Effects of a redox-active agent on lymphocyte activation and early gene expression patterns

Antioxidants can inhibit the proliferation of T lymphocytes induced by mitogens. This has been postulated to be due to their scavenging of reactive oxygen species which may act as second messengers in the antigen-induced signaling cascade leading to cell proliferation. When added concurrently with various mitogens, the thiol pyrrolidine dithiocarbamate (PDTC) inhibited the subsequent proliferation of lymphocytes. The extracellular copper chelator bathocuproine disulfonic acid (BCPS) increased the amount of PDTC needed for inhibition. We sought to determine the mechanism by which the two different treatments, PDTC (0.4 μM, copper-dependent) and PDTC (20 μM with BCPS, redox-sensitive) affected proliferation. We found that both inhibited the increase in expression of many of the genes, including IL-2 and MKP-2, that were induced early after stimulation of lymphocytes with phorbol myristate acetate and ionomycin. The inhibition of MKP-2 may have contributed to the enhancement observed by the thiol of mitogen-induced ERK phosphorylation. Of the two redox-sensitive, IL-2 regulating transcription factors, NF-κB and AP-1, the mitogen-induced activity of the former was inhibited by PDTC. Treatment of unstimulated cells with PDTC induced the expression of many genes, most notably several metallothioneins and heat shock proteins, and this may provide an alternative explanation for the inhibition of cellular proliferation.