P2X₇ receptors stimulate AKT phosphorylation in astrocytes

Abstract

1 Emerging evidence indicates that nucleotide receptors are widely expressed in the nervous system. Here, we present evidence that P2Y and P2X receptors, particularly the P2X 7 subtype, are coupled to the phosphoinositide 3-kinase (PI3K)/Akt pathway in astrocytes. 2 P2Y and P2X receptor agonists ATP, uridine 5 0 -triphosphate (UTP) and 2 0 ,3 0 -O-(4-benzoyl)-benzoyl ATP (BzATP) stimulated Akt phosphorylation in primary cultures of rat cortical astrocytes. BzATP induced Akt phosphorylation in a concentration-and time-dependent manner, similar to the effect of BzATP on Akt phosphorylation in 1321N1 astrocytoma cells stably transfected with the rat P2X 7 receptor. Activation was maximal at 5-10 min and was sustained for 60 min; the EC 50 for BzATP was approximately 50 mM. In rat cortical astrocytes, the positive effect of BzATP on Akt phosphorylation was independent of glutamate release. 3 The effect of BzATP on Akt phosphorylation in rat cortical astrocytes was significantly reduced by the P2X 7 receptor antagonist Brilliant Blue G and the P2X receptor antagonist iso-pyridoxal-5 0 -phosphate-6-azophenyl-2 0 ,4 0 -disulfonic acid, but was unaffected by trinitrophenyl-ATP, oxidized ATP, suramin and reactive blue 2. 4 Results with specific inhibitors of signal transduction pathways suggest that extracellular and intracellular calcium, PI3K and a Src family kinase are involved in the BzATP-induced Akt phosphorylation pathway. 5 In conclusion, our data indicate that stimulation of astrocytic P2X 7 receptors, as well as other P2 receptors, leads to Akt activation. Thus, signaling by nucleotide receptors in astrocytes may be important in several cellular downstream effects related to the Akt pathway, such as cell cycle and apoptosis regulation, protein synthesis, differentiation and glucose metabolism.

ATP Activates a Reactive Oxygen Species-dependent Oxidative Stress Response and Secretion of Proinflammatory Cytokines in Macrophages

“…As shown in Fig. 3, a short incubation of macrophages with ATP caused Akt phosphorylation to increase significantly, consistent with previous reports in macrophages and astrocytes (8,27). The increase in Akt phosphorylation could be inhibited by co-treatment of macrophages with NAC (Fig.…”

“…Ligation of Purinergic Receptors Leads to Activation of the PI3K Pathway-Extracellular ATP can activate PI3K in macrophages and other cell types (6,8,27). In many cell types, PI3K phosphorylates and activates the downstream Ser/Thr kinase, Akt/PKB, which promotes survival or controls metabolism through phosphorylation of multiple targets (28).…”

A Role for Mitogen-activated Protein KinaseErk1/2 Activation and Non-selective Pore Formation in P2X7 Receptor-mediated Thymocyte Death

“…Alternatively, P2X7R stimulation may activate two independent pathways, involving Src family tyrosine kinase(s) and PI3K, both leading to MEK1/2 activation. Jacques-Silva et al (61) have recently shown the activation of Akt via PI3K and Src family kinases in P2X7R-stimulated rat astrocytes. This observation contrasts with our finding that Akt is not phosphorylated in ATP-treated thymocytes, despite PI3K activation.…”

Coordinate pathways for nucleotide and EGF signaling in cultured adult neural progenitor cells

“…The GFAP-positive progenitor cells investigated in this study were multipotential and expressed the stem-cell marker nestin as well as the type-B cell-associated ectonucleotidases NTPDase2 and TNAP (Mishra et al, 2006;Langer et al, 2007), suggesting that they represent type-B cell-like neural precursors. Both RT-PCR and pharmacological experiments suggest that cultured astrocytes express a variety of P2Y and P2X receptors (Jacques-Silva et al, 2004;Washburn and Neary, 2006) whose functional impact is only partially understood. We have identified several P2 receptors (P2X and P2Y) in cultured adult neural progenitor cells but the RT-PCR data alone do not allow conclusions regarding the extent of translation and amount of functional protein.…”

“…In murine astrocytes, P2Y 6 mRNA was found to be absent (Lenz et al, 2000) whereas P2Y 4 receptor mRNA could be identified, in contrast to neural progenitors. Cultured astrocytes express the P2X 7 receptor and activation of this receptor stimulates Akt phosphorylation (Jacques-Silva et al, 2004), but P2X 7 receptor mRNA is essentially absent from cultured neural progenitors. The notion that the molecular features of neural progenitors only partially overlap with those of astrocytes is also supported by our observation that the fingerprint of ERK1/2 and CREB phosphorylation induced by ADPβS, UTP and EGF differs between neural progenitors and progenitor-derived astrocytes.…”