title: Molecular basis for the induction of an angiogenesis inhibitor, thrombospondin-1, by 5-fluorouracil.
abstract: 5-Fluorouracil (5-FU) is one of the most commonly used anticancer drugs in chemotherapy against various solid tumors. 5-FU dose-dependently increased the expression levels of intrinsic antiangiogenic factor thrombospondin-1 (TSP-1) in human colon carcinoma KM12C cells and human breast cancer MCF7 cells. We investigated the molecular basis for the induction of TSP-1 by 5-FU in KM12C cells. Promoter assays showed that the region with the Egr-1 binding site is critical for the induction of TSP-1 promoter activity by 5-FU. The binding of Egr-1 to the TSP-1 promoter was increased in KM12C cells treated with 5-FU. Immunofluorescence staining revealed that 5-FU significantly increased the level of Egr-1 in the nuclei of KM12C cells. The suppression of Egr-1 expression by small interfering RNA decreased the expression level of TSP-1. Furthermore, 5-FU induced the phosphorylation of p38 mitogen-activated protein kinase (MAPK) and heat shock protein 27 (HSP27). Blockade of the p38 MAPK pathway by SB203580 remarkably inhibited the phosphorylation of HSP27 induced by 5-FU and decreased the induction of Egr-1 and TSP-1 by 5-FU in KM12C cells. These findings suggest that the p38 MAPK pathway plays a crucial role in the induction of Egr-1 by 5-FU and that induced Egr-1 augments TSP-1 promoter activity, with the subsequent production of TSP-1 mRNA and protein.
authors.affiliation: Department of Molecular Oncology, Graduate School of Medical and Dental Sciences, Kagoshima University, Sakuragaoka, Kagoshima, Japan.
authors.forename: Hong-Ye
authors.initials: HY
authors.lastname: Zhao
authors.forename: Akio
authors.initials: A
authors.lastname: Ooyama
authors.forename: Masatatsu
authors.initials: M
authors.lastname: Yamamoto
authors.forename: Ryuji
authors.initials: R
authors.lastname: Ikeda
authors.forename: Misako
authors.initials: M
authors.lastname: Haraguchi
authors.forename: Sho
authors.initials: S
authors.lastname: Tabata
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Furukawa
authors.forename: Xiao-Fang
authors.initials: XF
authors.lastname: Che
authors.forename: Shaoxuan
authors.initials: S
authors.lastname: Zhang
authors.forename: Toshinori
authors.initials: T
authors.lastname: Oka
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukushima
authors.forename: Masayuki
authors.initials: M
authors.lastname: Nakagawa
authors.forename: Mayumi
authors.initials: M
authors.lastname: Ono
authors.forename: Michihiko
authors.initials: M
authors.lastname: Kuwano
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Akiyama