We recently showed that
angiotensin (ANG) II as well as mechanical stretch stimulated production of
tumor necrosis factor (TNF) in cardiac fibroblasts. Presently, we examined the molecular mechanisms by which ANGII and
lipopolysaccharide (LPS) upregulate
TNF-alpha gene expression. In neonatal rat cardiac fibroblasts, increased transcription of
TNF-alpha mRNA was detected as
luciferase activity associated with activity of the
TNF-alpha promoter. Progressive deletion from this promoter located the LPS-responsive region between -200 and -120 bp from the transcription initiation site, while the sequence between -120 and -70 bp was required for ANGII-induced expression. Next, we examined which cis-acting sequences in the
TNF-alpha promoter region were essential for induction of
TNF-alpha transcription. Competition analysis by electrophoretic mobility shift assay with and without specific
antibodies showed that LPS increased binding of Sp1 and Sp3 to the Sp1-binding site, while Egr-1 was unimportant. With ANGII, binding of ATF-2/c-jun to the CRE site was required for
TNF-alpha gene induction; neither Ets nor
NF-kappaB was essential. Mutation analysis confirmed that response to LPS relied upon the Sp1 site in the
TNF-alpha promoter, while the CRE-binding site was essential for stimulation by ANGII. We concluded that since
TNF-alpha gene expression is transcriptionally activated by ANGII or LPS in cardiac fibroblasts via different cis-acting sequences in the
TNF-alpha promoter and different transcriptional factors, mechanisms inducing TNF production differ between
heart failure or
cardiac hypertrophy and
infectious disease.