Regulation of initiation factors controlling protein synthesis on cultured astrocytes in lactic acid‐induced stress

Abstract

The goals of this work were first to assess whether the lactic acidosis observed in vivo in ischemia may by itself explain the inhibition of protein synthesis described in the literature and second to study the factors controlling the initiation of protein synthesis under lactic acid stress. Primary rat astrocyte cultures exposed to pH 5.25 underwent cell death and a strong inhibition of protein synthesis assessed by [3H]methionine incorporation, which was solely due to acidity of the extracellular medium and was not related to lactate concentrations. This result was associated with a weak phosphorylation of eukaryotic initiation factor (eIF)4E and a rapid phosphorylation of eIF2alpha via the kinases PKR and PKR-like endoplasmic reticulum kinase. The inhibition of PKR by PRI led first to a significant but not complete dephosphorylation of eIF2alpha that probably contributed to maintain the inhibition of the protein synthesis and second to surprising phosphorylations of extracellular signal-regulated protein kinase, p70S6K and eIF4E, suggesting a possible cross-link between the two pathways. Conversely, cell death was weak at pH 5.5. Protein synthesis was decreased to a lesser extent, the phosphorylation of eIF2alpha was limited, extracellular signal-regulated protein kinase 1/2 was activated and its downstream targets, p70S6K and eIF4E, were phosphorylated. However, the strong phosphorylation of eIF4E was not associated with an activation of the eIF4F complex. This last result may explain why protein synthesis was not stimulated at pH 5.5. However, when astrocytes were exposed at pH 6.2, corresponding to the lower pH observed in hyperglycemic ischemia, no modification in protein synthesis was observed. Consequently, lactic acidosis cannot, by itself, provide an explanation for the decrease in protein synthesis previously reported in vivo in ischemia.

Functional Interaction between Responses to Lactic Acidosis and Hypoxia Regulates Genomic Transcriptional Outputs

“…This is consistent with induced HIF-1α protein accumulation under hypoxia. Extreme acidity (pH=5.5) can lead to eIF2α phosphorylation and translation inhibition in astrocytes (37). eIF2α phosphorylation has also been shown to regulate the protein levels of HIF-1α (38).…”

Lactic Acid Induces Aberrant Amyloid Precursor Protein Processing by Promoting Its Interaction with Endoplasmic Reticulum Chaperone Proteins

“…Vantelon et al reported that exposure of astrocytes to 16 mM lactate did not alter protein synthesis and at pH values below 6, protein synthesis was decreased [20]. In addition, in the presence of lactic acid a strong and sustained phosphorylation of the eukaryotic initiation factor 2α (eIF2α), the central regulator of the ER stress response, was reported [20].…”

The Impact of Extracellular Low pH on the Anti-Tumor Efficacy Against Mesothelioma

“…2 may suggest that the activity of PKR is less important in the proliferation of mesothelioma under acidic condition. Acidic conditions, in fact, enhanced the phosphorylation of eIF2, but this was confirmed at pH lower than 5.5 and not over 6.2 in a partially PKR-independent manner (Vantelon et al, 2007). So the phosphorylation of eIF2 without PKR at pH 6.7 might not cause this PKR independency at pH 6.7.…”