Cyclosporin A (CsA) is an immunosuppressive drug that inhibits the activity of transcription factors of the nuclear factor of activated T cells (NFAT) family, interfering with the induction of cytokines and other inducible genes required for the immune response. Here we show that CsA inhibits migration of primary endothelial cells and angiogenesis induced by vascular endothelial growth factor (VEGF); this effect appears to be mediated through the inhibition of cyclooxygenase (Cox)-2, the transcription of which is activated by VEGF in primary endothelial cells. Consistent with this, we show that the induction of Cox-2 gene expression by VEGF requires NFAT activation. Most important, the CsA-mediated inhibition of angiogenesis both in vitro and in vivo was comparable to the Cox-2 inhibitor NS-398, and reversed by prostaglandin E₂. Furthermore, the in vivo corneal angiogenesis induced by VEGF, but not by basic fibroblast growth factor, was selectively inhibited in mice treated with CsA systemically. These findings involve NFAT in the regulation of Cox-2 in endothelial cells, point to a role for this transcription factor in angiogenesis, and may provide a novel mechanism underlying the beneficial effects of CsA in angiogenesis-related diseases such as rheumatoid arthritis and psoriasis.

The Cephalotaxus alkaloids harringtonine, homoharringtonine and isoharringtonine inhibit protein synthesis in eukaryotic cells. The alkaloids do not inhibit, in model systems, any of the steps of the initiation process but block poly(U)‐directed polyphenylalanine synthesis as well as peptide bond formation in the fragment reaction assay, the sparsomycin‐induced binding of (C)U‐A‐C‐C‐A‐[³H]Leu‐Ac, and the enzymic and the non‐enzymic binding of Phe‐tRNA to ribosomes. These results suggest that the Cephalotaxus alkaloids inhibit the elongation phase of translation by preventing substrate binding to the acceptor site on the 60‐S ribosome subunit and therefore block aminoacyl‐tRNA binding and peptide bond formation.However, the Cephalotaxus alkaloids do not inhibit polypeptide synthesis and peptidyl‐[³H]puromycin formation in polysomes. Furthermore, these alkaloids strongly inhibit [¹⁴C]trichodermin binding to free ribosomes but hardly affect the interaction of the antibiotic with yeast polysomes. These results clearly suggest that the Cephalotaxus alkaloids cannot interact with polysomes and therefore only inhibit the initial cycles of elongation. This explains the polysome run off that has been observed by some workers in the presence of harringtonine.

Our understanding of the key players involved in the differential regulation of T‐cell responses during inflammation, infection and auto‐immunity is fundamental for designing efficient therapeutic strategies against immune diseases. With respect to this, the inhibitory role of the lipid mediator prostaglandin E₂(PGE₂) in T‐cell immunity has been documented since the 1970s. Studies that ensued investigating the underlying mechanisms substantiated the suppressive function of micromolar concentrations of PGE₂in T‐cell activation, proliferation, differentiation and migration. However, the past decade has seen a revolution in this perspective, since nanomolar concentrations of PGE₂have been shown to potentiate Th1 and Th17 responses and aid in T‐cell proliferation. The understanding of concentration‐specific effects of PGE₂in other cell types, the development of mice deficient in each subtype of the PGE₂receptors (EP receptors) and the delineation of signalling pathways mediated by the EP receptors have enhanced our understanding of PGE₂as an immune‐stimulator. PGE₂regulates a multitude of functions in T‐cell activation and differentiation and these effects vary depending on the micro‐environment of the cell, maturation and activation state of the cell, type of EP receptor involved, local concentration of PGE₂and whether it is a homeostatic or inflammatory scenario. In this review, we compartmentalize the various aspects of this complex relationship of PGE₂with T lymphocytes. Given the importance of this molecule in T‐cell activation, we also address the possibility of using EP receptor antagonism as a potential therapeutic approach for some immune disorders.

We have previously reported that transcriptional induction of cyclooxygenase-2 (COX-2) isoenzyme occurs early after T cell receptor triggering, suggesting functional implications of cyclooxygenase activity in this process. Here, we identify the cis-acting elements responsible for the transcriptional activation of this gene in human T lymphocytes. COX-2 promoter activity was induced upon T cell activation both in primary resting T lymphocytes and in Jurkat cells. This induction was abrogated by inhibition of calcineurin phosphatase with the immunosuppressive drug cyclosporin A, whereas expression of an active calcineurin catalytic subunit enhanced COX-2 transcriptional activation. Moreover, cotransfection of nuclear factor of activated T cells (NFAT) wild type protein transactivated COX-2 promoter activity. Conversely, dominant negative mutants of NFATc or c-Jun proteins inhibited COX-2 induction. Electrophoretic mobility shift assays and site-directed mutagenesis allowed the identification of two regions of DNA located in the positions −117 and −58 relative to the transcriptional start site that serves as NFAT recognition sequences. These results emphasize the central role that the Ca²⁺/calcineurin pathway plays in COX-2 transcriptional regulation in T lymphocytes pointing to NFAT/activator protein-1 transcription factors as essential for COX-2 promoter regulation in these cells.