Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P42345 (mTOR)
 26,049 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Interleukin-6 (IL-6) is a prominent tumor growth factor for malignant multiple myeloma cells. In addition to its known activation of the Janus tyrosine kinase-STAT and RAS-MEK-ERK pathways, recent work suggests that IL-6 can also activate the phosphatidylinositol 3-kinase (PI3-K)/AKT kinase pathway in myeloma cells. Because activation of the PI3-K/AKT as well as RAS-MEK-ERK pathways may result in downstream stimulation of the p70(S6K) (p70) and phosphorylation of the 4E-BP1 translational repressor, we assessed these potential molecular targets in IL-6-treated myeloma cells. IL-6 rapidly activated p70 kinase activity and p70 phosphorylation. Activation was inhibited by wortmannin, rapamycin, and the ERK inhibitors PD98059 and UO126, as well as by a dominant negative mutant of AKT. The concurrent requirements for both ERK and PI3-K/AKT appeared to be a result of their ability to phosphorylate p70 on different residues. In contrast, IL-6-induced phosphorylation of 4E-BP1 was inhibited by rapamycin, wortmannin, and dominant negative AKT but ERK inhibitors had no effect, indicating ERK function was dispensable. In keeping with these data, a dominant active AKT mutant was sufficient to induce 4E-BP1 phosphorylation but could not by itself activate p70 kinase activity. Prevention of IL-6-induced p70 activation and 4E-BP1 phosphorylation by the mammalian target of rapamycin inhibitors rapamycin and CCI-779 resulted in inhibition of IL-6-induced myeloma cell growth. These results indicate that both ERK and PI3-K/AKT pathways are required for optimal IL-6-induced p70 activity, but PI3-K/AKT is sufficient for 4E-BP1 phosphorylation. Both effects are mediated via mammalian target of rapamycin function, and, furthermore, these effects are critical for IL-6-induced tumor cell growth.
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PMID:Signal pathways involved in activation of p70S6K and phosphorylation of 4E-BP1 following exposure of multiple myeloma tumor cells to interleukin-6. 1187 47

We have recently demonstrated that furin, PC5, and PC7, members of the subtilisin/kexin-like mammalian proprotein convertases (PCs), are found in rodent aorta. These PCs have been identified to activate several growth factors, adhesion molecules and extracellular matrix compounds by endoproteolytic cleavage. In the present study, we investigated the regulation of PC5 in vascular smooth muscle cells (VSMCs) in vitro and in vivo. Stimulation of rat aortic VSMCs with platelet-derived growth factor (PDGF)-BB (20 ng/mL), angiotensin II (Ang II, 1 micromol/L), or 10% fetal calf serum (FCS) for 48 hours increased DNA synthesis, as assessed by proliferating cell nuclear antigen (PCNA) immunoblotting. PC5 was strongly upregulated by PDGF-BB and 10% FCS (both 8-fold, P<0.05), whereas Ang II had no effect on PC5 protein levels compared with controls. The PCs furin and PC7, which display a comparable subcellular localization and cleavage activity, were found in VSMCs, but their levels did not increase following PDGF-BB, Ang II, or FCS stimulation. Time-course analysis revealed a rapid increase in PC5 levels after 30 minutes of PDGF-stimulation of VSMCs. PDGF-stimulated PC5 induction was inhibited by the PI3-kinase inhibitor wortmannin, and by rapamycin, an inhibitor of mTOR/p70(s6)-kinase (both P<0.05). In contrast, the mitogen-activated protein kinase (MAPK)-pathway inhibitor PD98059 did not inhibit PDGF-stimulated PC5 induction. Immunocytochemistry and in situ hybridization revealed low PC5 protein and mRNA levels in intact rat aorta in vivo. After balloon injury, PC5 protein and mRNA levels were strongly increased in proliferating PCNA-positive VSMCs. The present data demonstrate that PC5 is upregulated during proliferation of VSMCs in vivo and in vitro. We show that PDGF-induced PC5 expression is PI3-kinase/p70(s6)-kinase dependent. Thus, growth factors regulate the proprotein convertase PC5, which may play an important role during VSMC growth.
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PMID:Proprotein convertase PC5 regulation by PDGF-BB involves PI3-kinase/p70(s6)-kinase activation in vascular smooth muscle cells. 1188 80

The mitogen-stimulated protein kinase p70(s6k)/p85(s6k) (S6K) plays an essential role in cell proliferation and growth, with inhibitors of the S6K signalling pathway showing promise as anti-tumour therapeutics. Here, we report that the bisindolylmaleimide derivative Ro 31-6045, previously reported to be inactive as a kinase inhibitor, inhibited S6K activity in vivo with an IC50=8 microM. Structure/function analysis using mutant forms of S6K indicates that Ro 31-6045 inhibition is independent of the upstream activator mTOR. Ro 31-6045 will prove useful in elucidating the complex activation mechanism of S6K and its independence from mTOR will allow confirmation of functional data obtained using the mTOR inhibitor rapamycin.
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PMID:Ro 31-6045, the inactive analogue of the protein kinase C inhibitor Ro 31-8220, blocks in vivo activation of p70(s6k)/p85(s6k): implications for the analysis of S6K signalling. 1202 32

Tuberous sclerosis (TSC) is an autosomal dominant disorder characterized by the formation of hamartomas in a wide range of human tissues. Mutation in either the TSC1 or TSC2 tumour suppressor gene is responsible for both the familial and sporadic forms of this disease. TSC1 and TSC2 proteins form a physical and functional complex in vivo. Here, we show that TSC1-TSC2 inhibits the p70 ribosomal protein S6 kinase 1 (an activator of translation) and activates the eukaryotic initiation factor 4E binding protein 1 (4E-BP1, an inhibitor of translational initiation). These functions of TSC1-TSC2 are mediated by inhibition of the mammalian target of rapamycin (mTOR). Furthermore, TSC2 is directly phosphorylated by Akt, which is involved in stimulating cell growth and is activated by growth stimulating signals, such as insulin. TSC2 is inactivated by Akt-dependent phosphorylation, which destabilizes TSC2 and disrupts its interaction with TSC1. Our data indicate a molecular mechanism for TSC2 in insulin signalling, tumour suppressor functions and in the inhibition of cell growth.
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PMID:TSC2 is phosphorylated and inhibited by Akt and suppresses mTOR signalling. 1217 53

Signaling events involving angiotensin IV (ANG IV)-mediated pulmonary artery endothelial cell (PAEC) proliferation were examined. ANG IV significantly increased upstream phosphatidylinositide (PI) 3-kinase (PI3K), PI-dependent kinase-1 (PDK-1), extracellular signal-related kinases (ERK1/2), and protein kinase B-alpha/Akt (PKB-alpha) activities, as well as downstream p70 ribosomal S6 kinase (p70S6K) activities and/or phosphorylation of these proteins. ANG IV also significantly increased 5-bromo-2'-deoxy-uridine incorporation into newly synthesized DNA in a concentration- and time-dependent manner. Pretreatment of cells with wortmannin and LY-294002, inhibitors of PI3K, or rapamycin, an inhibitor of the mammalian target of rapamycin kinase and p70S6K, diminished the ANG IV-mediated activation of PDK-1 and PKB-alpha as well as phosphorylation of p70S6K. Although an inhibitor of mitogen-activated protein kinase kinase, PD-98059, but not rapamycin, blocked ANG IV-induced phosphorylation of ERK1/2, both PD-98059 and rapamycin independently caused partial reduction in ANG IV-mediated cell proliferation. However, simultaneous treatment with PD-98059 and rapamycin resulted in total inhibition of ANG IV-induced cell proliferation. These results demonstrate that ANG IV-induced DNA synthesis is regulated in a coordinated fashion involving multiple signaling modules in PAEC.
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PMID:Activation of multiple signaling modules is critical in angiotensin IV-induced lung endothelial cell proliferation. 1222 47

The mammalian target of rapamycin (mTOR) is a Ser/Thr (S/T) protein kinase, which controls mRNA translation initiation by modulating phosphorylation of the translational regulators PHAS-I and p70(S6K). Here we show that in vitro mTOR is able to phosphorylate these two regulators at comparable rates. Both (S/T)P sites, such as Thr36, Thr45, and Thr69 in PHAS-I and the h(S/T)h site (where h is a hydrophobic amino acid) Thr389 in p70(S6K), were phosphorylated. Rapamycin-FKBP12 inhibited mTOR activity. Surprisingly, the extent of inhibition depended on the substrate. Moreover, mutating Ser2035 in the rapamycin-binding domain (FRB) not only decreased rapamycin sensitivity as expected but also dramatically affected the sites phosphorylated by mTOR. The results demonstrate that mutations in Ser2035 are not silent with respect to mTOR activity and implicate the FRB in substrate recognition. The findings also impose new limitations on interpreting results from experiments in which rapamycin and/or rapamycin-resistant forms of mTOR are used to investigate mTOR function in cells.
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PMID:The rapamycin-binding domain governs substrate selectivity by the mammalian target of rapamycin. 1237 Feb 90

The p70 S6 kinase (p70(S6k)) is a Ser/Thr kinase that plays an important role in cell growth, transformation, and the transition of the cell cycle in mammalian cells. Because UV radiation has been reported to induce activation of p70(S6k), which is believed to play some role in the carcinogenic effects of sun exposure, the present study investigated the signaling pathways involved in this activation induced by UV radiation in mouse epidermal JB6 Cl41 cells. Exposure of cells to UV radiation led to marked increases in p70(S6k) activity and phosphorylation at Thr(389) and Thr(421)/Ser(424). UV radiation also generated reactive oxygen species as measured by electron spin resonance and by H(2)O(2) and O( minus sign, dot below )(2) fluorescence staining assays in JB6 Cl 41 cells. The scavenging of UV-generated H(2)O(2) by N-acety-L-cyteine (a general antioxidant) or catalase (a specific H(2)O(2) scavenger) inhibited p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424), whereas pretreatment of cells with sodium formate (an.OH radical scavenger) or superoxide dismutase (an O( minus sign, dot below )(2) radical scavenger) did not show any inhibitory effects. Importantly, UV-induced increases in p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424) were dramatically inhibited by pretreatment of cells with rapamycin, LY294002, or PD98059, whereas overexpression of dominant-negative mutants of PKClambda/iota and Akt1 did not inhibit p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424). These results demonstrated that H(2)O(2), phosphatidylinositol 3-kinase, and mammalian target of rapamycin were important players for UV-induced p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424), whereas Akt and atypical protein kinase C were not involved in this activation. The role of H(2)O(2) in p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424) was further supported by the findings that treatment of cells with H(2)O(2) also caused p70(S6k) phosphorylation at Thr(389) and Thr(421)/Ser(424).
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PMID:Ultraviolet-induced phosphorylation of p70(S6K) at Thr(389) and Thr(421)/Ser(424) involves hydrogen peroxide and mammalian target of rapamycin but not Akt and atypical protein kinase C. 1238 26

Phosphatase and tensin homologue deleted from chromosome 10 (PTEN) is a lipid phosphatase with putative tumor suppressing abilities, which is frequently mutated in prostate cancer. Loss of PTEN leads to constitutive activation of the phosphatidylinositol 3'-kinase/serine-threonine kinase (Akt) signal transduction pathway and has been associated with resistance to chemotherapy. This study aimed to determine the effects of PTEN status and treatment with rapamycin, an inhibitor of mTOR, in the response of prostate cancer cell lines to doxorubicin. The DU-145 PTEN-positive cell line was significantly more susceptible to the antiproliferative effects of doxorubicin as compared with the PTEN-negative PC-3 cell line. Transfection of PTEN into the PC3 cells decreased the activation of Akt and the downstream mTOR-regulated 70-kDa S6 (p70(s6k)) kinase and reversed the resistance to doxorubicin in these cells, indicating that changes in PTEN status/Akt activation modulate the cellular response to doxorubicin. Treatment of PC-3 PTEN-negative cells with rapamycin inhibited 70-kDa S6 kinase and increased the proliferative response of these cells to doxorubicin, so that it was comparable with the responses of PTEN-positive DU-145 cells and the PC-3-transfected cells. Furthermore, treatment of mice bearing the PTEN-negative PC-3 prostate cancer xenografts with CCI-779, an ester of rapamycin in clinical development combined with doxorubicin, inhibited the growth of the doxorubicin-resistant PC-3 tumors confirming the observations in vitro. Thus, rapamycin and CCI-779, by interacting with downstream intermediates in the phosphatidylinositol 3'-kinase/Akt signaling pathway, reverse the resistance to doxorubicin conferred by PTEN mutation/Akt activation. These results provide the rationale to explore in clinical trials whether these agents increase the response to chemotherapy of patients with PTEN-negative/Akt active cancers.
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PMID:Inhibitors of mTOR reverse doxorubicin resistance conferred by PTEN status in prostate cancer cells. 1241 39

Anchorage-independent growth is a hallmark of oncogenic transformation. We reported that the mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitor U0126 inhibited anchorage-independent growth of Ki-ras-transformed rat fibroblasts by simultaneously blocking both extracellular signal-regulated kinase (ERK) and mammalian target of rapamycin (mTOR)-p70(S6K) pathways. Here, we examined the effects of U0126 on the growth of eight human breast cancer cell lines. U0126 selectively repressed anchorage-independent growth of MDA-MB231 and HBC4 cells, two lines with constitutively activated ERK. Loss of contact with substratum triggers apoptosis in many normal cell types, a phenomenon termed anoikis. U0126 sensitized MDA-MB231 and HBC4 to anoikis, i.e., upon treatment with U0126, cells deprived of anchorage entered apoptosis, whereas adherent cells remained viable. Another MEK inhibitor PD98059 also induced anoikis sensitivity in MDA-MB231 cells but not in HBC4 cells. However, HBC4 cells were sensitized to anoikis when PD98059 was combined with the mTOR inhibitor rapamycin. To study the biochemical basis for induction of anoikis sensitivity, we examined the effects of the MEK inhibitors on ERK and p70(S6K) pathways in anchored versus nonanchored cells. As in Ki-ras-transformed rat fibroblasts, U0126 reduced activation of both ERK and p70(S6K) in MDA-MB231 and HBC4 cells, irrespective of anchorage. PD98059, in anchored cells, was more selective for the ERK pathway and did not significantly block the p70(S6K) pathway. Removal of anchorage substantially sensitized p70(S6K) to PD98059 in MDA-MB231 cells, whereas p70(S6K) in suspended HBC4 cells remained fairly refractory. U0126 was either without effect or less inhibitory on p70(S6K) in MDA-MB453 and SKBR3, two cell lines in which anoikis sensitivity was not induced. Thus, susceptibility of the p70(S6K) pathway to MEK inhibitors appeared to be an important determinant of anoikis sensitivity. The results indicate that concurrent inhibition of MEK-ERK and mTOR-p70(S6K) pathways induces apoptosis in MDA-MB231 and HBC4 cells when cells are deprived of anchorage but not when anchored. Inhibitors of MEK-ERK and mTOR-p70(S6K) pathways may provide a therapeutic strategy to selectively target neoplasms proliferating at ectopic locations, with acceptable effects on normal cells in their proper tissue context.
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PMID:Mitogen-activated protein/extracellular signal-regulated kinase kinase (MEK) inhibitors restore anoikis sensitivity in human breast cancer cell lines with a constitutively activated extracellular-regulated kinase (ERK) pathway. 1248 46

A contribution of intracellular dehydration to insulin resistance has been established in human subjects and in different experimental systems. Here the effect of hyperosmolarity (405 mosmol/l) on insulin-induced mitogen-activated protein (MAP) kinase phosphatase (MKP)-1 expression was studied in H4IIE rat hepatoma cells. Insulin induces robust MKP-1 expression which correlates with a vanadate-sensitive decay of extracellular-signal-regulated kinase (Erk-1/Erk-2) activity. Hyperosmolarity delays MKP-1 accumulation by insulin and this corresponds to impaired MKP-1 synthesis, whereas MKP-1 degradation remains unaffected by hyperosmolarity. Rapamycin, which inhibits signalling downstream from the mammalian target of rapamycin (mTOR) and a peptide inhibiting protein kinase C (PKC) zeta/lambda abolish insulin-induced MKP-1 protein but not mRNA expression, suggesting the involvement of the p70 ribosomal S6 protein kinase (p70S6-kinase) and/or the eukaryotic initiation factor 4E-binding proteins (4E-BPs) as well as atypical PKCs in MKP-1 translation. Hyperosmolarity induces sustained suppression of p70S6-kinase and 4E-BP1 hyperphosphorylation by insulin, whereas insulin-induced tyrosine phosphorylation of the insulin receptor (IR) beta subunit and the IR substrates IRS1 and IRS2, recruitment of the phosphoinositide 3-kinase (PI 3-kinase) regulatory subunit p85 to the receptor substrates as well as PI 3-kinase activation, and Ser-473 phosphorylation of protein kinase B and Thr-410/403 phosphorylation of PKC zeta/lambda are largely unaffected under hyperosmotic conditions. The hyperosmotic impairment of both, MKP-1 expression and p70S6-kinase hyperphosphorylation by insulin is insensitive to K(2)CrO(4), calyculin A and vanadate, and inhibition of the Erk-1/Erk-2 and p38 pathways. The suppression of MKP-1 may further contribute to insulin resistance under dehydrating conditions by allowing unbalanced MAP kinase activation.
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PMID:Osmotic regulation of insulin-induced mitogen-activated protein kinase phosphatase (MKP-1) expression in H4IIE rat hepatoma cells. 1252 77


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