Regulation of transforming growth factor-β1 gene expression by glucocorticoids in normal human T lymphocytes

Abstract

Glucocorticoids (GC) modulate immune function in a number of ways, including suppression of T cell proliferation and other IL-2-mediated T cell functions. These inhibitory effects are similar to those induced by transforming growth factor-β1 (TGF-β1), a cytokine with potent T cell inhibiting activities. We examined the hypothesis that GC effects may be at least partially achieved through modulation of the expression of the TGF-β1 gene in activated T cells. Normal T cells were cultured with or without purified phytohemagglutinin (PHA-p) and 4β-phorbol 12-myristate 13-acetate (PMA) in the presence or absence of the synthetic GC, dexamethasone (100-200 μg/ml). The production of latent and active forms of TGFβ by these cells were analyzed by immunoblotting and bioassays. The steady-state levels of TGF-β1 mRNA were analyzed in total RNA from these cells by Northern hybridizations using a human TGF-β1 cDNA. The results showed that dexamethasone caused an increase in TGFβ production and a dose-dependent two to fourfold increase in TGF-β1 mRNA in activated as well as in unstimulated T cells, 1 h after exposure of the cultures to the steroid. The increase in TGF-β1 mRNA levels by dexamethasone was further potentiated two to threefold by cycloheximide, suggesting that the steroid effect may be due to inhibition of the synthesis of proteins that decrease TGF-beta;1 gene transcription or the stability of its transcripts. Finally, in vitro nuclear transcription studies indicated the dexamethasone effects on TGF-β1 gene expression to be largely transcriptional.