Regulation of the insulin and asialoglycoprotein receptors via cGMP-dependent protein kinase.
Biotin regulation of asialoglycoprotein receptor expression and insulin receptor activity has been established in two human hepatoblastoma cell lines, Hep G2 and HuH-7. Second messenger cGMP mimics the effect of biotin on asialoglycoprotein receptor expression at the translational level. Metabolic labeling and subsequent immunoprecipitation indicate that the loss of insulin receptor activity during biotin deprivation was due to suppression of receptor synthesis. Evidence for posttranscriptional regulation of insulin receptor synthesis was provided by rapid biotin induction of receptor synthesis without an increase in gene transcript number. Addition of a cGMP-dependent protein kinase (cGK) inhibitor prevented biotin induction of the insulin and asialoglycoprotein receptors, suggesting that protein phosphorylation propagates the cGMP signal transduction cascade. Coatomer protein COPI was recently identified as the trans-acting factor that regulates in vitro translation of the asialoglycoprotein receptor. Biotin repletion of the culture medium resulted in the hyperphosphorylation of alpha-COP, which was prevented by simultaneous addition of the cGK inhibitor. These findings suggest that the end point of this cGMP signal cascade is modulated by cGK and that a phosphorylation reaction governs the expression of both receptor proteins.
De La Vega
L A
LA
Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Stockert
R J
RJ
D037263:Asialoglycoprotein Receptor; D001710:Biotin / Q000494:pharmacology; D020756:Coatomer Protein / Q000378:metabolism; D017869:Cyclic GMP-Dependent Protein Kinases / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D018197:Hepatoblastoma; D006801:Humans; D008113:Liver Neoplasms; D010766:Phosphorylation; D014176:Protein Biosynthesis / Q000187:drug effects / Q000502:physiology; D011972:Receptor, Insulin / Q000235:genetics*; D011956:Receptors, Cell Surface / Q000235:genetics*; D015290:Second Messenger Systems / Q000187:drug effects / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D014407:Tumor Cells, Cultured
D037263:Asialoglycoprotein Receptor; D020756:Coatomer Protein; D011956:Receptors, Cell Surface; D001710:Biotin; D011972:Receptor, Insulin; D017869:Cyclic GMP-Dependent Protein Kinases