Common Carp (Cyprinus Carpio) Insulin-like Growth Factor Binding Protein-2 (IGFBP-2): Molecular Cloning, Expression Profiles, and Hormonal Regulation in Hepatocytes

In the present study, we cloned IGFBP-2 cDNA from common carp (Cyprinus carpio) liver. The 1879 bp full-length cDNA encodes 274 amino acid residues containing a putative signal peptide of 22 residues. Two IGFBP-2 transcripts with estimated sizes of 2.2 and 1.5 kb have been detected with Northern blot analysis in liver. Relatively high levels of IGFBP-2 mRNA were observed in all regions of brain, liver, pituitary, ovary and testis. Intermediate levels were observed in white muscle, thymus gland and head kidney, while in retina, heart and other tissues IGFBP-2 mRNA levels were very low. A significant level of IGFBP-2 mRNA was firstly detected at lens formation stage, and it continued to increase to the highest level at blood cycling stage, and fell to a relatively high level until hatching. The expression pattern of IGFBP-2 mRNA was similar during different stages of testis and ovary. At recrudescing stage the expression level was extremely low, but it sharply increased to a high level at matured stage, and finally brought back to the very low level at regressed stage. Hepatocytes IGFBP-2 mRNA was greatly reduced by growth hormone but increased by insulin. PD-98059 and LY-294002, the specific inhibitor of MEK and PI3K, increased IGFBP-2 mRNA expression level and completely blocked the inhibitory effect of GH. It is suggested that the MAPK and PI3 kinase-signaling pathways were involved in the decrease of IGFBP-2 mRNA expression induced by GH in primary cultured hepatocytes.