Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.24 (mitogen-activated protein kinase)
 95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Insulin-like growth factor I (IGF-I)/insulin induced cytosolic p42/p44 mitogen-activated protein kinase (MAPK) activation in a time-dependent manner in fetal brown adipocytes, reaching a maximum at 5 min. Concurrently, nuclear p42/p44 MAPKs were also activated by IGF-I and insulin. This cytosolic and nuclear MAPK activation was totally prevented by pretreatment with the MAPK kinase (MEK1) inhibitor, PD98059. These results indicate that MEK mediates the IGF-I/insulin-induced p42/ p44 MAPK activation. IGF-I and insulin also increased the number of cells in the S + G2/M phases of the cell cycle, PCNA levels, and DNA synthesis at 24 h. This IGF-I/insulin-induced proliferation was completely blunted by the presence of MEK1 inhibitor. In contrast, inhibition of MEK1 potentiated the IGF-I-induced uncoupling protein (UCP-1) and the insulin-induced fatty acid synthase mRNAs expression after short and long-term treatments. Moreover, transient expression of a transfected active MEK construct (R4F) decreased IGF-I-induced UCP-1 and insulin-induced fatty acid synthase mRNA expression. These results demonstrate that p42/p44 MAPKs are essential intermediates for the IGF-I/insulin-induced mitogenesis, but may have a negative role in the regulation of adipocytic and thermogenic differentiation in brown adipocytes.
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PMID:p42/p44 mitogen-activated protein kinases activation is required for the insulin-like growth factor-I/insulin induced proliferation, but inhibits differentiation, in rat fetal brown adipocytes. 962 58

GH exerts adipogenic activity in several preadipocyte cell lines, whereas in primary rat preadipocytes, GH has an antiadipogenic activity. To better understand the molecular mechanism involved in adipocyte differentiation, the expression of adipocyte-specific genes was analyzed in differentiating preadipocytes in response to GH. We found that the expression of both adipocyte determination and differentiation factor 1 (ADD1) and peroxisome proliferator activated receptor gamma(PPARgamma) was induced in preadipocytes during differentiation. In the presence of GH, which markedly inhibited triglyceride accumulation, no reduction in the expression level of ADD1 was observed in response to GH, whereas there was a 50% reduction in the expression of PPARgamma. The DNA binding activity of the PPARgamma/retinoid X receptor-alpha(RXRalpha) to the ARE7 element from the aP2 gene was also reduced by approximately 50% in response to GH. GH inhibited the expression of late markers of adipocyte differentiation, fatty acid synthase, aP2, and hormone-sensitive lipase by 70-80%. The antiadipogenic effect of GH was not affected by the mitogen-activated protein (MAP) kinase/ extracellular-regulated protein (ERK) kinase inhibitor PD 98059, indicating that the mitogen-activated protein kinase pathway was not involved in GH inhibition of preadipocyte differentiation. The expression of preadipocyte factor-1/fetal antigen 1 was decreased during differentiation, and GH treatment prevented this down-regulation of Pref1/FA1. A possible role for Pref-1/FA1 in mediating the antiadipogenic effect of GH was indicated by the observation that FA1 inhibited differentiation as effectively as GH. These data suggest that GH exerts its inhibitory activity in adipocyte differentiation at a step after the induction of ADD1 but before the induction of genes required for terminal differentiation.
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PMID:Characterization of the inhibitory effect of growth hormone on primary preadipocyte differentiation. 971 40

Fatty acid synthase (FAS) is a critical enzyme in de novo lipogenesis. It catalyzes the seven steps in the conversion of malonyl-CoA and acetyl-CoA to palmitate. We have shown that the rate of FAS transcription is induced dramatically when fasted animals are refed with a high carbohydrate, fat-free diet or when streptozotocin-diabetic mice are given insulin. The FAS promoter was up-regulated by insulin through the proximal insulin response sequence containing an E-box motif at the -65-base pair position. Binding of upstream stimulatory factors to the -65 E-box is functionally required for insulin regulation of the FAS promoter. In the present study, we characterized signaling pathways in the insulin stimulation of FAS transcription using specific inhibitors for various signaling molecules and transfecting engineered phosphatidylinositol (PI) 3-kinase subunits and protein kinase B (PKB)/Akt. PD98059 and rapamycin, which inhibit MAP kinase and P70 S6 kinase, respectively, had little effect on the insulin-stimulated FAS promoter activity in 3T3-L1 adipocytes. On the other hand, wortmannin and LY294002, which specifically inactivate PI 3-kinase, strongly inhibited the insulin-stimulated FAS promoter activity. As shown in RNase protection assays, LY294002 also inhibited insulin stimulation of the endogenous FAS mRNA levels in 3T3-L1 adipocytes. Cotransfection of expression vectors for the constitutively active P110 subunit of PI 3-kinase resulted in an elevated FAS promoter activity in the absence of insulin and a loss of further insulin stimulation. Transfecting a dominant negative P85 subunit of PI 3-kinase decreased FAS promoter activity and blocked insulin stimulation. Furthermore, cotransfected wild-type PKB/Akt increased FAS promoter activity in the absence of insulin and a loss of insulin responsiveness of the FAS promoter. On the other hand, kinase-dead PKB/Akt acted in a dominant negative manner to decrease the FAS promoter activity and abolished its insulin responsiveness. These results demonstrate that insulin stimulation of fatty acid synthase promoter is mediated by the PI 3-kinase pathway and that PKB/Akt is involved as a downstream effector.
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PMID:Insulin stimulation of the fatty acid synthase promoter is mediated by the phosphatidylinositol 3-kinase pathway. Involvement of protein kinase B/Akt. 973 10

Our previous studies have shown that somatotropin (ST) antagonizes insulin stimulation of fatty acid synthase (FAS) enzyme activity and gene transcription in adipocytes. In the present study, inhibitors of insulin and ST signaling pathways were used to dissect the mechanisms by which these hormones regulate FAS gene expression in 3T3-F442A adipocytes. Treating 3T3-F442A adipocytes with 10 microM PD98059, an inhibitor of mitogen-activated protein (MAP) kinase, did not affect the induction of FAS mRNA by insulin. When cells were cultured with H-89 (10 microM), GF109203X (10 microM), or staurosporine (100 nM), inhibitors of protein kinase A, protein kinase C, and Janus kinase (JAK) 2, respectively, the inhibitory effect of ST on FAS mRNA levels was not altered. However, H-89 significantly decreased the stimulatory effect of insulin on FAS mRNA abundance. Moreover, treatment with okadaic acid (1 microM), a serine/threonine phosphatase inhibitor, abolished the induction of FAS mRNA by insulin. These results suggest that serine/threonine dephosphorylation and protein kinase A-dependent pathways are involved in the regulation of FAS gene expression by insulin, but MAP kinase is probably not involved. Furthermore, our data indicate that protein kinase A, protein kinase C, and JAK2 do not mediate the effect of ST on regulation of FAS mRNA abundance.
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PMID:Analysis of the signal pathways involved in the regulation of fatty acid synthase gene expression by insulin and somatotropin. 1137 39

Activation of fatty acid synthase (FAS) expression and fatty acid synthesis is a common event in tumor cells from a variety of human cancers and is closely linked to malignant transformation and to tumor virulence in population studies of human cancer. We now show that, in contrast to nutritional regulation of lipogenesis in liver or adipose tissue, changes in fatty acid metabolism during in vitro transformation of the human mammary epithelial cell line MCF-10a are driven by increases in epidermal growth factor signaling, acting in major part through the mitogen-activated protein (MAP) kinase and phosphatidylinositol (PI) 3-kinase signaling cascades. H-ras transformation of MCF-10a cells resulted in upregulation of MAP kinase and PI 3-kinase signals, upregulation of sterol regulatory element binding protein 1 (SREBP-1) transcription factor levels, and upregulation of FAS expression and FA synthesis. Deletion of the major SREBP binding site from the FAS promoter abrogated transcription in transformed MCF-10a cells. Inhibitors of MAP and PI 3-kinases downregulated SREBP-1 levels and decreased transcription from the FAS promoter, reducing FAS expression and fatty acid synthesis in transformed MCF-10a cells and in MCF-7 and HCT116 carcinoma cells. H-ras transformation sensitized MCF-10a cells to the FAS inhibitors cerulenin and C-75. These results confirm an important role for SREBP-1 in neoplastic lipogenesis, and provide a likely basis for the linkage of upregulated fatty acid metabolism with neoplastic transformation and with tumor virulence, since MAP and PI 3-kinase signaling contributes to both.
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PMID:Activation of fatty acid synthesis during neoplastic transformation: role of mitogen-activated protein kinase and phosphatidylinositol 3-kinase. 1221 16

Activation of fatty acid synthase (FAS) expression and fatty acid synthesis is a common event in human breast cancer. Sterol regulatory element binding proteins (SREBPs) are a family of transcription factors that regulate genes involved in lipid metabolism, including FAS. SREBP-1c expression is induced in liver and adipose tissue by insulin and by fasting/refeeding and is critical for nutritional regulation of lipogenic gene expression. In contrast, upregulation of fatty acid metabolism during in vitro transformation of human mammary epithelial cells and in breast cancer cells was driven by increased MAP kinase and PI 3-kinase signaling, which increased SREBP-1 levels. SREBP-1a was more abundant than SREBP-1c in many proliferative tissues and cultured cells and was thus a candidate to regulate lipogenesis for support of membrane synthesis during cell growth. We now show that SREBP-1c and FAS mRNA were both increased by H-ras transformation of MCF-10a breast epithelial cells and were both reduced by exposure of MCF-7 breast cancer cells to the MAP kinase inhibitor, PD98059, or the PI 3-kinase inhibitor, wortmannin, while SREBP-1a and SREBP-2 showed less variation. Similarly, the mRNA levels for FAS and SREBP-1c in a panel of primary human breast cancer samples showed much greater increases than did those for SREBP-1a and SREBP-2 and were significantly correlated with each other, suggesting coordinate regulation of SREBP-1c and FAS in clinical breast cancer. We conclude that regulation of FAS expression in breast cancer is achieved through modulation of SREBP-1c, similar to the regulation in liver and adipose tissue, although the upstream regulation of liopgenesis differs in these tissues.
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PMID:Regulation of fatty acid synthase expression in breast cancer by sterol regulatory element binding protein-1c. 1253 99

Insulin is a potent inducer of adipogenesis, and differentiation of adipocytes requires many components of the insulin signaling pathway, including the insulin receptor substrate IRS-1 and phosphatidylinositol 3-kinase (PI3K). Brown pre-adipocytes in culture exhibit low levels of insulin receptor (IR), and during differentiation there is both an increase in total IR levels and a shift in the alternatively spliced forms of IR from the A isoform (-exon 11) to the B isoform (+exon 11). Brown pre-adipocyte cell lines from insulin receptor-deficient mice exhibit dramatically impaired differentiation and an inability to regulate alternative splicing of the insulin receptor. Surprisingly, re-expression of either splice isoform of IR in the IR-deficient cells fails to rescue differentiation in these cells. Likewise, overexpression of IR in control IRlox cells also results in inhibition of differentiation and a failure to accumulate expression of the adipogenic markers peroxisome proliferator-activated receptor gamma, Glut4, and fatty acid synthase, although cells overexpressing IR retain the ability to activate PI3K and down-regulate mitogen-activated protein kinase (MAPK) phosphorylation. Thus, differentiation of brown adipocytes requires a timed and regulated expression of IR, and either the absence or overabundance of insulin receptors in these cells dramatically inhibits differentiation.
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PMID:Bi-directional regulation of brown fat adipogenesis by the insulin receptor. 2803 34

Insulin receptor substrate-1 (IRS-1) plays an essential role in mediating the insulin signals that trigger mitogenesis, lipid synthesis, and uncoupling protein-1 gene expression in mouse brown adipocytes. Expression of IRS-3 is restricted mainly to white adipose tissue; expression of this IRS protein is virtually absent in brown adipocytes. We have tested the capacity of IRS-3 to mediate insulin actions in IRS-1-deficient brown adipocytes. Thus, we expressed exogenous IRS-3 in immortalized IRS-1-/- brown adipocytes at a level comparable with that of endogenous IRS-3 in white adipose tissue. Under these conditions, IRS-3 signaling in response to insulin was observed, as revealed by tyrosine phosphorylation of IRS-3, and the activation of phosphatidylinositol (PI) 3-kinase associated with this recombinant protein. However, although insulin promoted the association of Grb-2 with recombinant IRS-3 in IRS-1-/- cells, the exogenous expression of this IRS family member failed to activate p42/44 MAPK and mitogenesis in brown adipocytes lacking IRS-1. Downstream of PI 3-kinase, IRS-3 expression restored insulin-induced Akt phosphorylation, which is impaired by the lack of IRS-1 signaling. Whereas the generation of IRS-3 signals enhanced adipocyte determination and differentiation-dependent factor 1/sterol regulatory element-binding protein (ADD-1/SREBP-1c) and fatty acid synthase mRNA and protein expression, activation of this pathway was unable to reconstitute CCAAT/enhancer-binding protein alpha and uncoupling protein-1 transactivation and gene expression in response to insulin. Similar results were obtained following insulin-like growth factor-I stimulation. In brown adipocytes expressing the IRS-3F4 mutant, the association of the p85alpha regulatory subunit via Src homology 2 binding was lost, but insulin nevertheless induced PI 3-kinase activity and Akt phosphorylation in a wortmannin-dependent manner. In contrast, activation of IRS-3F4 signaling failed to restore the induction of ADD-1/SREBP-1c and fatty acid synthase gene expression in IRS-1-deficient brown adipocytes. These studies demonstrate that recombinant IRS-3 may reconstitute some, but not all, of the signals required for insulin action in brown adipocytes. Thus, our data further implicate a unique role for IRS-1 in triggering insulin action in brown adipocytes.
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PMID:Role of IRS-3 in the insulin signaling of IRS-1-deficient brown adipocytes. 1294 2

A biologically aggressive subset of human breast cancers has been demonstrated to overexpress fatty acid synthase (FAS), the key enzyme of endogenous FA biosynthesis. This breast cancer-specific activation of FAS-dependent lipogenesis, an anabolic-energy-storage pathway of minor importance in normal cells, would render breast cancer cells more vulnerable to anti-metabolite interventions with FAS as therapeutic target. Not surprisingly, pharmacological inhibitors of FAS have been reported to produce both cytostatic and cytotoxic effects in human breast cancer cells, as well as to suppress DNA replication. However, the signal transduction pathway(s) that link FAS hyperactivity and breast cancer cell growth has been unresolved. Here, we have attempted to provide a systematic approach to assess the role of FAS signaling on the survival and proliferation of human breast cancer cells. First, we assessed the level of FAS protein in a panel of human breast cancer cell lines (MCF-7, MDA-MB-231, MDA-MB-453, MDA-MB-435, ZR-75B, T47-D, BT-474, and SK-Br3). FAS expression was graded from ++++ (overexpression) in SK-Br3 cells to + (very low expression) in MDA-MB-231 cells. No correlation was noted between FAS overexpression and estrogen receptor (ER) or progesterone receptor (PR) status, whereas a positive correlation was found between high levels of FAS expression and the amplification and/or overexpression of HER-2/neu oncogene. Because metabolic adaptation of breast cancer cells to the ambient fatty acid concentration may be relevant to the goal of utilizing FAS inhibition as a chemotherapeutic target, we evaluated the effect of exogenous dietary fatty acids on the cytotoxicity resulting from the inhibition of FAS activity. Pharmacological inhibition of FAS activity by the natural antibiotic cerulenin [(2S,3R)-2,3-epoxy-4-oxo-7E,10E-dodecadienamide] resulted in a dose-dependent cytotoxicity which positively paralleled the endogenous level of FAS. Supraphysiological levels of exogenous oleic acid (OA), a omega-9 monounsaturated fatty acid synthesized from a primary-end product of FAS palmitate, significantly diminished cell toxicity caused by cerulenin. Indeed, OA exposure significantly reduced FAS activity and expression by 55% in FAS-overexpressing SK-Br3 cells. omega-3 (alpha-linolenic acid, eicosapentaenoic acid and docosahexaenoic acid) and omega-6 (linoleic acid and arachidonic acid) polyunsaturated fatty acids (PUFAs), however, were unable to rescue breast cancer cells from cerulenin-induced cytotoxicity. Pharmacological blockade of FAS activity in FAS-overexpressing SK-Br3 cells resulted in apoptosis as determined by an enzyme-linked immunosorbent assay for histone-associated DNA fragments, and confirmed by TUNEL DNA-end labeling experiments. We further characterized signaling molecules that participate in the cellular events that follow inhibition of FAS activity and precede apoptosis in breast cancer cells. In SK-Br3 cells, cerulenin-induced inhibition of FAS activity resulted in down-regulation of p53, and up-regulation of cyclin-dependent kinase inhibitor (CDKi) p21WAF1/CIP1. Treatment with cerulenin or a novel small-molecule inhibitor of FAS C75 resulted in a dramatic accumulation of CDKi p27KIP1, which was accompanied by a noteworthy translocation of p27KIP1 from cytosol to cell nuclei. Strikingly, FAS inhibition also caused a significant activation of the Raf-mitogen-activated protein kinase (MEK) extracellular signal-regulated kinase (ERK1/2) cell survival pathway. Interestingly, we demonstrated that inhibition of FAS activity increased the nuclear-to-cytoplasmic ratio of BRCA1, a breast cancer tumor suppressor protein, as well as it induced a nuclear translocalization of the anti-apoptotic nuclear transcription factor-kappaB (NF-kappaB). In conclusion, here we demonstrate that: a) breast cancer cells retain dependence on endogenous fatty acid synthesis and sensitivity to FAS inhibition in the presence of supraphysiological levels of dietary fatty acids, supporting the notion that FAS inhibition may be useful in treFAS inhibition may be useful in treating breast cancer in vivo; b) endogenous fatty acid synthesis is functional in breast cancer cells and is vital since its pharmacological inhibition is cytotoxic by promoting apoptosis, and c) specific blockade of FAS activity induces the accumulation, activation, and/or cellular relocalization of multiple and diverse pro- and anti-apoptotic signaling pathways, suggesting that p53-p21WAF1/CIP1, ERK1/2 MAPK, p27KIP1, BRCA1, and NF-kappaB play a novel role in the breast cancer cell response to a metabolic stress after perturbation of FAS-dependent de novo fatty acid biosynthesis.
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PMID:Novel signaling molecules implicated in tumor-associated fatty acid synthase-dependent breast cancer cell proliferation and survival: Role of exogenous dietary fatty acids, p53-p21WAF1/CIP1, ERK1/2 MAPK, p27KIP1, BRCA1, and NF-kappaB. 1476 44

The Epstein-Barr virus (EBV) immediate-early (IE) protein BRLF1 (R) is a transcription factor that induces the lytic form of EBV infection. R activates certain early viral promoters through a direct binding mechanism but induces transcription of the other EBV IE gene, BZLF1 (Z), indirectly through cellular factors binding to a CRE motif in the Z promoter (Zp). Here we demonstrate that R activates expression of the fatty acid synthase (FAS) cellular gene through a p38 stress mitogen-activated protein kinase-dependent mechanism. B-cell receptor engagement of Akata cells also increases FAS expression. The FAS gene product is required for de novo synthesis of the palmitate fatty acid, and high-level FAS expression is normally limited to liver, brain, lung, and adipose tissue. We show that human epithelial tongue cells lytically infected with EBV (from oral hairy leukoplakia lesions) express much more FAS than uninfected cells. Two specific FAS inhibitors, cerulenin and C75, prevent R activation of IE (Z) and early (BMRF1) lytic EBV proteins in Jijoye cells. In addition, cerulenin and C75 dramatically attenuate IE and early lytic gene expression after B-cell receptor engagement in Akata cells and constitutive lytic viral gene expression in EBV-positive AGS cells. However, FAS inhibitors do not reduce lytic viral gene expression induced by a vector in which the Z gene product is driven by a strong heterologous promoter. In addition, FAS inhibitors do not reduce R activation of a naked DNA reporter gene construct driven by the Z promoter (Zp). These results suggest that cellular FAS activity is important for induction of Z transcription from the intact latent EBV genome, perhaps reflecting the involvement of lipid-derived signaling pathways or palmitoylated proteins. Furthermore, using FAS inhibitors may be a completely novel approach for blocking the lytic form of EBV replication.
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PMID:Fatty acid synthase expression is induced by the Epstein-Barr virus immediate-early protein BRLF1 and is required for lytic viral gene expression. 1504 35


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