Secretion of noncomplexed 'big' (10-18 kD) forms of insulin-like growth factor-II by 12 soft tissue sarcoma cell lines

The paraneoplastic production of pro-insulin-like growth factor-ii (IGF-II) forms causes tumour hypoglycaemias and presumably also has an effect on tu mour cell growth. We investigated the molecular weights of IGF-II forms and their ability to form complexes with IGF binding proteins (IGFBPs) in cond itioned culture media (CM) from 12 paediatric soft tissue sarcoma (STS) cel l lines and from two healthy fibroblast lines. Untreated CM were separated by size exclusion chromatography using biocompatible HPLC. Subsequently, IG F-II, IGFBP-2 and IGFBP-3 were determined in the HPLC fractions by specific RIAs. In the CM, IGF-II concentrations between 0.5 and 8.6 ng/10(6) cells were measured but no IGF-I was detectable. Parallel to this investigation, a high IGF-II mRNA level averaging 44.4 +/- 29.7% was measured by semi-quan titative RT-PCR. The STS cell lines secreted a higher proportion of big-IGF -ll forms reaching 10-18 kD (10-33% of the total IGF-II secreted) compared to the healthy fibroblasts (2.5-5%). At the same time, the proportion of IG F-II bound with IGFBP in complexes of 35-70 kD and 150 kD was reduced by up to 85% in CM from tumour cells. The tumour cell lines apparently secrete a different spectrum of IGF-II forms than healthy fibroblasts. The reduced a bility to form complexes with IGFBP and the higher molecular weight of the IGF-II forms produced by the tumour cells indicate that these forms could i n fact be the known tumour-associated pro-IGF-ll forms. Due to these charac teristics, the big-IGF-II forms probably have an altered biological effect on the tumour cells when compared to IGF-II. Copyright (C) 2000 S. Karger A G, Basel.