IGF-II in the pathogenesis of rhabdomyosarcoma: a prototype of IGFs involvement in human tumorigenesis.

Abstract

In recent years there has been a growing interest in the role of peptide growth factors in the regulation of the biologic behavior of several human malignancies. Among those peptides that might have importance in neoplastic pathogenesis are the insulin-like growth factors I and II (IGF-I and IGF-II). These proteins have been shown to stimulate myoblast proliferation and differentiation (1), to promote nutrient uptake and to inhibit proteolysis (2, 3). IGF-II mRNA is highly expressed in human skeletal fetal muscle tissue, but it is not detectable in normal adult skeletal muscle by standard Northern analysis and in situ hybridization (4). In mouse myoblasts, IGF-I and IGF-II mRNA levels increase transiently (IGF-II > > IGF-I) within 48-72 hours of the beginning of the myogenic differentiation process. The expression of mRNA is accompanied by secretion of the peptides in the culture medium that peaks at hour 92. IGF-I receptors increase transiently, doubling by 48 hours after the onset of differentiation, while IGF-II receptors increase and remain at a higher number throughout the differentiated state (5, 6). The production of IGF-binding proteins of Mr 29,000 to 32,000 is also induced throughout differentiation (7).