Human peripheral blood monocytes responded to stimulation of platelet-activating factor (PAF) with upregulation of the transcript for heparin-binding epidermal growth factor-like growth factor (HB-EGF), a potent mitogen for vascular smooth muscle cells. This function of PAF was observed at nanomolar concentrations of the ligand, starting at 30 min after stimulation. The PAF-induced up-regulation of HB-EGF mRNA was accompanied by an increase in κB binding activity. These functions of PAF appeared to be mediated through the cell surface PAF receptors, as two PAF receptor antagonists, WEB 2086 and L-659,989, blocked both the up-regulation of HB-EGF mRNA and κB binding activity induced by PAF. The antagonists, however, had no effect on phorbol ester-induced up-regulation of HB-EGF mRNA and κB binding activity. Pretreatment of monocytes with pertussis toxin inhibited these functions of PAF, whereas cholera toxin had no inhibitory effect. Pyrrolidine dithiocarbamate, an inhibitor for NF-κB activation, markedly reduced PAF-stimulated κB binding activity as well as up-regulation of HB-EGF mRNA. These results suggest a potential role of PAF in HB-EGF expression and provide evidence that this stimulation may occur through increased κB binding activity.