Muscarinic activation of mitogen-activated protein kinase in rat thyroid epithelial cells

Intracellular interactions of umeclidinium and vilanterol in human airway smooth muscle

Background

Intracellular mechanisms of action of umeclidinium (UMEC), a long-acting muscarinic receptor antagonist, and vilanterol (VI), a long-acting β₂-adrenoceptor (β₂R) agonist, were investigated in target cells: human airway smooth-muscle cells (ASMCs).

Materials and methods

ASMCs from tracheas of healthy lung-transplant donors were treated with VI, UMEC, UMEC and VI combined, or control compounds (salmeterol, propranolol, ICI 118.551, or methacholine [MCh]). Cyclic adenosine monophosphate (cAMP) was measured using an enzyme-linked immunosorbent assay, intracellular free calcium ([Ca²⁺]_i) using a fluorescence assay, and regulator of G-protein signaling 2 (RGS2) messenger RNA using real-time quantitative polymerase chain reaction.

Results

VI and salmeterol (10⁻¹²–10⁻⁶ M) induced cAMP production from ASMCs in a concentration-dependent manner, which was greater for VI at all concentrations. β₂R antagonism by propranolol or ICI 118.551 (10⁻¹²–10⁻⁴ M) resulted in concentration-dependent inhibition of VI-induced cAMP production, and ICI 118.551 was more potent. MCh (5×10⁻⁶ M, 30 minutes) attenuated VI-induced cAMP production (P<0.05), whereas pretreatment with UMEC (10⁻⁸ M, 1 hour) restored the magnitude of VI-induced cAMP production. ASMC stimulation with MCh (10⁻¹¹–5×10⁻⁶ M) resulted in a concentration-dependent increase in [Ca²⁺]_i, which was attenuated with UMEC pretreatment. Reduction of MCh-induced [Ca²⁺]_i release was greater with UMEC + VI versus UMEC. UMEC enhanced VI-induced RGS2 messenger RNA expression.

Conclusion

These data indicate that UMEC reverses cholinergic inhibition of VI-induced cAMP production, and is a more potent muscarinic receptor antagonist when in combination with VI versus either alone.

Airway and lung remodelling in chronic pulmonary obstructive disease: a role for muscarinic receptor antagonists?

Lung tissue remodelling in chronic inflammatory lung diseases has long been regarded as a follow-up event to inflammation. Recent studies have indicated that, although airway and lung tissue remodelling is often independent of inflammation, it precedes or causes inflammation. None of the available therapies has a significant effect on airway and lung tissue remodelling in asthma, bronchiectasis, fibrosis and chronic obstructive pulmonary disease (COPD). The goal of stopping or reversing lung tissue remodelling is difficult, as the term summarizes the net effect of independent events, including (1) cell proliferation, (2) cell volume increase, (3) cell migration, (4) modified deposition and metabolism of specific extracellular matrix components, and (5) local action of infiltrated inflammatory cells. The extracellular matrix of the lung has a very high turnover, and thus small changes may accumulate to significant structural pathologies, which seem to be irreversible. The most important question is 'why are pathological changes of the lung structure irreversible and resistant to drugs?' Many drugs have the potential to reduce remodelling mechanisms in vitro but fail in clinical trials. New evidence suggests that muscarinic receptor inhibitors have the potential to improve lung function through modifying tissue remodelling. However, the role of muscarinic receptors in lung remodelling, especially their supportive role for other remodelling driving factors, needs to be further investigated. The focus of this review is the role of muscarinic receptors in lung tissue remodelling as it has been reported in the human lung.

Acetylcholine induces mesenchymal stem cell migration via Ca2+ /PKC/ERK1/2 signal pathway

Acetylcholine (ACh) plays an important role in neural and non-neural function, but its role in mesenchymal stem cell (MSC) migration remains to be determined. In the present study, we have found that ACh induces MSC migration via muscarinic acetylcholine receptors (mAChRs). Among several mAChRs, MSCs express mAChR subtype 1 (m1AChR). ACh induces MSC migration via interaction with mAChR1. MEK1/2 inhibitor PD98059 blocks ERK1/2 phosphorylation while partially inhibiting the ACh-induced MSC migration. InsP3Rs inhibitor 2-APB that inhibits MAPK/ERK phosphorylation completely blocks ACh-mediated MSC migration. Interestingly, intracellular Ca(2+) ATPase-specific inhibitor thapsigargin also completely blocks ACh-induced MSC migration through the depletion of intracellular Ca(2+) storage. PKCα or PKCβ inhibitor or their siRNAs only partially inhibit ACh-induced MSC migration, but PKC-ζ siRNA completely inhibits ACh-induced MSC migration via blocking ERK1/2 phosphorylation. These results indicate that ACh induces MSC migration via Ca(2+), PKC, and ERK1/2 signal pathways.

Muscarinic cholinergic signaling in cervical cancer cells affects cell motility via ERK1/2 signaling

AIMS

The etiology of cervical cancer depends primarily on infection with human papillomaviruses, but tobacco smoking is the most important behavioral risk factor for this cancer. Therefore, we have previously confirmed involvement of nicotinic acetylcholine receptors (nAChRs) in cervical cancer biology. In order to comprehensively evaluate the role of cholinergic signaling in cervical cells, we have addressed additional participation of muscarinic acetylcholine receptors (mAChRs).

MAIN METHODS

We have studied the expression of mAChRs and cholinergic system components by reverse transcription PCR and Western blots, the motility of cervical cancer cells in cell culture, and the signaling from mAChRs via the ERK1/2 signaling pathway.

KEY FINDINGS

The cervical cancer cells HeLa, SiHa and CaSki express four of the five mAChRs, M1, M3, M4, and M5, and the acetylcholine (ACh) synthesizing and degrading enzymes choline acetyltransferase (ChAT), acetylcholinesterase (AChE), and butyrylcholinesterase (BChE), and vesicular ACh transporter (VAChT). mAChR-dependent signaling induces cervical cell motility, which requires ERK1/2 activation, and could be abrogated by mAChR antagonists.

SIGNIFICANCE

The epidemiological finding that tobacco smoke raises the prevalence of cervical cancer has led to analysis of the cholinergic signaling in cervical biology and carcinogenesis. Cervical cancer cells express several nAChRs and mAChRs, whose activation leads to changes of cellular properties such as increased motility and proliferation that favor a carcinogenic phenotype. The signaling involves intracellular phosphorylation cascades including ERK1/2.

[Characterization of muscarinic receptors in undifferentiated thyroid cells in Fisher rats]

INTRODUCTION

The parasympathetic autonomous nervous system exerts control over thyroid function by activation of the muscarinic receptors in follicular cells. Various pharmacological and molecular subtypes of muscarinic receptors (M(1), M(2), M(3), M(4), M(5)) have been identified in central nervous system and peripheral tissues. Controversy surrounds receptor characterization in thyroid cells.

MATERIALS AND METHODS

Undifferentiated Fisher rat thyroid epithelial cells (FRT) were cultured. Association and dissociation kinetics assays and antagonist competition studies of the binding of (3)H-N-methylscopolamine ((3)H-NMS) to muscarinic receptors were performed to demonstrate the presence of muscarinic receptors.

RESULTS

Specific muscarinic receptors in the plasma membrane of FRT cells were observed with an equilibrium dissociation constant (K(d)) of 0.44 nmol. The order of affinities obtained fitting the data to one binding site model in competition experiments with the muscarinic receptor antagonist was: dicyclomine > hexahydrosiladifenidol (HHSD) = 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP) > pirenzepine > himbacine = 11-[[2-[(diethylamino)methyl]- 1-piperidinyl]acetyl]-5,11-dihydro-6H-pyrido (414)benzodiazepine (AF-DX 116).

CONCLUSIONS

The results obtained indicate the existence of specific (3)H-NMS muscarinic binding sites located in the plasma membrane of FRT cells. The results obtained in competition experiments suggest that the receptors present in FRT cells belong to the M(3) subtype.

Enhanced proliferation of acinar and progenitor cells by prophylactic pilocarpine treatment underlies the observed amelioration of radiation injury to parotid glands

BACKGROUND

Administration of pilocarpine before irradiation can ameliorate radiation-induced hyposalivation. Indirect evidence suggests that this effect may be mediated through induction of a compensatory response. In this study, this hypothesis is tested directly, by assessing the proliferation of progenitor and secretory cells in irradiated and non-irradiated parotid gland tissue.

METHODS

In a rat model, parotid glands were unilaterally irradiated with a single dose of 15 Gy, 60 min after administration of pilocarpine (4.0mg/kg). Rats were sacrificed for proliferating cell nuclear antigen (PCNA) labelling, assessing the number of proliferating progenitor and secretory cells, before, and 10h, 1, 3, 7, 10, 20 and 30 days after irradiation.

RESULTS

A small radiation-induced increase in PCNA expressing cells was observed, both in the acinar (secretory cells) and intercalated duct cell (containing the progenitor cells) compartment. This increment was significantly enhanced in pilocarpine pre-treated glands. In fact, in this group of animals increased proliferation was observed both in the irradiated and the shielded gland.

CONCLUSIONS

Amelioration of early loss of rat salivary gland function after radiation by pilocarpine pre-treatment is, at least in part, due to compensatory mechanisms through increased proliferation of undamaged cells.

Distinct pathways of ERK activation by the muscarinic agonists pilocarpine and carbachol in a human salivary cell line

Cholinergic-muscarinic receptor agonists are used to alleviate mouth dryness, although the cellular signals mediating the actions of these agents on salivary glands have not been identified. We examined the activation of ERK1/2 by two muscarinic agonists, pilocarpine and carbachol, in a human salivary cell line (HSY). Immunoblot analysis revealed that both agonists induced transient activation of ERK1/2. Whereas pilocarpine induced phosphorylation of the epidermal growth factor (EGF) receptor, carbachol did not. Moreover, ERK activation by pilocarpine, but not carbachol, was abolished by the EGF receptor inhibitor AG-1478. Downregulation of PKC by prolonged treatment of cells with the phorbol ester PMA diminished carbachol-induced ERK phosphorylation but had no effect on pilocarpine responsiveness. Depletion of intracellular Ca2+ ([Ca2+]i by EGTA did not affect ERK activation by either agent. In contrast to carbachol, pilocarpine did not elicit [Ca2+]i mobilization in HSY cells. Treatment of cells with the muscarinic receptor subtype 3 (M3) antagonist N-(3-chloropropyl)-4-piperidnyl diphenylacetate decreased ERK responsiveness to both agents, whereas the subtype 1 (M1) antagonist pirenzepine reduced only the carbachol response. Stimulation of ERKs by pilocarpine was also decreased by M3, but not M1, receptor small interfering RNA. The Src inhibitor PP2 blocked pilocarpine-induced ERK activation and EGF receptor phosphorylation, without affecting ERK activation by carbachol. Our results demonstrate that the actions of pilocarpine and carbachol in salivary cells are mediated through two distinct signaling mechanisms-pilocarpine acting via M3 receptors and Src-dependent transactivation of EGF receptors, and carbachol via M1/M3 receptors and PKC-converging on the ERK pathway.

Ghrelin enhances the proliferating effect of thyroid stimulating hormone in FRTL-5 thyroid cells

Ghrelin regulates cell proliferation through the growth hormone secretagogue receptor (GHS-R). We confirmed the expression of GHS-R in FRTL-5 thyroid cells and investigated the effects of ghrelin in thyrocytes using FRTL-5 cells. Ghrelin increased intracellular calcium levels but not intracellular cyclic AMP levels. Ghrelin activated Erk within 2min, then activated Akt and STAT3. Erk phosphorylation was inhibited by the calcium inhibitor cyclopiazonic acid (CPA). Ghrelin alone did not stimulate FRTL-5 cell proliferation but enhanced the effects of thyroid stimulating hormone (TSH). Pretreatment with TSH potentiates the growth effects of ghrelin in thyroid cells, and p66Shc, a growth factor receptor adaptor protein, might mediate these synergistic effects. Ghrelin phosphorylated TSH-induced p66Shc, which was inhibited by CPA. Ghrelin did not affect the proliferation of ARO cells, which showed no increased expression of p66Shc after TSH treatment. Thus, ghrelin-induced intracellular calcium signaling enhanced the TSH-induced proliferation of thyrocytes, possibly mediated by the p66Shc pathway.

Proliferative actions of muscarinic receptors expressed in macrophages derived from normal and tumor bearing mice

Macrophages (Mps) are essential cellular components of the innate immune system. They are released from the bone marrow as immature monocytes and after circulating in the blood stream, migrate into tissues to undergo final differentiation into resident Mps. In general terms Mps behavior in breast tumors, was described as being either for or against tumor growth. Under certain well defined circumstances Mps are able to kill cells in two ways: direct tumor cytotoxicity or antibody dependent cytotoxicity. We had previously demonstrated that peritoneal Mps from LMM3 mammary tumor bearing mice (TMps) enhanced in vivo the LMM3 induced angiogenesis, promoting tumor growth while Mps from normal BALB/c mice (NMps) did not. In this work, we demonstrate that Mps, expressing functional muscarinic acetylcholine receptors, are able to proliferate in vitro in response to the muscarinic agonist carbachol. These peritoneal cells use two distinct metabolic pathways: TMps are primed by tumor presence and they proliferate mainly by activating arginase pathway and by producing high levels of prostaglandin E(2) via M(1)-M(3) receptors activation. In NMps, carbachol stimulates M(2) receptors function, triggering protein kinase C activity and induces moderate prostaglandin E(2) liberation via M(1) receptor.

Activation of calcium-dependent kinases and epidermal growth factor receptor regulate muscarinic acetylcholine receptor-mediated MAPK/ERK activation in thyroid epithelial cells

We previously showed that stimulation of muscarinic acetylcholine receptors (mAChR) by carbachol (Cch) caused a time- and dose-dependent increase of mitogen-activated protein kinase/extracellular signal-regulated kinases (MAPK/ERK) phosphorylation in thyroid epithelial cells. In this study, we demonstrated that mAChR stimulation also induced a time-dependent increase in the tyrosine phosphorylation of proline-rich tyrosine kinase 2 (Pyk2), which was prevented by pretreatment of thyroid epithelial cells with the specific Src-family tyrosine kinase inhibitor PP2. Besides, phosphorylation of Pyk2 was attenuated by chelation of extracellular Ca(2+) or inhibition of phospholipase C (PLC), and was evoked by thapsigargin, a specific microsomal Ca(2+)-ATPase inhibitor. Incorporation of Pyk2 antisense oligonucleotides in thyroid epithelial cells to down-regulated Pyk2 expression or pretreatment of cells with the Ca(2+)/calmodulin protein kinase II (CaM kinase II) inhibitor KN-62 significantly reduced Cch-induced MAPK/ERK phosphorylation. In addition, Cch-induced MAPK/ERK phosphorylation was partially inhibited by LY294002 and wortmannin, two selective inhibitors of phosphatidylinositol 3-kinase (PI3K), tyrphostin AG1478, a specific inhibitor of epidermal growth factor receptor (EGFR) kinase, and (-)-perillic acid, a post-translational inhibitor of small G-proteins isoprenylation. Taken together, our data suggest that Pyk2, CaM kinase II and Src-family tyrosine kinases are key molecules for the activation of MAPK/ERK cascade through the EGFR/Ras/Raf pathway in thyroid epithelial cells in response to mAChR stimulation.

Parathion effects on protein synthesis in the seminiferous tubules of mice

Agropesticides impart high risks of exposure for animals including humans. This work analysed the effect of parathion upon protein synthesis in seminiferous tubules cultured in vitro from adult male CF1 mice. They were incubated with parathion solutions (0.8, 0.4, 0.04, 0.004, 0.0004 mM) for 5 h. One hour after ending incubation tritiated leucine was added to each sample. In addition, groups treated with 0.8 mM parathion were incubated for 5 h, and thereafter transferred to a parathion-free medium; tritiated leucine incorporation was measured 1, 2, or 3 h afterwards. Results of protein synthesis denote an inhibitory dose-dependent effect of parathion. This is reversed after pesticide-free incubation. Testicular protein synthesis inhibition induced by parathion may compromise male fertility in view of the fact that, in spermatogenesis, proliferation (mitosis, meiosis) and cell differentiation occurs.

The nitrogen mustard melphalan activates mitogen-activated phosphorylated kinases (MAPK), nuclear factor-kappaB and inflammatory response in lung epithelial cells

To investigate how respiratory epithelial cells react to an alkylating agent, we exposed human bronchial (BEAS-2B) and alveolar (A549) cells to the nitrogen mustard derivative melphalan. The BEAS-2B cells were highly sensitive to melphalan, as shown by a reduced viability after a 10-min incubation with 300 microM melphalan. The A549 cells were less sensitive and required several hours of exposure to reduce significantly in viability. However, exposure to melphalan also induces activation of intracellular signal transduction pathways, as indicated by phosphorylation of extracellular signal-regulated kinase (ERK1/2) and p38 (proteins belonging to the family of stress-induced mitogen-activated phosphorylated kinases, MAPK) within 5 min, as well as translocation of the transcription factor nuclear factor (NF)-kappaB to the nucleus within 45 min. This early activation was followed by elevated levels of tumor necrosis factor (TNF)-alpha mRNA within 2 h. We also observed increased expression of intercellular adhesion molecule-1 (ICAM-1) on the surface of both cell lines 18 h after exposure to 25 microM melphalan and an increased adhesion of monocytes to the epithelial cells in vitro.In conclusion, we have demonstrated that alkylating compounds not only cause cell death of lung epithelial cells but also activate stress-associated MAPK signal transduction pathways and induce expression of mediators known to participate in the recruitment of inflammatory cells.

Activation of MAP kinase by muscarinic cholinergic receptors induces cell proliferation and protein synthesis in human breast cancer cells

Carbachol (Cch), a muscarinic acetylcholine receptor (mAChR) agonist, increases intracellular-free Ca(2+) mobilization and induces mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) phosphorylation in MCF-7 human breast cancer cells. Pretreatment of cells with the selective phospholipase C (PLC) inhibitor U73122, or incubation of cells in a Ca(2+)-free medium did not alter Cch-stimulated MAPK/ERK phosphorylation. Phosphorylation of MAPK/ERK was mimicked by phorbol 12-myristate acetate (PMA), an activator of protein kinase C (PKC), but Cch-evoked MAPK/ERK activation was unaffected by down-regulation of PKC or by pretreatment of cells with GF109203X, a PKC inhibitor. However, Cch-stimulated MAPK/ERK phosphorylation was completely blocked by myristoylated PKC-zeta pseudosubstrate, a specific inhibitor of PKC-zeta, and high doses of staurosporine. Pretreatment of human breast cancer cells with wortmannin or LY294002, selective inhibitors of phosphoinositide 3-kinase (PI3K), diminished Cch-mediated MAPK/ERK phosphorylation. Similar results were observed when MCF-7 cells were pretreated with genistein, a non-selective inhibitor of tyrosine kinases, or with the specific Src tyrosine kinase inhibitor PP2. Moreover, in MCF-7 human breast cancer cells mAChR stimulation induced an increase of protein synthesis and cell proliferation, and these effects were prevented by PD098059, a specific inhibitor of the mitogen activated kinase kinase. In conclusion, analyses of mAChR downstream effectors reveal that PKC-zeta, PI3K, and Src family of tyrosine kinases, but not intracellular-free Ca(2+) mobilization or conventional and novel PKC activation, are key molecules in the signal cascade leading to MAPK/ERK activation. In addition, MAPK/ERK are involved in the regulation of growth and proliferation of MCF-7 human breast cancer cells.

Activation of second messenger-dependent protein kinases induces muscarinic acetylcholine receptor desensitization in rat thyroid epithelial cells

Internalization and phosphorylation of G protein-coupled receptors (GPCR) are considered two important regulatory events of receptor signal transduction. In Fischer rat thyroid (FRT) epithelial cells, we have shown that muscarinic acetylcholine receptor (mAChR) stimulation induces intracellular Ca2+ mobilization via Ca2+ store release, capacitative Ca2+ entry and voltage-dependent Ca2+ channels activation. In the present study, the role of mAChR internalization and phosphorylation on receptor signalling pathway was examined by means of intracellular Ca2+ measurement in these cells. Exposure of FRT cells to carbachol (Cch), a mAChR agonist, resulted in a desensitization of receptor-mediated intracellular Ca2+ mobilization and induced the internalization of constitutively expressed mAChR in this cell type. Treatment of FRT cells with hypertonic sucrose, which markedly reduced agonist-receptor complex internalization, or phenylarsine oxide (PAO) diminished the Cch-induced intracellular Ca2+ response. Moreover, pretreatment of cells with phorbol-12-myristate-13-acetate (PMA), an activator of protein kinase C (PKC), completely abolished Cch-evoked Ca2+ mobilization, whereas it was significantly increased by the preincubation of cells with GF109203X, a selective inhibitor of PKC. We also found a marked decrease on Cch-stimulated Ca2+ mobilization in pretreated FRT cells with forskolin, an activator of protein kinase A (PKA), but the preincubation of cells with genistein, an inhibitor of protein tyrosine kinases, had no effect on Ca2+ mobilization induced by Cch. These findings seem to indicate that mAChR in FRT cells exhibit a desensitization, which may be mediated, at least in part, through activation of second messenger-dependent protein kinases and that receptor internalization could be necessary for signalling.

Effects of carbachol on rat Sertoli cell proliferation and muscarinic acetylcholine receptors regulation: an in vitro study

The aim of the present work was to study the effect of muscarinic agonist on cell proliferation and muscarinic acetylcholine receptors (mAChRs) regulation in rat Sertoli cells. Primary cultures of Sertoli cells were obtained from 8-day and 15-day old male Wistar rats. In proliferation assays, [methyl-3H]thymidine incorporation in Sertoli cells from 8-day and 15-day old rats reached a plateau after 60 min of carbachol incubation and decreased after 120 min of agonist incubation. Binding studies with [N-Methyl-3H]scopolamine ([3H]NMS) indicated a rapid loss of cell surface mAChRs when Sertoli cells from 15-day old rats were incubated with carbachol at 35 degrees C for 2 min. This effect was temperature-dependent. When the incubation of the cells was prolonged at 35 degrees C or at 4 degrees C, after the agonist had been washed away, 94% of mAChRs were present in the cell surface after 120 min incubation at 35 degrees C. At 4 degrees C, however, a low percentage of mAChRs was detected in the cell surface. In the presence of cycloheximide, the recycling of mAChRs to the cell surface was not changed, suggesting that the appearance of mAChRs on cell surface was not dependent on de novo receptor synthesis. In conclusion, our studies indicate that the activation of mAChRs may play a role in rat Sertoli cell proliferation. These receptors may be under regulation (internalization and recycling) when cells are exposed to muscarinic cholinergic agonist.