title: Differential regulation of Igf1 and Igf2 mRNA levels in tilapia hepatocytes: effects of insulin and cortisol on GH sensitivity.
abstract: Igf1 and Igf2 stimulate growth and development of vertebrates. In mammals, liver-derived endocrine Igf1 mediates the growth promoting effects of GH during postnatal life, whereas Igf2 stimulates placental and fetal growth and is not regulated by GH. Insulin enhances Igf1 production by the mammalian liver directly, and by increasing hepatocyte sensitivity to GH. We examined the regulation of igf1 and igf2 mRNA levels by GH, insulin, and cortisol, and the effects of insulin and cortisol on GH sensitivity in primary cultured hepatocytes of tilapia, a cichlid teleost. GH increased mRNA levels of both igf1 and igf2 in a concentration-related and biphasic manner over the physiological range, with a greater effect on igf2 mRNA level. Insulin increased basal igf2 mRNA level, and strongly increased GH-stimulated igf2 mRNA level, but slightly reduced basal igf1 mRNA level and did not affect GH-stimulated igf1 mRNA level. Cortisol inhibited GH stimulation of igf1, but increased GH stimulation of igf2 mRNA level. The synergistic effect of insulin and GH on igf2 mRNA level was confirmed in vivo. These results indicate that insulin and cortisol differentially modulate the response of igf1 and igf2 mRNA to GH in tilapia hepatocytes, and suggest that the regulation of liver Igf2 production differs between fish and mammals. Regulation of liver Igf2 production in fish appears to be similar to regulation of liver Igf1 production in mammals.
authors.affiliation: Hawaii Institute of Marine Biology, University of Hawaii, Kaneohe, USA.
authors.forename: Andrew L
authors.initials: AL
authors.lastname: Pierce
authors.forename: Jason P
authors.initials: JP
authors.lastname: Breves
authors.forename: Shunsuke
authors.initials: S
authors.lastname: Moriyama
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hirano
authors.forename: E Gordon
authors.initials: EG
authors.lastname: Grau
mesh_terms: D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002417:Cattle; D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D029941:Fish Proteins / Q000235:genetics*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation / Q000187:drug effects; D013006:Growth Hormone / Q000494:pharmacology; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D006854:Hydrocortisone / Q000494:pharmacology; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000235:genetics*; D007335:Insulin-Like Growth Factor II / Q000235:genetics*; D008099:Liver / Q000187:drug effects / Q000378:metabolism; D008297:Male; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012756:Sheep; D017210:Tilapia / Q000097:blood / Q000235:genetics*; D013997:Time Factors
chemical_list: D001786:Blood Glucose; D029941:Fish Proteins; D007004:Hypoglycemic Agents; D007328:Insulin; D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D013006:Growth Hormone; D006854:Hydrocortisone