Control of the Calcitonin Gene-related Peptide Enhancer by Upstream Stimulatory Factor in Trigeminal Ganglion Neurons

Ki-Youb Park,Andrew F Russo

doi:10.1074/jbc.m708662200

Abstract

The neuropeptide calcitonin gene-related peptide (CGRP) is a key player in migraine. However, the transcription factors controlling CGRP expression in the migraine-relevant trigeminal ganglion neurons are unknown. Previous in vitro studies demonstrated that upstream stimulatory factor (USF) 1 and USF2 bind to the CGRP neuroendocrine-specific 18-bp enhancer, yet discrepant overexpression results in cell lines, and the ubiquitous nature of the USF cast doubts about its role. To test the functional role of USF, we first demonstrated that small interfering RNAs directed against USF1 and USF2 reduced endogenous CGRP RNA and preferentially targeted the USF binding site at the 18-bp enhancer in the neuronal-like CA77 cell line. In cultured rat trigeminal ganglion neurons, knockdown of either USF1 or USF2 reduced CGRP promoter activity. Conversely, overexpression of USF1 or USF2 increased promoter activity. The activation was even greater upon cotransfection with an upstream activator of mitogen-activated protein kinases and was synergistic in a heterologous cell line. To begin to address the paradox of how ubiquitous USF proteins might direct neuronal-specific activity, we examined USF expression and used a series of adenoviral reporters in the cultured ganglia. Unexpectedly, there was more intense USF immunostaining in neurons than nonneuronal cells. Importantly, the 18-bp USF enhancer driving a minimal promoter was sufficient for neuronal specificity, although it was not the only site that directed neuronal expression. These results demonstrate that USF1 and USF2 are important contributors to neuronal-specific and mitogen-activated protein kinase regulation of the CGRP gene in trigeminal ganglion neurons.

Highlights

We have previously reported that a heterodimer of the transcription factor USF1 and USF2 binds to the 18-bp enhancer of the calcitonin gene-related peptide (CGRP) gene in vitro [11]
In this report we demonstrate that upstream stimulatory factor (USF) proteins are activators of the CGRP promoter in cultured neurons derived from rat trigeminal ganglia
The use of the CA77 cells was necessary because initial attempts to reduce endogenous CGRP RNA by USF1 and USF2 siRNAs in trigeminal ganglia cultures were not successful

Summary

Introduction

We have previously reported that a heterodimer of the transcription factor USF1 and USF2 binds to the 18-bp enhancer of the CGRP gene in vitro [11]. The activation by USF was only observed in this non-neuronal cell line that does not express the endogenous CGRP gene. In this report we demonstrate that USF proteins are activators of the CGRP promoter in cultured neurons derived from rat trigeminal ganglia.

Results

Conclusion