In vivo footprinting and functional analysis of the human c-sis/PDGF B gene promoter provides evidence for two binding sites for transcriptional activators.

摘要

By in vivo DMS footprint and reporter gene analyses we identified two transcription factor binding sites in the human c-sis/PDGF B gene promoter. The low basal activity of the PDGF B promoter in HeLa and undifferentiated K562 cells, which express low PDGF B mRNA levels, and in PC3 cells, which express a high PDGF B mRNA level, results from binding of a weak transcriptional activator between positions -64 and -61 relative to the transcription start site. Cytotrophoblast-like JEG-3 cells, which do not express the 3.5 kb PDGF B mRNA, contain a transcriptional activator directed at the -64/-61 sequence, but DNA methylation may render the endogenous promoter inaccessible to this activator. A CCACCCAC element at position -61/-54 was identified as the in vivo binding site for a strong transcriptional activator in phorbol ester-treated megakaryocytic K562 cells, which express a high PDGF B mRNA level. Primary human fibroblasts, which do not transcribe the PDGF B gene, contain a transcriptional activator that recognizes an element between positions -60 and -45 but does not bind to the endogenous unmethylated promoter. Our results show that the complex expression pattern of the human PDGF B gene involves the cell type-specific expression of weak and strong transcriptional activators and regulation of promoter accessibility to these factors.