LOCALIZATION AND CHARACTERIZATION OF EPIDERMAL GROWTH-FACTOR RECEPTORS ON HUMAN TESTICULAR TISSUE BY BIOCHEMICAL AND IMMUNOHISTOCHEMICAL TECHNIQUES

In the present study attempts were made to characterize the epidermal growth factor (EGF) receptor on human testicular tissue. A radioligand exchange assay with 125I-labelled EGF was used to detect a high affinity, low capacity, single binding site in the 105,000 g particulate fraction of human testicular tissue. Binding was optimal at 32°C following a 40-min incubation with a mean (± S.D.) dissociation constant of 327 ± 59 pmol/l (d.f.9). The number of binding sites ranged from 0.07 to 0.21 pmol/mg protein. Competition studies with other peptide hormones including LH, FSH, prolactin, insulin-like growth factor-I, fibroblast growth factor and nerve growth factor have confirmed the specificity of EGF for its receptor. The receptor was also found to be heat-labile and sensitive to trypsinization. Cross-linking experiments using disuccinimidyl suberate revealed major binding species at the 125 kDa region and this is thought to represent a proteolysed form of the receptor. Immunohistochemical localization of the receptors demonstrated their presence in the interstitial tissue and not within the seminiferous tubules. The presence of specific EGF binding in the interstitial tissue suggests that EGF may play some role in testicular steroidogenesis.