Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

---

Query: EC:2.7.10.1 (ERK)
95,504 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An important aspect of multi-step tumorigenesis is the mutational activation of genes of the RAS family, particularly in sporadic cancers of the pancreas, colon, lung and myeloid system. RAS genes encode small GTP-binding proteins that affect gene expression in a global way by acting as major switches in signal transduction processes, coupling extracellular signals with transcription factors. Oncogenic forms of RAS are locked in their active state and transduce signals essential for transformation, angiogenesis, invasion and metastasis via downstream pathways involving the RAF/MEK/ERK cascade of cytoplasmic kinases, the small GTP-binding proteins RAC and RHO, phosphatidylinositol 3-kinase and others. We have used subtractive suppression hybridization (SSH), a PCR-based cDNA subtraction technique, to contrast differential gene expression profiles in immortalized, non-tumorigenic rat embryo fibroblasts and in HRAS- transformed cells. Sequence and expression analysis of more than 1,200 subtracted cDNA fragments revealed transcriptional stimulation or repression of 104 ESTs, 45 novel sequences and 244 known genes in HRAS- transformed cells compared with normal cells. Furthermore, we identified common and distinct targets in cells transformed by mutant HRAS, KRAS and NRAS, as well as 61 putative target genes controlled by the RAF/MEK/ERK pathway in reverted cells treated with the MEK-specific inhibitor PD 98059.
...
PMID:A genome-wide survey of RAS transformation targets. 1065 59

Targeted disruption of both alleles of mouse sos1, which encodes a Ras-specific exchange factor, conferred mid-gestational embryonic lethality that was secondary to impaired placental development and was associated with very low placental ERK activity. The trophoblastic layers of sos1(-/-) embryos were poorly developed, correlating with high sos1 expression in wild-type trophoblasts. A sos1(-/-) cell line, which expressed readily detectable levels of the closely related Sos2 protein, formed complexes between Sos2, epidermal growth factor receptor (EGFR) and Shc efficiently, gave normal Ras.GTP and ERK responses when treated with EGF for < or =10 min and was transformed readily by activated Ras. However, the sos1(-/-) cells were resistant to transformation by v-Src or by overexpressed EGFR and continuous EGF treatment, unlike sos1(+/-) or wild-type cells. This correlated with Sos2 binding less efficiently than Sos1 to EGFR and Shc in cells treated with EGF for > or =90 min or to v-Src and Shc in v-Src-expressing cells, and with less ERK activity. We conclude that Sos1 participates in both short- and long-term signaling, while Sos2-dependent signals are predominantly short-term.
...
PMID:The Sos1 and Sos2 Ras-specific exchange factors: differences in placental expression and signaling properties. 1067 33

Monocytes-macrophages which serve as host immune cells to kill pathogens can often be "activated" after exposing to viruses, bacteria, cytokines as well as chemical substances, However, it is paradoxical that highly activated macrophages can be induced to become the suppressor ones by live microbes, microbial products, tumor, and autoimmune disease, although the mechanism remains unknown. Our previous experimental studies have shown that immuno-suppressor activities of suppressor macrophages on T, B and NK cells can be prevented by the treatment with LPS or supernatant in vitro from mitogen-stimulated lymphocytes, while, at the same time, the tumoricidal activities of those macrophages can be kept or even enhanced following the same treatment. This phenomenon was then termed as "immune modulation" For the understanding of its mechanism, we are now undertaking signal transduction in modulated macrophages. Since mitogen-activated protein kinase (MAPK) is an integration point of different signal transduction pathways, its cascade and regulation of activation are being investigated extensively by the assay of electrophoresis mobility shift. Recent results suggested that interaction of ligand-receptor triggers protein tyrosine kinase(PTK) activation leading to Ras-GTP binding with Raf-1 to phosphorylate MAPK kinase (MAPKK), the specific activator of MAPK. It is reported that PKC-alpha can directly phosphorylate or activate Raf-1 in NIH3 T3 cells. Raf-1 (74 KDa), with an intrinsic serine (Ser)-threonine (The) kinase activity, becomes hyperphosphorylated after activation which can be followed by gel mobility shift test. It has also been shown that a variety of extracellular factors stimulate a pair of MAPK p44 and MAPK p42 of MAPK family members. A significant property of activation of ERK 1 and ERK 2 is the requirement for the phosphorylation of both Thr-183 and Tyr-185 (at TEY motif) within in its protein kinase subdomain VIII. More recently, two other MAPK subtypes, p38 MAPK (mammalian equivalents of HOG1 in yeast) and JNK MAPK have been discovered. The requirement for activation of p38 MAPK for both Thr-180 and Tyr-182 (at TGY motif) has been shown. p38 MAPK is important in certain transcriptional regulatory pathways, since it can phosphorylate the following transcriptional factors: 1) Elk at Ser 383/389 for binding with SRE motif; 2). ATF 2 at Ser 69/71, forming a complex with Myc for DNA binding at CRE motif; 3) Max at Ser-62 to combine DNA of E-Box motif. p38 MAPK can be activated by LPS, inflammatory cytokines, such as TNF and IL-1, osmolarity. To examine the possibility that whether activation of Raf-1 and ERK 1, ERK2 and p38 MAPK can be regulated directly or/and differently by PKC and PKA pathways, herbimycin A (Ki = 0.9 mumol/L), a potent PTK inhibitor (J. Immunol. 155:3944-4003, 1995) at 2 mumol/L concentration was utilized to block Ras/Raf-1/MAPK cascade. After pre-incubation of macrophages with herbimycin A for 30 min or 90 min, cells were treated with LPS (10 micrograms/ml) and PMA (100 nmol/L) for 15 min. No inhibition of phosphorylation of Raf-1, MAPK p44 and MAPK p42 in response to LPS and PMA was observed (Fig. 1 and 3). However, forskolin, a cAMP inducer for protein kinase A (PKA) activation, inhibited the phosphorylation of LPS- and PMA-stimulated Raf-1, MAPK p44 and MAPK p42 (Fig. 2 and 4). Similarly, in agreement with a very recent report from David, M et al in NIH, in which they indicated that forskolin (30 mumol/L) inhibited IFN-beta-stimulated ERK activity by U 266 cells (J. Biol. Chem. 271: 4585-4588 1996), we found that the levels of phosphorylations of Raf-1 and ERK1 and ERK2 were declined when forskolin (30 mumol/L) was added to macrophages for 20 min at 37 degrees C prior to the stimulation by LPS and PMA. Interestingly, under the same condition, forskolin (30 mumol/L) stimulated the phosphorylation of LPS- and PMA-triggered p38 MAPK of murine peritoneal suppressor macrophages, suggesting that activatio
...
PMID:[Studies on cell signaling immunomodulated murine peritoneal suppressor macrophages: LPS and PMA mediate the activation of RAF-1, MAPK p44 and MAPK p42 and p38 MAPK]. 1068 11

Ras plays an important role in a variety of cellular functions, including growth, differentiation, and oncogenic transformation. For instance, Ras participates in the activation of Raf, which phosphorylates and activates mitogen-activated protein kinase kinase (MEK), which then phosphorylates and activates extracellular signal-regulated kinase (ERK), a mitogen-activated protein (MAP) kinase. Activation of MAP kinase appears to be essential for propagating a wide variety of extracellular signals from the plasma membrane to the nucleus. N17Ras, a GDP-bound dominant negative mutant, is used widely as an interfering mutant to assess Ras function in vivo. Surprisingly, we observed that expression of N17Ras inhibited the activity and phosphorylation of Elk-1, a physiological substrate of MAP kinases, in response to phorbol myristate acetate. The activity and phosphorylation of the MAP kinase hemagglutinin epitope (HA)-ERK1 were not affected by N17Ras in response to the same stimulus. Additionally, expression of N17Ras, but not L61S186Ras, a GTP-bound interfering mutant, inhibited MEK-induced Elk-1 phosphorylation, suggesting that inhibition of Elk-1 may be unique to GDP-bound Ras mutants. Finally, we observed that V12Ras-induced focus formation in NIH3T3 cells is inhibited by coexpression of GDP-bound Ras mutants, such as N17, A15, and N17N69. Therefore, N17Ras and V12 Ras may be codominant with respect to Elk-1 activation and cellular transformation. These results indicate that N17Ras appears to have at least two distinguishable functions: interference with endogenous Ras activation and inhibition of Elk-1 and transfomation. Furthermore, our data imply the possibility that GDP-bound Ras, like N17Ras, may have a direct role in signal transduction.
...
PMID:The dominant negative Ras mutant, N17Ras, can inhibit signaling independently of blocking Ras activation. 1072 31

In studies to define mechanisms of ERK activation in Chinese hamster ovary cells, we have observed an inverse correlation between CRKII-C3G complex formation and ERK activity. That is, we were able to coprecipitate the guanine nucleotide exchange factor C3G with the adaptor protein CRKII in lysates from suspended cells that had low ERK activity, but we could not do so or could do so less efficiently in lysates of adherent cells with increased ERK activity. Consistent with the presence of a functional CRKII-C3G complex, we detected more GTP-loaded RAP1 in suspension than adherent lysates. Overexpression of cDNAs encoding B-RAF, CRKII W109L, and PTP1B C215S activated ERK in suspension cells, the latter two constructs also disrupting CRKII-C3G complex formation. Finally, we have also observed that certain integrin alpha subunit cytoplasmic splice variants differentially regulate ERK1/2 but also in a manner that correlated with levels of a CRKII-C3G complex. Thus, these data suggest the involvement of integrins in an ERK suppression pathway mediated by CRKII-C3G complex formation and downstream signaling from activated RAP1.
...
PMID:The association of CRKII with C3G can be regulated by integrins and defines a novel means to regulate the mitogen-activated protein kinases. 1077 17

In PC12 cells, Ha-Ras modulates multiple effector proteins that induce neuronal differentiation. To regulate these pathways Ha-Ras must be located at the plasma membrane, a process normally requiring attachment of farnesyl and palmitate lipids to the C terminus. Ext61L, a constitutively activated and palmitoylated Ha-Ras that lacks a farnesyl group, induced neurites with more actin cytoskeletal changes and lamellipodia than were induced by farnesylated Ha-Ras61L. Ext61L-triggered neurite outgrowth was prevented easily by co-expressing inhibitory Rho, Cdc42, or p21-activated kinase but required increased amounts of inhibitory Rac. Compared with Ha-Ras61L, Ext61L caused 2-fold greater Rac GTP binding and phosphatidylinositol 3-kinase activity in membranes, a hyperactivation that explained the numerous lamellipodia and ineffectiveness of Rac(N17). In contrast, Ext61L activated B-Raf kinase and ERK phosphorylation more poorly than Ha-Ras61L. Thus, accentuated differentiation by Ext61L apparently results from heightened activation of one Ras effector (phosphatidylinositol 3-kinase) and suboptimal activation of another (B-Raf). This surprising unbalanced effector activation, without changes in the designated Ras effector domain, indicates the Ext61L C-terminal alternations are a new way to influence Ha-Ras-effector utilization and suggest a broader role of the lipidated C terminus in Ha-Ras biological functions.
...
PMID:Mutation of Ha-Ras C terminus changes effector pathway utilization. 1080 8

We characterized a novel guanine nucleotide exchange factor (GEF) for Ras family G proteins that is highly homologous to CalDAG-GEFI, a GEF for Rap1 and R-Ras, and to RasGRP/CalDAG-GEFII, a GEF for Ras and R-Ras. This novel GEF, referred to as CalDAG-GEFIII, increased the GTP/GDP ratio of Ha-Ras, R-Ras, and Rap1 in 293T cells. CalDAG-GEFIII promoted the guanine nucleotide exchange of Ha-Ras, R-Ras, and Rap1 in vitro also, indicating that CalDAG-GEFIII exhibited the widest substrate specificity among the known GEFs for Ras family G proteins. Expression of CalDAG-GEFIII was detected in the glial cells of the brain and the glomerular mesangial cells of the kidney by in situ hybridization. CalDAG-GEFIII activated ERK/MAPK most efficiently, followed by CalDAG-GEFII and CalDAG-GEFI in 293T cells. JNK activation was most prominent in cells expressing CalDAG-GEFII, followed by CalDAG-GEFIII and CalDAG-GEFI. Expression of CalDAG-GEFIII induced neuronal differentiation of PC12 cells and anchorage-independent growth of Rat1A cells less efficiently than did CalDAG-GEFII. Thus, co-activation of Rap1 by CalDAG-GEFIII apparently attenuated Ras-MAPK-dependent neuronal differentiation and cellular transformation. Altogether, CalDAG-GEFIII activated a broad range of Ras family G proteins and exhibited a biological activity different from that of either CalDAG-GEFI or CalDAG-GEFII.
...
PMID:CalDAG-GEFIII activation of Ras, R-ras, and Rap1. 1083 26

The effects of the 5'-truncated Rgr oncogene, a previously shown specific guanine exchange factor for Ral in vitro, in stimulating proliferation, cell transformation and gene expression were investigated. We have established TetRgr cell lines in which expression of Rgr can be inhibited by the presence of tetracycline in the medium. Using this system, we show that Rgr overexpressing cells are morphologically transformed and grow in a disorganized manner. At the transcriptional level, Rgr enhances the activity of the serum response element and c-Jun. Rgr induces phosphorylation of ERKs, p38 and JNK kinases, and increases the levels of the GTP-bound forms of Ral and Ras. Ras activation could account for the broad spectra of effects displayed by Rgr. The important role of these pathways is confirmed by experiments in which the transcriptional activation events can be blocked by dominant negative versions of Ras, Ral and Rho. Among all the Rgr-induced pathways, the Ras-Raf-MEK-ERK cascade is essential for the transforming properties of Rgr. Additional analysis has shown that the activation of this pathway by Rgr is not due to a feed back mechanism mediated by the Grb2 adaptor protein. Oncogene (2000).
...
PMID:The Rgr oncogene (homologous to RalGDS) induces transformation and gene expression by activating Ras, Ral and Rho mediated pathways. 1085 Oct 75

Although the Ras subfamily of GTPases consists of approximately 20 members, only a limited number of guanine nucleotide exchange factors (GEFs) that couple extracellular stimuli to Ras protein activation have been identified. Furthermore, no novel downstream effectors have been identified for the M-Ras/R-Ras3 GTPase. Here we report the identification and characterization of three Ras family GEFs that are most abundantly expressed in brain. Two of these GEFs, MR-GEF (M-Ras-regulated GEF, KIAA0277) and PDZ-GEF (KIAA0313) bound specifically to nucleotide-free Rap1 and Rap1/Rap2, respectively. Both proteins functioned as Rap1 GEFs in vivo. A third GEF, GRP3 (KIAA0846), activated both Ras and Rap1 and shared significant sequence homology with the calcium- and diacylglycerol-activated GEFs, GRP1 and GRP2. Similarly to previously identified Rap GEFs, C3G and Smg GDS, each of the newly identified exchange factors promoted the activation of Elk-1 in the LNCaP prostate tumor cell line where B-Raf can couple Rap1 to the extracellular receptor-activated kinase cascade. MR-GEF and PDZ-GEF both contain a region immediately N-terminal to their catalytic domains that share sequence homology with Ras-associating or RalGDS/AF6 homology (RA) domains. By searching for in vitro interaction with Ras-GTP proteins, PDZ-GEF specifically bound to Rap1A- and Rap2B-GTP, whereas MR-GEF bound to M-Ras-GTP. C-terminally truncated MR-GEF, lacking the GEF catalytic domain, retained its ability to bind M-Ras-GTP, suggesting that the RA domain is important for this interaction. Co-immunoprecipitation studies confirmed the interaction of M-Ras-GTP with MR-GEF in vivo. In addition, a constitutively active M-Ras(71L) mutant inhibited the ability of MR-GEF to promote Rap1A activation in a dose-dependent manner. These data suggest that M-Ras may inhibit Rap1 in order to elicit its biological effects.
...
PMID:Identification of guanine nucleotide exchange factors (GEFs) for the Rap1 GTPase. Regulation of MR-GEF by M-Ras-GTP interaction. 1093 4

We have investigated heat shock stimulation of MAPK cascades in an interleukin 3-dependent cell line, BaF3. Following exposure to 42 degrees C, the stress-activated JNK MAPKs were phosphorylated and activated, but p38 MAPKs remained unaffected. Surprisingly, heat shock also activated ERK MAPKs in a potent (>60-fold), delayed (>30 min), and sustained (>/=120 min) manner. These characteristics suggested a novel mechanism of ERK MAPK activation and became the focus of this study. A MEK-specific inhibitor, PD98059, inhibited heat shock ERK MAPK activation by >75%. Surprisingly, a role for Ras in the heat shock response was eliminated by the failure of a dominant-negative Ras(Asn-17) mutant to inhibit ERK MAPK activation and the failure to observe increases in Ras.GTP. Heat shock also failed to stimulate activation of A-, B-, and c-Raf. Instead, a serine/threonine phosphatase inhibitor, okadaic acid, activated ERK MAPK in a similar manner to heat shock. Furthermore, pretreatment with suramin, generally recognized as a broad range inhibitor of growth factor receptors, inhibited both okadaic acid-stimulated and heat shock-stimulated ERK MAPK activity by >40%. Inhibiting ERK MAPK activation during heat shock with PD98059 enhanced losses in cell viability. These results demonstrate Ras- and Raf-independent ERK MAPK activation maintains cell viability following heat shock.
...
PMID:The mechanism of heat shock activation of ERK mitogen-activated protein kinases in the interleukin 3-dependent ProB cell line BaF3. 1100 8


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---