Receptor-Independent Activation of Cardiac Adenylyl Cyclase by GDP and Membrane-Associated Nucleoside Diphosphate Kinase. A New Cardiotonic Mechanism?

Activation of Heterotrimeric G Proteins by a High Energy Phosphate Transfer via Nucleoside Diphosphate Kinase (NDPK) B and Gβ Subunits

“…Particularly in the intact cell, where GTP concentrations are in the upper micromolar range, evidence for a mechanism beyond the sole synthesis of GTP appears mandatory to support this hypothesis. On the other hand, we have shown recently (10) that NDPK activates G proteins and regulates adenylyl cyclase activity in canine cardiac sarcolemmal membranes. This activation required the catalytic activity of NDPK (synthesis of GTP) but was clearly distinct from the effect of exogenous GTP, suggesting a more direct interaction of NDPK and G proteins.…”

Interaction of nucleoside diphosphate kinase B with heterotrimeric G protein βγ dimers: consequences on G protein activation and stability

“…Interestingly, the net effect of the NDPK B-mediated regulation of adenylyl cyclase activity in failing hearts was an inhibition, which obviously correlates to the relative prevalence of Gα i in CHF (Neumann et al 1988). In contrast, in sarcolemmal membranes of canine hearts, NDPK stimulates adenylyl cyclase via Gα s (Niroomand et al 1997). Thus, it is tempting to speculate that at Gα s and Gα i subunits nonselectively form heterotrimers with NDPK B/Gβγ complexes, and thereby, any alteration in the prevalence of the one or the other Gα subunit decides whether the net effect is receptor-independent stimulation (Gα s prevalence) or inhibition (Gα i prevalence) of adenylyl cyclase activity.…”

“…Numerous in vitro studies, mainly performed in crude membrane preparations, have revealed G protein activation through this enzymatic activity of NDPK (reviewed by Otero 1990Otero , 2000Kimura 1993;Piacentini and Niroomand 1996). Already in this early days, it was found that locally formed, NDPK-derived GTP or its poorly hydrolysable analogue GTPγS are more potent in activating heterotrimeric G proteins than exogenously added GTP or GTPγS Niroomand et al 1997). Two hypotheses to explain such data have mainly been discussed: (1) substrate channelling, which in this case means local, NDPK-catalysed formation of GTP from ATP and GDP in immediate vicinity of the G protein Otero et al 1988;Jakobs and Wieland 1989; or (2) the transfer of the high energy phosphate intermediately present on His118 of the NDPK directly onto the GDP still bound to the Gα subunit of the heterotrimer or monomeric GTPases (Kikkawa et al 1990;Randazzo et al 1991).…”

“…The identity of the proposed membrane-bound histidine kinase to catalyse this reaction remained, however, elusive (Nürnberg et al 1996, Kowluru 2002. Also, in this phosphotransfer reaction, the phosphorylation of GDP bound to Gα was a matter of debate (Wieland et al 1993;Kaldenberg-Stasch et al 1994;Hohenegger et al 1996;Kowluru et al 1996;Niroomand et al 1997). The same experimental constraints, which cannot exclude the spontaneous release of the Gα-bound GDP and re-binding of formed GTP, apply here, and some experimental data are clearly arguing against a direct transfer on Gα-bound GDP (Hohenegger et al 1996).…”

“…Notably, like already shown in a variety of membrane systems in the early 1990s, in the H10 membrane in vitro assay, the NDPK B and Gα s -dependent stimulation of adenylyl cyclase was largely suppressed when the phosphate acceptor substrate GDP was replaced by its analogue, guanosine 5′-O-(2-thio)diphosphate (GDPβS). GDPβS binds to Gα subunits with similar affinity than GDP but is a poor substrate for NDPK (Niroomand et al 1997) and Phospho-Gβ (Wieland et al 1993). Most interestingly, an even stronger reduction in Gα s -dependent cAMP accumulation then with H118 mutant was obtained when Gβ 1 H266Lγ 2 was adenovirally overexpressed in H10 cells.…”