Nitric oxide synthase (NOS2) mutation in Dahl/Rapp rats decreases enzyme stability

The pathogenesis of salt-sensitive hypertension remains poorly defined, but a role for nitric oxide (NO) has been suggested. The Dahl/Rapp salt-sensit ive rat possesses a defect in NO synthesis that is overcome by supplementat ion with L-arginine, which increases NO and cGMP production and prevents sa lt-sensitive hypertension. An S714P mutation of inducible NO synthase (NOS2 ) was subsequently identified. The current report examined the functional s ignificance of an S714P mutation in NOS2. COS-7 cells were transiently tran sfected with cDNA of wild-type NOS2 and S714P and S714A mutants of NOS2, an d enzyme function was determined. Whereas steady-state mRNA levels did not differ, immunoblot analysis demonstrated decreased levels of NOS2 protein. Metabolic labeling experiments confirmed a reduced half-life of the S714P m utation. Nitrite production, which was dependent on the concentration Of L- arginine in the medium, was diminished in cells transfected with the S714P mutant, compared with the wild type and the S714A mutant. These data provid e a biochemical explanation of the physiological abnormalities of NOS2 in t he Dahl/Rapp salt-sensitive rat and suggest that a posttranslational mechan ism involving the proteasome may be responsible for the diminished NO produ ction observed in response to increased dietary salt intake in these animal s.