Normal Human Mesothelial Cells and Mesothelioma Cell Lines Express Insulin-like Growth Factor I and Associated Molecules1

Insulin-like growth factor (IGF) I has important growth regulatory functions in normal growth and development. IGF-I is also a mitogen for a number of cancer cell lines; however, its autocrine effect has not been well established. In this study, the expression of IGF-I, its receptor, and its major serum-binding protein were examined in 5 normal human mesothelial (NHM) cell samples and 11 pleura) mesothelioma cell lines. All MINI cells and mesothelioma cell lines expressed IGF-I, IGF-binding protein 3 (IGFBP-3), and IGF-I receptor mRNA by either Northern blot or reverse transcription polymerase chain reaction analysis. IGF-I (0.136 ±0.024 ng/ml, mean ±SEM) and IGFBP-3 (18.5 ±3.2 ng/ml) proteins were readily detected in the conditioned medium of mesothelioma cell lines but were not greater than corresponding measurements in that of NHM cells (IGF-I, 0.120 ±0.080 ng/ml; IGFBP-3, 15.9 ± 1.3 ng/ml). Exogenous recombinant IGF-I stimulated cell proliferation of NHM cells, demon strating the presence of a functional IGF-I receptor. Our results suggest that IGF-I may function as an autocrine growth stimulus in normal pro liferating mesothelial cells, which may contribute to their malignant trans formation.