Epidermal growth factor prohormone is secreted in human urine

Examination of adult human urine by immunoblot analysis with antiserum specific to human recombinant 6-kDa epidermal growth factor (EGF) reveals the presence of an immunoreactive protein with a molecular mass of 165 kDa. This protein is consistently found in the morning (first) but not in day urine of adult males and females. Day urine contains variable proportions of four other high-molecular-weight EGFs with approximate molecular masses of 97, 66, 50, and 42 kDa. The 165-kDa EGF immunoreactive protein reacts with mouse amino-terminal EGF prohormone (proEGF) antiserum and comigrates with mouse urinary proEGF, suggesting that the protein is the human EGF prohormone. The 165-kDa human proEGF exhibits strong binding affinity to concanavalin A, indicating that it is glycosylated. Immunoblotting of urine in infants and children of various age groups demonstrates the presence of proEGF in all age groups, but its concentration is highest in children 2-4 yr of age. These findings, taken together with secretion of proEGF of similar molecular mass in mouse and rat urine, suggest that renal proEGF secretion is an evolutionarily conserved phenomenon and may have an important function or functions distal to the site of its synthesis.