Metabolism and Effects of Epidermal Growth Factor and Related Growth Factors in Mammals*

Abstract

The initial observations of Stanley Cohen in the 1960s established that EGF induced in vivo effects such as precocious eyelid opening and tooth eruption. Subsequently the actions of EGF have been extensively explored in cell culture systems. The receptor for EGF was characterized as a prototype model for other growth factors and the now extensive in vitro data indicate multiple functions for EGF. Moreover, EGF and EGF receptors have been characterized in many tissues, and EGF has been identified in most body fluids of several mammalian species. Interestingly, neither EGF antibody administration to newborn animals nor passive immunization of pregnant rodents against EGF has caused major deleterious effects (except the delay in epidermal maturation events), as might be expected from the in vitro studies. This is in contrast to the effects of nerve growth factor antiserum in developing rodents. Also, to date, no pathological EGF deficiency disorder has been characterized. However, the EGF family of growth factors appears to be important in mammalian development and function, although the precise roles and significance are not yet clear. Members of the family may have a role in embryogenesis and fetal growth since receptors have been identified in fetal tissues. Available evidence suggests that TGF alpha subserves the growth factor family roles in fetal development. In the developing postnatal animal pro-EGF mRNA, immunoreactive EGF, immunoreactive TGF alpha, and EGF receptors are present in many tissues. EGF also is produced and secreted by the maternal mammary gland, and mammary derived EGF appears to be important in gut development in the neonatal rodent. There is now extensive data to indicate important hormone-EGF interactions. In the postnatal period, thyroid and steroid hormones including retinoic acid have been shown to modulate EGF and/or EGF receptors in several tissues. GH increases EGF binding in liver and increases urine EGF concentrations. Moreover, EGF stimulates secretion of several hypothalamic and pituitary hormones, increases placental production of hCG and human chorionic somatomammotropin, increases adrenal cortisol production, and inhibits testicular, ovarian, and thyroid hormone secretions. As summarized in this review EGF has been implicated in a number of developmental events including palate and skin differentiation, growth of hair follicles, eye opening and tooth eruption, lung maturation, gut and liver growth, and differentiation of neurons. These EGF actions probably are mediated via autocrine, paracrine, and endocrine routes. A role for salivary and urine EGF in the maintenance of adult stomal, gut, and urinary epithelial surface integrity seems likely, although not yet proven.(ABSTRACT TRUNCATED AT 400 WORDS)