Regulator of Calcineurin 1 (RCAN1) Facilitates Neuronal Apoptosis through Caspase-3 Activation

Xiulian Sun,秀莲 孙,Yili Wu,伊丽 吴,Bin Chen,Zhuohua Zhang,Weihui Zhou,Yigang Tong,贻刚 童,Junying Yuan,Kun Xia,Hinrich Gronemeyer,Richard A Flavell,Weihong Song,伟宏 宋

doi:10.1074/jbc.m110.177519

Abstract

Individuals with Down syndrome (DS) will inevitably develop Alzheimer disease (AD) neuropathology sometime after middle age, which may be attributable to genes triplicated in individuals with DS. The characteristics of AD neuropathology include neuritic plaques, neurofibrillary tangles, and neuronal loss in various brain regions. The mechanism underlying neurodegeneration in AD and DS remains elusive. Regulator of calcineurin 1 (RCAN1) has been implicated in the pathogenesis of DS. Our data show that RCAN1 expression is elevated in the cortex of DS and AD patients. RCAN1 expression can be activated by the stress hormone dexamethasone. A functional glucocorticoid response element was identified in the RCAN1 isoform 1 (RCAN1-1) promoter region, which is able to mediate the up-regulation of RCAN1 expression. Here we show that overexpression of RCAN1-1 in primary neurons activates caspase-9 and caspase-3 and subsequently induces neuronal apoptosis. Furthermore, we found that the neurotoxicity of RCAN1-1 is inhibited by knock-out of caspase-3 in caspase-3(-/-) neurons. Our study provides a novel mechanism by which RCAN1 functions as a mediator of stress- and Aβ-induced neuronal death, and overexpression of RCAN1 due to an extra copy of the RCAN1 gene on chromosome 21 contributes to AD pathogenesis in DS.

Highlights

From the ‡Townsend Family Laboratories, Department of Psychiatry, Brain Research Center, Graduate Program in Neuroscience, University of British Columbia, Vancouver, British Columbia V6T 1Z3, Canada, the §Qilu Hospital of Shandong University, Jinan, Shandong 250012, China, the ¶Center for Neuroscience and Aging, The Burnham Institute, La Jolla, California 92037, the ʈDepartment of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, the **National Laboratory of Medical Genetics of China, Central South University, Changsha, Hunan 410078, China, the ‡‡Department of Cell Biology and Signal Transduction, Institut de Genetique et de Biologie Moleculaire et Cellulaire/CNRS/INSERM/ULP, 67404 Illkirch Cedex, C U de Strasbourg, France, and the §§Section of Immunobiology, Yale University School of Medicine, New Haven, Connecticut 06520
Our study provides a novel mechanism by which Regulator of calcineurin 1 (RCAN1) functions as a mediator of stress- and A␤-induced neuronal death, and overexpression of RCAN1 due to an extra copy of the RCAN1 gene on chromosome 21 contributes to Alzheimer disease (AD) pathogenesis in Down syndrome (DS)
RCAN1 Expression Is Elevated in the Brains of DS Fetus and AD Patients—Previous studies have shown that RCAN1 mRNA is elevated in the brains of DS and AD patients [17, 38], indicating that RCAN1 gene expression is up-regulated at the transcriptional level

Summary

Introduction

To analyze the transcriptional activity of the RCAN1 promoter, a series of luciferase reporter gene plasmids containing different upstream deletions of the RCAN1 promoter were constructed and transfected into HEK293 and SH-SY5Y cells. To examine whether the effect of glucocorticoids is specific for the RCAN1 exon 1 promoter, a 1200-bp DNA fragment upstream of RCAN1 exon 4 was cloned into promoterless luciferase reporter plasmid pGL3-Basic to generate pDE4Luc. Dexamethasone markedly increased isoform 1 promoter activity (from 175.33 Ϯ 3.74 to 268.86 Ϯ 14.2 RLU, p Ͻ 0.001), whereas it had no effect on isoform 4 promoter activity (from 117.47 Ϯ 2.51 to 112.17 Ϯ 2.39 RLU, p Ͼ 0.05) (Fig. 4H).

Results

Conclusion