RESUMO
Adenosine binds to a class of G-protein coupled receptors, which are further distinguished as A(1), A(2a), A(2b) and A(3) adenosine receptors. As we have shown earlier, the stable adenosine analogue NECA (N6-(R)-phenylisopropyladenosine) stimulates IL-6 expression in the human astrocytoma cell line U373 MG via the A(2b) receptor. The mechanism by which NECA promotes astrocytic IL-6 expression has not been identified. By using various inhibitors of signal transduction, we found that p38 mitogen-activated protein kinases (MAPK) activation (inhibitor SB202190), but not extracellular signal-regulated kinase (ERK) (PD98059) and c-jun N-terminal kinase (JNK)(SP600125), is essential in the NECA-induced signalling cascade that leads to the increase in IL-6 synthesis in U373 MG cells. Results obtained with protein kinase C (PKC) inhibitors that have different substrate specificities, indicated that the PKC delta and epsilon isoforms are also involved in adenosine receptor A(2b) dependent upregulation of IL-6 expression. This is supported by the fact that NECA induced the activation of PKC delta and epsilon in U373 MG cells.
Assuntos
Adenosina/metabolismo , Astrocitoma/metabolismo , Interleucina-6/metabolismo , Proteína Quinase C/metabolismo , Receptor A2B de Adenosina/metabolismo , Transdução de Sinais/fisiologia , Proteínas Quinases p38 Ativadas por Mitógeno/metabolismo , Agonistas do Receptor A2 de Adenosina , Linhagem Celular Tumoral , Inibidores Enzimáticos/farmacologia , MAP Quinases Reguladas por Sinal Extracelular/antagonistas & inibidores , MAP Quinases Reguladas por Sinal Extracelular/genética , MAP Quinases Reguladas por Sinal Extracelular/metabolismo , Humanos , Proteínas Quinases JNK Ativadas por Mitógeno/antagonistas & inibidores , Proteínas Quinases JNK Ativadas por Mitógeno/genética , Proteínas Quinases JNK Ativadas por Mitógeno/metabolismo , Proteína Quinase C/antagonistas & inibidores , Proteína Quinase C/genética , Proteína Quinase C-delta , Proteína Quinase C-épsilon , RNA Mensageiro/efeitos dos fármacos , RNA Mensageiro/metabolismo , Transdução de Sinais/efeitos dos fármacos , Regulação para Cima/efeitos dos fármacos , Regulação para Cima/fisiologia , Proteínas Quinases p38 Ativadas por Mitógeno/antagonistas & inibidores , Proteínas Quinases p38 Ativadas por Mitógeno/genéticaRESUMO
The "regulators of g-protein signalling" (RGS) comprise a large family of proteins that limit by virtue of their GTPase accelerating protein domain the signal transduction of G-protein coupled receptors. RGS proteins have been implicated in various neuropsychiatric diseases such as schizophrenia, drug abuse, depression and anxiety and aggressive behaviour. Since conditions associated with a large increase of adenosine in the brain such as seizures or ischemia were reported to modify the expression of some RGS proteins we hypothesized that adenosine might regulate RGS expression in neural cells. We measured the expression of RGS-2,-3, and -4 in both transformed glia cells (human U373 MG astrocytoma cells) and in primary rat astrocyte cultures stimulated with adenosine agonists. Expression of RGS-2 mRNA as well as RGS2 protein was increased up to 30-fold by adenosine agonists in astrocytes. The order of potency of agonists and the blockade by the adenosine A2B-antagonist MRS1706 indicated that this effect was largely mediated by adenosine A2B receptors. However, a smaller effect was observed due to activation of adenosine A2A receptors. In astrocytoma cells adenosine agonists elicited an increase in RGS-2 expression solely mediated by A2B receptors. Expression of RGS-3 was inhibited by adenosine agonists in both astrocytoma cells and astrocytes. However while this effect was mediated by A2B receptors in astrocytoma cells it was mediated by A2A receptors in astrocytes as assessed by the order of potency of agonists and selective blockade by the specific antagonists MRS1706 and ZM241385 respectively. RGS-4 expression was inhibited in astrocytoma cells but enhanced in astrocytes by adenosine agonists.
Assuntos
Astrócitos/metabolismo , Reguladores de Proteínas de Ligação ao GTP/genética , Regulação da Expressão Gênica , Receptores A2 de Adenosina/metabolismo , Adenosina/farmacologia , Agonistas do Receptor A2 de Adenosina/farmacologia , Animais , Astrocitoma/genética , Astrocitoma/metabolismo , Linhagem Celular Tumoral , Humanos , Proteínas RGS/genética , RNA Mensageiro/genética , RatosRESUMO
Recent in-vitro data indicate that depletion of neural cells of myo-inositol by virtue of down-regulation of the high-affinity sodium-myo-inositol co-transporter (SMIT) may be a common mechanism of action of the mood stabilizers lithium, valproate and carbamazepine. The authors sought to investigate whether or not down-regulation of SMIT also occurs in vivo in bipolar patients. Expression of SMIT mRNA was measured in neutrophils of bipolar patients either unmedicated or treated with lithium salts or valproate and in neutrophils of unmedicated, matched healthy controls using quantitative real-time PCR. The content of SMIT mRNA was significantly reduced in neutrophils of lithium-treated bipolar patients compared to controls and to untreated bipolar patients. Untreated bipolar I patients but not bipolar II patients exhibited a significantly higher expression of SMIT mRNA than controls. Neutrophils of bipolar I patients treated with valproate exhibited a significantly lower expression of SMIT mRNA than untreated bipolar I patients but did not differ from controls. These results suggest that lithium and valproate down-regulate SMIT mRNA in vivo in patients. In addition the data provide first evidence that up-regulation of SMIT might be associated with an increased risk for bipolar I disorder.