Insulin regulation of human hepatic growth hormone receptors: divergent effects on biosynthesis and surface translocation.
Insulin modulates the biological actions of GH, but little is known about its effect on human hepatic GH receptors (GHRs). Using the human hepatoma cell line HuH7 as a model, we investigated insulin regulation of total, intracellular, and cell surface GHRs and receptor biosynthesis and turnover. Insulin up-regulated total and intracellular GHRs in a concentration-dependent manner. It increased surface GHRs in a biphasic manner, with a peak response at 10 nmol/L, and modulated GH-induced Janus kinase-2 phosphorylation in parallel with expression of surface GHRs. The abundance of GHR messenger ribonucleic acid and protein, as assessed by RT-PCR and Western analysis, respectively, markedly increased with insulin treatment. To examine whether insulin regulates GHRs at the posttranslational level, its effects on receptor surface translocation and internalization were investigated. Insulin suppressed surface translocation in a concentration-dependent manner, whereas internalization was unaffected. Moreover, insulin actions on total GHRs and surface translocation were inhibited by PD98059 and wortmannin, respectively. In conclusion, insulin regulates hepatic GHR biosynthesis and surface translocation in a reciprocal manner, with surface receptor availability the net result of the divergent effects. The divergent actions of insulin appear to be mediated by the mitogen-activated protein kinase and phosphatidylinositol 3-kinase pathways, respectively.
Leung
K C
KC
Pituitary Research Unit, Garvan Institute of Medical Research, St. Vincent's Hospital, Sydney, New South Wales 2010, Australia. k.leung@garvan.unsw.edu.au
Doyle
N
N
Ballesteros
M
M
Waters
M J
MJ
Ho
K K
KK
D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D019382:Human Growth Hormone / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000502:physiology*; D007457:Iodine Radioisotopes; D053614:Janus Kinase 2; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008114:Liver Neoplasms, Experimental / Q000378:metabolism; D010766:Phosphorylation; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface / Q000187:drug effects / Q000378:metabolism*; D011986:Receptors, Somatotropin / Q000096:biosynthesis / Q000187:drug effects / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014407:Tumor Cells, Cultured; D000077191:Wortmannin
D000730:Androstadienes; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007328:Insulin; D007457:Iodine Radioisotopes; D011518:Proto-Oncogene Proteins; D011956:Receptors, Cell Surface; D011986:Receptors, Somatotropin; D019382:Human Growth Hormone; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D000077191:Wortmannin