Transforming growth factor-beta1 inhibits beta2-adrenoceptor gene transcription

Transforming growth factor-beta1 (TGF-beta1) has been shown to modulate beta-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 beta2-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-beta1 caused a time-dependent decrease in beta2-adrenoceptor mRNA, and in receptor number after 24 h. Furthermore, nuclear run-on assays showed a 35% reduction in the transcription rate of the beta2-adrenoceptor gene with no alteration in stability of the beta2-adrenoceptor mRNA. After TGF-beta1 treatment, the basal, procaterol- and forskolin-stimulated cAMP accumulations were also decreased. Cycloheximide inhibited TGF-beta1-mediated reduction of beta2-adrenoceptor mRNA and protein, whilst alone caused induction of beta2-adrenoceptor mRNA without any effect on receptor number. In summary, TGF-beta1 induces beta2-adrenoceptor desensitization through the alteration in adenylyl cyclase activity and down-regulation of beta2-adrenoceptor mRNA and protein through the reduction in the rate of beta2-adrenoceptor gene transcription.