A key functional role for the insulin-like growth factor 1 N-terminal pentapeptide

Abstract

In order to elucidate the role of the N-terminus of insulin-like growth factor 1 (IGF-1) with respect to its biological properties, we chemically synthesized analogues of IGF-1 truncated by one to five amino acid residues from the N-terminus. In a bioassay that measured the stimulation of protein synthesis in rat L6 myoblasts, the concentrations required to produce a half-maximal response were: IGF-1, 13 ng/ml; des-(1)-IGF-1, 10 ng/ml; des-(1-2)-IGF-1, 13 ng/ml; des-(1-3)-IGF-1, 1.5 ng/ml; des-(1-4)-IGF-1, 5.1 ng/ml; des-(1-5)-IGF-1, 1200 ng/ml. When tested for their abilities to compete with 125I-IGF-1 binding to L6 myoblasts at 3 degrees C, the concentrations required for 50% competition were: IGF-1, des-(1)-IGF-1 and des-(1-2)-IGF-1, 20 ng/ml; des-(1-3)-IGF-1, 14 ng/ml; des-(1-4)-IGF-1, 40 ng/ml; des-(1-5)-IGF-1, greater than 1000 ng/ml. Receptor-binding experiments at 25 degrees C, however, gave results suggesting that the myoblasts were secreting a binding protein selective for the three longest peptides. This interpretation was confirmed by binding studies with medium conditioned by the L6 myoblasts as well as binding protein purified from MDBK-cell-conditioned medium. In both cases IGF-1, des-(1)-IGF-1 and des-(1-2)-IGF-1 competed for tracer IGF-1 binding at least 60-fold better than did the three shorter peptides. The results obtained account for the increased potency of des-(1-3)-IGF-1 and des-(1-4)-IGF-1, since their activities are not attenuated by the binding protein, and the relatively lower potency of des-(1-4)-IGF-1 is a consequence of this peptide binding less well to the L6-myoblast receptor.

Insulin-Like Growth Factor-I Regulation of Immune Function: A Potential Therapeutic Target in Autoimmune Diseases?

“…The IGF-I structural variant, IGF-I Des 1-3, can also be generated as a consequence of proteolytic digestion (Maake et al, 1997). This analog represents an IGF-IRspecific activator that lacks the N-terminal three amino acids (Bagley et al, 1989;Ross et al, 1989;Yamamoto and Murphy, 1995;Jansson et al, 1997). It exhibits high affinity for the type I receptor but does not bind FIG.…”

Interaction of insulin-like growth factor (IGF)-I and -II with IGF binding protein-2: mapping the binding surfaces by nuclear magnetic resonance

“…Swapping the B-domain of IGF-I for the corresponding insulin B-domain conferred IGFBP binding ability on insulin (De Vroede et al 1985), and replacement of the IGF-I B-domain with the insulin B-domain reduced serum IGFBP binding . Glu 3 of IGF-I was shown by site-directed mutagenesis and deletion analyses to contribute to the IGFBP interaction (Bagley et al 1989), as does the corresponding residue in IGF-II, Glu 6 (Francis et al 1993). IGF-I B-domain residues Gln 15 and Phe 16 are also important, with their mutation, in combination with Glu 3 and Thr 4 to the corresponding insulin residues, decreasing binding to serum IGFBP by up to 600-fold .…”

Enhancement of maternal lactation performance during prolonged lactation in the mouse by mouse GH and long-R3-IGF-I is linked to changes in mammary signaling and gene expression

“…From the standpoint of interactions with the type-I IGF receptor, des(1-3)IGF-I and wild-type IGF-I are equivalent, while LR3 has somewhat reduced affinity (Ballard et al 1986, Bagley et al 1989. The impact of this reduced affinity appears minimal from a biological standpoint since LR3 maintains greater potency than wild-type IGF-I in both in vitro and in vivo assays (Ballard et al 1986, Tomas et al 1993.…”