The E-selectin cell adhesion protein plays a critical role in mediating adherence of leukocytes to endothelium at sites of inflammation. Cytokine-induced E-selectin expression on the surface of endothelial cells is transient; mRNA expression peaks at 3-4 h after induction and returns to basal levels within 24 h. The mechanism for this transcriptional down-modulation is not known. Promoter binding factors responsible for induced gene expression include NF-kappaB, which binds at three sites within the E-selectin promoter, and HMG-I(Y), which binds to the A/T-rich core found at the centre of these binding sites. Distamycin is an antibiotic that also binds A/T-rich DNA and inhibits HMG-I(Y) DNA binding. To study the role of HMG-I(Y) in E-selectin expression, we have examined the effect of distamycin on the cytokine-induced E-selectin expression cycle. We found that distamycin prolonged E-selectin expression, both by sustaining mRNA transcription and by extending the transcript's half-life. The distamycin effect on transcription was mediated through one of the three NF-kappaB-HMG-I(Y) binding sites (NF-kappaBII) within the promoter. This suggests that the NF-kappaB-HMG-I(Y) complex interacting at the NF-kappaBII site plays a role not only in cytokine induction of E-selectin expression, but also in its down-modulation.