Formation of distinct signalling complexes involving phosphatidylinositol 3‐kinase activity with stimulation of epidermal growth factor or insulin‐like growth factor‐I in human skin fibroblasts

We recently described a better correlation of DNA synthesis with phosphatidylinositol (PI) 3‐kinase than with mitogen‐activated protein (MAP) kinase stimulated by insulin‐like growth factor (IGF)‐I or epidermal growth factor (EGF) in human skin fibroblasts (Takahashi et al., 1997, Endocrinology 138:741–750). IGF‐I–induced PI 3‐kinase activation is generally mediated via insulin receptor substrate (IRS)‐1, but EGF‐induced PI 3‐kinase activation is mediated by various signalling molecules such as ErbB3 and c‐Cbl in different cells. We therefore investigated the mechanism regulating PI 3‐kinase in human skin fibroblasts by comparing complexes involving PI 3‐kinase when stimulated by IGF‐I or EGF and found that p115 and p105, which were tyrosine‐phosphorylated by EGF stimulation and associated with SHP‐2, were also associated with the p85 subunit of PI 3‐kinase by EGF. Anti‐SHP‐2 and anti‐p85 subunits of PI 3‐kinase antibodies did not coprecipitate tyrosine‐phosphorylated EGF receptor or ErbB3; in addition, p115 and p105 appeared to be distinct from tyrosine‐phosphorylated c‐Cbl. Thus, tyrosine‐phosphorylated p115 and p105 may provide a novel platform recruiting p85, which may simultaneously bind to SHP‐2. In contrast, tyrosine phosphorylation of p115 or p105 was undetectable by immunoblot with IGF‐I stimulation, and PI 3‐kinase activity was mediated via IRS‐1 phosphorylated with IGF‐I stimulation, little of which was associated with SHP‐2. Thus, EGF and IGF‐I cause formation of a distinct signalling complex which associates with p85 subunit of PI 3‐kinase. J Cell Physiol 178:69–75, 1999. © 1999 Wiley‐Liss, Inc.