK4 revealed substrate specificity of the individual kinases.Our work demonstrates that the in vitro-labeling assay represents an effective, specific and highly sensitive test for determining kinase-substrate relationships.
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Project description:An improved understanding of pathogenic pathways in AKI may identify novel therapeutic approaches. Previously, we conducted unbiased liquid chromatography-tandem mass spectrometry-based protein expression profiling of the renal proteome in mice with acute folate nephropathy. Here, analysis of the dataset identified enrichment of pathways involving NFκB in the kidney cortex, and a targeted data mining approach identified components of the noncanonical NFκB pathway, including the upstream kinase mitogen-activated protein kinase kinase kinase 14 (MAP3K14), the NFκB DNA binding heterodimer RelB/NFκB2, and proteins involved in NFκB2 p100 ubiquitination and proteasomal processing to p52, as upregulated. Immunohistochemistry localized MAP3K14 expression to tubular cells in acute folate nephropathy and human AKI. In vivo, kidney expression levels of NFκB2 p100 and p52 increased rapidly after folic acid injection, as did DNA binding of RelB and NFκB2, detected in nuclei isolated from the kidneys. Compared with wild-type mice, MAP3K14 activity-deficient aly/aly (MAP3K14aly/aly) mice had less kidney dysfunction, inflammation, and apoptosis in acute folate nephropathy and less kidney dysfunction and a lower mortality rate in cisplatin-induced AKI. The exchange of bone marrow between wild-type and MAP3K14aly/aly mice did not affect the survival rate of either group after folic acid injection. In cultured tubular cells, MAP3K14 small interfering RNA targeting decreased inflammation and cell death. Additionally, cell culture and in vivo studies identified the chemokines MCP-1, RANTES, and CXCL10 as MAP3K14 targets in tubular cells. In conclusion, MAP3K14 promotes kidney injury through promotion of inflammation and cell death and is a promising novel therapeutic target.
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