Isolation of a cDNA clone encoding rat insulin-like growth factor-II precursor.
Insulin-like growth factor-I (IGF-I) and IGF-II are mitogenic polypeptides of relative molecular mass (Mr) approximately 7,500 isolated from human plasma each containing four peptide domains in a single chain and identical at more than 60% of their amino acid loci. The B- and A-domains of the IGFs are approximately 40% identical to the B- and A-chains of human insulin. IGF-I and IGF-II have similar in vitro biological activities and receptor reactivity, but are immunologically distinct. IGF-I appears to mediate the effects of growth hormone on cartilage to promote skeletal growth whereas IGF-II may have a special role in fetal development and in the central nervous system. To investigate the in vivo role of IGF-II, we have studied IGF-II biosynthesis in the BRL-3A rat liver cell line. BRL-3A cells synthesize and secrete a 7,484 Mr protein 93% identical to human IGF-II and representing rat IGF-II (rIGF-II). Rat IGF-II is synthesized as a approximately 22,000 Mr prepro-rIGF-II (ref. 12) from 12 S poly(A)+mRNA. In addition, approximately 20,000 Mr pro-rIGF-II has been identified in lysates of biosynthetically labelled intact BRL-3A cells. We report here the isolation of an almost complete cDNA clone for rIGF-II. Our results indicate that pro-rIGF-II is synthesized as a 156 amino acid peptide precursor (17,619 Mr) containing mature rIGF-II 1-67 at its amino-terminus and an 89-residue carboxy-terminal peptide extension.
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics; D006133:Growth Substances / Q000235:genetics*; D007328:Insulin / Q000235:genetics*; D008970:Molecular Weight; D010455:Peptides / Q000235:genetics*; D011498:Protein Precursors / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D013002:Somatomedins / Q000235:genetics*
D006133:Growth Substances; D007328:Insulin; D010455:Peptides; D011498:Protein Precursors; D012333:RNA, Messenger; D013002:Somatomedins; D004247:DNA