Abnormal expression and structural modification of the insulin‐like growth‐factor‐ii gene in human colorectal tumors

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Abstract
The insulin‐like growth factor II (IGF‐II) is a small protein implicated in fetal growth and development. It may play a role in the neoplastic process. The IGF‐II gene is located on the short arm of chromosome 11 near insulin and c‐Ha‐ras I genes. Three distinct promoters control the transcription of this gene, leading to different IGF‐II mRNA species. We have analyzed 21 human colorectal tumors and found overexpression of IGF‐II in 6 of them (30%). When compared with expression in normal adjacent tissues, IGF‐II mRNA increase in these tumors was either moderate (2‐ to 15‐fold) or very marked (200‐ to 800‐fold). In situ hybridization experiments confirmed that high IGF‐II mRNA amounts were localized in cancer cells of the tumors overexpressing the IGF‐II gene. In addition, DNA analysis revealed a structural modification of one IGF‐II locus in one tumor characterized by very high IGF‐II mRNA.