Tumor Necrosis Factor Activates Angiotensinogen Gene Expression by the Rel A Transactivator

Abstract

Angiotensinogen encodes the only known precursor of angiotensin II, a critical regulator of the cardiovascular system. Transcriptional control of angiotensinogen in hepatocytes is an important regulator of circulating angiotensinogen concentrations. Angiotensinogen transcription is increased by the inflammatory cytokine tumor necrosis factor (TNF)-α by a nuclear factor–κB–like protein binding to an inducible enhancer called the acute-phase response element. By gel mobility shift assays, we observe two specific acute-phase response element–binding complexes, C1 and C2. The abundance of C2 is not changed by TNF treatment. In contrast, C1 is faintly detected in untreated cells, and its abundance increases by fivefold after stimulation. We identify the nuclear factor–κB subunits in these complexes using subunit-specific antibodies in the gel mobility “supershift” assay. The transcriptionally inert nuclear factor–κB DNA-binding subunit NF-κB1 is present in both control and stimulated hepatocyte nuclei. Its abundance changes weakly upon TNF stimulation. In contrast, the potent transactivating protein Rel A is not found in unstimulated hepatocyte nuclei and is recruited by TNF-α into the C1 DNA-binding complex. Overexpression of Rel A results in acute-phase response element transcription. Cotransfection of a chimeric GAL4–Rel A protein with GAL4 DNA-binding sites is a strategy that allows for selective study of Rel A. The GAL4:Rel A chimera is a TNF-α–inducible transactivator. Deletion of the amino-terminal 254 amino acids of Rel A produces a constitutive activator (that is no longer TNF-α inducible). The cytokine induction of Rel A, then, is mediated through its amino-terminal 254 amino acids. We conclude that Rel A:NF-κB1 is a crucial cytokine-inducible transcription factor complex regulating angiotensinogen gene synthesis in hepatocytes and may be involved in controlling the activity of the renin-angiotensin system.