Abstract

The causative gene of Fukuyama congenital muscular dystrophy (fukutin) is involved in formation of the basement membrane through glycosylation of alpha-dystroglycan. However, there are other proposed functions that have not been fully understood. Using cultured astrocytes (1321N1), we found nuclear localization of fukutin and a positive relationship between fukutin expression and cell proliferation. Among potential proteins regulating cell proliferation, we focused on cyclin D1, by reverse-transcription polymerase chain reaction, Western blotting, immunocytochemistry, enzyme-linked immunosorbent assay (ELISA), and sandwich ELISA. Expression of cyclin D1 was significantly downregulated by fukutin knockdown and significantly upregulated by fukutin overexpression. Moreover, fukutin was proven to bind to the activator protein-1 (AP-1) binding site of cyclin D1 promoter, as well as the AP-1 component c-Jun. The c-Jun phosphorylation status was not significantly influenced by knockdown or overexpression of fukutin. The present results provide in vitro evidence for a novel function of fukutin, which participates in cell proliferation by enhancing cyclin D1 expression through forming a complex with AP-1. It is likely that fukutin is a potential cofactor of AP-1.

Highlights

  • Fukuyama-type congenital muscular dystrophy (FCMD) is an inherited disease that is characterized by congenital anomalies of the central nervous system (CNS) and eye, as well as myopathy [1,2]

  • We investigated the molecular biological mechanisms via which fukutin exerts cell proliferation ability using molecular biological approaches, including reverse-transcription polymerase chain reaction (RT-PCR) analysis and enzyme-linked immunosorbent assay (ELISA), focusing on astrocytes, the most common cell type of the CNS

  • Earlier studies documented that fukutin protein is localized in the Golgi apparatus

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Summary

Introduction

Fukuyama-type congenital muscular dystrophy (FCMD) is an inherited disease that is characterized by congenital anomalies of the central nervous system (CNS) and eye, as well as myopathy [1,2]. Initial studies focused on implications for fukutin protein in the glycosylation of alpha-dystroglycan (α-DG), which bears close relevance to formation of the basement membrane [4,5]. Fukutin functions except for α-DG glycosylation have not been fully characterized by molecular biological approaches. In the CNS of patients with FCMD, hypoglycosylation of α-DG due to downregulation of fukutin is responsible for impaired basement membrane formation of the glial limitans, leading to congenital malformations, including polymicrogyria [6]. Since the glia limitans originates from foot processes of astrocytes, it is evident that altered astrocytes give rise to the formation of CNS lesions in FCMD [7,8]

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