Haselbacher G, Custer M, Lutz U, Humbel R E
Biochemisches Institut, University of Zürich, Switzerland.
Biochem Biophys Res Commun. 1992 Aug 31;187(1):279-86. doi: 10.1016/s0006-291x(05)81489-5.
We synthesized the N-terminal hexapeptide fragment of IGF II to study potential binding to NMDA receptors in analogy to the N-terminal tripeptide of IGF I. The amino acid sequence of the hexapeptide is furthermore identical with the C-terminal sequence of the casiragua insulin B chain. The hexapeptide did not bind to the NMDA receptors, but was found to promote [3H]-thymidine incorporation into fibroblasts at concentrations of 10(-8) - 10(-5) M in a dose-dependent manner. Since [125I]-hexapeptide did not bind to IGF receptors, indirect competition studies using either labelled IGFs or insulin had to be used. The competition of hexapeptide at a concentration of 10(-5) M with labelled IGF I or II was about equal to that of 10(-9) M IGF I or II. IGF receptors were apparently up-regulated by the hexapeptide, as has also been described for insulin. When using casiragua insulin as labelled ligand, IGF II and casiragua insulin competed with equal potency, whereas the hexapeptide at 10(-7) M caused an apparent up-regulation of the casiragua insulin binding sites. Our results that the hexapeptide stimulates [3H]-thymidine incorporation and up-regulates IGF II and casiragua insulin binding sites may be connected to one or several of the following findings: the hystricomorph insulins--of which the casiragua insulin is a member--stimulate DNA synthesis to a greater extent than other insulins; the insulin and type 1 IGF receptor binding regions are localized predominantly in the C-terminal region of the insulin B chain; and the "cooperative" site regulating the affinity of the insulin receptor is also located in the C-terminal region of the insulin B chain. Further experiments will be needed to clarify the exact mechanism.
我们合成了IGF II的N端六肽片段，以研究其与NMDA受体的潜在结合，这是类比于IGF I的N端三肽进行的。此外，该六肽的氨基酸序列与casiragua胰岛素B链的C端序列相同。该六肽不与NMDA受体结合，但发现在10(-8)-10(-5)M浓度范围内以剂量依赖方式促进[3H]-胸腺嘧啶核苷掺入成纤维细胞。由于[125I]-六肽不与IGF受体结合，因此必须使用标记的IGF或胰岛素进行间接竞争研究。10(-5)M浓度的六肽与标记的IGF I或II的竞争与10(-9)M IGF I或II的竞争大致相当。正如胰岛素的情况一样，六肽显然上调了IGF受体。当使用casiragua胰岛素作为标记配体时，IGF II和casiragua胰岛素具有同等效力的竞争，而10(-7)M的六肽导致casiragua胰岛素结合位点明显上调。我们的结果表明，六肽刺激[3H]-胸腺嘧啶核苷掺入并上调IGF II和casiragua胰岛素结合位点，这可能与以下一个或几个发现有关：casiragua胰岛素所属的豪猪型胰岛素比其他胰岛素更能刺激DNA合成；胰岛素和1型IGF受体结合区域主要位于胰岛素B链的C端区域；调节胰岛素受体亲和力的“协同”位点也位于胰岛素B链的C端区域。需要进一步的实验来阐明确切机制。
