Aims: To study changes in the expression of insulin-like growth factors (IGFs) and their receptors, as well as production of the IGF-I and IGF-II polypeptides, in adenocarcinoma of the colon.
Methods: Malignant tissue obtained at operation was used. Total RNA was extracted and specific IGF-I and IGF-II and their receptor mRNAs were measured by a solution hybridisation RNase protection assay. IGF-I and IGF-II polypeptides were measured by specific immunoassays.
Results: All normal tissues expressed IGF-II, IGF-I receptor, and IGF-II/mannose-6-phosphate (Man-6-P) receptor. IGF-I mRNA could not be detected but the polypeptide was present in small but equal amounts in normal and malignant tissue. IGF-II was expressed 40 times more abundantly in colonic tumours than in adjacent normal tissue and the concentration of the corresponding polypeptide was twice as high in the malignant tissue. IGF-I receptor expression was increased by a factor of 2.5 and IGF-II/Man-6-P receptor by a factor of 4.
Conclusions: This study confirms that in adenocarcinoma of the human colon there is increased expression of IGF-I receptor and IGF-II. Furthermore, IGF-II/Man-6-P receptor message is increased and the increase in IGF-II message is accompanied by a doubling of the IGF-II protein in the tumour tissue compared with the adjacent normal tissue. These findings suggest that the IGF-II/Man-6-P receptor may also be involved in development of adenocarcinoma of the colon. There is rapidly accumulating evidence implicating the IGF system in the development of malignancy of the large bowel.