MAP kinases--ubiquitous signal transducers and potentially important components of the cell cycling machinery in eukaryotes

Molecular interaction study of N1-p-fluorobenzyl-cymserine with TNF-α , p38 kinase and JNK kinase

Alzheimer's disease (AD) is an age-related neurodegenerative disease distinguished by progressive memory loss and cognitive decline. It is accompanied by classical neuropathological changes, including cerebral deposits of amyloid- beta peptide (Aβ) containing senile plaques, neurofibrillary tangles (NFTs) of phosphorylated tau (p-tau), and clusters of activated glial cells. Postmortem studies strongly support a critical role for neuroinflammation in the pathogenesis of AD, with activated microglia and reactive astrocytes surrounding senile plaques and NFTs. These are accompanied by an elevated expression of inflammatory mediators that further drives Aβ and p-tau generation. Although epidemiological and experimental studies suggested that long-term use of non-steroidal anti-inflammatory drugs (NSAIDs) may lessen AD risk by mitigating inflammatory responses, primary NSAID treatment trials of AD have not proved successful. Elevated systemic butyrylcholinesterase (BuChE) levels have been considered a marker of low-grade systemic inflammation, and BuChE levels are reported elevated in AD brain. Recent research indicates that selective brain inhibition of BuChE elevates acetylcholine (ACh) and augments cognition in rodents free of the characteristic undesirable actions of acetylcholinesterase- inhibitors (AChE-Is). Hence, centrally active BuChE-selective-inhibitors, cymserine analogs, have been developed to test the hypothesis that BuChE-Is would be efficacious and better tolerated than AChE-Is in AD. The focus of the current study was to undertake an in-silico evaluation of an agent to assess its potential to halt the self-propagating interaction between inflammation,Aβ and p-tau generation. Molecular docking studies were performed between the novel BuChE-I, N1-p-fluorobenzyl-cymserine (FBC) and inflammatory targets to evaluate the potential of FBC as an inhibitor of p38, JNK kinases and TNF-α with respect to putative binding free energy and IC50 values. Our in-silico studies support the ability of FBC to bind these targets in a manner supportive of anti-inflammatory action that is subject to molecular dynamics and physiochemical studies for auxiliary confirmation.

RGD- and MLD-disintegrins, jarastatin and EC3, activate integrin-mediated signaling modulating the human neutrophils chemotaxis, apoptosis and IL-8 gene expression

The effects of jarastatin (JT), a monomeric RGD-disintegrin, were compared with those of the heterodimeric MLD-disintegrin, EC3, on human neutrophil activation and functions. Both disintegrins inhibited neutrophil chemotaxis induced by fMet-Leu-Phe and were also potent chemotactic agents. These effects were accompanied by an increase in actin polymerization, and both were inhibited by genistein, a tyrosine kinase inhibitor. While JT, but not other RGD-disintegrins, inhibited EC3-induced chemotaxis, EC3 was not able to inhibit JT effect. The chemotactic effect of JT was blocked by anti-alpha(M) antibody whereas anti-alpha(9)beta(1) inhibited EC3 effect. Both JT and EC3 induced focal adhesion kinase (FAK) and phosphoinositide 3-kinase (PI3K) activation. Accordingly, LY294002, a PI3K inhibitor, impaired their chemotactic effect on neutrophils. JT induced Erk-2 translocation to nucleus and a delay of the spontaneous apoptosis of neutrophils in vitro. In contrast, EC3 inhibited Erk-2 activation and had a proapoptotic effect. These effects were reverted by PD98059, an MEK 1/2 inhibitor and blocked by z-VAD-FMK, a caspase inhibitor. In addition, JT, but not EC3, increased the IL-8 mRNA levels in neutrophils. The data indicate that JT and EC3 directly activate an integrin-coupled signaling and modulate the MAPK pathway in different ways, leading the neutrophils to express different functional response.

The effect of humic acid on the adhesibility of neutrophils

Humic acid (HA), a fluorescent allomelanin, has been implicated as an etiological agent of Blackfoot disease (BFD), a peripheral vascular disease prevailing in the southwest of Taiwan. Clinical and pathological studies reveal that it is similar to atherosclerosis. In this report, the effect of HA on human neutrophils is studied because prolonged and enhanced activation of neutrophils adhered on endothelium may damage the endothelium and initiate the process of thrombosis and vasculitis.

METHODS

Neutrophils, treated with various concentrations of HA, were added to culture plates, cultured human umbilical vein endothelial cells (HUVECs), or human umbilical vein endothelium tissue culture for 15 or 30 min. The adhesion of neutrophils was measured qualitatively and quantitatively. The mechanism of neutrophil activation was studied with free radical production and various kinase measurements and their activities' assays.

RESULTS

HA was shown to enhance, in a dose-dependent manner, the adhesion of neutrophils on the culture plates, cultured human umbilical vein endothelial cells, and human umbilical vein endothelium tissue culture. The adhesion-enhancing ability of HA is elicited through activation of ERK, P38 mitogen-activated kinase (P38MAPK), and phosphoinositide 3 kinase (PI3K) in neutrophils. HA also induces the NF-kappaB activation in neutrophils.

CONCLUSION

HA treatment markedly enhanced adhesion and superoxide radical production of neutrophils, the characteristics of activated neutrophils; and all these stimulation effects were blocked by several kinase inhibitors, reflecting the involvement of the ERK, P38MAPK, and PI3K on the activation of neutrophils. The induction of NF-kappaB implied that the consequence of neutrophil activation by HA were similar to other stimulants. The prolonged neutrophil activation will further damage endothelium cell and cause thrombosis, vaculitis, as well as arteriosclerosis. This may partially explain why HA consumption will cause BFD.

p38 Mitogen-Activated Protein Kinase Activation Is Required for Human Neutrophil Function Triggered by TNF-α or FMLP Stimulation

Mitogen-activated protein (MAP) kinase-mediated signal-transduction pathways convert extracellular stimulation into a variety of cellular functions. However, the roles of MAP kinases in neutrophils are not well understood yet. Protein phosphorylation analysis of cellular MAP kinases indicates that exposure of human neutrophils to chemotactic factor FMLP as well as granulocyte-macrophage CSF, PMA, or ionomycin rapidly induced the activation of p38 and p44/42 MAP kinases, but stimulation with inflammatory cytokine TNF-α triggered the activation of p38 MAP kinase only. To study the cellular functions of these MAP kinases, the inhibitor SB20358, which specifically inhibited enzymatic activity of cellular p38 MAP kinase, and the inhibitor PD98059, which specifically blocked the induced protein phosphorylation and activation of p44/42 MAP kinase in intact neutrophils, were utilized. Inhibition of the cellular p38 MAP kinase activation almost completely abolished the TNF-α-stimulated IL-8 production and superoxide generation of human neutrophils. In addition, the FMLP-induced neutrophil chemotaxis as well as superoxide generation were suppressed markedly by inhibiting the activation of cellular p38 MAP kinase, but not p44/42 MAP kinase. Moreover, RIA indicates that the activation of cellular p38 MAP kinase was required for the neutrophil IL-8 production stimulated by granulocyte-macrophage CSF or LPS as well as TNF-α, but not for that induced by PMA or ionomycin. These results demonstrate that the activation of cellular p38 MAP kinase is indispensable for the TNF-α- or FMLP-mediated cellular functions in human neutrophils, and suggest that p38 MAP kinase may play a different role in response to distinct stimulation.

Phosphorylation of microtubule-associated proteins from the ovaries of hemipteran insects by MPF and MAP kinase: possible roles in the regulation of microtubules during oogenesis

Nutritive tubes that link the developing oocytes to the nurse cells in ovarioles of hemipteran insects contain extensive arrays of microtubules. These are established, then later depolymerised, by developmentally regulated processes. Breakdown of the microtubules corresponds with the activation of M-phase promoting factor (MPF) and mitogen-activated protein kinase (MAP kinase), later in oogenesis, as the oocytes proceed to arrest at the first meiotic metaphase [Lane and Stebbings, Roux's Arch Dev Biol 205:150-159 (1995)]. The mechanisms that lead to the breakdown of nutritive tube microtubules are unknown. Here, we have investigated the possibility that the insect ovarian microtubules are regulated by MPF- or MAP kinase-dependent phosphorylation, focusing upon the prominent high molecular weight microtubule-associated protein (HMW MAP) enriched in this system, which is a potential target for protein kinase activity in vivo. We have purified the prominent HMW MAPs from the ovaries of two species of hemipterans, and have shown them to be substrates in vitro for the activities of MPF and MAP kinase. However, although the catalytic component of MPF (p34cdc2) is present within microtubule-rich portions of hemipteran ovarioles, we have found that neither this protein nor its regulatory partner (cyclin B) co-purify with microtubules during taxol-mediated microtubule isolation.

Inhibition of insulin- and insulin-like growth factor-I-stimulated growth of human breast cancer cells by 1,25-dihydroxyvitamin D3 and the vitamin D3 analogue EB1089

1,25 Dihydroxyvitamin D3 (1,25-(OH)2D3) and a number of synthetic vitamin D3 analogues with low calcaemic activity, have been shown to inhibit breast cancer cell growth in vitro as well as in vivo. The purpose of the present study was to investigate a possible interaction of 1,25-(OH)2D3 and the vitamin D3 analogue EB1089 with the insulin-IGF-I regulatory system. The oestrogen receptor-positive MCF-7 human breast cancer cells used in this study are able to grow autonomously and their growth is stimulated by insulin. In order to avoid interference of IGF-binding proteins (IGF-BPs), we used an analogue of IGF-I, long R3 IGF-I, which stimulated MCF-7 cell growth similar to insulin. The growth stimulation by insulin and by long R3 IGF-I was completely inhibited by 1,25-(OH)2D3 and EB1089. Autonomous growth was also inhibited by 1,25-(OH)2D3 and EB1089. The analogue EB1089 was active at 50 times lower concentrations than 1,25-(OH)2D3. It was shown that growth inhibition was not achieved through downregulation of insulin and IGF-I binding after 48 h. Paradoxically, after prolonged treatment (8 days), an upregulation of insulin and IGF-I binding was observed. Two possible intracellular mediators of the insulin-IGF mitogenic signal are C-FOS and mitogen-activated protein (MAP) kinase. Insulin-induced C-FOS mRNA was inhibited by 1,25-(OH)2D3, suggesting that it could be involved in the growth inhibition by 1,25-(OH)2D3. MAP kinase activation appeared not to be involved in growth stimulation by both insulin and IGF-I. Together, the present study demonstrates that vitamin D3 compounds can block the mitogenic activity of insulin and IGF-I, which may contribute to their tumour suppressive activity observed in vivo.

Effects of endothelin on mitogen-activated protein kinase activity and protein synthesis in isolated adult feline cardiac myocytes

The growth-promoting effects of endothelin-1 (ET-1) were examined in adult heart cells. The activity of mitogen-activated protein kinases (MAPKs) was measured in cytosolic extracts of isolated adult feline cardiac myocytes incubated with and without ET-1. Kinase activity was assessed by phosphorylation of the exogenous substrate, myelin basic protein. ET-1 stimulated the activity of MAPK up to 4-fold, with peak activation occurring between five and ten minutes after addition of ET-1. Polyclonal antisera raised against a 14-amino acid sequence of the erk-2 gene product, a MAPK isoform, identified two major bands in cytosolic extracts of the cardiac myocytes. Partial purification of kinase activities using Mono Q anion-exchange chromatography demonstrated two major peaks of myelin basic protein kinase activity. Subsequent immunoblots of the eluted fractions demonstrated that the immunoreactive bands observed in the cytosolic extracts eluted in those fractions possessing kinase activity. Overnight pretreatment of the cardiac myocytes with 100 ng/ml pertussis toxin inhibited the ET-1 stimulated increase in MAPK activity by 50 - 70%, but did not alter stimulation by 100 nM phorbol 12-myristate 13-acetate (PMA). These data suggest that stimulation of MAPK by ET-1 may be mediated by more than one pathway. MAPK has been shown to be activated in the intracellular transmission of growth factor signals. Indicative of a growth effect in this adult heart cell model, myocytes exposed to increasing concentrations of ET-1 demonstrated a dose dependent increase in [3H]-phenylalanine incorporation into cellular protein. This response was blocked by staurosporine and partially inhibited by pretreatment with pertussis toxin, again suggesting the possible involvement of multiple early signals. These data from isolated adult cardiac myocytes further support the hypothesis that ET-1 has a role in the regulation of cardiac growth.

Neurotropic factors, retrograde axonal transport and cell signalling

In vitro studies have recently identified receptors and signal transduction systems for many neurotrophic factors. In vivo, however, target-derived factors act over distances that are too great to be accounted for by simple diffusion of factors or classical second messengers. The active translocation of neurotrophic factors from the axon to the cell body by receptor-mediated retrograde transport provides a means by which factors presented at distal sites may influence somal signal transduction. We hypothesize that retrograde transport of receptors and other receptor-associated proteins leads to signalling at the cell body.

Molecular cloning and tissue distribution of PHAS-I, an intracellular target for insulin and growth factors

Although the actions of insulin and a number of growth factors that signal via protein-tyrosine kinase receptors are believed to involve increased phosphorylation of key intracellular proteins, relatively few of the downstream phosphoproteins have been identified. In this report we describe a cDNA encoding one of the most prominent insulin-stimulated phosphoproteins in rat adipocytes. The cDNA encodes a protein, designated PHAS-I, which has 117 amino acids and a M(r) of 12,400. When translated in vitro and subjected to SDS/PAGE, PHAS-I migrates anomalously, having an apparent M(r) of 21,000. The predicted amino acid composition is interesting in that approximately 45% of the PHAS-I protein is accounted for by only four amino acids--serine, threonine, proline, and glycine. The PHAS-I gene is expressed in a variety of tissues, although the highest levels of mRNA are present in fat and skeletal muscle, two of the most insulin-responsive tissues. The nucleotide and deduced amino acid sequences of PHAS-I differ from any that have been reported, and homology screening provided no clues concerning the function of the protein. However, in view of its tissue distribution and the fact that the protein is phosphorylated in response to insulin, we speculate that PHAS-I is important in insulin action.

Identification of the functional components of the Ras signaling pathway regulating pituitary cell-specific gene expression

Ras, a small GTP-binding protein, is required for functional receptor tyrosine kinase signaling. Ultimately, Ras alters the activity of specific nuclear transcription factors and regulates novel patterns of gene expression. Using a rat prolactin promoter construct in transient transfection experiments, we show that both oncogenic Ras and activated forms of Raf-1 kinase selectively stimulated the cellular rat prolactin promoter in GH4 rat pituitary cells. We also show that the Ras signal is completely blocked by an expression vector encoding a dominant-negative Raf kinase. Additionally, using a molecular genetic approach, we determined that inhibitory forms of p42 mitogen-activated protein kinase and an Ets-2 transcription factor interfere with both the Ras and the Raf activation of the rat prolactin promoter. These findings define a functional requirement for these signaling constituents in the activation of the prolactin gene, a cell-specific gene which marks the lactotroph pituitary cell type. Further, this analysis allowed us to order the components in the Ras signaling pathway as it impinges on regulation of prolactin gene transcription as Ras-->Raf kinase-->mitogen-activated protein kinase-->Ets. In contrast, we show that intact c-Jun expression inhibited the Ras-induced activation of the prolactin promoter, defining it as a negative regulator of this pathway, whereas c-Jun was able to enhance the Ras activation of an AP-1-driven promoter in GH4 cells. These data show that c-Jun is not the nuclear mediator of the Ras signal for the highly specialized, pituitary cell-specific prolactin cellular promoter. Thus, we have defined a model system which provides an ideal paradigm for studying Ras/Raf signaling pathways and their effects on neuroendocrine cell-specific gene regulation.

Identification of the functional components of the Ras signaling pathway regulating pituitary cell-specific gene expression

Ras, a small GTP-binding protein, is required for functional receptor tyrosine kinase signaling. Ultimately, Ras alters the activity of specific nuclear transcription factors and regulates novel patterns of gene expression. Using a rat prolactin promoter construct in transient transfection experiments, we show that both oncogenic Ras and activated forms of Raf-1 kinase selectively stimulated the cellular rat prolactin promoter in GH4 rat pituitary cells. We also show that the Ras signal is completely blocked by an expression vector encoding a dominant-negative Raf kinase. Additionally, using a molecular genetic approach, we determined that inhibitory forms of p42 mitogen-activated protein kinase and an Ets-2 transcription factor interfere with both the Ras and the Raf activation of the rat prolactin promoter. These findings define a functional requirement for these signaling constituents in the activation of the prolactin gene, a cell-specific gene which marks the lactotroph pituitary cell type. Further, this analysis allowed us to order the components in the Ras signaling pathway as it impinges on regulation of prolactin gene transcription as Ras-->Raf kinase-->mitogen-activated protein kinase-->Ets. In contrast, we show that intact c-Jun expression inhibited the Ras-induced activation of the prolactin promoter, defining it as a negative regulator of this pathway, whereas c-Jun was able to enhance the Ras activation of an AP-1-driven promoter in GH4 cells. These data show that c-Jun is not the nuclear mediator of the Ras signal for the highly specialized, pituitary cell-specific prolactin cellular promoter. Thus, we have defined a model system which provides an ideal paradigm for studying Ras/Raf signaling pathways and their effects on neuroendocrine cell-specific gene regulation.

Rapid activation of the MAP kinase pathway in hematopoietic cells by erythropoietin, granulocyte-macrophage colony-stimulating factor and interleukin-3

MAP kinases are a family of serine/threonine specific protein kinases becoming activated in response to different proliferative stimuli by phosphorylation at both threonine and tyrosine residues. We report the involvement of MAP kinases in the signal transduction of the hematopoietic growth factors erythropoietin (EPO), granulocyte macrophage colony-stimulating factor (GM-CSF) and interleukin-3 (IL-3) in the factor dependent human erythroleukemic cell line TF-1, suggesting a crucial role of these enzymes in the regulation of proliferation of hematopoietic cells. Both time course and degree of MAP kinase activation were similar for all three cytokines. A slightly lower stimulation effect of EPO corresponds to the observation that EPO stimulated cells proliferate at a lower rate.

An epidermal growth factor receptor/ret chimera generates mitogenic and transforming signals: evidence for a ret-specific signaling pathway

A chimeric expression vector which encoded for a molecule encompassing the extracellular domain of the epidermal growth factor (EGF) receptor (EGFR) and the intracellular domain of the ret kinase (EGFR/ret chimera) was generated. Upon ectopic expression in mammalian cells, the EGFR/ret chimera was correctly synthesized and transported to the cell surface, where it was shown capable of binding EGF and transducing an EGF-dependent signal intracellularly. Thus, the EGFR/ret chimera allows us to study the biological effects and biochemical activities of the ret kinase under controlled conditions of activation. Comparative analysis of the growth-promoting activity of the EGFR/ret chimera expressed in fibroblastic or hematopoietic cells revealed a biological phenotype clearly distinguishable from that of the EGFR, indicating that the two kinases couple with mitogenic pathways which are different to some extent. Analysis of biochemical pathways implicated in the transduction of mitogenic signals also evidenced significant differences between the ret kinase and other receptor tyrosine kinases. Thus, the sum of our results indicates the existence of a ret-specific pathway of mitogenic signaling.

An epidermal growth factor receptor/ret chimera generates mitogenic and transforming signals: evidence for a ret-specific signaling pathway

A chimeric expression vector which encoded for a molecule encompassing the extracellular domain of the epidermal growth factor (EGF) receptor (EGFR) and the intracellular domain of the ret kinase (EGFR/ret chimera) was generated. Upon ectopic expression in mammalian cells, the EGFR/ret chimera was correctly synthesized and transported to the cell surface, where it was shown capable of binding EGF and transducing an EGF-dependent signal intracellularly. Thus, the EGFR/ret chimera allows us to study the biological effects and biochemical activities of the ret kinase under controlled conditions of activation. Comparative analysis of the growth-promoting activity of the EGFR/ret chimera expressed in fibroblastic or hematopoietic cells revealed a biological phenotype clearly distinguishable from that of the EGFR, indicating that the two kinases couple with mitogenic pathways which are different to some extent. Analysis of biochemical pathways implicated in the transduction of mitogenic signals also evidenced significant differences between the ret kinase and other receptor tyrosine kinases. Thus, the sum of our results indicates the existence of a ret-specific pathway of mitogenic signaling.

Networking with mitogen-activated protein kinases

Mitogen activated protein (MAP) kinases and their target ribosomal protein S6 (RSK) kinases have been recognized as shared components in the intracellular signaling pathways of many diverse cytokines. Recent studies have extended this protein kinase cascade by identifying the major activator of vertebrate MAP kinases as a serine/threonine/tyrosine-protein kinase called MEK, which is related to yeast mating factor-regulated protein kinases encoded by the STE7 and byr1 genes. MEK, in turn, may be activated following its phosphorylation on serine by either of the kinases encoded by proto-oncogenes raf1 or mos, as well as by p78mekk, which is related to the yeast STE11 and byr2 gene products. Isoforms of all of these protein kinases may specifically combine to assemble distinct modules for intracellular signal transmission. However, the fundamental architecture of these protein kinase cascades has been highly conserved during eukaryotic evolution.

Molecular cloning, expression, and characterization of the human mitogen-activated protein kinase p44erk1

p44erk1 is a member of a family of tyrosyl-phosphorylated and mitogen-activated protein (MAP) kinases that participate in cell cycle control. A full-length erk1 cDNA was isolated from a human hepatoma cell line (Hep G2) library. The erk1 cDNA clone shared approximately 96% predicted amino acid identity with partial sequences of rodent erk1 cognates, and the erk1 gene was assigned to human chromosome 16 by hybrid panel analysis. Human erk1 expressed in Escherichia coli as a glutathione S-transferase fusion (GST-Erk1) protein was substantially phosphorylated on tyrosine in vivo. It underwent further autophosphorylation in vitro (up to 0.01 mol of P per mol) at the regulatory Tyr-204 site and at additional tyrosine and serine residues. Threonine autophosphorylation, presumably at the regulatory Thr-202 site, was also detected weakly when the recombinant kinase was incubated in the presence of manganese, but not in the presence of magnesium. Before and after cleavage of the GST-Erk1 protein with thrombin, it exhibited a relatively high level of myelin basic protein phosphotransferase activity, which could be reduced eightfold by treatment of the kinase with the protein-tyrosine phosphatase CD45, but not by treatment with the protein-serine/threonine phosphatase 2A. The protein-tyrosine kinase p56lck catalyzed phosphorylation of GST-Erk1 at two autophosphorylations sites, including Tyr-204, and at a novel site. A further fivefold stimulation of the myelin basic protein phosphotransferase activity of the GST-Erk1 was achieved in the presence of a partially purified MAP kinase kinase from sheep platelets. Under these circumstances, there was primarily an enhancement of the tyrosine phosphorylation of GST-Erk1. This MAP kinase kinase also similarly phosphorylated a catalytically compromised version of GST-Erk1 in which Lys-71 was converted to Ala by site-directed mutagenesis.

Molecular cloning, expression, and characterization of the human mitogen-activated protein kinase p44erk1

p44erk1 is a member of a family of tyrosyl-phosphorylated and mitogen-activated protein (MAP) kinases that participate in cell cycle control. A full-length erk1 cDNA was isolated from a human hepatoma cell line (Hep G2) library. The erk1 cDNA clone shared approximately 96% predicted amino acid identity with partial sequences of rodent erk1 cognates, and the erk1 gene was assigned to human chromosome 16 by hybrid panel analysis. Human erk1 expressed in Escherichia coli as a glutathione S-transferase fusion (GST-Erk1) protein was substantially phosphorylated on tyrosine in vivo. It underwent further autophosphorylation in vitro (up to 0.01 mol of P per mol) at the regulatory Tyr-204 site and at additional tyrosine and serine residues. Threonine autophosphorylation, presumably at the regulatory Thr-202 site, was also detected weakly when the recombinant kinase was incubated in the presence of manganese, but not in the presence of magnesium. Before and after cleavage of the GST-Erk1 protein with thrombin, it exhibited a relatively high level of myelin basic protein phosphotransferase activity, which could be reduced eightfold by treatment of the kinase with the protein-tyrosine phosphatase CD45, but not by treatment with the protein-serine/threonine phosphatase 2A. The protein-tyrosine kinase p56lck catalyzed phosphorylation of GST-Erk1 at two autophosphorylations sites, including Tyr-204, and at a novel site. A further fivefold stimulation of the myelin basic protein phosphotransferase activity of the GST-Erk1 was achieved in the presence of a partially purified MAP kinase kinase from sheep platelets. Under these circumstances, there was primarily an enhancement of the tyrosine phosphorylation of GST-Erk1. This MAP kinase kinase also similarly phosphorylated a catalytically compromised version of GST-Erk1 in which Lys-71 was converted to Ala by site-directed mutagenesis.

Complexes of Ras.GTP with Raf-1 and mitogen-activated protein kinase kinase

The guanosine triphosphate (GTP)-binding protein Ras functions in regulating growth and differentiation; however, little is known about the protein interactions that bring about its biological activity. Wild-type Ras or mutant forms of Ras were covalently attached to an insoluble matrix and then used to examine the interaction of signaling proteins with Ras. Forms of Ras activated either by mutation (Gly12Val) or by binding of the GTP analog, guanylyl-imidodiphosphate (GMP-PNP) interacted specifically with Raf-1 whereas an effector domain mutant, Ile36Ala, failed to interact with Raf-1. Mitogen-activated protein kinase (MAP kinase) activity was only associated with activated forms of Ras. The specific interaction of activated Ras with active MAP kinase kinase (MAPKK) was confirmed by direct assays. Thus the forming of complexes containing MAPKK activity and Raf-1 protein are dependent upon the activity of Ras.