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

We studied whether the beta-adrenergic agonist, isoproterenol (ISO), regulates Na,K-ATPase in alveolar epithelial cells (AEC) via a mitogen-activated protein kinase (MAPK)/extracellular signaling related kinase (ERK) dependent pathway. ISO increased ERK activity in AEC by 10 min via a beta-adrenergic receptor, protein kinase A (PKA)-dependent mechanism. Activation of the MAPK pathway by ISO, resulted in increased Na,K-ATPase beta1 and alpha1 subunit protein abundance in whole cell lysates, which resulted in functional Na, K-ATPases at the basolateral membranes. ISO did not change the alpha1 or beta1 mRNA steady state levels, but rapamycin, the inhibitor of the mammalian target of rapamycin, also blocked the ISO-mediated increase in Na,K-ATPase total protein abundance, suggesting a posttranscriptional regulation. We conclude that ISO, regulates the Na,K-ATPase in AEC via PKA, ERK and rapamycin-sensitive mechanisms.
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PMID:beta-agonists regulate Na,K-ATPase via novel MAPK/ERK and rapamycin-sensitive pathways. 1111 25

Tubules may arise during branching morphogenesis through several mechanisms including wrapping, budding, cavitation and cord hollowing. In this report we present evidence that is consistent with renal proximal tubule formation through a process of cord hollowing (a process that requires the concomitant establishment of apicobasal polarity and lumen formation). Pockets of lumen filled with Lucifer Yellow were observed within developing cords of rabbit renal proximal tubule cells in matrigel. The observation of Lucifer Yellow accumulation suggests functional polarization. In the renal proximal tubule Lucifer Yellow is initially transported intracellularly by means of a basolaterally oriented p-aminohippurate transport system, followed by apical secretion into the lumen of the nephron. Consistent with such polarization in developing tubules, Triticum vulgare was observed to bind to the lumenal membranes within pockets of Lucifer Yellow-filled lumens. As this lectin binds apically in the rabbit renal proximal tubule, T. vulgare binding is indicative of the emergence of an apical domain before the formation of a contiguous lumen. Both epidermal growth factor and hepatocyte growth factor stimulated the formation of transporting tubules. The stimulatory effect of both epidermal growth factor and hepatocyte growth factor on tubulogenesis was inhibited by PD98059, a mitogen activated protein kinase kinase inhibitor, rather than by wortmannin, an inhibitor of phosphoinositide 3-kinase. Nevertheless, Lucifer Yellow-filled lumens were observed in tubules that formed in the presence of PD98059 as well as with wortmannin, indicating that these drugs did not prevent the process of cavitation. By contrast, rapamycin, an inhibitor of the mammalian target of rapamycin, prevented the process of cavitation without affecting the frequency of formation of developing cords. Multicellular cysts were observed to form in 8-bromocyclic AMP-treated cultures. As these cysts did not similarly accumulate Lucifer Yellow lumenally, it is very likely that processes other than organic anion accumulation are involved in the process of cystogenesis, including the Na,K-ATPase.
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PMID:Both mitogen activated protein kinase and the mammalian target of rapamycin modulate the development of functional renal proximal tubules in matrigel. 1507 42

We have investigated the expression and regulation of the Na(+)-K(+)-2Cl(-) cotransporter (NKCC) by insulin and hyperosmotic stress in L6 rat skeletal muscle cells. NKCC was identified by immunoblotting as a 170 kDa protein in L6 myotubes and mediated 54% of K(+) ((86)Rb(+)) influx based on the sensitivity of ion transport to bumetanide, a NKCC inhibitor. The residual (86)Rb(+) influx occurred via the Na(+),K(+)-ATPase and other transporters not sensitive to bumetanide or ouabain. NKCC-mediated (86)Rb(+) influx was enhanced significantly ( approximately 1.6-fold) by acute cell exposure to insulin, but was inhibited significantly by tyrosine kinase inhibitors, wortmannin and rapamycin, consistent with a role for the insulin receptor tyrosine kinase, phosphoinositide 3 (PI3)-kinase and mTOR, respectively, in cotransporter activation. In contrast, the hormonal activation of NKCC was unaffected by inhibition of the classical Erk-signalling pathway. Subjecting L6 myotubes to an acute hyperosmotic challenge (420 mosmol l(-1)) led to a 40% reduction in cell volume and was accompanied by a rapid stimulation of NKCC activity ( approximately 2-fold). Intracellular volume recovered to normal levels within 60 min, but this regulatory volume increase (RVI) was prevented if bumetanide was present. Unlike insulin, activation of NKCC by hyperosmolarity did not involve PI3-kinase but was suppressed by inhibition of tyrosine kinases and the Erk pathway. While inhibition of tyrosine kinases, using genistein, led to a complete loss in NKCC activation in response to hyperosmotic stress, immunoprecipitation of NKCC revealed that the cotransporter was not regulated directly by tyrosine phosphorylation. Simultaneous exposure of L6 myotubes to insulin and hyperosmotic stress led to an additive increase in NKCC-mediated (86)Rb(+) influx, of which, only the insulin-stimulated component was wortmannin-sensitive. Our findings indicate that L6 myotubes express a functional NKCC that is rapidly activated in response to insulin and hyperosmotic shock by distinct intracellular signalling pathways. Furthermore, activation of NKCC in response to hyperosmotic-induced cell shrinkage represents a critical component of the RVI mechanism that allows L6 muscle cells to volume regulate.
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PMID:Signalling mechanisms underlying the rapid and additive stimulation of NKCC activity by insulin and hypertonicity in rat L6 skeletal muscle cells. 1528 43

Our previous studies on cardiac myocytes showed that positive inotropic concentrations of the digitalis drug ouabain activated signaling pathways linked to Na(+)-K(+)-ATPase through Src and epidermal growth factor receptor (EGFR) and led to myocyte hypertrophy. In view of the known involvement of phosphatidylinositol 3-kinase (PI3K)-Akt pathways in cardiac hypertrophy, the aim of the present study was to determine whether these pathways are also linked to cardiac Na(+)-K(+)-ATPase and, if so, to assess their role in ouabain-induced myocyte growth. In a dose- and time-dependent manner, ouabain activated Akt and phosphorylation of its substrates mammalian target of rapamycin and glycogen synthase kinase in neonatal rat cardiac myocytes. Akt activation by ouabain was sensitive to PI3K inhibitors and was also noted in adult myocytes and isolated hearts. Ouabain caused a transient increase of phosphatidylinositol 3,4,5-trisphosphate content of neonatal myocytes, activated class IA, but not class IB, PI3K, and increased coimmunoprecipitation of the alpha-subunit of Na(+)-K(+)-ATPase with the p85 subunit of class IA PI3K. Ouabain-induced activation of ERK1/2 was prevented by Src, EGFR, and MEK inhibitors, but not by PI3K inhibitors. Activation of Akt by ouabain, however, was sensitive to inhibitors of PI3K and Src, but not to inhibitors of EGFR and MEK. Similarly, ouabain-induced myocyte hypertrophy was prevented by PI3K and Src inhibitors, but not by an EGFR inhibitor. These findings 1) establish the linkage of the class IA PI3K-Akt pathway to Na(+)-K(+)-ATPase and the essential role of this linkage to ouabain-induced myocyte hypertrophy and 2) suggest cross talk between these PI3K-Akt pathways and the signaling cascades previously identified to be associated with cardiac Na(+)-K(+)-ATPase.
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PMID:Association of PI3K-Akt signaling pathway with digitalis-induced hypertrophy of cardiac myocytes. 1772 97

Autophagy, a highly conserved cellular mechanism wherein various cellular components are broken down and recycled through lysosomes, has been implicated in the development of heart failure. However, tools to measure autophagic flux in vivo have been limited. Here, we tested whether monodansylcadaverine (MDC) and the lysosomotropic drug chloroquine could be used to measure autophagic flux in both in vitro and in vivo model systems. Using HL-1 cardiac-derived myocytes transfected with GFP-tagged LC3 to track changes in autophagosome formation, autophagy was stimulated by mTOR inhibitor rapamycin. Administration of chloroquine to inhibit lysosomal activity enhanced the rapamycin-induced increase in the number of cells with numerous GFP-LC3-positive autophagosomes. The chloroquine-induced increase of autophagosomes occurred in a dose-dependent manner between 1 microM and 8 microM, and reached a maximum 2 hour after treatment. Chloroquine also enhanced the accumulation of autophagosomes in cells stimulated with hydrogen peroxide, while it attenuated that induced by Bafilomycin A1, an inhibitor of V-ATPase that interferes with fusion of autophagosomes with lysosomes. The accumulation of autophagosomes was inhibited by 3-methyladenine, which is known to inhibit the early phase of the autophagic process. Using transgenic mice expressing 3 mCherry-LC3 exposed to rapamycin for 4 hr, we observed an increase in mCherry-LC3-labeled autophagosomes in myocardium, which was further increased by concurrent administration of chloroquine, thus allowing determination of flux as a more precise measure of autophagic activity in vivo. MDC injected 1 hr before sacrifice colocalized with mCherry-LC3 puncta, validating its use as a marker of autophagosomes. This study describes a method to measure autophagic flux in vivo even in non-transgenic animals, using MDC and chloroquine.
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PMID:A method to measure cardiac autophagic flux in vivo. 1821 95

Both glucagon-like peptide 2 (GLP-2) and glucocorticosteroids enhance intestinal uptake in mature animals. Maternal stimuli may cause intestinal adaptation in the offspring. We hypothesized that administering GLP-2, dexamethasone (DEX) or a combination of GLP-2+DEX to rat dams during pregnancy and lactation would enhance intestinal sugar uptake in their offspring. Rat dams were treated with GLP-2 (0.1 microg/g/day), DEX (0.128 microg/g/day), a combination of GLP-2+DEX or placebo. Glucose and fructose uptake was assessed in their suckling offspring using an in vitro intestinal ring uptake technique. The protein abundance of SGLT1, GLUT5, GLUT2, Na(+)K(+)-ATPase and selected signals was determined by immunohistochemistry; GLP-2 caused hypertrophy of the jejunal enterocytes and increased ileal villous height. Jejunal fructose uptake was reduced by GLP-2, DEX and GLP-2+DEX. V(max) for jejunal glucose uptake was reduced with DEX and GLP-2+DEX. These declines were not explained by alterations in transporter abundance. Decreases in Akt and mTOR abundance were associated with declines in transporter activity. We speculate that the intrinsic activity of the sugar transporters was modified via the P13K pathway. In conclusion, maternal GLP-2 and DEX reduced intestinal sugar uptake in their offspring. This may have nutritional implications for the offspring of mothers treated with GLP-2 or steroids.
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PMID:Maternal dexamethasone and GLP-2 have early effects on intestinal sugar transport in their suckling rat offspring. 1899 47

Here we show that ouabain-induced cell growth regulation is intrinsically coupled to changes in the cellular amount of Na/K-ATPase via the phosphoinositide 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. Ouabain increases the endocytosis and degradation of Na/K-ATPase in LLC-PK1, human breast (BT20), and prostate (DU145) cancer cells. However, ouabain stimulates the PI3K/Akt/mTOR pathway and consequently up-regulates the expression of Na/K-ATPase in LLC-PK1 but not BT20 and DU145 cells. This up-regulation is sufficient to replete the plasma membrane pool of Na/K-ATPase and to stimulate cell proliferation in LLC-PK1 cells. On the other hand, ouabain causes a gradual depletion of Na/K-ATPase and an increased expression of cell cycle inhibitor p21(cip), which consequently inhibits cell proliferation in BT20 and DU145 cells. Consistently, we observe that small interfering RNA-mediated knockdown of Na/K-ATPase is sufficient to induce the expression of p21(cip) and slow the proliferation of LLC-PK1 cells. Moreover, this knockdown converts the growth stimulatory effect of ouabain to growth inhibition in LLC-PK1 cells. Mechanistically, both Src and caveolin-1 are required for ouabain-induced activation of Akt and up-regulation of Na/K-ATPase. Furthermore, inhibition of the PI3K/Akt/mTOR pathway by rapamycin completely blocks ouabain-induced expression of Na/K-ATPase and converts ouabain-induced growth stimulation to growth inhibition in LLC-PK1 cells. Taken together, we conclude that changes in the expression of Na/K-ATPase dictate the growth regulatory effects of ouabain on cells.
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PMID:Changes in sodium pump expression dictate the effects of ouabain on cell growth. 1932 30

X-linked myopathy with excessive autophagy (XMEA) is a childhood-onset disease characterized by progressive vacuolation and atrophy of skeletal muscle. We show that XMEA is caused by hypomorphic alleles of the VMA21 gene, that VMA21 is the diverged human ortholog of the yeast Vma21p protein, and that like Vma21p it is an essential assembly chaperone of the V-ATPase, the principal mammalian proton pump complex. Decreased VMA21 raises lysosomal pH, which reduces lysosomal degradative ability and blocks autophagy. This reduces cellular free amino acids, which upregulates the mTOR pathway and mTOR-dependent macroautophagy, resulting in proliferation of large and ineffective autolysosomes that engulf sections of cytoplasm, merge together, and vacuolate the cell. Our results uncover macroautophagic overcompensation leading to cell vacuolation and tissue atrophy as a mechanism of disease.
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PMID:VMA21 deficiency causes an autophagic myopathy by compromising V-ATPase activity and lysosomal acidification. 2087 70

Emerging evidence suggests that autophagic modulators have therapeutic potential. This study aims to identify novel autophagic inducers from traditional Chinese medicinal herbs as potential antitumor agents. Using an image-based screen and bioactivity-guided purification, we identified alisol B 23-acetate, alisol A 24-acetate, and alisol B from the rhizome of Alisma orientale as novel inducers of autophagy, with alisol B being the most potent natural product. Across several cancer cell lines, we showed that alisol B-treated cells displayed an increase of autophagic flux and formation of autophagosomes, leading to cell cycle arrest at the G(1) phase and cell death. Alisol B induced calcium mobilization from internal stores, leading to autophagy through the activation of the CaMKK-AMPK-mammalian target of rapamycin pathway. Moreover, the disruption of calcium homeostasis induces endoplasmic reticulum stress and unfolded protein responses in alisol B-treated cells, leading to apoptotic cell death. Finally, by computational virtual docking analysis and biochemical assays, we showed that the molecular target of alisol B is the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase. This study provides detailed insights into the cytotoxic mechanism of a novel antitumor compound.
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PMID:Alisol B, a novel inhibitor of the sarcoplasmic/endoplasmic reticulum Ca(2+) ATPase pump, induces autophagy, endoplasmic reticulum stress, and apoptosis. 2019

The hallmark pathologies of sporadic inclusion-body myositis (s-IBM) muscle fibers are autophagic vacuoles and accumulation of ubiquitin-positive multiprotein aggregates that contain amyloid-beta or phosphorylated tau in a beta-pleated sheet amyloid configuration. Endoplasmic reticulum stress (ERS) and 26S proteasome inhibition, also associated with s-IBM, putatively aggrandize the accumulation of misfolded proteins. However, autophagosomal-lysosomal pathway formation and function, indicated by autophagosome maturation, have not been previously analyzed in this system. Here we studied the autophagosomal-lysosomal pathway using 14 s-IBM and 30 disease control and normal control muscle biopsy samples and our cultured human muscle fibers in a microenvironment modified to resemble aspects of s-IBM pathology. We report for the first time that in s-IBM, lysosomal enzyme activities of cathepsin D and B were decreased 60% (P < 0.01) and 40% (P < 0.05), respectively. We also detected two indicators of increased autophagosome maturation, the presence of LC3-II and decreased mammalian target of rapamycin-mediated phosphorylation of p70S6 kinase. Moreover, in cultured human muscle fibers, ERS induction significantly decreased activities of cathepsins D and B, increased levels of LC3-II, decreased phosphorylation of p70S6 kinase, and decreased expression of VMA21, a chaperone for assembly of lysosomal V-ATPase. We conclude that in s-IBM muscle, decreased lysosomal proteolytic activity might enhance accumulation of misfolded proteins, despite increased maturation of autophagosomes, and that ERS is a possible cause of s-IBM-impaired lysosomal function. Thus, unblocking protein degradation in s-IBM muscle fibers may be a desirable therapeutic strategy.
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PMID:Impaired autophagy in sporadic inclusion-body myositis and in endoplasmic reticulum stress-provoked cultured human muscle fibers. 2061 43


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