Mast cell adenosine receptor characteristics and signaling

Roles of substance P and ATP in the subepithelial fibroblasts of rat intestinal villi

The ingestion of food and water induces chemical and mechanical signals that trigger peristaltic reflexes and also villous movement in the gut. In the intestinal villi, subepithelial fibroblasts under the epithelium form contractile cellular networks and closely contact to the varicosities of substance P and nonsubstance P afferent neurons. Subepithelial fibroblasts of the duodenal villi possess purinergic receptor P2Y1 and tachykinin receptor NK1. ATP and substance P induce increase in intracellular Ca(2+) and cell contraction in subepithelial fibroblasts. They are highly mechanosensitive and release ATP by mechanical stimuli. Released ATP spreads to form an ATP "cloud" with nearly 1μM concentration and activates the surroundings via P2Y1 and afferent neurons via P2X receptors. These findings suggest that villous subepithelial fibroblasts and afferent neurons interact via ATP and substance P. This mutual interaction may play important roles in the signal transduction of mechano reflex pathways including a coordinate villous movement and also in the maturation of the structure and function of the intestinal villi.

Adenosine induces cell-cycle arrest and apoptosis in androgen-dependent and -independent prostate cancer cell lines, LNcap-FGC-10, DU-145, and PC3

BACKGROUND

Adenosine has been shown to inhibit cell growth and induce apoptosis in the several cancer cells via intrinsic and extrinsic pathway. The present study was designed to understand the mechanism underlying adenosine-induced apoptosis in the DU-145, PC3, and LNcap-FGC10 human prostate cancer cells.

METHODS

To observe cell viability and proliferation, MTT assay, cell counting, and BrdU assay were carried out in DU-145, PC3, and LNcap-FGC10 cells. Apoptosis was assessed with the analysis of cell cycle, Hoechst 33258 staining, propidium iodide and annexin-V staining, reactive oxygen species (ROS) formation, mitochondrial membrane potential (ΔΨM) measurement, caspase-3 activity assay, Bcl-2 and Bax protein expression. Moreover, the expression of adenosine receptors and the effects of adenosine receptor (A(1) , A(2a) , and A(3) ) antagonists were examined.

RESULT

Adenosine significantly reduced cell proliferation in a dose-dependent manner in DU-145, PC3, and LNcap-FGC10 cell lines. Adenosine induced arrest in the cell-cycle progression in G0/G1 phase through Cdk4/cyclinD1-mediated pathway. Adenosine induced apoptosis, which was determined by morphological changes and increased sub-G1 population. Furthermore, increase of ROS, loss of MMP, activation of caspase-3, and down-regulation of Bcl-2 expression was observed. A(1) , A(2a) , A(2b) , and A(3) adenosine receptors mRNA are expressed in the cell lines. Moreover, adenosine-induced apoptosis was inhibited by MRS1220, A(3) adenosine receptor antagonist.

CONCLUSION

Our results suggest that adenosine induced apoptosis in prostate cancer cells via the mitochondrial pathway and is related to the adenosine receptors. These data might suggest that adenosine could be used as an agent for the treatment of prostate cancer.

IL-1 beta and TNF-alpha regulation of the adenosine receptor (A2A) expression: differential requirement for NF-kappa B binding to the proximal promoter

Adenosine is a potent endogenous regulator of airway inflammation that acts through specific receptor subtypes that can either cause constriction (A1R, A2BR, and A3R) or relaxation (A2AR) of the airways. We therefore examined the effects of key inflammatory mediators on the expression of the A2AR in a lung epithelial cell line (A549). IL-1beta and TNF-alpha increased the expression of the A2AR gene at the mRNA and protein levels. In contrast, LPS had no effect on A2AR gene expression. IL-1beta and TNF-alpha rapidly activated p50 and p65, but not C-Rel, RelB, or p52, and both IL-1beta- and TNF-alpha-stimulated A2AR expression was inhibited by the IkappaB kinase 2 inhibitor AS602868 in a concentration-dependent manner. Using chromatin immunoprecipitation assays, we demonstrate that IL-1beta can enhance p65 association with putative kappaB binding sites in the A2AR promoter in a temporal manner. In contrast, TNF-alpha failed to enhance p65 binding to these putative sites. Functionally, the two most 5' kappaB sites were important for IL-1beta-, but not TNF-alpha-, induced A2AR promoter reporter gene activity. Finally, neither TNF-alpha nor Il-1beta had any effect on A2AR mRNA transcript degradation. These results directly implicate a major role for NF-kappaB in the regulation of A2AR gene transcription by IL-1beta and TNF-alpha but suggest that the effects of TNF-alpha on A2AR gene transcription are not mediated through the proximal promoter.

Signaling through Toll-like receptors triggers HIV-1 replication in latently infected mast cells

Evidence that human progenitor mast cells are susceptible to infection with CCR5-tropic strains of HIV-1 and that circulating HIV-1-infected FcepsilonRIalpha(+) cells with a similar progenitor phenotype have been isolated from AIDS patients has led to speculation that mast cells may serve as a potential reservoir for infectious HIV-1. In this study, progenitor mast cells, developed in vitro from CD34(+) cord blood stem cells, were experimentally infected with the CCR5-tropic strain HIV-1Bal after 28 days in culture as they reached their HIV-1-susceptible progenitor stage. HIV-1 p24 Ag levels were readily detectable by day 7 postinfection (PI), peaked at 2-3 wk PI as mature (tryptase/chymase-positive) HIV-1 infection-resistant mast cells emerged, and then steadily declined to below detectable limits by 10 wk PI, at which point integrated HIV-1 proviral DNA was confirmed by PCR quantitation in ( approximately 34% of) latently infected mast cells. Stimulation by ligands for Toll-like receptor (TLR) 2, TLR4, or TLR9 significantly enhanced viral replication in a dose- and time-dependent manner in both HIV-1-infected progenitor and latently infected mature mast cells, without promoting degranulation, apoptosis, cellular proliferation, or dysregulation of TLR agonist-induced cytokine production in infected mast cells. Limiting dilution analysis of TLR activated, latently infected mature mast cells indicated that one in four was capable of establishing productive infections in A301 sentinel cells. Taken together, these results indicate that mast cells may serve both as a viral reservoir and as a model for studying mechanisms of postintegration latency in HIV infection.

Presynaptic inhibition of spontaneous acetylcholine release induced by adenosine at the mouse neuromuscular junction

1. At the mouse neuromuscular junction, adenosine (AD) and the A(1) agonist 2-chloro-N(6)-cyclopentyl-adenosine (CCPA) induce presynaptic inhibition of spontaneous acetylcholine (ACh) release by activation of A(1) AD receptors through a mechanism that is still unknown. To evaluate whether the inhibition is mediated by modulation of the voltage-dependent calcium channels (VDCCs) associated with tonic secretion (L- and N-type VDCCs), we measured the miniature end-plate potential (mepp) frequency in mouse diaphragm muscles. 2. Blockade of VDCCs by Cd(2+) prevented the effect of the CCPA. Nitrendipine (an L-type VDCC antagonist) but not omega-conotoxin GVIA (an N-type VDCC antagonist) blocked the action of CCPA, suggesting that the decrease in spontaneous mepp frequency by CCPA is associated with an action on L-type VDCCs only. 3. As A(1) receptors are coupled to a G(i/o) protein, we investigated whether the inhibition of PKA or the activation of PKC is involved in the presynaptic inhibition mechanism. Neither N-(2[p-bromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide (H-89, a PKA inhibitor), nor 1-(5-isoquinolinesulfonyl)-2-methyl-piperazine (H-7, a PKC antagonist), nor phorbol 12-myristate 13-acetate (PHA, a PKC activator) modified CCPA-induced presynaptic inhibition, suggesting that these second messenger pathways are not involved. 4. The effect of CCPA was eliminated by the calmodulin antagonist N-(6-aminohexil)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7) and by ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid-acetoxymethyl ester epsilon6TDelta-BM, which suggests that the action of CCPA to modulate L-type VDCCs may involve Ca(2+)-calmodulin. 5. To investigate the action of CCPA on diverse degrees of nerve terminal depolarization, we studied its effect at different external K(+) concentrations. The effect of CCPA on ACh secretion evoked by 10 mm K(+) was prevented by the P/Q-type VDCC antagonist omega-agatoxin IVA. 6. CCPA failed to inhibit the increases in mepp frequency evoked by 15 and 20 mm K(+). We demonstrated that, at high K(+) concentrations, endogenous AD occupies A1 receptors, impairing the action of CCPA, since incubation with 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, an A(1) receptor antagonist) and adenosine deaminase (ADA), which degrades AD into the inactive metabolite inosine, increased mepp frequency compared with that obtained in 15 and 20 mm K(+) in the absence of the drugs. Moreover, CCPA was able to induce presynaptic inhibition in the presence of ADA. It is concluded that, at high K(+) concentrations, the activation of A(1) receptors by endogenous AD prevents excessive neurotransmitter release.

Signalling from adenosine receptors to mitogen-activated protein kinases

The purine nucleoside adenosine acts via four distinct adenosine receptor subtypes: the adenosine A(1), A(2A), A(2B), and A(3) receptor. They are all G protein-coupled receptors (GPCR) coupling to classical second messenger pathways such as modulation of cAMP production or the phospholipase C (PLC) pathway. In addition, they couple to mitogen-activated protein kinases (MAPK), which could give them a role in cell growth, survival, death and differentiation. Although each of the adenosine receptors can activate one or more of the MAPKs, the mechanisms appear to differ substantially, both between receptor subtypes in the same cell type and between the same receptor in different cell types.

Adenosine and its role in asthma

Endogenous adenosine formed from ADP and AMP by the action of ATPase and 5'-nucleotidase is known to cause bronchoconstriction and asthma in humans. It has been suggested that this action of adenosine is due to its binding to specific purino receptors in the mast cells in the lungs and consequent release of mediators which elicit bronchoconstriction and asthma. The release of these mediators leading to asthma was also believed to be due to vagal stimulation by adenosine. Though the role of adenosine in causing bronchoconstriction leading to asthma is well confirmed the actual mode of action and details of the mechanisms involved in the clinical manifestation of asthma remain unclear.

Acute paw oedema induced by local injection of adenosine A(1), A(2) and A(3) receptor agonists

The present study used plethysmometry to examine oedema following local injection of selective adenosine A(1), A(2) and A(3) receptor agonists and inhibitors of adenosine metabolism into the hindpaw of the rat. N(6)-Cyclopentyladenosine and L-N(6)-phenylisopropyladenosine (A(1)), 2-[p(2-carboxyethyl) phenethylamino]-5'-N-ethylcarboxamidoadenosine hydrochloride (CGS21680) (A(2A)) and N(6)-benzyl-5'-N-ethylcarboxamido adenosine (N(6)-B-NECA) (A(3)) all produced an increase in paw volume (N(6)N(6)-cyclopentyladenosine, L-N(6)CGS21680). At the highest dose, each agent also produced a systemically mediated suppression of oedema. Oedema by N(6)-cyclopentyladenosine was blocked by caffeine, 8-cyclopentyl-1,3-dimethylxanthine and enprofylline. Oedema by CGS21680 was blocked by caffeine and 8-cyclopentyl-1, 3-dimethylxanthine. Oedema by N(6)-B-NECA was blocked by enprofylline, but not by caffeine or 8-cyclopentyl-1, 3-dimethylxanthine, or by systemic administration of MRS 1191. Oedema by both N(6)-cyclopentyladenosine and N(6)-B-NECA was blocked by mepyramine, ketanserin and phentolamine, but that by CGS21680 was not. The adenosine kinase inhibitor 5'-amino-5'-deoxyadenosine and the adenosine deaminase inhibitor 2'-deoxycoformycin produced only a limited increase in paw volume, and this was blocked by caffeine. This study demonstrates an acute paw oedema response following local administration of adenosine A(1), A(2) and A(3) receptor agonists, which likely results from different mechanisms of action in each case.

Chemotaxis of Rat Mast Cells Toward Adenine Nucleotides

Rat mucosal mast cells express P2 purinoceptors, occupation of which mobilizes cytosolic Ca2+ and activates a potassium conductance. The primary function of this P2 system in mast cell biology remains unknown. Here, we show that extracellular ADP causes morphological changes in rat bone marrow-cultured mast cells (BMMC) typical of those occurring in cells stimulated by chemotaxins, and that the nucleotides ADP, ATP, and UTP are effective chemoattractants for rat BMMC. ADP was also a chemotaxin for murine J774 monocytes. The nucleotide selectivity and pertussis toxin sensitivity of the rat BMMC migratory response suggest the involvement of P2U receptors. Poorly hydrolyzable derivatives of ADP and ATP were effective chemotaxins, obviating a role for adenosine receptors. Buffering of external Ca2+ at 100 nM or reduction of the electrical gradient driving Ca2+ entry (by elevating external K+) blocked ADP-driven chemotaxis, suggesting a role for Ca2+ influx in this process. Anaphylatoxin C5a was a potent chemotaxin (EC50 ≈0.5 nM) for J774 monocytes, but it was inactive on rat BMMC in the presence or absence of laminin. Ca2+ removal or elevated [K+] had modest effects on C5a-driven chemotaxis of J774 cells, implicating markedly different requirements for Ca2+ signaling in C5a- vs ADP-mediated chemotaxis. This is supported by the observation that depletion of Ca2+ stores with thapsigargin completely blocked migration induced by ADP but not C5a. These findings suggest that adenine nucleotides liberated from parasite-infested tissue could participate in the recruitment of mast cells by intestinal mucosa.

Insight into adenosine receptor function using antisense and gene-knockout approaches

The extensive role of adenosine in discriminating input from the extracellular environment is effected through a series of cell membrane-spanning proteins--the adenosine A1, A2A, A2B and A3 receptors. New genetic and epigenetic tools have emerged that facilitate the elucidation of the function of these receptors with greater specificity than is generally possible with traditional antagonist drugs. These tools include antisense oligonucleotides (epigenetic) and gene 'knockin' and 'knockout' mice (genetic) and are discussed in this article by Jonathan Nyce.