Expression of insulin-like growth factor I (IGF-I) in nevi and melanomas

Expression of IGF-I mRNA and protein was evaluated in pigmented lesions by in situ hybridization and immunohistochemistry. An IGF-I cDNA clone (phigf1) was subcloned into pBluescript KS II-. Both sense and antisense 35S riboprobes were prepared and used for in situ hybridization on formalin-fixed, paraffin-embedded specimens. Control hybridizations with a beta-actin probe were also performed. Grains were counted in 787-microns2 melanocytic areas of sections hybridized with the antisense IGF-I probe. Seven common nevi contained a mean of 218 grains; nine dysplastic nevi, a mean of 463 grains; eight early primary melanomas, a mean of 402 grains; five advanced primary melanomas, a mean of 217 grains; and nine metastatic melanomas, a mean of 194 grains. The differences between common and dysplastic nevus, common nevus and early melanoma, early and advanced primary melanoma, and early primary melanoma and metastatic melanoma were statistically significant. Keratinocytes also expressed abundant IGF-I message. IGF-I protein was demonstrable by immunohistochemistry in melanocytes and keratinocytes. These results suggest that progression-associated variation occurs in the net expression of IGF-I mRNA in melanocytic tumors.