Insulin-like growth factor binding protein 2 is a growth inhibitory protein conserved in zebrafish.
Fish serum contains several specific binding proteins for insulin-like growth factors (IGFBPs). The structure and physiological function of these fish IGFBPs are unknown. Here we report the complete primary sequence of a zebrafish IGFBP deduced from cDNA clones isolated by library screening and rapid amplification of cDNA ends. The full-length 1,757-bp cDNA encodes a protein of 276 aa, which contains a putative 22-residue signal peptide and a 254-residue mature protein. The mature zebrafish IGFBP has a predicted molecular size of 28,440 Da and shows high sequence identity with human IGFBP-2 (52%). The sequence identities with other human IGFBPs are <37%. Chinese hamster ovary cells stably transfected with the zebrafish IGFBP-2 cDNA secreted a 31-kDa protein, which bound to IGF-I and IGF-II with high affinity, but did not bind to Des(1-3)IGF-I or insulin. Northern blot analyses revealed that the zebrafish IGFBP-2 transcript is a 1.8-kb band expressed in many embryonic and adult tissues. In adult zebrafish, IGFBP-2 mRNA levels were greatly reduced by growth hormone treatment but increased by prolonged fasting. When overexpressed or added to cultured zebrafish and mammalian cells, the zebrafish IGFBP-2 significantly inhibited IGF-I-stimulated cell proliferation and DNA synthesis. These results indicate that zebrafish IGFBP-2 is a negative growth regulator acting downstream in the growth hormone-IGF-I axis.
Duan
C
C
Department of Biology, University of Michigan, Ann Arbor, MI 48109, USA. cduan@umich.edu
Ding
J
J
Li
Q
Q
Tsai
W
W
Pozios
K
K
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D017124:Conserved Sequence; D017077:Culture Media, Conditioned / Q000494:pharmacology; D015870:Gene Expression; D005786:Gene Expression Regulation; D015723:Gene Library; D013006:Growth Hormone / Q000494:pharmacology; D006131:Growth Inhibitors / Q000235:genetics*; D018971:Insulin-Like Growth Factor Binding Protein 2 / Q000235:genetics*; D007334:Insulin-Like Growth Factor I / Q000037:antagonists & inhibitors; D008969:Molecular Sequence Data; D009747:Nutritional Physiological Phenomena; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D014018:Tissue Distribution; D015027:Zebrafish / Q000235:genetics*
D017077:Culture Media, Conditioned; D006131:Growth Inhibitors; D018971:Insulin-Like Growth Factor Binding Protein 2; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone