Transforming growth factor-β1 inhibits β2-adrenoceptor gene transcription

Abstract

Transforming growth factor-β1 (TGF-β1) has been shown to modulate β-adrenoceptor number and function in cultured human tracheal smooth muscle cells and cardiac fibroblasts, but the mechanism is unclear. In this study, we have characterized the β2-adrenoceptor expression by radioligand binding assay, Northern blot analysis and measurement of intracellular cAMP accumulation in a human embryonic lung fibroblast cell line (HEL299 cells). Treatment with TGF-β1 caused a time-dependent decrease in β2-adrenoceptor mRNA, and in receptor number after 24 h. Furthermore, nuclear run-on assays showed a 35% reduction in the transcription rate of the β2-adrenoceptor gene with no alteration in stability of the β2-adrenoceptor mRNA. After TGF-β1 treatment, the basal, procaterol- and forskolin-stimulated cAMP accumulations were also decreased. Cycloheximide inhibited TGF-β1-mediated reduction of β2-adrenoceptor mRNA and protein, whilst alone caused induction of β2-adrenoceptor mRNA without any effect on receptor number. In summary, TGF-β1 induces β2-adrenoceptor desensitization through the alteration in adenylyl cyclase activity and down-regulation of β2-adrenoceptor mRNA and protein through the reduction in the rate of β2-adrenoceptor gene transcription.