%0 Journal Article
%T Functional promoter upstream p53 regulatory sequence of IGFBP3 that is silenced by tumor specific methylation
%A Tadashi Hanafusa
%A Toshiyuki Shinji
%A Hidenori Shiraha
%A Kazuhiro Nouso
%A Yoshiaki Iwasaki
%A Eichiro Yumoto
%A Toshiro Ono
%A Norio Koide
%J BMC Cancer
%D 2005
%I BioMed Central
%R 10.1186/1471-2407-5-9
%X In this study, we examined the p53 consensus sequences upstream of the IGFBP-3 promoter for the p53 induced expression of IGFBP-3. Deletion, mutagenesis, and methylation constructs of IGFBP-3 promoter were assessed in the human hepatoblastoma cell line HepG2 for promoter activity.Deletions and mutations of these sequences completely abolished the expression of IGFBP-3 in the presence of p53 overexpression. In vitro methylation of these p53 consensus sequences also suppressed IGFBP-3 expression. In contrast, the expression of IGFBP-3 was not affected in the absence of p53 overexpression. Further, we observed by electrophoresis mobility shift assay that p53 binding to the promoter region was diminished when methylated.From these observations, we conclude that four out of eleven p53 consensus sequences upstream of the IGFBP-3 promoter are essential for the p53 induced expression of IGFBP-3, and hypermethylation of these sequences selectively suppresses p53 induced IGFBP-3 expression in HepG2 cells.Insulin-like growth factor binding protein (IGFBP)-3 is a multifunctional protein ferrying insulin-like growth factors (IGFs) in circulation and mediating growth suppression signals in cells. Serum IGFBP-3 protein (< 5000 ng/ml) complexes with IGFs and an acid labile subunit (ALS), to extend the half lives and modulate the bio-availability of IGFs [1]. While a precise mechanism of action is not clear, the growth suppressive activity of IGFBP-3 depends on its nuclear translocation [2]. Other growth suppressors such as p53, retinoic acids, transforming growth factor (TGF)-¦Â, and tumor necrosis factor (TNF)-¦Á induce IGFBP-3 as a mediator of growth suppression [3-6]. The growth suppression by IGFBP-3 is independent from the modulation of IGFs action [7-9]. The functional importance of the IGFBP-3 in the growth suppression is noteworthy.IGFBP-3 is produced in most tissues, but the main site of production is liver. It is produced by non-parenchymal cells (endothelial and Kupffer ce
%U http://www.biomedcentral.com/1471-2407/5/9