Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.12.2 (MEK)
 18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The Raf-1-MEK-MAPK pathway plays an important role in transducing extracellular growth factor signaling into altered nuclear transcription factor function. The benzoquinone ansamycin Geldanamycin (GA) specifically binds to the heat shock protein HSP90 and alters its complex with Raf-1. This leads to a decrease in Raf-1 levels and to disruption of the Raf-1-MEK-MAPK signaling pathway. The enhanced degradation of Raf-1 protein was prevented by inhibitors of the proteasome, while inhibition of lysosomal or other proteases was ineffective. Raf-1 that was protected from GA-induced degradation was of higher molecular weight and showed a laddering pattern consistent with its polyubiquitination. Unlike Raf-1 in untreated cells, the protein was insoluble in Triton X100- or NP40-based buffers. Signaling through this pathway was inhibited by GA, concomitant with loss of Raf-1 protein, but was restored if Raf-1 was protected from GA-induced degradation by proteasome inhibitors.
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PMID:Geldanamycin-induced destabilization of Raf-1 involves the proteasome. 936 23

At doses of 10-115 microg/kg, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) decreased body and adipose tissue weights of mature female rats. Doses below 10 microg TCDD/kg decreased body and adipose tissue weights of immature, but not mature females. Doses of 2 and 10 microg TCDD/kg decreased adipose tissue epidermal growth factor receptor (EGFR) binding activity 5 and 7 days later in immature and mature females, respectively. At these times, there was a decrease in the activities of tyrosine kinase (TK), mitogen-activated protein kinase (MAP2K), and protein kinase A (PKA). In mature females, estradiol (E2, 15 microg/kg) increased TK and PKA activities and decreased MAP2K activity. In immature females, E2 decreased TK and PKA activities but not MAP2K activity. TCDD abolished the stimulatory effect of E2 on TK and PKA in mature females, and in immature females TCDD potentiated the negative effect of E2 on all three kinases. TCDD decreased binding of [3H]E2 to cytosolic and nuclear estrogen receptors (ERs) of mature and immature females, and antagonized the stimulatory effect of E2 on ER binding activity. E2 increased DNA binding activity of the estrogen response element (ERE) and activator protein-1, and TCDD antagonized this effect. Geldanamycin, an inhibitor of Src tyrosine kinase, reduced the effects of TCDD on body and adipose tissue weights. Geldanamycin antagonized the effects of TCDD on EGFR binding activity and TK activity. In cell-free preparations, TCDD antagonized E2 action on TK activity in mature females, as well as E2 action on PKA activity in immature females. We hypothesize that TCDD antagonizes E2 action in female adipose tissues through disruption of common cytosolic signal transduction pathways.
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PMID:Interruption of estradiol signal transduction by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) through disruption of the protein phosphorylation pathway in adipose tissues from immature and mature female rats. 960 31

Confocal laser scanning microscopy was used to identify the cells within organotypic slice cultures of the developing mouse cerebral cortex that respond to estradiol treatment by phosphorylation of ERK1 and ERK2. Estrogen-responsive cells resembled neurons morphologically and expressed the neuronal marker microtubule-associated protein 2B. The intracellular distribution of the phospho-ERK signal was both cytoplasmic and nuclear, but inhibition of protein synthesis abolished the appearance of the nuclear signal. ERK1and ERK2 also coimmunoprecipitated with heat shock protein 90 (Hsp90) in the cerebral cortical explants. Geldanamycin effectively disrupted this association and prevented ERK phosphorylation. Surprisingly, MEK2 but not MEK1 was the principal mediator of estradiol-induced activation of ERK. Our data demonstrate the requirement for Hsp90 in estrogen-induced activation of ERK1 and ERK2 by MEK2 in the developing mouse cerebral cortex and also provide insight into alternative mechanisms by which estradiol may influence cytoplasmic and nuclear events in responsive neurons via the MAP kinase cascade.
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PMID:Estradiol-induced phosphorylation of ERK1/2 in explants of the mouse cerebral cortex: the roles of heat shock protein 90 (Hsp90) and MEK2. 1174 28

A requirement for cyclin D2 in G(1)-to-S phase progression has been definitively established in mature B cells stimulated via the B cell antigen receptor (BCR). However, the identity of constituents of the BCR signaling cascade that leads to cyclin D2 accumulation remains incomplete. We report that inhibition of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK)-1/2 blocked BCR-induced activation of extracellular signal-regulated kinase (ERK). Inhibition of the MEK1/2-ERK pathway was sufficient to abrogate BCR-induced cyclin D2 expression at the mRNA and protein levels. Disruption of endogenous heat shock protein 90 (hsp90) function with geldanamycin abrogated BCR-induced cyclin D2 expression and proliferation. Geldanamycin effects were attributed to a selective depletion of cellular Raf-1 that interrupted BCR-coupled activation of MEK1/2 and ERK. By contrast, signaling through the phosphatidylinositol 3-kinase and protein kinase C pathways was not affected, suggesting that disruption of hsp90 function did not cause a general impairment of BCR signaling. These results suggest that the MEK1/2-ERK pathway is essential for BCR signaling to cyclin D2 accumulation in ex vivo splenic B lymphocytes. Furthermore, these findings imply that hsp90 function is required for BCR signaling through the Raf-1-MEK1/2-ERK pathway but not through the phosphatidylinositol 3-kinase- or protein kinase C-dependent pathways.
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PMID:Requirement for a hsp90 chaperone-dependent MEK1/2-ERK pathway for B cell antigen receptor-induced cyclin D2 expression in mature B lymphocytes. 1182 72

Diabetes has been reported to increase the expression of cytochrome P450 (CYP) 2E1 messenger RNA (mRNA) and protein several-fold, and enhanced expression has been associated with elevated ketone bodies. Primary cultured rat hepatocytes were used to explore ketone body and insulin regulation of CYP2E1 expression. Hydroxybutyrate and acetoacetate (AC), alone or in combination, either failed to affect or decreased CYP2E1 mRNA levels by up to 90% relative to untreated hepatocytes. Insulin produced a concentration-dependent decrease in CYP2E1 mRNA levels, and insulin receptor immunoprecipitation showed a correspondence between receptor phosphorylation and the decrease in CYP2E1 mRNA levels at physiologic levels of insulin. Phosphatase inhibitors decreased CYP2E1 mRNA levels by greater than 95%. The phosphatidylinositol 3-kinase (PI3-kinase) inhibitors wortmannin or LY294002 and rapamycin, an inhibitor of p70 S6 kinase phosphorylation, ameliorated the insulin-mediated decrease in CYP2E1 mRNA levels. Geldanamycin, which inhibits Src kinase, also abrogated the insulin-mediated decrease in CYP2E1 mRNA levels. In contrast, the protein kinase C (PKC) inhibitor bisindolylmaleimide, the mitogen-activated protein kinase kinase (MEK) inhibitor PD98059, and the p38 mitogen-activated protein (MAP) kinase inhibitor SB202190 did not affect the insulin-mediated decrease in CYP2E1. CYP2E1 mRNA half-life decreased from approximately 48 hours in the absence of insulin to approximately 15 hours at 10 nmol/L insulin, and this decrease was prevented by wortmannin. The half-life of CYP2B mRNA was increased by insulin, whereas that of CYP3A was unaffected. Analysis of CYP2E1 gene transcription using heterogeneous nuclear RNA (hnRNA) showed that insulin suppressed CYP2E1 transcription. In conclusion, these data show involvement of transcriptional and posttranscriptional mechanisms in the insulin-mediated regulation of CYP2E1 and implicate PI3-kinase, p70 S6 kinase, and Src kinase in mediating these effects.
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PMID:Insulin signaling in the transcriptional and posttranscriptional regulation of CYP2E1 expression. 1182 98

Geldanamycin is a benzoquinone ansamycin antibiotic that manifests anti-cancer activity through the inhibition of HSP90-chaperone function. The HSP90 molecular chaperone is expressed at high levels in a wide variety of human cancers including melanoma, leukemia, and cancers in colon, prostate, lung, and breast. In cancer cells dependent upon mutated and/or over-expressed oncogene proteins, HSP90 is thought to have a critical role in regulating the stability, folding, and activity of HSP90-associated proteins, so-called "client proteins". These client proteins include the growth-stimulating proteins and kinases that support malignant transformation. Recently, oncogenic activating BRAF mutants have been identified in variety of cancers where constitutive activation of the MEK/ERK MAPK signaling pathway is the key for tumorigenesis, and they have been shown to be client proteins for HSP90. Accordingly, HSP90 inhibition can suppress certain cancer-causing client proteins and therefore represents an important therapeutic target. The molecular mechanism underlying the anti-cancer effect of HSP90 inhibition is complicated. Geldanamycin and its derivatives have been shown to induce the depletion of mutationally-activated BRAF through several mechanisms. In this review, we will describe the HSP90-inhibitory mechanism, focusing on recent progress in understanding HSP90 chaperone structure-function relationships, the identification of new HSP90 client proteins and the development of HSP90 inhibitors for clinical applications.
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PMID:Geldanamycin and its anti-cancer activities. 1985 Apr 5

Heat shock protein 90 (HSP90) is expressed ubiquitously in a variety of cell types including osteoblasts. HSP90 acts as a key driver of proteostasis under pathophysiological conditions. Here, we investigated the involvement of HSP90 in extracellular ATP-stimulated interleukin (IL)-6 synthesis and HSP90 downstream signalling in osteoblast-like MC3T3-E1 cells. In osteoblasts, extracellular ATP stimulates the synthesis of IL-6, a bone-remodelling agent. Geldanamycin, 17-allylamino-17-demethoxy-geldanamycin (17-AAG) and onalespib, three different HSP90 inhibitors, amplified the ATP-stimulated IL-6 release. Geldanamycin increased IL-6 mRNA expression elicited by ATP. ATP enhanced the triiodothyronine-induced osteocalcin release, but HSP90 inhibitors suppressed the release. Extracellular ATP induced the phosphorylation of p44/p42 mitogen-activated protein kinase (MAPK), p38 MAPK, c-Jun N-terminal kinase (JNK), p70 S6 kinase, Akt, and myosin phosphatase-targeting subunit (MYPT), a Rho-kinase substrate. SB203580, an inhibitor of p38 MAPK, suppressed ATP-stimulated IL-6 release. Inhibitors of MEK1/2 (PD98059), JNK (SP600125), upstream kinase of p70 S6 kinase (rapamycin) and Akt (deguelin), all increased IL-6 release. Y27632, a Rho-kinase inhibitor, failed to affect the IL-6 release stimulated by ATP. Geldanamycin and 17-AAG both amplified ATP-induced p38 MAPK phosphorylation, although geldanamycin inhibited the phosphorylation of Akt induced by ATP. In addition, SB203580 significantly reduced the amplification by geldanamycin of the IL-6 release. Taken together, our results strongly suggest that HSP90 inhibitors up-regulate extracellular ATP-stimulated IL-6 synthesis via amplification of p38 MAPK activation in osteoblasts. SIGNIFICANCE OF THE STUDY: Heat shock protein 90 (HSP90) acts as a key driver of proteostasis under pathophysiological conditions in a variety of cell types. We have previously shown that HSP90 is expressed at high levels in osteoblast-like MC3T3-E1 cells, even in their quiescent state, consistent with HSP90 performing an important physiological function in osteoblasts. In the present study, we investigated whether HSP90 is implicated in extracellular ATP-induced interleukin (IL)-6 synthesis in osteoblast-like MC3T3-E1 cells. Our results strongly suggest that HSP90 inhibitors up-regulate extracellular ATP-stimulated IL-6 synthesis via amplification of p38 mitogen-activated protein kinase activation in osteoblasts.
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PMID:HSP90 inhibitors strengthen extracellular ATP-stimulated synthesis of interleukin-6 in osteoblasts: Amplification of p38 MAP kinase. 3256 86