Biomedical subjects

R J Davis

Publications and source records attributed to R J Davis.

At least 19 recordsLinked to original sources

PubMed1995

Cdc42 and PAK-mediated signaling leads to Jun kinase and p38 mitogen-activated protein kinase activation.

The PAK family of protein kinases has been suggested as a potential target of the Cdc42 and Rac GTPases based on studies in vitro. We show that PAK-3 is activated by Cdc42 in vivo. Both, activated (GTPase-defective) Cdc42 and a constitutively active PAK-3 mutant stimulated the activity of Jun kinase 1 (JNK1) in transfected cells. Activated Cdc42 also stimulated the activity of the related p38 mitogen-activated protein kinase but was a less effective activator of ERK2. The effect of Cdc42 on JNK activity was similar to that of the potent inflammatory cytokine interleukin-1 (IL-1). The observation that a dominant-negative Cdc42 mutant inhibited IL-1 activation of JNK1 indicates a role for Cdc42 in IL-1 signaling. These results suggest that Cdc42 and PAK may mediate the effects of cytokines on transcriptional regulation.

Adenosine Triphosphate↗

PubMed1995

Opposing effects of ERK and JNK-p38 MAP kinases on apoptosis.

Apoptosis plays an important role during neuronal development, and defects in apoptosis may underlie various neurodegenerative disorders. To characterize molecular mechanisms that regulate neuronal apoptosis, the contributions to cell death of mitogen-activated protein (MAP) kinase family members, including ERK (extracellular signal-regulated kinase), JNK (c-JUN NH2-terminal protein kinase), and p38, were examined after withdrawal of nerve growth factor (NGF) from rat PC-12 pheochromocytoma cells. NGF withdrawal led to sustained activation of the JNK and p38 enzymes and inhibition of ERKs. The effects of dominant-interfering or constitutively activated forms of various components of the JNK-p38 and ERK signaling pathways demonstrated that activation of JNK and p38 and concurrent inhibition of ERK are critical for induction of apoptosis in these cells. Therefore, the dynamic balance between growth factor-activated ERK and stress-activated JNK-p38 pathways may be important in determining whether a cell survives or undergoes apoptosis.

Alkaloids↗

PubMed1995

Integration of MAP kinase signal transduction pathways at the serum response element.

The ternary complex factor (TCF) subfamily of ETS-domain transcription factors bind with serum response factor (SRF) to the serum response element (SRE) and mediate increased gene expression. The TCF protein Elk-1 is phosphorylated by the JNK and ERK groups of mitogen-activated protein (MAP) kinases causing increased DNA binding, ternary complex formation, and transcriptional activation. Activated SRE-dependent gene expression is induced by JNK in cells treated with interleukin-1 and by ERK after treatment with phorbol ester. The Elk-1 transcription factor therefore integrates MAP kinase signaling pathways in vivo to coordinate biological responses to different extracellular stimuli.

Animals↗

PubMed1995

Pro-inflammatory cytokines and environmental stress cause p38 mitogen-activated protein kinase activation by dual phosphorylation on tyrosine and threonine.

Protein kinases activated by dual phosphorylation on Tyr and Thr (MAP kinases) can be grouped into two major classes: ERK and JNK. The ERK group regulates multiple targets in response to growth factors via a Ras-dependent mechanism. In contrast, JNK activates the transcription factor c-Jun in response to pro-inflammatory cytokines and exposure of cells to several forms of environmental stress. Recently, a novel mammalian protein kinase (p38) that shares sequence similarity with mitogen-activated protein (MAP) kinases was identified. Here, we demonstrate that p38, like JNK, is activated by treatment of cells with pro-inflammatory cytokines and environmental stress. The mechanism of p38 activation is mediated by dual phosphorylation on Thr-180 and Tyr-182. Immunofluorescence microscopy demonstrated that p38 MAP kinase is present in both the nucleus and cytoplasm of activated cells. Together, these data establish that p38 is a member of the mammalian MAP kinase group.

Animals↗

PubMed1995

The MAP kinase signal transduction pathway is activated by the endogenous cannabinoid anandamide.

Anandamide is an endogenous ligand for delta 9-tetrahydrocannabinol (THC) receptors. Incubation of cultured cells with anandamide or THC causes increased arachidonic acid release and eicosanoid biosynthesis. Here we demonstrate that the MAP kinase signal transduction pathway contributes to this response. Treatment of WI-38 fibroblasts with anandamide causes increased MAP kinase activity and increased phosphorylation of the arachidonate-specific cytoplasmic phospholipase A2 (cPLA2). Significantly, MAP kinase phosphorylates and activates cPLA2 [Lin, et al., Cell, 72 (1993) 269-278]. The MAP kinase signal transduction pathway may therefore mediate the effects of anadamide on cPLA2 activation and arachidonic acid release.

Arachidonic Acid↗

PubMed1995

Independent human MAP-kinase signal transduction pathways defined by MEK and MKK isoforms.

Mammalian mitogen-activated protein (MAP) kinases include extracellular signal-regulated protein kinase (ERK), c-Jun amino-terminal kinase (JNK), and p38 subgroups. These MAP kinase isoforms are activated by dual phosphorylation on threonine and tyrosine. Two human MAP kinase kinases (MKK3 and MKK4) were cloned that phosphorylate and activate p38 MAP kinase. These MKK isoforms did not activate the ERK subgroup of MAP kinases, but MKK4 did activate JNK. These data demonstrate that the activators of p38 (MKK3 and MKK4), JNK (MKK4), and ERK (MEK1 and MEK2) define independent MAP kinase signal transduction pathways.

Amino Acid Sequence↗

PubMed1995

Transcription factor ATF2 regulation by the JNK signal transduction pathway.

Treatment of cells with pro-inflammatory cytokines or ultraviolet radiation causes activation of the c-Jun NH2-terminal protein kinase (JNK). Activating transcription factor-2 (ATF2) was found to be a target of the JNK signal transduction pathway. ATF2 was phosphorylated by JNK on two closely spaced threonine residues within the NH2-terminal activation domain. The replacement of these phosphorylation sites with alanine inhibited the transcriptional activity of ATF2. These mutations also inhibited ATF2-stimulated gene expression mediated by the retinoblastoma (Rb) tumor suppressor and the adenovirus early region 1A (E1A) oncoprotein. Furthermore, expression of dominant-negative JNK inhibited ATF2 transcriptional activity. Together, these data demonstrate a role for the JNK signal transduction pathway in transcriptional responses mediated by ATF2.

Activating Transcription Factor 2↗

PubMed1994

Differential activation of ERK and JNK mitogen-activated protein kinases by Raf-1 and MEKK.

Growth factors activate mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinases (ERKs) and Jun kinases (JNKs). Although the signaling cascade from growth factor receptors to ERKs is relatively well understood, the pathway leading to JNK activation is more obscure. Activation of JNK by epidermal growth factor (EGF) or nerve growth factor (NGF) was dependent on H-Ras activation, whereas JNK activation by tumor necrosis factor alpha (TNF-alpha) was Ras-independent. Ras activates two protein kinases, Raf-1 and MEK (MAPK, or ERK, kinase) kinase (MEKK). Raf-1 contributes directly to ERK activation but not to JNK activation, whereas MEKK participated in JNK activation but caused ERK activation only after overexpression. These results demonstrate the existence of two distinct Ras-dependent MAPK cascades--one initiated by Raf-1 leading to ERK activation, and the other initiated by MEKK leading to JNK activation.

3T3 Cells↗

PubMed1994

MAP kinase binds to the NH2-terminal activation domain of c-Myc.

The transcription factor c-Myc is a substrate for phosphorylation by MAP kinases. Here we demonstrate that MAP kinase binds to c-Myc. The NH2-terminal region (residues 1-100) is necessary and sufficient for this interaction. Binding to c-Myc is not dependent on the state of MAP kinase activation. However, the c-Myc/MAP kinase complex is disrupted by ATP. Together, these observations indicate that substrate binding interactions contribute to the specificity of phosphorylation by MAP kinases.

Adenosine Triphosphate↗

PubMed1994

An osmosensing signal transduction pathway in mammalian cells.

The osmotic balance between the cytoplasmic and extracellular compartments of cells is critical for the control of cell volume. A mammalian protein kinase, Jnk, which is a distant relative of the mitogen-activated protein kinase group, was activated by phosphorylation on threonine and tyrosine in osmotically shocked cells. The activation of Jnk may be relevant to the biological response to osmotic shock because the expression of human Jnk in the yeast Saccharomyces cerevisiae rescued a defect in growth on hyper-osmolar media. These data indicate that related protein kinases may mediate osmosensing signal transduction in yeast and mammalian cells.

Amino Acid Sequence↗

PubMed1994

Fusion of PAX7 to FKHR by the variant t(1;13)(p36;q14) translocation in alveolar rhabdomyosarcoma.

Although the t(2;13)(q35;q14) translocation has been found in most cases of the pediatric cancer alveolar rhabdomyosarcoma, several cases have been reported with a variant t(1;13)(p36;q14) translocation. Our findings indicate that this t(1;13) rearranges PAX7 on chromosome 1 and fuses it to FKHR on chromosome 13. This fusion results in a chimeric transcript consisting of 5' PAX7 and 3' FKHR regions, which is similar to the 5' PAX3-3' FKHR transcript formed by the t(2;13). The 5' PAX3 and PAX7 regions encode related DNA binding domains, and therefore we postulate that these translocations create similar chimeric transcription factors that alter expression of a common group of target genes.

Amino Acid Sequence↗

PubMed1994

JNK1: a protein kinase stimulated by UV light and Ha-Ras that binds and phosphorylates the c-Jun activation domain.

The ultraviolet (UV) response of mammalian cells is characterized by a rapid and selective increase in gene expression mediated by AP-1 and NF-kappa B. The effect on AP-1 transcriptional activity results, in part, from enhanced phosphorylation of the c-Jun NH2-terminal activation domain. Here, we describe the molecular cloning and characterization of JNK1, a distant relative of the MAP kinase group that is activated by dual phosphorylation at Thr and Tyr during the UV response. Significantly, Ha-Ras partially activates JNK1 and potentiates the activation caused by UV. JNK1 binds to the c-Jun transactivation domain and phosphorylates it on Ser-63 and Ser-73. Thus, JNK1 is a component of a novel signal transduction pathway that is activated by oncoproteins and UV irradiation. These properties indicate that JNK1 activation may play an important role in tumor promotion.

Amino Acid Sequence↗

PubMed1994

The native structure of the activated Raf protein kinase is a membrane-bound multi-subunit complex.

Raf is a mitogen-stimulated protein kinase that functions as a component of the signaling cascade that leads to the stimulation of mitogen-activated protein kinase. Here we show that the native structure of Raf is a large multi-subunit protein complex with an apparent mass of 300-500 kDa that interacts with Ras and the mitogen-activated protein kinase kinase Mek. Analysis of the structure of the Raf complex demonstrates that it contains a single Raf protein kinase together with the molecular chaperones hsp90 and p50. The Raf-hsp90-p50 complex was observed in starved cells and in cells activated with serum or phorbol ester. Thus, changes in complex formation with hsp90 and p50 are not required for activation of the Raf protein kinase. However, Raf activation caused by Ras was associated with the translocation of the cytoplasmic Raf-hsp90-p50 complex to the cell membrane. Significantly, it is only the membrane-bound complex that exhibits increased protein kinase activity. Thus, the Ras-activated Raf protein kinase functions as a membrane-bound multi-subunit complex.

Amino Acid Sequence↗

PubMed1994

Control of MAP kinase activation by the mitogen-induced threonine/tyrosine phosphatase PAC1.

Intracellular signalling following mitogenic stimulation of quiescent cells involves the initiation of a phosphorylation cascade that leads to the rapid and reversible activation of the mitogen-activated protein (MAP) kinases ERK1 and ERK2. MAP kinase activation is mediated by dual phosphorylation within the motif Thr-Glu-Tyr by MAP kinase kinase (MEK). Following activation, the MAP kinases translocate into the nucleus where they phosphorylate several transduction targets, including transcription factors. We have previously identified PAC1 as an immediate-early mitogen-inducible tyrosine phosphatase in nuclei of T cells. Here we present several lines of evidence indicating that PAC1 is a physiologically relevant MAP kinase phosphatase. Recombinant PAC1 in vitro is a dual-specific Thr/Tyr phosphatase with stringent substrate specificity for MAP kinase. Constitutive expression of PAC1 in vivo leads to inhibition of MAP kinase activity normally stimulated by epidermal growth factor, phorbol myristyl acetate, or T-cell receptor crosslinking. The inactivation of MAP kinase by PAC1 results in inhibition of MAP kinase-regulated reporter gene expression.

Calcium-Calmodulin-Dependent Protein Kinases↗

PubMed1994

MAPKs: new JNK expands the group.

Mitogen-activated protein kinases (MAPKs) are activated by dual phosphorylation on threonine and tyrosine in response to a wide array of extracellular stimuli. In the yeast Saccharomyces cerevisiae, a series of extracellular stimuli. In the yeast Saccharomyces cerevisiae, a series of MAPK signal transduction pathways have been demonstrated to control many cellular functions. By contrast, mammalian MAPKs are more poorly understood. However, recent studies have established important roles for three separate groups of mammalian MAPKs, which are characterized by distinct dual phosphorylation motifs. Together, these protein kinases mediate signal transduction in mammalian tissues and control many aspects of cellular physiology.

Amino Acid Sequence↗

PubMed1994

Mitogen-activated protein (MAP) kinase phosphorylation of MAP kinase kinase: determination of phosphorylation sites by mass spectrometry and site-directed mutagenesis.

Mitogen-activated protein kinase kinase (MKK) phosphorylates and activates mitogen-activated protein kinase (MAPK) in response to stimulation of various eukaryotic signaling pathways. Conversely, a recent report showed that MAPK phosphorylates MKK in vitro [Matsuda, S., Gotoh, Y., and Nishida, E. (1993) J. Biol. Chem. 268, 3277-3281]. To gain insight into the function of this feedback phosphorylation, we identified the major sites targeted for phosphorylation by MAPK and examined whether such a modification plays a role in regulating the basal and stimulated MKK activities. Two phosphopeptides generated by tryptic digestion of MAPK-phosphorylated MKK were identified by electrospray ionization mass spectrometry. Cyanogen bromide cleavage also yielded two phosphopeptides whose sequence overlapped with the tryptic phosphopeptides. Both sets of phosphopeptides contained candidate MAPK target sites at Thr292 and Thr386 that fit the consensus sequence ProXThr*Pro. Replacement of either Thr292 or Thr386 with alanine by site-directed mutagenesis reduced the phosphate incorporation respectively to 32 or 75% that of wild type MKK. Replacement of both threonine residues with alanine reduced phosphate incorporation to 2.5% that of wild type enzyme. Comparison of MAPK-phosphorylated vs. unphosphorylated MKK showed no significant differences in basal or Raf-1-stimulated MKK activity. We conclude that the phosphorylation of MKK at Thr292 and Thr386 does not interfere with catalysis in vitro.

Amino Acid Sequence↗

PubMed1994

Signal transduction by tumor necrosis factor mediated by JNK protein kinases.

JNK protein kinases are distantly related to mitogen-activated protein kinases (ERKs) and are activated by dual phosphorylation on Tyr and Thr. The JNK protein kinase group includes the 46-kDa isoform JNK1. Here we describe the molecular cloning of a second member of the JNK group, the 55-kDa protein kinase JNK2. The activities of both JNK isoforms are markedly increased by exposure of cells to UV radiation. Furthermore, JNK protein kinase activation is observed in cells treated with tumor necrosis factor. Although both JNK isoforms phosphorylate the NH2-terminal activation domain of the transcription factor c-Jun, the activity of JNK2 was approximately 10-fold greater than that of JNK1. This difference in c-Jun phosphorylation correlates with increased binding of c-Jun to JNK2 compared with JNK1. The distinct in vitro biochemical properties of these JNK isoforms suggest that they may have different functions in vivo. Evidence in favor of this hypothesis was obtained from the observation that JNK1, but not JNK2, complements a defect in the expression of the mitogen-activated protein kinase HOG1 in the yeast Saccharomyces cerevisiae. Together, these data indicate a role for the JNK group of protein kinases in the signal transduction pathway initiated by proinflammatory cytokines and UV radiation.

Amino Acid Sequence↗

PubMed1993

Mitogen-activated protein kinase stimulation by a tyrosine kinase-negative epidermal growth factor receptor.

Mutation of the epidermal growth factor receptor (EGF-R) within the ATP binding subdomain results in a receptor that lacks tyrosine kinase activity and is defective in signal transduction. However, this kinase-negative EGF-R is able to activate MAP kinase (Campos-Gonzalez, R., and Glenny, J. R. (1992) J. Biol. Chem. 267, 14535-14538). This observation suggests that signal initiation by the EGF-R can occur by a mechanism that is independent of the receptor tyrosine kinase activity. Here, we report that the kinase-negative EGF-R is phosphorylated on tyrosine in EGF-treated cells. The mechanism of tyrosine phosphorylation can be accounted for by the action of EGF to stimulate a protein kinase activity that is associated with the kinase-negative EGF-R. This protein kinase activity is not intrinsic to the receptor and can be separated from the EGF-R by incubation with 0.5 M NaCl. MAP kinase activation by the kinase-negative EGF-R may therefore occur by a mechanism that requires a receptor-associated tyrosine kinase. Thus, it is unnecessary to propose a novel kinase-independent mechanism of signal initiation to account for MAP kinase activation by the kinase-negative EGF-R.

Amino Acid Sequence↗