An AP-1 site is involved in the NGF induction of IL-1α in PC12 cells

Abstract

The nerve growth factor which induces phenotypic changes in PC12 pheochromocytoma cells also induces the expression of the proinflammatory cytokine interleukin 1α in these cells. We have studied the signal transduction and transcriptional mechanisms involved in this induction of interleukin 1α by nerve growth factor. The nerve growth factor induction of interleukin 1α transcription PC12 cells is exerted via the TrkA receptor, as demonstrated by inhibition of the nerve growth factor stimulated increases in the interleukin 1α mRNA levels by the TrkA specific alkaloid K-252a. The promoter region(s) involved in induction of interleukin 1α expression by nerve growth factor in PC12 pheochromocytoma cells were studied by deletion mutagenesis in a part of the 5′ regulatory region of the human interleukin 1α gene (bases −163 to +64). This promoter region was inserted into the promoterless pBLCAT3 plasmid, using the interleukin 1α 5′ fragment as the promoter to drive nerve growth factor inducible expression of the CAT (chloramphenicol acetyl transferase) reporter gene. Four mutants, with deletions of 9–15 bases in the 5′ regulatory region of the human interleukin 1α gene, were constructed: three deleted stretches correspond to regions with high sequence similarity to region in other genes, coding for nerve growth factor-induced proteins, e.g. NGFI-A, NGFI-B, NGFI-C, ERK2 and VGF gene. These deletions of which some reduced the basal, non-nerve growth factor stimulated expression of the CAT reporter protein, do not prevent the two- to threefold induction by nerve growth factor. The deletion which eliminated a putative AP-1 binding site, immediately upstream of the transcription start site in the interleukin 1α promoter, almost completely prevented the nerve growth factor mediated induction of CAT reporter gene expression, suggesting that in PC12 cells the major site of nerve growth factor regulation of interleukin 1α expression is at this AP-1 site.