IL-6 expression induced by adenosine A2b receptor stimulation in U373 MG cells depends on p38 mitogen activated kinase and protein kinase C

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.

Substance P induces expression of the corticotropin-releasing factor receptor 1 by activation of the neurokinin-1 receptor

The neuropeptide substance P (SP) has been found to be possibly involved in the etiology of affective and anxiety disorders. However, the molecular mechanisms underlying this involvement are still poorly understood. In this study, we used macroarrays to investigate the differential gene expression profile induced by SP, particularly of genes which have been shown to be involved in the pathophysiology of affective disorders. As a model system, we used the human astrocytoma cell line U373 MG as well as primary rat astroglial cells, which both are known to express functional neurokinin-1 receptors (NK-1-R) and to secret various cytokines upon stimulation with SP. Among several regulated genes, we found that SP (100 and 1000 nM) induced the expression of the corticotropin-releasing factor receptor 1 (CRF1 receptor). Further analyses revealed that this induction was mediated (a) via NK-1-R, as the selective NK-1-R-antagonist L-733,060 (1 microM) strongly inhibited SP-induced CRF1 receptor expression, and (b) intracellularly, by protein kinase C, p42/44 and p38 mitogen-activated protein kinases (MAPK), as shown by using specific inhibitors of signal transduction pathways. In conclusion, this study demonstrates that SP induces CRF1 receptor expression in cells of the CNS, which may be of potential interest for a better understanding of the interplay between SP and the stress hormone axis and, thus, diseases like affective or anxiety disorders. Further studies are needed to substantiate this link in vivo.

Valproic acid inhibits substance P-induced activation of protein kinase C epsilon and expression of the substance P receptor

The neuropeptide substance P (SP) has been hypothesized to be involved in the etiopathology of affective disorders. This hypothesis is based on the findings that neurokinin-1-receptor antagonists have antidepressant effects in depressed patients and that SP may worsen mood. In this study, we investigated the effect of the mood-stabilizing agents valproic acid (VPA), carbamazepine, and lithium on SP-induced gene expression. As a model system, we used primary rat astrocytes and human astrocytoma cells, which both express functional SP-receptors and, upon stimulation with SP, synthesize interleukin-6 (IL-6), a cytokine which has been shown to be elevated during the acute depressive state. We found that VPA dose-dependently inhibited SP-induced IL-6 synthesis which was seen with pre-incubation periods of 30 min, 3, 7 and 14 days, whereas carbamazepine and lithium showed no inhibitory effect. The inhibitory effect of VPA was not mediated by inhibition of the stress-regulated kinases p38 and p42/44 (Erk1/2) but by inhibition of protein kinase C epsilon activation. Furthermore, VPA down-regulated the expression of the substance P receptor (neurokinin(NK)-1-receptor) as assessed by real-time PCR. Whether both mechanisms contribute to the mood-stabilizing properties of VPA has to be evaluated in further studies.