Role of guanine nucleotide binding protein in the activation of polyphosphoinositide phosphodiesterase

Abstract

Interaction of ligands with 'Ca2+-mobilizing' receptors is thought to result in the generation of two second messengers, inositol trisphosphate and diacylglycerol, from a common substrate, phosphatidylinositol 4,5-bisphosphate (PtdIns(4,5)P2) (refs 1, 2), a component of plasma membranes. It is not known how the occupation of such receptors is translated into the activation of the catalytic unit polyphosphoinositide (PPI) phosphodiesterase, and then to cellular activation, but our recent experiments suggest that GTP regulatory proteins may be involved. In mast cells, non-hydrolysable analogues of GTP introduced and then trapped in the cytosol are able to substitute for external ligands in inducing exocytosis, a well-defined Ca2+-dependent process, suggesting that guanine nucleotide regulatory proteins may act by stimulating the catalytic activity of the PPI phosphodiesterase. We now provide evidence that mast cell secretion is inhibited by internalized neomycin, a compound known to interact with PPI. We also show that the PPI phosphodiesterase of human neutrophil plasma membranes can be activated simply by adding GTP analogues in the presence of concentrations of Ca2+ that pertain in unstimulated cells. These findings strongly support the idea that the coupling factor linking receptor and PPI phosphodiesterase is a guanine nucleotide binding protein analogous to those involved in the activation and inhibition of adenylate cyclase.

Human neutrophil cytosolic phospholipase C: partial characterization

“…Stimulation of inositol lipid hydrolysis by guanine nucleotides compatible with involvement of G proteins in the activity of neutrophil PLC has been described by many investigators [8][9][10][29][30][31][32]. In our hands, the activity of neutlophil cytosolic PLC assayed in lipid vesicles or in heat-inactivated membranes devoid of active G proteins was not affected by GTPyS (Table Ill).…”

G Protein control of inositol lipids in intact vascular smooth muscle

“…Other investigators have demonstrated that either GTP or the non-hydrolyzable GTP analogue, GTP-& could stimulate the breakdown of PIP2 to form IP, in either cultured smooth muscle cell membranes [18] or in the homogenate of canine coronary arteries 1191. Similar studies have demonstrated that GTPyS could stimulate the breakdown of PIP2 in either permeable cells or membranes from a variety of tissues [7,8]. These experiments indicate that one or more G proteins most likely mediate the action of a contractile agonist on phospholipase C directly.…”

Stimulation of phosphatidylinositol 4‐phosphate phosphorylation in human placenta membranes by GTPγS

“…In this respect it is worth comparing the rate of PI kinase of 10 mU/mg protein with that of PIP kinase of 0.4 mU/mg protein (both calculated from the present study). This would mean that PIP kinase represents the rate limiting step during the formation of PIP2, and that an activation of this step, through an increase of PIPz, might exert control on phospholipase C. That the substrate supply for phospholipase C is limited and that the inositol lipid kinases may therefore be under separate control have also been discussed elsewhere [11]. Previous findings from this laboratory that insulin activates phospholipase C in fat cells [10] seem to have been confirmed recently [12,13].…”