The β2 subunit inhibits stimulation of the α1/β1 form of soluble guanylyl cyclase by nitric oxide: Potential relevance to regulation of blood pressure

Abstract

Cytosolic guanylyl cyclases (GTP pyrophosphate-lyase [cyclizing; EC 4.6.1.2]), primary receptors for nitric oxide (NO) generated by NO synthases are obligate heterodimers consisting of an α and a β subunit. The α1/β1 form of guanylyl cyclase has the greatest activity and is considered the universal form. An isomer of the β1 subunit, i.e., β2, has been detected in the liver and kidney, however, its role is not known. In this study, we investigated the function of β2. Immunoprecipitation experiments showed that the β2 subunit forms a heterodimer with the α1 subunit. NO-stimulated cGMP formation in COS 7 cells cotransfected with the α1 and β2 subunits was ~ 1/3 of that when α1 and β1 subunits were cotransfected. The β2 subunit inhibited NO-stimulated activity of the α1/β1 form of guanylyl cyclase and NO-stimulated cGMP formation in cultured smooth muscle cells. Our results provide the first evidence that the β2 subunit can regulate NO sensitivity of the α1/β1 form of guanylyl cyclase. Northern analysis for guanylyl cyclase subunits was performed on RNA from kidneys of Dahl salt-sensitive rats, which have been shown to have decreased renal sensitivity to NO. Compared to the Dahl salt-resistant rat, message for β2 was increased, β1 was decreased, and α1 was unchanged. These results suggest a molecular basis for decreased renal guanylyl cyclase activity, i.e., an increase in the α1/β2 heterodimer, and decrease in the α1/β1 heterodimer.