Ethanol-induced transcriptional activation of programmed cell death 4 (Pdcd4) is mediated by GSK-3β signaling in rat cortical neuroblasts.

Mary Latha Rathinam,Dhanashree Vedpathak,George I. Henderson,Amanjot Kaur Riar,Srinivas Mummidi,Wenzhe Ho,Lenin Mahimainathan,Madhusudhanan Narasimhan

doi:10.1371/journal.pone.0098080

Abstract

Ingestion of ethanol (ETOH) during pregnancy induces grave abnormalities in developing fetal brain. We have previously reported that ETOH induces programmed cell death 4 (PDCD4), a critical regulator of cell growth, in cultured fetal cerebral cortical neurons (PCNs) and in the cerebral cortex in vivo and affect protein synthesis as observed in Fetal Alcohol Spectrum Disorder (FASD). However, the mechanism which activates PDCD4 in neuronal systems is unclear and understanding this regulation may provide a counteractive strategy to correct the protein synthesis associated developmental changes seen in FASD. The present study investigates the molecular mechanism by which ethanol regulates PDCD4 in cortical neuroblasts, the immediate precursor of neurons. ETOH treatment significantly increased PDCD4 protein and transcript expression in spontaneously immortalized rat brain neuroblasts. Since PDCD4 is regulated at both the post-translational and post-transcriptional level, we assessed ETOH’s effect on PDCD4 protein and mRNA stability. Chase experiments demonstrated that ETOH does not significantly impact either PDCD4 protein or mRNA stabilization. PDCD4 promoter-reporter assays confirmed that PDCD4 is transcriptionally regulated by ETOH in neuroblasts. Given a critical role of glycogen synthase kinase 3β (GSK-3β) signaling in regulating protein synthesis and neurotoxic mechanisms, we investigated the involvement of GSK-3β and showed that multifunctional GSK-3β was significantly activated in response to ETOH in neuroblasts. In addition, we found that ETOH-induced activation of PDCD4 was inhibited by pharmacologic blockade of GSK-3β using inhibitors, lithium chloride (LiCl) and SB-216763 or siRNA mediated silencing of GSK-3β. These results suggest that ethanol transcriptionally upregulates PDCD4 by enhancing GSK-3β signaling in cortical neuroblasts. Further, we demonstrate that canonical Wnt-3a/GSK-3β signaling is involved in regulating PDCD4 protein expression. Altogether, we provide evidence that GSK-3β/PDCD4 network may represent a critical modulatory point to manage the protein synthetic anomalies and growth aberrations of neural cells seen in FASD.

Highlights

Fetal alcohol spectrum disorder (FASD) is a global health problem
Since neuron development is progeny dependent, in the current study we investigated whether ethanol-induced programmed cell death 4 (PDCD4) changes are conserved in mitotic neuroblasts, the immediate precursor of neurons
These results indicates that ETOH time and dose-dependently upregulates PDCD4 protein in proliferating neuroblasts, similar to our prior findings in postmitotic neurons

Summary

Introduction

Fetal alcohol spectrum disorder (FASD) is a global health problem. FASD encompasses a gamut of permanent birth defects caused by maternal alcohol consumption during pregnancy affecting 1 in every 100 live births in United States and Europe [1,2]. Several mechanisms apparently contribute to the alcohol-induced disruption of fetal brain development. Among these mechanisms are suppression of protein and DNA synthesis [11,12], inhibition of cell adhesion molecules [13] interference with cell cycle progression [14], alteration in receptor function [15,16,17], increased oxidative stress [18,19,20] altered glucose metabolism [21,22] disruption of endoplasmic reticulum [23], altered activity of growth factors [24] or other cell-signaling pathways [25] and abberant developmental regulation of gene expression [26]

Methods

Results

Conclusion