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Wenhui Su and Xinchun Liu

protein transportation to distinct membrane domains ( Schimmoller et al . 1998 , Takai et al . 2001 , Pfeffer 2007 ). In Madin-Darby canine kidney (MDCK) cells, the active form of RAB13 was revealed to inhibit protein kinase A (PKA

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Guillaume Pidoux and Kjetil Taskén

second messenger cAMP. Next, this leads to activation of effector molecules such as cAMP-dependent protein kinase A (PKA; Tasken & Aandahl 2004 , Beene & Scott 2007 , Taylor et al . 2008 ; Fig. 1 ). Figure 1 cAMP signal pathways. Ligand binding to

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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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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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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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MB Sewer and MR Waterman

Steroid hormone biosynthesis in the adrenal cortex is controlled by the peptide hormone adrenocorticotropin (ACTH), which acts to increase intracellular cAMP and results in the activation of cAMP-dependent protein kinase A (PKA) and subsequent increase in steroidogenic gene transcription. Protein phosphorylation by PKA activates transcription of genes encoding steroidogenic enzymes; however the precise proteins which are phosphorylated remain to be determined. We have recently shown that phosphoprotein phosphatase (PP) activity is essential for cAMP-dependent transcription of the human CYP17 (hCYP17) gene in H295R adrenocortical cells. The aim of our current studies was to determine if inhibition of PP activity attenuates cAMP-dependent mRNA expression of other steroidogenic genes in H295R cells. Using various inhibitors of serine/threonine and tyrosine PPs, we examined the role of phosphatase activity on cAMP-dependent transcription of steroidogenic genes in the adrenal cortex. CYP11A, CYP11B1/2, CYP21, and adrenodoxin also require PP activity for cAMP-stimulated gene expression. Inhibition of both serine/threonine and tyrosine PP activities suppresses the cAMP-dependent mRNA expression of several steroidogenic genes, suggesting that a dual-specificity PP is essential for conveying ACTH/cAMP-stimulated transcription. We propose that PKA phosphorylates and activates a dual-specificity phosphatase, which mediates steroidogenic gene transcription in response to ACTH/cAMP.

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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.

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Zhor Bouizar, Bruno Ragazzon, Lucie Viou, Mariuccia Hortane, Jerôme Bertherat and Marthe Rizk-Rabin

similar to those of PPNAD ( Bertherat et al . 2003 ). Moreover, in vitro studies have indicated that PRKAR1A gene mutation (non-sense mRNA or truncated R1A) stimulates protein kinase A (PKA) activity ( Groussin et al . 2002 a , b , 2006 ). However

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Misa Nakamura, Bo Han, Toshihide Nishishita, Yanhua Bai and Kennichi Kakudo

, a MEK1 inhibitor, and calphostin C (CC), a protein kinase C (PKC) inhibitor, were obtained from Calbiochem (La Jolla, CA, USA). The protein kinase A (PKA) inhibitor H89 was obtained from Seikagaku Corp. (Tokyo, Japan) and dimethyl sulfoxide from Wako