Identification of Repressor Element 1 in Secretin/PACAP/VIP Genes

Positive allosteric regulation of PAC1-R up-regulates PAC1-R and its specific ligand PACAP

PAC1-R is a recognized preferential receptor for the neuropeptide of pituitary adenylate cyclase-activating polypeptide (PACAP), which mediates neuroprotective and nerve regenerative activities of PACAP. In this study, we found that in both PAC1R-CHO cells with high expression of PAC1R-eGFP and retinal ganglion cells (RGC-5) with the natural expression of PAC1-R, oligo-peptide PACAP(28-38) and the positively charged arginine-rich penetrating peptide TAT, as positive allosteric modulators of PAC1-R, significantly trigger the nuclear translocation of PAC1-R. The chromatin immunoprecipitation (ChIP)-PCR results show that the nuclear translocated PAC1-R binds with the promoter regions of PAC1-R and its specific ligand PACAP. The up-regulated promoter activities of PAC1-R and PACAP induced by PACAP(28-38) or TAT are positively correlative with the increase of the expression levels of PAC1-R and PACAP. Moreover, the nuclear translocation of PAC1-R induced by PACAP(28-38) or TAT is significantly inhibited by the mutation of PAC1-R on Cys25 and the palmitoylation inhibitor 2-bromopalmitate. Meanwhile, the increase in both PAC1-R and PACAP levels and the neuroprotective activities of PACAP(28-38) and TAT in MPP-induced cell model of Parkinson ' s disease are synchronously inhibited by 2-bromopalmitate, which are positively correlated with the nuclear translocation of PAC1-R induced by PACAP(28-38) or TAT. Bioinformatics analysis and motif enrichment analysis following ChIP-sequencing show that the transcription factors including SP1, Zic2, GATA1, REST and YY1 may be recruited by nuclear PAC1-R and involved in regulating the promoter activities of PAC1-R and PACAP. ChIP-sequencing and related bioinformatics analysis show that the downstream target genes regulated by the nuclear PAC1-R are mostly involved in the process of cellular stress and related to neuroprotection, neuronal genesis and development.

Pituitary adenylate cyclase-activating polypeptide is regulated by alternative splicing of transcriptional repressor REST/NRSF in nerve injury

AIMS

The pathophysiological mechanism for neuropathic pain (NP), one of the most common types of intractable pain, remains largely unknown. We previously reported that pituitary adenylate-cyclase activating polypeptide (PACAP) is required for the development of spinal sensitization and induction of NP. Previous in vitro studies suggest that PACAP transcription unit has two RE1-like elements and that the transcriptional repressor REST controls expression of PACAP gene. However the regulation of PACAP gene through its RE1 sites in vivo has not been studied. We have analyzed the functional role of PACAP gene RE1 element following nerve injury.

MAIN METHODS

An L5-spinal nerve transection (L5-SNT) in mice was used as a model of spinal injury. DRGs after the L5-SNT were studied.

KEY FINDINGS

PACAP mRNA increased in the DRG following spinal nerve injury. REST4, an alternatively spliced isoform of REST was shown to be regulated by the splicing activator (nSR100) and nSR100 itself also increased. Overexpression of either REST4 or nSR100 in vitro increased PACAP expression, while overexpression of REST repressed PACAP mRNA production. Reporter gene analysis showed that a novel RE1 previously predicted by in silico analysis was indeed functional. ChIP analysis showed that REST bound significantly to this RE1 in the DRG of naïve mice, while REST binding to this RE1 was decreased following spinal nerve injury. The expression of REST was decreased by nSR100-dependent alternative splicing of the REST gene, leading to derepression of PACAP.

SIGNIFICANCE

PACAP expression in the DRG following spinal nerve injury is controlled through a novel RE1 by REST.

Neuron-restrictive silencer factor functions to suppress Sp1-mediated transactivation of human secretin receptor gene

In the present study, a functional neuron restrictive silencer element (NRSE) was initially identified in the 5' flanking region (-83 to -67, relative to ATG) of human secretin receptor (hSCTR) gene by promoter assays coupled with scanning mutation analyses. The interaction of neuron restrictive silencer factor (NRSF) with this motif was later indicated via gel mobility shift and ChIP assays. The silencing activity of NRSF was confirmed by over-expression and also by shRNA knock-down of endogenous NRSF. These studies showed an inverse relationship between the expression levels of NRSF and hSCTR in the cells. As hSCTR gene was previously shown to be controlled by two GC-boxes which are regulated by the ratio of Sp1 to Sp3, in the present study, the functional interactions of NRSF and Sp proteins to regulate hSCTR gene was investigated. By co-immunoprecipitation assays, we found that NRSF could be co-precipitated with Sp1 as well as Sp3 in PANC-1 cells. Interestingly, co-expressions of these factors showed that NRSF could suppress Sp1-mediated, but not Sp3-mediated, transactivation of hSCTR. Taken together, we propose here that the down-regulatory effects of NRSF on hSCTR gene expression are mediated via its suppression on Sp1-mediated transactivation.