Mouse NGF promoter upstream sequences do not affect gene expression in mouse fibroblasts

The expression of nerve growth factor (NGF) is tightly controlled in a tissue-specific manner during development and in response to injury. In fibroblasts and in other cell types, expression of NGF is regulated at the transcriptional level. In order to elucidate the mechanism of this regulation, we have undertaken the analysis of the mouse NGF promoter in a mouse fibroblast cell line (LTA), using transient transfection of NGF promoter-human growth hormone (hGH) reporter gene plasmids. We find that sequences between +8bp and +120bp, containing an AP-1 site, confer increased levels of expression from the full length and truncated NGF promoters. When this region is deleted, a significant decrease in expression is observed from both the full length promoter and truncated versions thereof. A gradual increase in expression is observed with successive 5' deletions of both the AP-1 containing and AP-1 deleted promoters; this effect results from the juxtapositioning of adjacent plasmid sequences closer to the transcription initiation site and not from deletion of promoter sequences as was previously reported. When the NGF promoter is analyzed using a luciferase reporter plasmid, these 5' promoter deletions have no significant effect on reporter gene expression in fibroblasts. Thus, sequences downstream of the transcription start site influence NGF promoter activity in fibroblasts, but sequences upstream of the TATA box fail to affect promoter activity in these cells.