Effects of 2-Chlorodeoxyadenosine and Gold Sodium Thiomalate on Human bcl-2 Gene Expression

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Abstract
Aberrant expression of apoptosis-related genes, including the "cell death suppressor gene" bcl-2, may play an important pathogenetic role in cancer and autoimmune diseases, In vivo upregulation of bcl-2 mRNA in synovial lining cells of patients with rheumatoid arthritis but not in patients with osteoarthritis has been recently found. In the present study we investigated whether agents exerting beneficial effects in patients with rheumatoid arthritis, namely the long used Gold Sodium Thiomalate (GST) and the novel immunosuppressive, purine analogue 2-chlorodeoxyadenosine (2-CdA), a lymphocyte apoptosis-inducing agent interfere directly with induction of bcl-2 mRNA expression. The phytohemagglutinin (PHA)-induced in vitro proliferation of normal human peripheral blood lymphocytes was significantly inhibited by non-toxic concentrations of 2-CdA and GST which are within the range of in vivo plasma concentrations in patients receiving the respective treatment. Using mRNA dot-blot analysis and hybridization with an IL-2-specific probe we found that GST, similarly to dexamethasone that served as control, suppressed the PHA-induced IL-2 mRNA accumulation dose-dependently. In contrast, 2-CdA (0.1 microgram/ml) at concentrations that inhibit by 80-90% the PHA-induced proliferative responses of lymphocytes did not affect IL-2 mRNA accumulation. Hybridization with a bcl-2-specific probe showed that the activation-induced accumulation and kinetics of bcl-2 mRNA were not changed in the presence of a wide range of concentrations of either GST or 2-CdA. Similarly, the mRNA accumulation of the "house-keeping" control gene beta-action remained unchanged by both agents. These findings indicate that biosynthesis of bcl-2 is not specifically affected by GST and CdA, suggesting that the immunomodulating effects of these agents, including their efficacy in suppressing chronic arthritis, are not related with a bcl-2-dependent mechanism.