Role of cAMP inhibition of p44/p42 mitogen-activated protein kinase in potentiation of protein secretion in rat lacrimal gland

2007 ◽  
Vol 293 (5) ◽  
pp. C1551-C1560 ◽  
Author(s):  
Chika Funaki ◽  
Robin R. Hodges ◽  
Darlene A. Dartt
Keyword(s):  
Protein Kinase ◽  
Protein Secretion ◽  
Lacrimal Gland ◽  
Mitogen Activated Protein Kinase ◽  
Adrenergic Agonist ◽  
Mapk Activity ◽  
Mitogen Activated Protein ◽  
Epidermal Growth ◽  
Camp Levels

We previously found that addition of cAMP and a Ca2+/PKC-dependent agonist causes synergism or potentiation of protein secretion from rat lacrimal gland acini. In the present study we determined whether cAMP decreases p44/p42 mitogen-activated protein kinase (MAPK) activity in the lacrimal gland. Since we know that activation of MAPK attenuates protein secretion stimulated by Ca2+- and PKC-dependent agonists, we also determined whether this activation causes potentiation of secretion. Freshly prepared rat lacrimal gland acinar cells were incubated with dibutyryl cAMP (DBcAMP), carbachol (a cholinergic agonist), phenylephrine (an α1-adrenergic agonist), or epidermal growth factor (EGF). The latter three agonists are known to activate p44/p42 MAPK. p44/p42 MAPK activity and protein secretion were measured. As measured by Western blot analysis, DBcAMP inhibited both basal and agonist-stimulated p44/p42 MAPK activity. Cellular cAMP levels were increased by 1) using two different cell-permeant cAMP analogs, 2) activating adenylyl cyclase (L-858051), or 3) activation of Gs-coupled receptors (VIP). The cell-permeant cAMP analogs, L-858051, and VIP inhibited basal p44/p42 MAPK activity by 50, 40, and 40%, respectively. DBcAMP and VIP inhibited carbachol- and EGF-stimulated MAPK activity. cAMP, but not VIP, inhibited phenylephrine-stimulated MAPK activity. Potentiation of secretion was detected when carbachol, phenylephrine, or EGF was simultaneously added with DBcAMP. We conclude that increasing cellular cAMP levels inhibits p44/p42 MAPK activity and that this could account for potentiation of secretion obtained when cAMP was elevated and Ca2+ and PKC were increased by agonists.

scholarly journals Neuritogenesis Induced by Thyroid Hormone-treated Astrocytes Is Mediated by Epidermal Growth Factor/Mitogen-activated Protein Kinase-Phosphatidylinositol 3-Kinase Pathways and Involves Modulation of Extracellular Matrix Proteins

2002 ◽  
Vol 277 (51) ◽  
pp. 49311-49318 ◽  
Author(s):  
Rodrigo Martinez ◽  
Flávia Carvalho Alcantara Gomes
Keyword(s):  
Extracellular Matrix ◽  
Growth Factor ◽  
Protein Kinase ◽  
Mitogen Activated Protein Kinase ◽  
Phosphatidylinositol 3 Kinase ◽  
Ecm Proteins ◽  
Mitogen Activated Protein ◽  
Epidermal Growth ◽  
Phosphatidylinositol 3

Thyroid hormone (T3) plays a crucial role in several steps of cerebellar ontogenesis. By using a neuron-astrocyte coculture model, we have investigated the effects of T3-treated astrocytes on cerebellar neuronal differentiationin vitro. Neurons plated onto T3-astrocytes presented a 40–60% increase on the total neurite length and an increment in the number of neurites. Treatment of astrocytes with epidermal growth factor (EGF) yielded similar results, suggesting that this growth factor might mediate T3-induced neuritogenesis. EGF and T3 treatment increased fibronectin and laminin expression by astrocytes, suggesting that astrocyte neurite permissiveness induced by these treatments is mostly due to modulation of extracellular matrix (ECM) components. Such increase in ECM protein expression as well as astrocyte permissiveness to neurite outgrowth was reversed by the specific EGF receptor tyrosine kinase inhibitor, tyrphostin. Moreover, studies using selective inhibitors of several transduction-signaling cascades indicated that modulation of ECM proteins by EGF is mainly through a synergistic activation of mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways. In this work, we provide evidence of a novel role of EGF as an intermediary factor of T3 action on cerebellar ontogenesis. By modulating the content of ECM proteins, EGF increases neurite outgrowth. Our data reveal an important role of astrocytes as mediators of T3-induced cerebellar development and partially elucidate the role of EGF and mitogen-activated protein kinase/phosphatidylinositol 3-kinase pathways on this process.

α1-Adrenergic and cholinergic agonists activate MAPK by separate mechanisms to inhibit secretion in lacrimal gland

2003 ◽  
Vol 284 (1) ◽  
pp. C168-C178 ◽  
Author(s):  
Isao Ota ◽  
Driss Zoukhri ◽  
Robin R. Hodges ◽  
José D. Rios ◽  
Vanja Tepavcevic ◽  
...  
Keyword(s):  
Protein Secretion ◽  
Lacrimal Gland ◽  
Egf Receptor ◽  
Mitogen Activated Protein Kinase ◽  
Dependent Manner ◽  
Concentration Dependent Manner ◽  
Signaling Mechanisms ◽  
Mitogen Activated Protein ◽  
Secretion Inhibition

The purpose of this study was to determine the role of p42/p44 mitogen-activated protein kinase (MAPK) in α1-adrenergically and cholinergically stimulated protein secretion in rat lacrimal gland acinar cells and the pathways used by these agonists to activate MAPK. Acini were isolated by collagenase digestion and incubated with the α1-adrenergic agonist phenylephrine or the cholinergic agonist carbachol, and activation of MAPK and protein secretion were then measured. Phenylephrine and carbachol activated MAPK in a time- and concentration-dependent manner. Inhibition of MAPK significantly increased phenylephrine- and carbachol-induced protein secretion. Inhibition of EGF receptor (EGFR) with AG1478, an inhibitor of the EGFR tyrosine kinase activity, significantly increased phenylephrine- but not carbachol-induced protein secretion. Whereas phenylephrine-induced activation of MAPK was completely inhibited by AG1478, activation of MAPK by carbachol was not. Phenylephrine stimulated tyrosine phosphorylation of the EGFR, whereas carbachol stimulated p60Src, and possibly Pyk2, to activate MAPK. We conclude that, in the lacrimal gland, activation of MAPK plays an inhibitory role in α1-adrenergically and cholinergically stimulated protein secretion and that these agonists use different signaling mechanisms to activate MAPK.

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