SHIMIZU, M.; DICKEY, J.T.; FUKADA, H.; DICKHOFF, W.W.; NOAA-Fisheries and Univ. of Washington, Seattle; NOAA-Fisheries and Univ. of Washington, Seattle; NOAA-Fisheries and Univ. of Washington, Seattle; NOAA-Fisheries and Univ. of Washington, Seattle: Cloning of salmon insulin-like growth factor binding proteins

Insulin-like growth factor binding proteins (IGFBPs) inhibit or potentiate the activity of IGFs depending on the type of IGFBP and cellular environment. Six IGFBPs have been identified in mammals. In teleosts, evidence of four to five IGFBPs have been found, although the sequence information on the multiple IGFBPs is available only in a few species: zebrafish and fugu. In salmon, at least three IGFBPs exist in the circulation. Our goals are to identify those salmon IGFBPs and study their physiological roles. In this study, we cloned salmon IGFBPs by PCR using degenerate primers designed based on N-terminal amino acid sequences from purified salmon IGFBPs, and sequences conserved in each and among all IGFBPs. Liver total RNA and mRNA of chinook salmon were reverse transcribed to generate first-strand cDNA. Subsequent PCR using different combinations of degenerate primers amplified several bands. Specific PCR bands were subcloned into a vector and sequenced. Thus far, partial cDNA sequences of salmon IGFBP-1, -2, -3 and -5 have been obtained. In addition, two different sequences have been assigned as salmon IGFBP-2. Salmon IGFBPs showed high homologies to mammalian and fish IGFBP counterparts, having cysteine rich N- and C-terminal regions and variable mid-regions. These results indicate that the primary structures of salmon IGFBPs are well conserved. However, there are still some conflicts between protein and cDNA data regarding the identity of salmon IGFBPs. Further analysis is needed to definitively identify each salmon IGFBP. (Supported by NRI-CSREES USDA-2003-03314)