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Guillaume Pidoux and Kjetil Taskén

phosphorylation is one of the most common post-translational modifications and is controlled by the opposing actions of various specific protein kinases and phosphatases (PPs). The phosphorylation status of a protein may affect its enzymatic activity, cellular

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Wenhui Su and Xinchun Liu

al . 2009 , 2010 a , Li et al . 2011 , Su et al . 2012 a ), polarity proteins (i.e. PAR3/6, CDC42, scribble protein complex, etc.; Wong et al . 2008 , 2010 , Su et al . 2012 b ), and non-receptor protein tyrosine kinases (i.e. c-Yes, focal

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Nektarios Barabutis, Agnieszka Siejka, Andrew V Schally, Norman L Block, Renzhi Cai and Joseph L Varga

resultant activation of protein kinase A ( Gaylinn 1999 , Ramirez et al . 1999 ). Pituitary type GHRH receptor, pGHRH-R, is a class II G protein-coupled receptor with seven transmembrane domains and is homologous with the receptors for VIP, PACAP, and

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T Ichikawa, K Horie-Inoue, K Ikeda, B Blumberg and S Inoue

vitamin Ks, geranylgeraniol (GGO), and SXR agonists failed to induce the expression of GDF15 and STC2 genes, although a protein kinase A (PKA) activator forskolin (FSK) induced the expression of both genes. Our findings indicate that GDF15 and STC2 are

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J Kim, L Jia, M R Stallcup and G A Coetzee

signal cascades, such as mitogen-activated protein kinase (MAPK), janus-activated kinase (JAK), signal transducers and activators of transcription (STAT), and protein kinase A (PKA) ( Culig et al. 1994 , Nazareth & Weigel 1996 , Reinikainen et al

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Yu-Feng Zhao, Damien J Keating, Maria Hernandez, Dan Dan Feng, Yulong Zhu and Chen Chen

binds to insulin receptors, which possess protein tyrosine kinase (PTK) activity. Crucial mechanisms such as β-cell growth, differentiation and survival are regulated via PTK signaling pathways ( Rhodes & White 2002 ). The acute application of genistein

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Maurizio Longo, Barbara Peruzzi, Dario Fortunati, Veronica De Luca, Stefanie Denger, Gianfranco Caselli, Silvia Migliaccio and Anna Teti

closely upstream of a half estrogen-responsive element (½ ERE) is shared by a variety of gene promoters ( Denger et al. 2001 a , b ), well established as downstream targets of protein kinase C (PKC) pathways. In the present study, the involvement of PKCs

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M Hołysz, N Derebecka-Hołysz and W H Trzeciak

( Trzeciak & Boyd 1974 , Boyd et al . 1975 ). ACTH binds to a specific receptor coupled with membrane-bound adenylyl cyclase; thus, cAMP is generated and activates the protein kinase A (PKA) signal transduction pathway, which leads to phosphorylation and

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Maria Sörhede Winzell and Bo Ahrén

). GLP-1 receptor activation in islets involves stimulation of adenylate cyclase activity leading to increased formation of cAMP and activation of protein kinase A (PKA; Gromada et al . 1998 ). This in turn results in altered ion channel activity and

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B W McFerran and S B Guild

ABSTRACT

The ACTH-secreting mouse AtT-20/D16–16 anterior pituitary tumour cell line was used to study adenosine 3′,5′-cyclic monophosphate (cAMP)-dependent protein kinase A (PKA) and protein kinase C (PKC) involvement in stimulus-secretion coupling pathways. In permeabilised AtT-20 cells under calcium ion-free conditions, forskolin (10 μm), CRH-41 (100 nm), guanosine 5′-O-(3-thiotriphosphate) (GTP-γ-S; 100 μm) but not mastoparan (10 μm) stimulated cAMP accumulation. Measurement of ACTH secretion under identical incubation conditions revealed that GTP-γ-S and mastoparan significantly stimulated ACTH secretion but forskolin and CRH-41 did not. This dissociates cAMP accumulation from ACTH secretion under calcium ion-free conditions and indicated that the effects of mastoparan and GTP-γ-S on ACTH secretion are not mediated by cAMP production. Calcium ions (1 nm to 1 mm) stimulated ACTH secretion from electrically permeabilised cells in a concentration-dependent manner. cAMP (100μm) and phorbol 12-myristate 13-acetate (PMA; 100 nm) synergistically enhanced the response to calcium ions. cAMP did not stimulate ACTH secretion in the absence of calcium ions nor did it alter the concentrations at which calcium stimulated ACTH secretion. This suggests that stimulation of ACTH secretion via the calcium-dependent pathway is necessary before any cAMP-mediated enhancement of secretion is manifest. PMA, however, did stimulate ACTH secretion in the absence of calcium ions, indicating distinct mechanisms for PKC-evoked secretion. Co-incubation with cAMP and PMA did not exceed the secretory response obtained with the combination of PMA and calcium ions. CRH-41 (1 pm to 100 nm) and forskolin (1 nm to 100μm) stimulated ACTH secretion from intact cells in a concentration-dependent manner. Co-incubation with PMA (100 nm) further enhanced the ACTH response to CRH-41 and forskolin; the effects were simply additive. The present study indicates that there are distinct roles for PKA and PKC in stimulussecretion coupling in AtT-20 cells. The PKA-dependent pathway, acting in concert with the calcium messenger system, serves as part of the stimulus-secretion coupling pathway by which activation of CRH-41 receptors control ACTH secretion. The PKC-dependent pathway, in contrast, seems to be independent of the calcium messenger system and may represent a separate control mechanism of ACTH secretion.