scholarly journals A Novel Cyclic AMP-Dependent Epac-Rit Signaling Pathway Contributes to PACAP38-Mediated Neuronal Differentiation

2006 ◽  
Vol 26 (23) ◽  
pp. 9136-9147 ◽  
Author(s):  
Geng-Xian Shi ◽  
Holger Rehmann ◽  
Douglas A. Andres
Keyword(s):  
Protein Kinase ◽  
Cyclic Amp ◽  
Neuronal Differentiation ◽  
Function Analysis ◽  
Small Gtpase ◽  
Mitogen Activated Protein Kinase ◽  
Dependent Manner ◽  
Nucleotide Exchange ◽  
Loss Of Function ◽  
Stimulation Of

ABSTRACT Pituitary adenylate cyclase-activating polypeptide (PACAP38) stimulation results in the activation of Gsα protein-coupled receptors to regulate neuronal differentiation in a cyclic AMP (cAMP)-dependent manner. These pathways involve protein kinase A (PKA)-dependent processes, but a growing body of evidence indicates that cAMP also regulates cellular functions through PKA-independent signaling cascades. Here we show that the Rit small GTPase is regulated by PACAP38 in a cAMP-dependent but PKA-independent fashion. Rit activation results from stimulation of the cAMP-activated guanine nucleotide exchange factor Epac but does not appear to rely upon the activation of Rap GTPases, the accepted cellular Epac substrates. Although RNA interference studies demonstrated that Epac is required for PACAP38-mediated Rit activation, neither Epac1 nor Epac2 activates Rit directly, indicating that Epac signals to Rit through a novel mechanism in which Rap signaling is not essential. Loss-of-function analysis demonstrated that Rit makes an important contribution to PACAP38-mediated neuronal differentiation. Surprisingly, although Rit is required for sustained extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase signaling following nerve growth factor stimulation of pheochromocytoma 6 (PC6) cells, Rit silencing selectively suppressed PACAP38-elicited activation of p38, without obvious effects on ERK signaling in the same cells. Moreover, the ability of PACAP38 to stimulate CREB-dependent transcription and to promote neurite outgrowth was inhibited by Rit knockdown. Together, these studies identify an unsuspected connection between cAMP and Rit signaling pathways and imply that Rit can function downstream of Gsα/cAMP/Epac in a novel signal transduction pathway necessary for PACAP38-mediated neuronal differentiation and CREB signaling.

scholarly journals Pituitary Adenylate Cyclase-Activating Polypeptide 38-Mediated Rin Activation Requires Src and Contributes to the Regulation of Hsp27 Signaling during Neuronal Differentiation

2008 ◽  
Vol 28 (16) ◽  
pp. 4940-4951 ◽  
Author(s):  
Geng-Xian Shi ◽  
Ling Jin ◽  
Douglas A. Andres
Keyword(s):  
Protein Kinase ◽  
Adenylate Cyclase ◽  
Neurite Outgrowth ◽  
Neuronal Differentiation ◽  
Function Analysis ◽  
Mitogen Activated Protein Kinase ◽  
Signaling Cascades ◽  
Critical Element ◽  
Dependent Manner ◽  
Pituitary Adenylate Cyclase

ABSTRACT Pituitary adenylate cyclase-activating polypeptide 38 (PACAP38) is a potent neuropeptide that acts through G-protein-coupled receptors. While it is well established that PACAP mediates both neurotrophic and neurodevelopmental effects, the signaling cascades that underlie these diverse actions remain incompletely characterized. Here we show that the Ras-related Rin GTP-binding protein, a GTPase that is expressed predominantly in neurons, is regulated by PACAP38 signaling, and loss-of-function analysis demonstrates that Rin makes an essential contribution to PACAP38-mediated pheochromocytoma cell differentiation. Rin is activated following stimulation of both Gsα and Giα cascades but does not rely upon cyclic AMP (cAMP)-, Ca2+-, or Epac-dependent signaling pathways. Instead, Rin is activated in a Src kinase-dependent manner. Surprisingly, Rin knockdown significantly inhibits PACAP38-mediated neurite outgrowth, without affecting mitogen-activated protein kinase signaling cascades. Instead, Rin loss attenuates PACAP38-mediated HSP27 activation by disrupting a cAMP-protein kinase A cascade. RNA interference-mediated HSP27 silencing suppresses both PACAP38- and Rin-mediated neurite outgrowth, while expression of a constitutively active Rin mutant increases both HSP27 protein and phospho-HSP27 levels, supporting a role for Rin-HSP27 signaling in neuronal differentiation. Together, these observations identify an unsuspected role for Rin in neuronal PACAP signaling and establish a novel Gα-Src-Rin-HSP27 signal transduction pathway as a critical element in PACAP38-mediated neuronal differentiation signaling.

scholarly journals Progesterone secretion by luteinizing human granulosa cells: a possible cAMP-dependent but PKA-independent mechanism involved in its regulation

2004 ◽  
Vol 183 (1) ◽  
pp. 51-60 ◽  
Author(s):  
E C Chin ◽  
D R E Abayasekara
Keyword(s):  
Protein Kinase ◽  
Adenylate Cyclase ◽  
Granulosa Cells ◽  
Mitogen Activated Protein Kinase ◽  
Dependent Manner ◽  
Nucleotide Exchange ◽  
Independent Manner ◽  
Human Granulosa Cells ◽  
Progesterone Secretion ◽  
Dose Dependent

The corpus luteum formed after luteinization of follicular cells secretes progesterone under the control of luteinizing hormone (LH). Binding of LH to its G-protein-coupled receptor leads to the activation of the adenylate cyclase/ cyclic AMP (cAMP)/cAMP-dependent protein kinase (PKA) signalling pathway. The identification of a new class of cAMP-binding proteins termed ‘guanine nucleotide exchange factors’ (cAMP-GEFs) provides a means by which changes in cAMP could yield actions that are independent of PKA. Hence, in this study, we have explored the hypothesis that steroidogenesis in luteinizing cells is mediated in both a cAMP/PKA-dependent and cAMP-dependent, but PKA-independent, manner. Human granulosa cells were isolated from follicular aspirates of women undergoing assisted conception. Luteinizing human granulosa cells were cultured for up to 3 days in the presence of human (h)LH and the adenylate cyclase activator forskolin in the added presence or absence of increasing doses of the PKA inhibitors H89 (N-[2-(4-bromocinnamylamino)ethyl] 5-isoquinoline) and PKI (myristoylated protein kinase A inhibitor amide 14–22) or the cAMP antagonist, Rp-cAMP. Agonist-stimulated progesterone secretion was inhibited in a dose-dependent manner by the PKA inhibitors and the cAMP antagonist, with decreasing sensitivity as luteinization progressed. Pretreatment of granulosa cells for 4 h with human (h)LH reduced the effectiveness of H89 in inhibiting progester-one secretion. Under basal conditions, cAMP-GEFI expression increased progressively throughout culture, and this could be further enhanced when cells were incubated with increasing doses of LH and forskolin. Furthermore, incubation of cells in the presence of increasing concentrations of the novel cAMP-GEF-specific cAMP analogue, 8 CPT-2 ME-cAMP (8-(4-chloro-phenylthio)-2′-0-methyladenosine-3′,5′-cyclic monophosphate), increased progesterone secretion in a dose-dependent manner. The results show that increases in cAMP generated by LH and forskolin, in addition to activating PKA, also induce increases in cAMP-GEFI protein expression in luteinizing human granulosa cells. In addition, activation of cAMP-GEFI results in increased progesterone secretion. Hence, increases in cAMP lead to the activation of PKA-dependent, as well as PKA-independent but cAMP-dependent (via cAMP-GEFI), signalling mechanisms. Since cAMP-GEFs have the capacity to activate the mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3-K)/protein kinase B (PKB) signalling pathways, these may provide the potential mechanisms by which cAMP-dependent but PKA-independent progesterone synthesis is regulated.

scholarly journals Phosphorylation and activation of p42 and p44 mitogen-activated protein kinase are required for the P2 purinoceptor stimulation of endothelial prostacyclin production

1996 ◽  
Vol 320 (1) ◽  
pp. 221-226 ◽  
Author(s):  
Viral PATEL ◽  
Colin BROWN ◽  
Adele GOODWIN ◽  
Neil WILKIE ◽  
Michael R BOARDER
Keyword(s):  
Protein Kinase ◽  
Tyrosine Phosphorylation ◽  
Kinase Activity ◽  
Kinase Inhibitor ◽  
Mitogen Activated Protein Kinase ◽  
Dependent Manner ◽  
Western Blots ◽  
Mitogen Activated Protein ◽  
Two Peaks ◽  
Stimulation Of

Extracellular ATP and ADP, released from platelets and other sites stimulate the endothelial production of prostacyclin (PGI2) by acting on G-protein-coupled P2Y1 and P2Y2 purinoceptors, contributing to the maintenance of a non-thrombogenic surface. The mechanism, widely described as being dependent on elevated cytosolic [Ca2+], also requires protein tyrosine phosphorylation. Here we show that activation of both these P2 receptor types leads to the tyrosine phosphorylation and activation of both the p42 and p44 forms of mitogen-activated protein kinase (MAPK). 2-Methylthio-ATP and UTP, selectively activating P2Y1 and P2Y2 purinoceptors respectively, and ATP, a non-selective agonist at these two receptors, stimulate the tyrosine phosphorylation of both p42mapk and p44mapk, as revealed by Western blots with an antiserum specific for the tyrosine-phosphorylated forms of the enzymes. By using separation on Resource Q columns, peptide kinase activity associated with the phosphorylated MAPK enzymes distributes into two peaks, one mainly p42mapk and one mainly p44mapk, both of which are stimulated by ATP with respect to kinase activity and phospho-MAPK immunoreactivity. Stimulation of P2Y1 or P2Y2 purinoceptors leads to a severalfold increase in PGI2 efflux; this was blocked in a dose-dependent manner by the selective MAPK kinase inhibitor PD98059. This drug also blocked the agonist-stimulated increase in phospho-MAPK immunoreactivity for both p42mapk and p44mapk but left the phospholipase C response to P2 agonists essentially unchanged. Olomoucine has been reported to inhibit p44mapk activity. Here we show that in the same concentration range olomoucine inhibits activity in both peaks from the Resource Q column and also the agonist stimulation of 6-keto-PGF1, but has no effect on agonist-stimulated phospho-MAPK immunoreactivity. These results provide direct evidence for the involvement of p42 and p44 MAPK in the PGI2 response of intact endothelial cells: we have shown that both the endothelial P2Y purinoceptors are linked to activation of MAPK, and that activation of this pathway is a requirement for the stimulation by ATP/ADP of endothelial PGI2 production.

scholarly journals Mastoparan promotes exocytosis and increases intracellular cyclic AMP in human platelets. Evidence for the existence of a Ge-like mechanism of secretion

1992 ◽  
Vol 281 (2) ◽  
pp. 465-472 ◽  
Author(s):  
C P D Wheeler-Jones ◽  
T Saermark ◽  
V V Kakkar ◽  
K S Authi
Keyword(s):  
Protein Kinase C ◽  
Protein Kinase ◽  
Cyclic Amp ◽  
G Protein ◽  
Human Platelets ◽  
Dependent Manner ◽  
Kinase C ◽  
Reversible Electroporation ◽  
Dose Dependent ◽  
Stimulation Of

Recent studies have shown that mastoparan, an amphiphilic peptide derived from wasp venom, accelerates guanine nucleotide exchange and GTPase activity of purified GTP-binding proteins. In the present study we have examined the functional consequences of exposure of intact human platelets to mastoparan. Mastoparan promoted rapid (less than or equal to 1 min) dose-dependent increases in 5-hydroxy[14C]tryptamine and beta-thromboglobulin release from dense-granule and alpha-granule populations respectively. The exocytotic response did not result from a lytic effect of mastoparan and occurred in the complete absence of platelet shape change and aggregation. Liberation of [3H]arachidonate and increases in cytosolic [Ca2+] (detected with fura 2) were not observed in platelets stimulated with mastoparan. Similarly, in platelets preloaded with [3H]inositol during reversible electroporation, mastoparan did not cause the accumulation of [3H]inositol phosphates. Mastoparan-induced secretion was unaffected by preincubation with either the protein kinase C inhibitor staurosporine (10 nM-10 microM) or prostacyclin (PGI2; 100 ng/ml) and was not accompanied by phosphorylation of the 45 kDa protein kinase C substrate or the 20 kDa protein normally associated with platelet activation. The G-protein inhibitor guanosine 5′-[beta-thio]diphosphate (GDP[S]; 1 mM) attenuated the secretion induced by mastoparan in both intact and saponin-permeabilized platelets. Encapsulation of GDP[S] during reversible permeabilization inhibited mastoparan-induced secretion, providing evidence for an intracellular action of GDP[S]. In all these studies thrombin (0.05-0.2 unit/ml) elicited characteristic responses, and thrombin-induced secretion was inhibited by staurosporine, PGI2 and GDP[S]. Mastoparan also increased intra-platelet cyclic AMP in a dose-dependent manner. Mastoparan and PGI2 increased 32P incorporation into a protein of approx. 24 kDa, whereas phosphorylation of a 50 kDa substrate was only seen in PGI2-stimulated platelets. These results indicate that mastoparan promotes secretion by a mechanism which does not involve stimulation of phospholipase C and suggest that the secretory event may result either from a direct fusogenic action of mastoparan and/or from stimulation of the putative exocytosis-linked G-protein, Ge.

scholarly journals Activation of the Ral and Phosphatidylinositol 3′ Kinase Signaling Pathways by the Ras-Related Protein TC21

2001 ◽  
Vol 21 (11) ◽  
pp. 3750-3762 ◽  
Author(s):  
Marta Rosário ◽  
Hugh F. Paterson ◽  
Christopher J. Marshall
Keyword(s):  
Protein Kinase ◽  
Dna Synthesis ◽  
Signaling Pathways ◽  
Human Tumor ◽  
Small Gtpase ◽  
Mitogen Activated Protein Kinase ◽  
Nucleotide Exchange ◽  
Phosphatidylinositol 3 Kinase ◽  
Phosphatidylinositol 3

ABSTRACT TC21 is a member of the Ras superfamily of small GTP-binding proteins that, like Ras, has been implicated in the regulation of growth-stimulating pathways. We have previously identified the Raf/mitogen-activated protein kinase pathway as a direct TC21 effector pathway required for TC21-induced transformation (M. Rosário, H. F. Paterson, and C. J. Marshall, EMBO J. 18:1270–1279, 1999). In this study we have identified two further effector pathways for TC21, which contribute to TC21-stimulated transformation: the phosphatidylinositol 3′ kinase (PI-3K) and Ral signaling pathways. Expression of constitutively active TC21 leads to the activation of Ral A and the PI-3K-dependent activation of Akt/protein kinase B. Strong activation of the PI-3K/Akt pathway is seen even with very low levels of TC21 expression, suggesting that TC21 may be a key small GTPase-regulator of PI-3K. TC21-induced alterations in cellular morphology in NIH 3T3 and PC12 cells are also PI-3K dependent. On the other hand, activation of the Ral pathway by TC21 is required for TC21-stimulated DNA synthesis but not transformed morphology. We show that inhibition of Ral signaling blocks DNA synthesis in human tumor cell lines containing activating mutations in TC21, demonstrating for the first time that this pathway is required for the proliferation of human tumor cells. Finally, we provide mechanisms for the activation of these pathways, namely, the direct in vivo interaction of TC21 with guanine nucleotide exchange factors for Ral, resulting in their translocation to the plasma membrane, and the direct interaction of TC21 with PI-3K. In both cases, the effector domain region of TC21 is required since point mutations in this region can interfere with activation of downstream signaling.

scholarly journals Cross Talk between β-Adrenergic and Bradykinin B2Receptors Results in Cooperative Regulation of Cyclic AMP Accumulation and Mitogen-Activated Protein Kinase Activity

2001 ◽  
Vol 21 (24) ◽  
pp. 8452-8460 ◽  
Author(s):  
Sabine Hanke ◽  
Bernd Nürnberg ◽  
Detlef H. Groll ◽  
Claus Liebmann
Keyword(s):  
Protein Kinase ◽  
Cyclic Amp ◽  
Cross Talk ◽  
Mitogen Activated Protein Kinase ◽  
Protein Kinase Activity ◽  
Downstream Signaling ◽  
Mapk Activity ◽  
Cyclic Amp Accumulation ◽  
Mitogen Activated Protein ◽  
Stimulation Of

ABSTRACT Costimulation of G protein-coupled receptors (GPCRs) may result in cross talk interactions between their downstream signaling pathways. Stimulation of GPCRs may also lead to cross talk regulation of receptor tyrosine kinase signaling and thereby to activation of mitogen-activated protein kinase (MAPK). In COS-7 cells, we investigated the interactions between two particular mitogenic receptor pathways, the endogenously expressed β-adrenergic receptor (β-AR) and the transiently transfected human bradykinin (BK) B2receptor (B2R). When β-AR and B2R are costimulated, we found two different cross talk mechanisms. First, the predominantly Gq protein-coupled B2R is enabled to activate a Gi protein and, subsequently, type II adenylate cyclase. This results in augmentation of β-AR-mediated cyclic AMP (cAMP) accumulation by BK, which alone is unable to increase the cAMP level. Second, independently of BK-induced superactivation of the cAMP system, costimulation of β-AR leads to protein kinase A-mediated blockade of phospholipase C activation by BK. Thereby, the pathway from B2R to MAPK, which essentially involves protein kinase C activation, is selectively switched off. The MAPK activation in response to isoproterenol was not affected due to costimulation. Furthermore, in the presence of isoproterenol, BK lost its ability to stimulate DNA synthesis in COS-7 cells. Thus, our findings might establish a novel paradigm: cooperation between simultaneously activated mitogenic pathways may prevent multiple stimulation of MAPK activity and increased cell growth.

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