Transcription factor NF-κB is necessary for up-regulation of type 1 angiotensin II receptor mRNA in rat cardiac fibroblasts treated with tumor necrosis factor-α or interleukin-1β

Tumor necrosis factor-a (TNF-alpha) and interleukin-1beta up-regulate type 1 angiotensin IIreceptor (AT(1)) mRNA and protein in cultured neonatal rat cardiac fibroblasts. The use of pharmacologic inhibitors and a degradation-resistant mutant IkappaB-alpha demonstrated that the transcription factor nuclear factor-kappaB (NF-kappaB) is necessary for cytokine-induced AT, up-regulation. The increase in AT(1) mRNA with TNF-alpha treatment is slow, reaching Significance by 6-12 h and peaking by 24-48 h. Electrophoretic mobility shift assays revealed that NF-kappaB nuclear translocation was maintained for greater than or equal to24 h with a single dose of TNF-alpha. Since prolonged NF-KB activation appeared necessary to maximize AT(1) up-regulation, the mechanism of persistent NF-kappaB activation was studied further. Stimulation with TNF-alpha induced a >10x increase in IkappaB kinase (IKK) activity that quickly diminished by 20 min. IkappaB-alpha and IkappaB-beta proteins were degraded during this time, and IkappaB-alpha was resynthesized subsequently by NF-kappaB-dependent transcription. However, IkappaB isoforms and IKK activity did not return completely to unstimulated values during a 12-h time course. These results suggest that low but persistent IKK activity and IkappaB degradation lead to prolonged NF-kappaB nuclear translocation and maximal AT(1) up-regulation in the continued presence of TNF-alpha.