Insulin-like growth factor-II expression in carcinoma in colon cell lines: implications for autocrine actions

In the gastrointestinal tract, insulin-like growth factor-II (IGF-II) messenger RNA (mRNA) is localized mainly in mesenchymal cells, and is more abundant in the fetus than in the adult. The purposes of this study are to characterize the gene expression of IGF-II at the mRNA and protein level in seven different epithelial cell lines derived from colon carcinomas and to determine the action of IGF-II and IGF-receptors on a colon carcinoma cell line.

Insulin-like growth factor-II mRNAs were examined by Northern analysis; conditioned media from colon carcinoma cells were concentrated, chromatographed, and examined by a specific IGF-II radioreceptor assay. Insulin-like growth factor receptors were examined by radioligand binding assays. The mitogenic role of IGF-II was determined by a 3-(4,5-dimethylthiazol-2yl)-2,5-diphenyltetrazolium bromide assay.

Multiple sizes of IGF-II mRNAs were expressed in all colon carcinoma cell lines tested (six human cell lines: HCT116, COLO 205, COLO 320 DM, LoVo, DLD-1, and HT29, and one mouse cell line: MC-26). In the conditioned media of COLO 205 and HCT116 cells, 7.5 kilodaltons IGF-II and high molecular form (IGF-II and IGF binding protein complex) were detected. Both Type I and Type II IGF receptors were present on COLO 205 cells whose growth was stimulated by IGF-II. Addition of anti-IGF-I receptor and anti-IGF-II antibody in the cell culture significantly depressed growth of the COLO 205 cell line in the presence or absence of exogenous IGF-II.

Insulin-like growth factor-II mRNAs are expressed in human and mouse colon carcinoma cell lines, which may induce production of a significant amount of biologically active IGF-II protein. The IGF-II secreted by COLO 205 cells may stimulate cell growth in an autocrine fashion through the Type I IGF receptors.