Tumor necrosis factor downregulates an endothelial nitric oxide synthase mRNA by shortening its half-life.
Nitric oxide (NO), which accounts for the biological properties of endothelium-derived relaxing factor, is generated by NO synthase (NOS). The vascular endothelium contains two types of NOS: one is constitutively expressed (cNOS), and the other is inducible. Endothelium-mediated vasorelaxation is impaired in atherosclerotic vessels. To determine whether tumor necrosis factor (TNF)-alpha, which is commonly found in atherosclerotic lesions, has an effect on NOS message, we measured cNOS mRNA levels in TNF-treated human umbilical vein endothelial cells (HUVECs) by RNA blot analysis with a cNOS cDNA probe. TNF-alpha markedly reduced cNOS mRNA levels in HUVECs in a dose- and time-dependent manner. In response to 3 ng/mL TNF-alpha, cNOS mRNA levels began to decrease at 4 hours and diminished to only 5% of control levels at 24 hours. As little as 0.1 ng/mL TNF-alpha reduced cNOS mRNA levels by 50%. This reduction in cNOS message in response to TNF-alpha depended on protein synthesis as it was blocked by cycloheximide. In nuclear runoff experiments, TNF-alpha did not change the rate of cNOS gene transcription. cNOS mRNA is very stable under basal conditions, with a half-life of 48 hours; however, treatment with TNF-alpha shortened this half-life to 3 hours. TNF-alpha thus appears to decrease cNOS mRNA levels by increasing the rate of mRNA degradation. TNF-induced reductions in cNOS mRNA levels may have an important effect on impaired endothelium-mediated vasorelaxation in atherosclerosis.
Yoshizumi
M
M
Cardiovascular Biology Laboratory, Harvard School of Public Health, Boston, MA 02115.
Perrella
M A
MA
Burnett
J C
JC
Lee
M E
ME
D000594:Amino Acid Oxidoreductases / Q000378:metabolism*; D001483:Base Sequence; D015536:Down-Regulation / Q000502:physiology*; D004730:Endothelium, Vascular / Q000378:metabolism*; D006207:Half-Life; D006801:Humans; D008969:Molecular Sequence Data; D019001:Nitric Oxide Synthase; D016133:Polymerase Chain Reaction / Q000379:methods; D012333:RNA, Messenger / Q000378:metabolism*; D014158:Transcription, Genetic; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*; D014471:Umbilical Veins
D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D019001:Nitric Oxide Synthase; D000594:Amino Acid Oxidoreductases