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Signal-transducing GTP-binding proteins of mammalian heart and lungs
V A Tkachuk1, S I Hoffenberg, M G Starikova
1Institute of Experimental Cardiology, Academy of Medical Sciences, Moscow, USSR.
Insights
Signal-transducing proteins in mammalian heart and lungs were studied. Pertussis toxin and cholera toxin modified G-proteins, affecting adenylate cyclase activity and guanine nucleotide binding.
Area of Science:
- Molecular Cardiology
- Cellular Signaling
- G-Protein Signaling
Background:
- Mammalian heart sarcolemma contains three distinct G-proteins: Gi, Gp, and Gs.
- G-proteins are crucial signal transducers in cellular pathways.
Purpose of the Study:
- To investigate the role of G-proteins in mammalian heart and lung tissues.
- To characterize the effects of ADP-ribosylation on G-protein function.
Main Methods:
- ADP-ribosylation assays using pertussis toxin (PT) and cholera toxin (CT).
- Analysis of adenylate cyclase activity following G-protein modification.
- Investigation of G-protein interactions with guanine nucleotides.
Main Results:
- Pertussis toxin ADP-ribosylation of Gi increased adenylate cyclase activity and blocked carbachol inhibition.
- Isoproterenol's activating effect on adenylate cyclase was preserved after Gi modification.
- Endogenous ADP-ribosylation of Gi abolished PT-induced ADP-ribosylation.
- Gpp(NH)p modulated PT and CT-induced ADP-ribosylation.
- Soluble Gi and Gs proteins were identified in lung cytosol.
Conclusions:
- G-protein modification by ADP-ribosylation significantly impacts signal transduction pathways in heart and lung.
- PT-induced ADP-ribosylation of Gi affects adenylate cyclase regulation.
- Soluble G-proteins in lung cytosol can be modified by PT and CT.
Abstract:
Signal-transducing GTP-binding Proteins of Mammalian Heart and Lungs. Journal of Molecular and Cellular Cardiology (1989) 21 (Suppl I) 91-95. Three distinct G-proteins have been found in mammalian heart sarcolemma: Gi (alpha i = 40 kDa, beta = 36 kDa, and lambda less than 14 kDa), Gp (alpha p = 23 kDa, beta = 36 kDa, and lambda less than 14 kDa), and Gs (alpha s = 42 kDa). ADP-ribosylation of sarcolemmal alpha i by pertussis toxin (PT) or preincubation of sarcolemma with protein kinase C and PMA resulted in increased adenylate cyclase activity and blockade of GTP-dependent inhibition by carbachol whereas the GTP-dependent activating effect of isoproterenol on the adenylate cyclase was preserved. ADP-ribosylation of alpha i in sarcolemma by endogenous NADP-sensitive ADP-ribosyltransferase abolished the PT-induced ADP-ribosylation of alpha i. Gpp (NH)p attenuated the PT-induced ADP-ribosylation of alpha i and promoted the cholera toxin (CT)-induced ADP-ribosylation of alpha s. The CT-induced alpha s ADP-ribosylation was enhanced in the presence of heart cytosol. Soluble Gi- and Gs-proteins were identified in lung cytosol. The 40 kDa alpha i in membrane and soluble fractions was ADP-ribosylated by PT, while the soluble 42 kDa alpha s was ADP-ribosylated by CT in lung tissue. The ADP-ribosylation of soluble alpha i by PT-suppressed guanyl nucleotide binding to Gi. The apparent molecular mass of partially purified soluble Gi was 75 kDa.