Involvement of G i/o proteins in nerve growth factor-stimulated phosphorylation and degradation of tuberin in PC-12 cells and cortical neurons.
Tuberin is a critical translation regulator whose role in nerve growth factor (NGF)-promoted neuronal survival has not been documented. In the present study, we examined the ability of NGF to regulate tuberin in PC-12 cells and primary cortical neurons. Incubation of serum-deprived cells with NGF stimulated tuberin phosphorylation and induced proteosome-mediated tuberin degradation. Inhibition of the phosphatidylinositol-3-kinase (PI3K) by wortmannin or overexpression of the kinase dead Akt mutant completely blocked the NGF-induced tuberin phosphorylation and degradation. It is interesting that the NGF-induced tuberin phosphorylation was partially blocked by pertussis toxin or overexpression of regulators of G protein signaling (regulator of G protein signaling Z1 and Galpha-interacting protein), suggesting the participation of G(i/o) proteins. The use of transducin as a Gbetagamma scavenger indicated that Gbetagamma subunits rather than Galpha(i/o) acted as the signal transducer. Epidermal growth factor can similarly induce tuberin phosphorylation and degradation via a PI3K/Akt pathway in PC-12 cells, but these responses were insensitive to pertussis toxin treatment. Treatment of PC-12 cells with a specific agonist to the G(i)-coupled alpha(2)-adrenoceptor also stimulated tuberin phosphorylation transiently, further demonstrating the involvement of G(i/o) signaling in tuberin regulation in PC-12 cells. Finally, overexpression of nonphosphorylable tuberin attenuated NGF-promoted survival of PC-12 cells, suggesting that the phosphorylation and degradation of tuberin are important for NGF-promoted cell survival. Together, this study demonstrates the regulatory effect of NGF and G(i/o) signaling on tuberin.
Wu
Eddy H T
EH
Department of Biochemistry, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon, Hong Kong, China.
Wong
Yung H
YH
D000818:Animals; D000068438:Brimonidine Tartrate; D002470:Cell Survival; D002540:Cerebral Cortex / Q000378:metabolism*; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000502:physiology*; D044387:GTP-Binding Protein beta Subunits / Q000502:physiology; D044388:GTP-Binding Protein gamma Subunits / Q000502:physiology; D005998:Glycine / Q000031:analogs & derivatives*; D020932:Nerve Growth Factor / Q000494:pharmacology*; D037342:Pertussis Toxin / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D012097:Repressor Proteins / Q000378:metabolism*; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
D000068438:Brimonidine Tartrate; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D005998:Glycine; D020932:Nerve Growth Factor; D037342:Pertussis Toxin; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011810:Quinoxalines; D012097:Repressor Proteins; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; C084257:PC 12 ester; C494920:Akt1 protein, rat