Localization and regulation of IGF-I and IGF-II mRNA

Abstract

Insulin-like growth factors I and II (IGF-I and -H) are peptide mitogens that exert a wide range of biological actions in many tissues and cell types. The actions of the IGFs include metabolic and differentiative effects as well as their capacity to stimulate cell proliferation. (Humbel 1984; Froesch et al. 1985; Van Wyk 1984). Traditionally the IGFs were considered as hormones that are transported in the circulation to act on target cells in an endocrine fashion (Humbel 1984; Froesch et al. 1985; Van Wyk et al. 1984). Based on studies of perfused liver (Schwander et al. 1983), liver derived cell lines (Moses et al. 1980), and primary cultures oliver cells (Richmond et al. 1985), the liver was considered the major source of serum IGFs. The IGFs do not appear to be stored in the liver to an appreciable extent, however, since the concentrations of IGFs are higher in blood perfusing the liver than in extracts of liver. More recently, cultured expiants of many tissues in addition to liver have been found to secrete immunoreactive IGFs into media (D’Ercole et al. 1984). Extracts of multiple tissues in addition to liver also contain higher concentrations of immunoreactive IGF than can be attributed to concentrations in blood perfusing the tissues (D’Ercole et al. 1984, 1986). These observations have raised the possibility that in addition to the endocrine actions of IGFs transported to target cells via the circulation, there may be paracrine or autocrine actions of IGFs synthesized locally in multiple tissues (D’Ercole et al. 1984,1986).