Expression of Claudin7 Is Tightly Associated with Epithelial Structures in Synovial Sarcomas and Regulated by an Ets Family Transcription Factor, ELF3

Yoshiki Kohno,Junya Toguchida,Yasuko Shima,Nobuhito Araki,Kohichi Nishijo,Seiji Otsuka,Kotaro R Shibata,Daisuke Uejima,Takashi Nakamura,Norifumi Naka,Takeshi Okamoto,Tatsuya Ishibe,Kenichi Fukiage,Satoshi Nagayama,Tomitaka Nakayama,Tomoki Aoyama,Yasuaki Nakashima

doi:10.1074/jbc.m608389200

Abstract

Synovial sarcoma, a soft tissue sarcoma that develops in adults, is pathologically subclassified into monophasic spindle synovial sarcoma and biphasic synovial sarcoma with epithelial components. The molecular mechanism building the epithelial components in biphasic synovial sarcoma is totally unknown. Here we investigated claudins, critical molecules in the tight junction, in biphasic synovial sarcoma. Expression profiles of 21 claudins in 17 synovial sarcoma tumor samples, including 9 biphasic tumors, identified claudin4, claudin7, and claudin10 as biphasic tumor-related claudins, and immunohistochemical analyses demonstrated the localization of these claudins in the epithelial component in biphasic tumors, with claudin7 the most closely associated with the epithelial component. The mRNA expression and protein localization of claudin7 coincided with those of the ELF3, an epithelia-specific member of the Ets family of transcription factors. Luciferase reporter assays demonstrated that the presence of the Ets-binding site at -150 in the promoter region of the claudin7 gene was critical for the transcriptional activity, and gel shift and chromatin immunoprecipitation assays confirmed the binding of ELF3 to the Ets site at -150. Inhibition of ELF3 expression by small interfering RNA simultaneously down-regulated the mRNA expression of the claudin7 gene, and the introduction of ELF3 expression in claudin7-negative cell lines induced mRNA expression of the claudin7 gene. Therefore, the induction of claudin7 expression by ELF3 appears critical to the formation of the epithelial structures in biphasic synovial sarcoma.

Highlights

All nine biphasic tumors were positive, but only a faint signal was detected in one of eight monophasic tumors. These results indicated the strong association of CLDN7 with the epithelial structures in synovial sarcoma (SS)
We have identified CLDN4, -7, and -10 as major constituents of the epithelial structures in biphasic SS
CLDN4 was initially cloned as a receptor for Clostridium perfringens enterotoxin (CPETR1) [33] and later identified as a member of the CLDN family by a data base search using homology with the CLDN1 and -2 genes [34]

Summary

Introduction

Association of CLND7 with ELF3—ELF3 (E74-like factor 3) is a member of the Ets family of transcription factors, whose expression is restricted to epithelial cells, and known to be involved in the regulation of epithelium-specific gene products such as keratins [30, 31]. The mRNA expression of the ELF3 gene along with other members of the ELF family (ELF1, -2, -4, and -5 genes) in SS tumor tissues and cell lines was investigated (Fig. 3).

Results

Conclusion