Intercellular adhesion molecule-1 (ICAM-1) plays an important role in adhesion phenomena involved in the immune response. The strength of adhesion has been shown to be modulated by changes in ICAM-1 gene expression. In T cells, signaling pathways are intimately regulated by an equilibrium between protein-tyrosine kinases and protein tyrosine phosphatases (PTP). The use of bis-peroxovanadium (bpV) compounds, a class of potent PTP inhibitors, enabled us to investigate the involvement of phosphotyrosyl phosphatases in the regulation of ICAM-1 gene expression in human T cells. Here, we demonstrate for the first time that inhibition of PTP results in an increase of ICAM-1 surface expression on both human T lymphoid and primary mononuclear cells. The crucial role played by the NF-kappaB-, Ets-, and pIgammaRE-binding sites in bpV[pic]-mediated activation of ICAM-1 was demonstrated using various 5' deletion and site-specific mutants of the ICAM-1 gene promoter driving the luciferase reporter gene. Co-transfection experiments with trans-dominant mutants and electrophoretic mobility shift assays confirmed the importance of constitutive and inducible transcription factors that bind to specific responsive elements in bpV-dependent up-regulation of ICAM-1 surface expression. Altogether, these observations suggest that expression of ICAM-1 in human T cells is regulated by phosphotyrosyl phosphatase activity through NF-kappaB-, Ets-, and STAT-1-dependent signaling pathways.