Background: The transcription factor, repressor of GATA-3 (ROG), can simultaneously suppress the expression of T helper cells (Th1 and Th2) cytokines. Since the suppression of Th2 cytokines by GATA-3 is well understood, it is postulated that there are other molecular targets of ROG that can suppress the expression of the Th1 cytokines. We hypothesized that ROG might suppress the stimulators of T lymphocyte cytokines such as CD3, CD28, and inducible costimulator (ICOS), or indirectly enhance the expression of cytokine suppressors such as T lymphocyte-associated antigen-4 (CTLA-4) and CD45. The objective of this study was to clarify the molecular targets of ROG involved in suppressing Th1 or Th2 cytokines.
Methods: Real-time quantitative PCR (RT-PCR) and Western blotting were performed to evaluate the mRNA and protein levels of CD3, CD28, ICOS, CTLA-4, and CD45 in Th1 and Th2 cells during various levels of ROG expression. Enzyme-linked immunosorbent assay (ELISA) was used to measure the levels of interferon-γ (IFN-γ) and interleukin (IL)-4 in culture media of Th1 and Th2 cells.
Results: The results showed that the mRNA and protein levels of ROG were relatively low in Th1 and Th2 cells (P < 0.01). After ROG-pcDNA3.1 transfection, the mRNA and protein level of ROG was significantly elevated, while the expression of ICOS, IFN-γ, and IL-4 was markedly down-regulated (P < 0.01). Conversely, transfection of ROG-siRNA led to inhibition of ROG expression and up-regulation of ICOS, IFN-γ and IL-4 (P < 0.01). However, the expression levels of CD3, CD28, CTLA-4 and CD45 did not change in either ROG-pcDNA3.1 or ROG-siRNA-transfected Th1 and Th2 cells (P > 0.05).
Conclusion: It is concluded that ROG can inhibit the expression of Th1 and Th2 cytokines by down-regulating the expression of ICOS, which might be a potential molecular target for asthma treatment.