Background & Aims: Intercellular adhesion molecule 1 (ICAM-1) receptors are expressed at low levels on human colonic circular smooth muscle cells (HCCSMCs) and their expression is increased in patients with Crohn's disease. We investigated the roles of transcription factors Sp1 and nuclear factor κ B (NF-κB) in the regulation of ICAM-1 expression on HCCSMCs and examined whether ICAM-1 expression mediates the suppression of contractility in response to TNFα. Methods: Experiments were performed on primary cultures of HCCSMCs and fresh human colonic circular muscle strips. Results: TNFα treatment of HCCSMCs induced rapid and prolonged accumulation of ICAM-1 messenger RNA (mRNA) and protein. NF-κB inhibition before, but not after, 1 hour of TNFα-stimulation blocked the expression of ICAM-1. TNFα significantly enhanced Sp1/DNA binding. Sp1 bound to the 3′ flanking region of a variant κB site in the -192/-172 region of ICAM-1 promoter. Mutation of this region abolished the response to TNFα. The treatment of HCCSMCs with Sp1 antisense oligonucleotides (ODNs) blocked the expression of ICAM-1, but sense ODNs had no effect. Protein kinase C ζ (PKCζ) inhibition before or 3 hours after stimulation with TNFα also blocked the expression of ICAM-1. TNFα treatment of circular muscle strips pretreated with ICAM-1 sense ODNs or control medium significantly reduced their response to acetylcholine, whereas pretreatment with antisense ODNs blocked this effect. Conclusions: The expression of ICAM-1 on HCCSMCs in response to TNFα is regulated by transcription factors Sp1 and NF-κB binding independently to the -192/-172 region of the ICAM-1 promoter. The expression of ICAM-1 plays a critical role in the suppression of cell contractility in response to TNFα.
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