The nerve growth factor which induces phenotypic changes in PC12 pheochromocytoma cells also induces the expression of the proinflammatory cytokine interleukin 1 alpha in these cells. We have studied the signal transduction and transcriptional mechanisms involved in this induction of interleukin 1 alpha by nerve growth factor. The nerve growth factor induction of interleukin 1 alpha transcription in PC12 cells is exerted via the TrkA receptor, as demonstrated by inhibition of the nerve growth factor stimulated increases in the interleukin 1 alpha mRNA levels by the TrkA specific alkaloid K-252a. The promoter region(s) involved in induction of interleukin 1 alpha 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 1 alpha gene (bases -163 to +64). This promoter region was inserted into the promoterless pBLCAT3 plasmid, using the interleukin 1 alpha 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 1 alpha gene, were constructed: three deleted stretches correspond to regions with high sequence similarity to regions 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 1 alpha 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 1 alpha expression is at this AP-1 site.