Genetics of receptors for bioactive polypeptides: expression of the human EGF receptor gene and internalization and processing of the receptor-bound EGF in human-mouse cell hybrids.

We previously postulated that the structural gene for epidermal growth factor (EGF) receptor is located on human chromosome 7 (1,2). In this study, EGF receptor and certain postreceptor functions were further analyzed in a unique cell hybrid line, C2B5, that retains only one human chromosome of an X;7 translocation besides a nearly complete mouse parental genome. Kinetics and Scatchard analysis of [125I]EGF binding to the C2B5 hybrid cells indicated that they carry a single class of EGF receptors with a dissociation constant of 4 x 10(-10) M. The receptors expressed in the hybrids are proven to be immunologically of human nature. The human EGF receptors now embedded in essentially mouse plasma membrane are subject to "down regulation" mediated by the ligand EGF. Analysis of the cell-bound EGF indicated that internalization and processing take place in the human-mouse cell hybrids. The degradation of EGF appears to be through a lysosomal pathway since it was substantially delayed or inhibited by lysosomotropic agents.