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

While most untransformed cells require substrate attachment for growth (anchorage dependence), the oncogenic transformed cells lack this requirement (anchorage independence) and are often tumorigenic. However, the mechanism of loss of anchorage dependence is not fully understood. When rat normal fibroblasts were cultured in suspension without substrate attachment, the cell cycle arrested in G1 phase and the cyclin-dependent kinase inhibitor p27Kip1 protein and its mRNA accumulated. Conditional expression of oncogenic Ras induced the G1-S transition of the cell cycle and significantly shortened the half-life of p27Kip1 protein without altering its mRNA level. Inhibition of the activation of mitogen-activated protein (MAP) kinase by cyclic AMP-elevating agents and a MEK inhibitor prevented the oncogenic Ras-induced degradation of p27Kip1. These results suggest that the loss of substrate attachment induces the cell cycle arrest through the up-regulation of p27Kip1 mRNA, but the oncogenic Ras confers anchorage independence by accelerating p27Kip1 degradation through the activation of the MAP kinase signaling pathway. Furthermore, we have found that p27Kip1 is phosphorylated by MAP kinase in vitro and the phosphorylated p27Kip1 cannot bind to and inhibit cdk2.
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PMID:Induction of p27Kip1 degradation and anchorage independence by Ras through the MAP kinase signaling pathway. 926 3

Transforming growth factor (TGF)-beta is a potent growth suppressor of epithelial cells. Resistance to TGF-beta, however, occurs frequently in solid tumors of epithelial origin and contributes to the uncontrolled growth of these tumors. Although mutant receptor proteins contribute to TGF-beta insensitivity, deregulation of TGF-beta signaling cascades represents an equally important mechanism underlying TGF-beta resistance. Identification of abnormal regulation of signaling components in tumor epithelial cells will lead to the development of selective therapeutic approaches to repair the relevant signaling cascade(s) and reverse the growth anomaly. Within the past few years, great strides have been made in defining signaling pathways for TGF-beta. For example, our laboratory has demonstrated a direct correlation between TGF-beta-mediated growth inhibition of epithelial cells and activation of Ras and three members of the mitogen-activated protein kinase (MAPK) superfamily. The TGF-beta signaling events were sustained, dose-dependent, and absent in TGF-beta-resistant cells. Further, up-regulation of both p27Kip1 and p21Cip1, nuclear events important for the growth inhibitory effect of TGF-beta, are completely dependent upon the activation of Ras. However, Ras-independent pathways are also activated simultaneously with the Ras/MAPK pathways to mediate the final TGF-beta growth inhibitory outcome. One such pathway includes the SMAD signaling components that control TGF-beta-mediated gene transcription, currently under active study by a number of laboratories, including our own. Future efforts in this field will focus on defining the significance of these signaling proteins and pathways in mediating specific TGF-beta responses. Moreover, additional novel signaling proteins are sure to be identified.
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PMID:Transforming growth factor-beta signaling in epithelial cells. 936 79

Cell cycle re-entry requires the growth factor-stimulation of at least two distinct classes of protein kinases: (i) the p42/p44 MAP kinases activated by the Ras > Raf > MKK cascade and (ii) the G1 cyclin-dependent protein kinases (CDKs). Specific inactivation of either class of kinase arrests fibroblasts in G1. Growth factors promote nuclear translocation and persistent activation of p42/p44 MAP kinases during the entire G0/G1 period. Here, we demonstrate that induction of cyclin D1, and therefore cdk4/6 activity associated with, is positively controlled by the p42/p44 MAP kinase cascade whereas the parallel cytokines/stress-activated p38MAP kinase cascade is antagonistic. Finally, using an antisense approach we demonstrate that p27Kip1 plays a key role in setting the growth factor-dependency of the G0 state.
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PMID:A temporal and biochemical link between growth factor-activated MAP kinases, cyclin D1 induction and cell cycle entry. 955 82

Basic fibroblast growth factor (bFGF, FGF-2) is progressively lost from mammary epithelial cells as they become malignant. To investigate the effects of restoring the expression of bFGF in breast cancer cells, we constructed MCF-7 cells that permanently overexpress 18-kD cytoplasm-localizing bFGF (MCF-7/deltaA(FGF)(18) cells) and cells that express both the 18-kD along with the 22- and 24-kD nucleus-localizing bFGF peptides (MCF-7/NCF(FGF)(18,22,24) cells), using retroviral transduction. These stable cell constructs grew more slowly and had a larger fraction of their populations in the G0/G1 phase of the cell cycle than control cells. All forms of bFGF were eluted from MCF-7/NCF(FGF)(18,22,24) cell monolayers with 2 M NaCl, in contrast to fibroblasts that were demonstrated to secrete only the 18-kD bFGF isoform. High-affinity binding of 18-kD 125I-bFGF to these cells was significantly decreased, probably because of competitive binding by the autocrine-secreted bFGF. Recombinant 18-kD bFGF that was previously demonstrated in our laboratory to inhibit proliferation, activate MAP kinase, and induce the cyclin-dependent kinase inhibitor p21WAF1/CIP1 in MCF-7 cells, further inhibited MCF-7/deltaA(FGF)(18) cells but had no effect on MCF-7/NCF(FGF)(18,22,24) cells. The total cellular content of the high-affinity FGF receptors 1-3 was unchanged, but FGF receptor 4 was decreased in MCF-7/NCF(FGF)(18,22,24) cells. Both cell types overexpressing bFGF isoforms had elevated levels of the cyclin-dependent kinase inhibitor p27Kip1 but not that of p21WAF1/CIP1. In MCF-7/deltaA(FGF)(18) cells, FGFR1 and MAP kinase were constitutively phosphorylated. Exogenous recombinant 18-kD bFGF did not accentuate these effects but did induce an increase in the levels of p21WAF1/CIP1 corresponding to the further inhibition induced by exogenous bFGF in these cells. In MCF-7/NCF(FGF)(18,22,24) cells, FGFR1 and MAP kinase were not phosphorylated at baseline nor upon stimulation with recombinant bFGF, and exogenous bFGF only had a minimal effect on low steady-state p21WAF1/CIP1 levels. However, stimulation of these cells with phorbol ester or insulin did result in MAP kinase phosphorylation. While growth-inhibited in the G1 phase of the cell cycle, MCF-7/NCF(FGF)(18,22,24) cells retained active isoforms of cdk2 and the hyperphosphorylated form of Rb. These data suggest that high molecular weight forms of bFGF overexpressed in MCF-7 cells do not activate the receptor-mediated MAP kinase pathway, and do not induce p21WAF1/CIP1 in an autocrine manner, but inhibit proliferation through other, possibly direct nuclear signalling mechanisms.
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PMID:Overexpression of basic fibroblast growth factor in MCF-7 human breast cancer cells: lack of correlation between inhibition of cell growth and MAP kinase activation. 980 50

Growth factor-stimulated DNA synthesis in a variety of cell lines has been shown to be decreased after overnight (or longer) treatment with the 3-hydroxy-3-methylglutaryl CoA reductase inhibitors, the statins. Although this anti-mitogenic effect had been presumed to be the result of the impairment of Ras lipidation, a stable modification (T1/2 approximately 20 h), this study provides new data demonstrating that brief (approximately 1 h) pretreatment of rat vascular smooth muscle cells with 100 microM pravastatin before platelet-derived growth factor-BB (PDGF-BB) stimulation results in attenuation of DNA synthesis through a Ras-independent mechanism. PDGF-BB-stimulated PDGF-beta receptor tyrosine phosphorylation, Ras activity, and mitogen-activated protein/extracellular signal-regulated kinase activity are unaffected by from 10 min to 1 h of pravastatin incubation, while Raf activity is markedly increased after 1 h of pravastatin. Phosphatidylinositol-3 kinase activity and phosphorylation of its downstream effector Akt are decreased after 1 h pravastatin incubation. Rho is stabilized by pravastatin, and ADP-ribosylation of Rho by C3 exoenzyme decreases PDGF-stimulated phosphatidylinositol-3 kinase activity, mimicking the effect of pravastatin on this signaling protein. Levels of the cyclin-dependent kinase inhibitor p27Kip1 are increased when cells were preincubated with pravastatin for 1 h and then exposed to PDGF, and apoptosis is induced by pravastatin incubation times as short as 1 to 4 h. Thus, short-term, high-dose pravastatin inhibits vascular smooth muscle cell growth and induces apoptosis independently of Ras, likely by means of the drug's effect on p27Kip1, mediated by Rho and/or phosphatidylinositol-3 kinase. This work demonstrates for the first time that the statins may be therapeutically useful when applied for short periods of time such that potential toxicity of long-term statin use (such as chronic Ras inhibition) may be avoided, suggesting future therapeutic directions for statin research.
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PMID:Short-term pravastatin mediates growth inhibition and apoptosis, independently of Ras, via the signaling proteins p27Kip1 and P13 kinase. 1047 39

The ErbB2 receptor tyrosine kinase is overexpressed in a variety of human tumours. In order to understand the mechanism by which ErbB2 mediates tumour proliferation we have functionally inactivated the receptor using an intracellularly expressed, ER-targeted single-chain antibody (scFV-5R). Inducible expression of scFv-5R in the ErbB2-overexpressing SKBr3 breast tumour cell line leads to loss of plasma membrane localized ErbB2. Simultaneously, the activity of ErbB3, MAP kinase and PKB/Akt decreased dramatically, suggesting that active ErbB2/ErbB3 dimers are necessary for sustained activity of these kinases. Loss of functional ErbB2 caused the SKBr3 tumour cells to accumulate in the G1 phase of the cell cycle. This was a result of reduction in CDK2 activity, which was mediated by a re-distribution of p27Kip1 from sequestering complexes to cyclin E/CDK2 complexes. The level of c-Myc and D-cyclins, proteins involved in p27KiP1 sequestration, decreased in the absence of functional ErbB2. Ectopic expression of c-Myc led to an increase in D cyclin levels, CDK2 activity and resulted in a partial G1 rescue. We propose that c-Myc is a primary effector of ErbB2-mediated oncogenicity and functions to prevent normal p27Kip1 control of cyclinE/CDK2.
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PMID:Effects of oncogenic ErbB2 on G1 cell cycle regulators in breast tumour cells. 1076 21

An enhanced vasoconstriction and vascular smooth muscle cell proliferation are involved in pathogenesis of hypertension. Beta3-blockers are effective for treatment of hypertensive patients. Recently the new beta1-receptor blocker nebivolol showed a different hemodynamic profile from those of other classic beta-blockers. In this study we hypothesized that nebivolol may also have different effects on smooth muscle cell proliferation compared with other beta-blockers such as atenolol. Human aortic smooth muscle cells (SMCs) were cultured, and cell growth was determined by increase in cell number. Growth-signaling molecules such as mitogen-activated protein kinase (p42mapk) and S6-kinase (p70S6K) and cell-cycle regulatory proteins (i.e., Cdk2, p27Kip1, and pRb) were analyzed by immunoblotting. In cultured human aortic SMCs, cell number was markedly increased in response to 5% fetal calf serum (FCS) over 6 days (87 +/- 11 x 10(3)/well), which was inhibited by nebivolol (10(-8)-10(-5) M; 25 +/- 2 x 10(3)/well; n = 6; p < 0.05), but not by atenolol. 5% FCS activated p42mapk, S6K, and Cdk2, but downregulated p27Kip1 and hyperphosphorylated pRb. Nebivolol prevented Cdk2 activation without influencing p42mapk, S6K, pRB, and p27Kip1. Thus, the new beta1-blocker nebivolol exhibits antiproliferative effect on human SMC through inactivation of Cdk2. This effect of nebivolol may have advantages over other beta-blockers in treatment of patients with cardiovascular disease.
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PMID:Nebivolol inhibits human aortic smooth muscle cell growth: effects on cell cycle regulatory proteins. 1083 16

To understand the molecular mechanisms by which anti-p185HER2 antibody and the ligand heregulin inhibit tumor growth, we have investigated several signaling proteins and pathways. We report here that anti-p185HER2 monoclonal antibody ID5 induced tyrosine phosphorylation of HER2 in SKBr3 breast cancer cells that overexpress p185HER2. Heregulin beta1 induced phosphorylation of both HER3 and HER2. ID5 produced a greater association of phospholipase C (PLC)-gamma1 with HER2 than did heregulin. Concordantly, ID5, but not heregulin, increased PLC-gamma1 activity. However, the G1 cell cycle arrest and induction of p27Kip1 produced by ID5 were not affected by the inhibition of PLC-gamma. ID5 preferentially induced binding of the Mr 46,000 isoform of SHC to HER2, whereas heregulin preferentially induced binding of the Mr 52,00 isoform of SHC to HER3. Heregulin, but not ID5, induced the p85 subunit of phosphatidylinositol 3'-kinase (PI3-K) to interact with HER3. Heregulin induced sustained activation of P13-K signaling, whereas ID5 had only a transient effect. Heregulin, but not ID5, activated the c-Jun-NH2-terminal kinase cascade. Pretreatment of SKBr3 cells with ID5 decreased heregulin-induced association of HER2 with HER3 as well as the activation of c-Jun-NH2-terminal kinase and PI3-K activities. Inhibition of the mitogen-activated protein kinase pathway in SKBr3 cells did not affect heregulin-induced G2-M-phase arrest, apoptosis, and differentiation. Heregulin-induced apoptosis could be blocked by inhibition of p70s6k, but not by inhibition of PI3-K. Heregulin-induced differentiation could be eliminated by inhibition of PI3-K. We conclude that ID5 and heregulin signal via different pathways, although both agents can inhibit the clonogenic growth of cells that overexpress HER2.
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PMID:Differential signaling by an anti-p185(HER2) antibody and heregulin. 1091 64

The Akt/PKB protein kinase is implicated in the control of cell cycle progression and the suppression of apoptosis in cancer cells. Here we describe the use of a conditionally active form of Akt/PKB (M+ Akt:ER*) to study the ability of this protein to influence biological processes that are central to the process of oncogenic transformation of mammalian cells. Activation of M+ Akt:ER* in Rat1 cells elicited alterations in cell morphology and promoted anchorage-independent growth in agarose with high efficiency. Consistent with these observations, activation of M+ Akt:ER* suppressed the apoptosis of Rat1 cells that occurs after the detachment of these cells from extracellular matrix. Furthermore, activation of M+ Akt:ER* was sufficient to promote the progression of quiescent Rat1 cells into the S and G2-M phases of the cell cycle. In accord with this is the observation that activation of M+ Akt:ER* led to decreased expression of the cyclin-dependent kinase inhibitor p27Kip1 with a concomitant increase in cyclin-dependent kinase-2 activity. Perhaps surprisingly, activation of M+ Akt:ER* or expression of a constitutively active form of Akt led to rapid activation of MAP/ERK Kinase (MEK) and the extracellular signal-regulated kinase (ERK)/mitogen-activated protein (MAP) kinases in Rat1 cells. However, pharmacological inhibition of MEK by PD098059 did not inhibit the morphological alterations of Rat1 cells that occur after M+ Akt:ER* activation. These data suggest that M+ Akt:ER* can activate a number of pathways in Rat1 cells, leading to significant alterations in a number of biological processes. The conditional transformation system described here will allow further elucidation of the ability of Akt to contribute to both the normal response of cells to mitogenic stimulation and the aberrant proliferation observed in cancer cells.
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PMID:Oncogenic transformation of cells by a conditionally active form of the protein kinase Akt/PKB. 1091 95

The functional role of the cyclin-dependent kinase inhibitor (CDKI) p21CIP1 in differentiation of human myelomonocytic leukemia cells (U937) exposed to low concentrations of the antimetabolite 1-beta-D-arabino-furanosylcytosine (ara-C) was examined utilizing a cell line stably expressing a p21CIP1 antisense construct. Continuous exposure to 50 nM ara-C led to marked induction of p21CIP1 at 48-72 h in empty-vector control cells but not in their antisense-expressing counterparts (p21AS/F4 and B8). Such treatment induced expression of the myelomonocytic differentiation marker CD11b in approximately 35% of control cells, but no evidence of maturation was noted in antisense-expressing lines. However, antisense-expressing cells exposed to low concentrations of ara-C exhibited a reciprocal increase in apoptosis, manifested by the appearance of cells with classic morphologic features and hypodiploid quantities of DNA, reduced mitochondrial membrane potential (deltapsim), an increase in cytochrome c release into the cytosol, cleavage/activation of procaspases-9 and -3, and degradation of PARP and p27Kip1. Whereas empty-vector control cells exposed to 50 nM ara-C exhibited a decline in Bcl-2 expression, dephosphorylation of pRb, and an initial accumulation in S-phase, antisense-expressing cells did not. However, c-Myc down-regulation induced by low concentrations of ara-C was, if anything, more complete in antisense-expressing cells. Exposure of control but not antisense-expressing cells to ara-C led to phosphorylation/activation of MAP kinase at 24 h; moreover, the specific MEK/MAP kinase inhibitor PD98059 enhanced low-dose ara-C-mediated apoptosis only in wild-type cells. Lastly, exposure to 50 nM ara-C for 72 h resulted in detectable levels of cytoplasmic p21CIP1, a phenomenon associated with resistance to apoptosis, only in empty vector controls. Collectively, these findings demonstrate a functional role for p21CIP1 in leukemic cell maturation induced by low concentrations of ara-C. They also indicate that, as in the case of more conventional differentiation-inducers such as phorbol esters, disruption of the p21CIP1 response after exposure to low concentrations of the cytotoxic drug ara-C prevents leukemic cells from engaging a maturation program, but instead directs them along an apoptotic pathway.
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PMID:Evidence of a functional role for the cyclin-dependent kinase inhibitor p21CIP1 in leukemic cell (U937) differentiation induced by low concentrations of 1-beta-D-arabinofuranosylcytosine. 1099 87


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