1,721,051 research outputs found
Intracellular signal transduction pathways induced by leptin in C2C12 cells
No full textAs experimental evidence suggests that leptin may have direct effects on peripheral tissues, we investigated some of the transductional molecules induced by leptin in C2C12 cells. In immunoprecipitation experiments using anti-p85 antibodies (a regulatory subunit of phosphatidylinositol-3-kinase; PI3K), we observed a significant increase in PI3K activity. Immunoblot analyses showed that Akt, GSK3, ERK1, ERK2, and p38 mitogen-activated protein kinase (p38 MAPK) phosphorylation significantly increased after leptin treatment. Protein kinase C (PKC)-zeta was also activated by leptin, as documented by an immunocomplex kinase assay and immunoblotting experiments. The treatment of C2C12 cells with Wortmannin before leptin administration inhibited induction of the phosphorylation of ERKs (extracellular signal-regulated kinases) but not that of p38 MAPK, whereas pre-treatment with a PKC-zeta inhibitor partially decreased ERK phosphorylation. Taken together, our in vitro results further support the hypothesis that leptin acts acutely on skeletal muscle tissue through some of the components of insulin signalling, including PKC-zeta. (c) 2005 International Federation for Cell Biology. Published by Elsevier Ltd. All rights reserved
Early intracellular events induced by in vivo leptin treatment in mouse skeletal muscle
No full textExperimental evidence suggests that leptin may exert direct effects on peripheral tissues. In this study we investigated some transductional molecules in skeletal muscle, after intraperitoneal leptin injection in wild-type and ob/ob mice. By immunoprecipitation and immunoblotting with anti-phosphotyrosine antibodies, we observed a modified pattern of phosphotyrosine proteins. We then identified an increase in JAK2, IRS1 and IRS2 tyrosine-phosphorylation and in their association with p85, a subunit of PI3K. The increase in PI3K activity in immunoprecipitated p85 did not reach statistical significance, however, both Akt and GSK3 resulted significantly hyper-phosphorylated. Bad, an Akt substrate involved in cell survival, appeared modified in its phosphorylation. ERK1, ERK2 and p38 MAP kinase phosphorylation significantly increased, even if the latter only in wild-type animals. Finally, by EMSA experiments, we documented that leptin increased the DNA binding capacity of Stat3 homodimers and AP-1. Thus, leptin appears to activate, within minutes, some insulin signalling molecules. Stat3 and AP-1 activation by gene expression remodelling could subsequently trigger more leptin-specific effects. Further, leptin might play a still underestimated role in cell survival
Signal transduction pathway of prolactin in rat liver
No full textWe previously reported that a single intraperitoneal injection of prolactin (PRL) in female adult rats rapidly and transiently activates mitogen-activated protein kinase (MAPK) in the liver. Here we analysed the PRL signalling pathway that accounts for MAPK activation. We found that total liver MAPK kinase-1 phosphorylating activity and Raf-1 activity significantly increase after PRL treatment, following a time course that accounts for the activation of MAPK. We also identified a significant increase in the phosphotyrosine content of the 52 kDa Shc protein, accompanied by an increase in Shc coimmunoprecipitated Grb2. which suggests the Ras involvement by PRL. We found that Janus kinase (JAK)2 tyrosine kinase, which appears constitutively associated with the PRL receptor expressed in the liver, is activated and associated with Shc proteins after in vivo PRL treatment. Taken together our data provide evidence that in vivo PRL activates the Shc-Ras-Raf-MAPK cascade in the liver by the involvement of JAK2 and suggests the possibility that the liver short form of PRL receptor plays a role in triggering this signalling pathway
Leptin rapidly activates PPARs in C2C12 muscle cells
No full textExperimental evidence suggests that leptin operates on the tissues, including skeletal muscle, also by modulating gene expression. Using electrophoretic mobility shift assays, we have shown that physiological doses of leptin promptly increase the binding of C2C12 cell nuclear extracts to peroxisome proliferator-activated receptor (PPAR) response elements in oligonucleotide probes and that all three PPAR isoforms participate in DNA-binding complexes. We pre-treated C2C12 cells with AACOCF(3), a specific inhibitor of cytosolic phospholipase A(2) (cPLA(2)), an enzyme that supplies ligands to PPARs, and found that it abrogates leptin-induced PPAR DNA-binding activity. Leptin treatment significantly increased cPLA(2) activity, evaluated as the release of [H-3]arachidonic acid from pre-labelled C2C12 cells, as well as phosphorylation. Further, using MEK1 inhibitor PD-98059 we showed that leptin activates cPLA(2) through ERK induction. These results support a direct effect of leptin on skeletal Muscle cells, and suggest that the hormone may modulate muscle transcription also by precocious activation of PPARs through ERK cPLA(2) pathway. (c) 2005 Elsevier Inc. All rights reserved
Rapid stimulation of mitogen-activated protein kinase of rat liver by prolactin
Full text linkIntraperitoneal prolactin administration to female rats caused a rapid and transient stimulation of hepatic mitogen-activated kinase (MAP kinase) activity measured in vitro as cytosolic phosphotransferase capacity towards two specific substrates. Myelin basic protein kinase activity of MAP kinase immunoprecipitates confirmed the specificity and magnified the prolactin effect. Immunoblot experiments with anti-(MAP kinase) and anti-phosphotyrosine antibodies showed changes in both electrophoretic mobility and phosphotyrosine content of 40 and 44 kDa isoenzymes suggesting that prolactin affects these isoforms. Concomitant with the increase in MAP kinase activity, prolactin induced tyrosine phosphorylation in a number of liver proteins, suggesting a rapid involvement of tyrosine kinases which might be correlated in some way with MAP kinase activation. Protein kinase C activity, which has been implicated in the regulation of MAP kinase and in mediating the prolactin effect, does not seem to participate in MAP kinase activation
The liver response to in vivo heat shock involves the activation of MAP kinases and RAF and the tyrosine phosphorylation of Shc proteins
No full textWe have investigated the mechanisms of signal transduction in the response of liver to heat shock in vivo. By immunoblot experiments we have shown that heat shock decreases the electrophoretic mobility of the 40 and 43 kDa mitogen activated protein kinases (MAPKs) and we have found a significant increase of MAPK activity measured as phosphotransferase capacity of both cytosolic extracts and MAPK immunoprecipitates. To elucidate the signalling pathway which accounts for MAPK activation, we focused our attention on its upstream factors, Raf and Ras. We have shown that, heat shock activates Raf-1 kinase and causes an increase in phosphotyrosine content of the 52 kDa Shc protein accompanied by an increment in the amount of coimmunoprecipitated Grb2. These findings provide the first evidence that the Ras-Raf-MAPK pathway is activated in liver during heat shock in vivo
New perspectives in the treatment of neuroendocrine tumors
No full textCharacterization of new and specific molecular features of the neuroendocrine tumors (NET) has prompted the development of more selective targeted pharmacological agents, potentially useful in the therapy of these tumors. NET express in a high percentage of cases the somatostatin receptors and type I and II interferon receptors. In addition, these tumors seem to have an extraordinary vascularization with high expression of proangiogenic molecules, such as vascular endothelial growth factor, and specific tyrosine kinase receptors. In this review article, we discuss the potential role and future perspectives of universal somatostatin analogues, new types of interferons and emerging inhibitors of angiogenesis in the treatment of NET.Characterization of new and specific molecular features of the neuroendocrine tumors (NET) has prompted the development of more selective targeted pharmacological agents, potentially useful in the therapy of these tumors. NET express in a high percentage of cases the somatostatin receptors and type I and II interferon receptors. In addition, these tumors seem to have an extraordinary vascularization with high expression of proangiogenic molecules, such as vascular endothelial growth factor, and specific tyrosine kinase receptors. In this review article, we discuss the potential role and future perspectives of universal somatostatin analogues, new types of interferons and emerging inhibitors of angiogenesis in the treatment of NET
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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