Column chromatographic characterization of complex formation of pro-IGF-II isoforms with acid labile subunit and IGF-binding proteins associated with non-islet cell tumour induced hypoglycaemia

• Published in: Growth hormone & IGF research Vol. 24; no. 6; pp. 233 - 238
• Main Authors: van Veggel, K.M, Huits, R.M.H.G, Donker, G.H, Lentjes, E.G.W.M, van Doorn, J
• Format: Journal Article
• Language: English
• Published: Scotland Elsevier Ltd 01-12-2014
• Subjects: Adult; Advanced Basic Science; Big IGF-II; Carcinoma, Hepatocellular - complications; Carcinoma, Hepatocellular - metabolism; Carcinoma, Hepatocellular - pathology; Chromatography, Gel - methods; Complex formation; Endocrinology & Metabolism; Humans; Hypoglycaemia; Hypoglycemia - etiology; Hypoglycemia - metabolism; Hypoglycemia - pathology; IGF; Insulin-Like Growth Factor Binding Proteins - metabolism; Insulin-Like Growth Factor II - metabolism; Liver Neoplasms - complications; Liver Neoplasms - metabolism; Liver Neoplasms - pathology; Male; Non-islet cell tumour hypoglycaemia; Paraneoplastic Syndromes - complications; Paraneoplastic Syndromes - metabolism; Paraneoplastic Syndromes - pathology; Phosphorylation; Protein Isoforms; Protein Precursors - metabolism; Tyrosine - metabolism; IGF; Complex formation; Hypoglycaemia; Big IGF-II; Non-islet cell tumour hypoglycaemia
• ISSN: 1096-6374; 1532-2238
• DOI: 10.1016/j.ghir.2014.08.002

Abstract Objective and design Non-islet cell tumour induced hypoglycaemia (NICTH) is a paraneoplastic phenomenon that is associated with the formation of several isoforms of pro-insulin like growth factor 2 (pro-IGF-II), or so called “big” IGF-II. Disturbance of ternary complex formation by big IGF-II is assumed to be a crucial early event in the pathogenic cascade of hypoglycaemia. By size-exclusion chromatography, we investigated complex formation by adding different naturally occurring isoforms of pro-IGF-II to pooled normal adult serum. Results were compared with the analysis of the serum from a patient with NICTH. Results Gel filtration experiments with the serum of a patient with NICTH demonstrated that ternary complex formation was severely compromised. The various forms of pro-IGF-II did not induce a shift of IGF-binding protein 3 (IGFBP-3) from 150 kD towards smaller binary complexes in the normal adult serum, suggesting that they did not interfere with the interaction between the acid labile subunit and IGFBP-3. Instead, unglycosylated recombinant pro-IGF-II[1–104] was capable of forming a 150 kD complex. In contrast, predominantly glycosylated and unglycosylated pro-IGF-II[1–87] eluted in the free unbound form. We showed that mature IGF-II and isoforms of pro-IGF-II were able to phosphorylate the IGF-I receptors of MC7 cells, albeit to a markedly lesser extent than IGF-I. When the patient's serum was tested in this system, the IGF-I receptor phosphorylation activity was considerably less than that in sera from age matched healthy individuals. Conclusion We postulate that, alongside the presence of big IGF-II in the circulation, additional steps are required to stimulate the release of IGF-II and pro-IGF-II isoforms from IGFBPs in vivo. These factors may be proteases, that are present in the local environment of the tumour and in insulin-sensitive tissues.