IN-VIVO EXPRESSION OF THE INSULIN-LIKE GROWTH-FACTOR-I (IGF-I) RECEPTOR IN CONGENITAL PIGMENTED NEVI

Growth of normal melanocytes, nevus cells and primary melanoma cells i s enhanced by insulin/insulin-like growth factor-I (IGF-I) in vitro. I t has been shown that a melanoma cell line possesses the IGF-I recepto r which plays a role in activation of the chemotactic response. Little is known about the in vivo expression of the IGF-I receptor and its r ole in melanocytic lesions. In an immunohistochemical study, we invest igated the expression of IGF-I receptor in frozen sections of congenit al pigmented nevi from 10 patients (ages 8 months to 4 yrs) using the monoclonal antibody alpha IR(3), which specifically recognizes the ext racellular alpha subunit of the IGF-I receptor. The proliferative acti vity of the nevus cells was examined by staining with Ki67 monoclonal antibody (reactive with all actively cycling cells). IGF-I receptor wa s found to be widely expressed by the cell surface of the nevus cells. Membrane staining was occasionally stronger in the superficial portio n of the congenital pigmented nevi. In contrast, Ki67-positive cells w ere only sparsely scattered throughout the nevi with some tendency to localization to the superficial portion. This study indicates that in vivo the IGF-I receptor is widely expressed by congenital pigmented ne vus cells. As opposed to keratinocytes, in which IGF-I receptor expres sion defines the proliferation pool of the normal and disordered epide rmis, the IGF-I receptor is expressed by all nevus cells, irrespective of their proliferative status. Further studies are needed to assess w hether the IGF-I receptor expression can serve as a marker for increas ed risk for development of malignancy in various types of benign melan ocytic lesions. (C) Munksgaard 1996.