The inhibitory gamma subunit of the type 6 retinal cyclic guanosine monophosphate phosphodiesterase is a novel intermediate regulating p42/p44 mitogen-activated protein kinase signaling in human embryonic kidney 293 cells

The inhibitory gamma subunits of the retinal rod and cone photoreceptor typ e 6 retinal cyclic guanosine monophosphate phosphodiesterase (PDE gamma) ar e expressed in non-retinal tissues. Here, we show that PDE gamma interacts with the G-protein-coupled receptor kinase 2 signaling system to regulate t he epidermal growth factor- and thrombin-dependent stimulation of p42/p44 m itogen-activated protein kinase in human embryonic kidney 293 cells. This i s based upon several lines of evidence. First, the transfection of cells wi th an antisense rod PDE gamma plasmid construct, which reduced endogenous r od PDE gamma expression, ablated the epidermal growth factor- and thrombin- dependent stimulation of p42/p44 mitogen-activated protein kinase. Second, the transfection of cells with recombinant rod or cone PDE gamma and/or G-p rotein-coupled receptor kinase 2 increased the stimulation of p42/p44 mitog en-activated protein kinase by epidermal growth factor or thrombin. In cont rast, a G-protein-coupled receptor kinase 2 phosphorylation-resistant rod P DE gamma mutant failed to increase the epidermal growth factor- or thrombin -dependent stimulation of p42/p44 mitogen-activated protein kinase and, in fact, functioned as a dominant negative. Thrombin also stimulated the assoc iation of endogenous rod PDE gamma with dynamin II, which was increased in cells transfected with rod PDE gamma or G-protein-coupled receptor kinase 2 . Dynamin II plays a critical role in regulating endocytosis of receptor si gnal complexes required for activation of p42/p44 mitogen-activated protein kinase. Therefore, PDE gamma may have an important role in promoting endoc ytosis of receptor signal complexes leading to the activation of p42/p44 mi togen-activated protein kinase. We conclude that PDE-gamma is an entirely n ovel intermediate regulating mitogenic signaling from both receptor tyrosin e kinase and G-protein-coupled receptors in human embryonic kidney 293 cell s.