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In our earlier studies of the signaling cross-talk between nucleotide receptors in an in vitro glioma model (C6 cell line) under prolonged serum deprivation conditions, a growth arrest of the cells and expression shift from P2Y1 to P2Y12 receptors was found. The aim of the present work was to test if siRNA silencing of P2Y1 receptor changes P2Y12 expression similarly as following the serum deprivation and which physiological downstream pathways it affects. Here we demonstrate for the first time the efficiency of siRNA technology in silencing P2Y nucleotide receptors in glioma C6 cell line. Moreover, P2Y12 proved to be insensitive to the P2Y1 receptor silencing. The effect of the P2Y1 silencing on calcium signaling was less pronounced then the extent of the protein change itself, exactly as was the case for the serum starvation experiments. Phosphorylation of ERK and Akt kinases were studied as the downstream effect of P2Y1-evoked signaling and similar effects as in the case of serum deprivation were found for ERK, and even stronger ones for Akt phosphorylation.
After insults microglia cells act by migrating to the site of injury, phagocyting cell debris and secreting inflammatory mediators, among which are cytokines, chemokines, cysteinyl leukotrienes (cysLTs) and purinergic molecules. The recently discovered GPR17 is structurally related to P2Y purinergic and cysLT receptors. Little is known about its regulation in microglia except that, in animal models, GPR17 was found in these cells exclusively after ischemic injury. The aim of this study was to identify in vitro signals that can trigger GPR17 expression in reactive microglia in vivo. Realtime PCR showed that in primary rat microglia cells, a low level of GPR17 can be increased by conditioned medium from oxygen and glucose deprived neurons or by prolonged deprivation of growth factors, but not by typical “danger signals” like ATP or cysLT. Among other known activators of microglia cells, lipopolysaccharide caused a decrease of GPR17 expression, but GPR17 receptor agonists and zymosan (a stimulator of phagocytosis) led to its increase in a time-dependent manner. It is still not known how long, after induction, GPR17 receptors remain in the membrane and what function they may play. However preliminary results showed that GPR17 expression may participate in the acquisition of a detrimental or a beneficial phenotype of microglia.
Inhibition of Rho-associated protein kinase (ROCK) activity in glioma C6 cells induces changes in actin cytoskeleton organization and cell morphology similar to those observed in other types of cells with inhibited RhoA/ROCK signaling pathway. We show that phosphorylation of myosin light chains (MLC) induced by P2Y2 receptor stimulation in cells with blocked ROCK correlates in time with actin cytoskeleton reorganization, F-actin redistribution and stress fibers assembly followed by recovery of normal cell morphology. Presented results indicate that myosin light-chain kinase (MLCK) is responsible for the observed phosphorylation of MLC. We also found that the changes induced by P2Y2 stimulation in actin cytoskeleton dynamics and morphology of cells with inhibited ROCK, but not in the level of phosphorylated MLC, depend on the presence of calcium in the cell environment.
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