A mammalian protein involved in receptor-mediated endocytosis specifically binds to phosphatidylinositol 3-kinase. More specifically it binds to the Bcr homology domain of the p85 subunit of phosphatidylinositol 3-kinase. Phathoidylinositol 3-kinase also binds to platelet derived growth factor receptor. Other receptors may also bind, including those for insulin, insulin-like growth factor-1, colony stimulating factor 1, nerve growth factor, hepatocyte growth factor, stem cell growth factor, and epidermal growth factor. Mitogenesis is the consequence of the binding and internalization of these growth factors. Inhibition of the process of receptor-mediated internalization inhibits mitogenesis.