ATP-stimulated c-fos andzif268 mRNA expression is inhibited by chemical hypoxia in a rat brain-derived type 2 astrocyte cell line, RBA-2

Abstract

The stimulus-transcriptional coupling during ischemia/hypoxia was examined for ATP-stimulated expression of immediate early genes (IEGs; c-fos, zif268, c-myc and nur77) in a rat brain-derived type 2 astrocyte cell line, RBA-2. Incubation of cells with 1 mM of extracellular ATP stimulated time-dependent expression of c-fos and zif268. ATP induced the largest increases in zif268 mRNA and a lesser one in c-fos mRNA. ATP also induced a slight increase in nur77 mRNA but was ineffective in inducing c-myc expression in these cells. Brief exposure of cells to potassium cyanide to simulate chemical hypoxia induced 9-fold and 7-fold transient increases in c-fos and zif268 expression, respectively, but did not affect c-myc or nur77 expression. When cyanide and ATP were added together, the expression of c-fos and zif268 expression was inhibited, and the effect was mimicked by simulating chemical hypoxia with sodium azide. To elucidate the mechanism involved, the effect of cyanide on ATP-stimulated increases in intracellular Ca(2+) concentrations, [Ca(2+)](i), and phospholipase D (PLD) activities were measured. Cyanide induced an increase in [Ca(2&plus);](i) and further enhanced the ATP-stimulated increases in [Ca(2+)](i) and PLD activities. Nevertheless, metabolic inhibitor, iodoacetate, blocked the ATP-induced c-fos and partially inhibited zif268 expression, and deprivation of cells with glucose also inhibited the ATP-induced c-fos expression. Taken together, these results demonstrate that both extracellular ATP and chemical hypoxia induce c-fos and zif268 expression in RBA-2 type 2 astrocytes. The chemical hypoxia inhibited ATP-stimulated c-fos and zif268 expression is not due to alterations in Ca(2+) and PLD signaling, and is at least partially related to metabolic disturbance in these cells.

Nur77 Gene Knockout Alters Dopamine Neuron Biochemical Activity and Dopamine Turnover

“…However, this reduction of COMT expression was found throughout the brain, suggesting that both neuronal (membrane-bound isoform) and nonneuronal (soluble isoform) COMT expression might have been altered by the knockout. Indeed, COMT is expressed in both neurons and type 2 astrocytes (Karhunen et al 1995), and Nur77 can be induced in type 2 astrocytes by various stimuli (Hung et al 2000). Reduced 3-MT contents in the striatal complex also reinforces the possibility that the membrane-bound isoform of the enzyme is altered in Nur77 −/− mice.…”

Differential effects of neonatal norepinephrine lesions on immediate early gene expression in developing and adult rat brain

“…There is evidence that Arc, c-fos and zif268 are highly expressed in neurons but are also found in astrocytes and glia (Worley et al, 1991; Lyford et al, 1995; Hung et al, 2000; Rodriguez et al, 2008; Nakazawa et al, 2008; Reznikov et al, 2008). Therefore the expression detected in this study reflects contributions from both of these neuronal populations.…”

The Transcription Factor C-Myc Suppresses MiR-23b and MiR-27b Transcription during Fetal Distress and Increases the Sensitivity of Neurons to Hypoxia-Induced Apoptosis

“…In particular, Greenway et al reported that the effect of hypoxia on c-Myc in turtles is organ-specific, and c-Myc protein expression is increased in kidney and brain after hypoxia [ 22 ]. Hung et al reported that chemical hypoxia causes 2.2-fold increases in c-Myc mRNA expression in a rat brain-derived type 2 astrocyte cell line [ 23 ]. It has been reported that c-Myc represses miR-23a and miR-23b at the transcriptional level in human P-493B lymphoma cells and PC3 prostate cancer cells [ 24 ].…”