Remote control of activity-dependent BDNF gene promoter-I transcription mediated by REST/NRSF

Abstract

To know the role of repressor element-1 (RE-1)-silencing transcription factor (REST) in activity-dependent gene transcription in neurons, we investigated whether the Ca²⁺ signal-induced transcription of brain-derived neurotrophic factor promoter-I (BDNF-PI) is repressed by RE-1 located in exon II from far downstream of BDNF promoter-II (BDNF-PII). By constructing plasmids in which the location between BDNF-PI, -PII, and -RE-1 is maintained, we found, by conducting promoter assays with cortical neurons, that the promoter activity was constitutively repressed through the actions of BDNF-RE-1 but activated by Ca²⁺ signals evoked via membrane depolarization, which was due to BDNF-PI but not to BDNF-PII. The over-expression of REST reduced the level of transcriptional activation through the N- and C-terminals, suggesting the recruitment of a histone deacetylase. On over-expression of REST, an increased depolarization did not allow the activation. Thus, REST remotely represses activity-dependent gene transcription, the level of which controls the magnitude of the repression.

Introduction

Repressor element-1 (RE-1, also called neuron-restrictive silencer element; NRSE) is a conserved 21–23 bp motif that binds RE-1-silencing transcription factor (REST, also called neuron-restrictive silencing factor; NRSF) [1], [2] and is found in a large number of neuronal genes [3], the expression of which is silenced in non-neuronal cells through the actions of histone deacetylase (HDAC) recruited by both the N- and C-terminal repression domains of full-length (FL)-REST [4], [5], [6], [7]. The gene for brain-derived neurotrophic factor (BDNF), a member of the neurotrophin family, is a REST-target gene. The rat BDNF gene consists of eight untranslated 5′-exons (exons I–VIII) and a common translated 3′-exon (IX) encoding a prepro-BDNF protein [8]. There are multiple promoters located upstream of the respective 5′-exons and the molecular mechanisms for the activation of BDNF gene promoter-I and -IV have been well elucidated in terms of calcium (Ca²⁺) signals evoked via membrane depolarization and transcriptional regulation mediated by cAMP-response element-binding protein (CREB) [9], [10].

Recently, evidence has accumulated that a decrease in the expression of FL-REST is required for the differentiation of pluripotent cells into lineage-restricted neuronal progenitors during neurogenesis in the dentate gyrus of the hippocampus [11], [12], [13], accompanying the expression of neuron-specific genes that are targeted by REST [11]. On the other hand, neuronal activity is required for the differentiation of newly generated neurons and their integration into neuronal networks during neurogenesis [14], [15], [16], [17]. Thus, it is important to know how REST expression and the activity-dependent gene transcription are related to the control of neuronal differentiation.

So far, it has been accepted that the BDNF-RE-1 is located around 100 bp upstream of BDNF exon II [18]. Based on the new nomenclature of the rat BDNF gene [8] and the EMBL data bank, however, we found that BDNF-RE-1 is located within exon II of the rat BDNF gene. Therefore, it is important to know whether BDNF-RE-1 remotely controls activity-dependent BDNF-PI activation though BDNF-PII is located between BDNF-PI and BDNF-RE-1. For this purpose, we constructed reporter plasmids containing BDNF-PI, -PII, and -RE-1, the locations of which are maintained as they are in genomic DNA, and investigated the effect of BDNF-RE-1 on the activity-dependent gene transcription of BDNF-PI.