Identification of common polymorphisms in the coding sequence of the human MSH receptor (MCIR) with possible biological effects.

The extension locus has been identified in many mammalian species as a gene that determines the relative amounts of eumelanin and phaeomelanin pigments in hair and skin. In at least three species, this locus has been demonstrated to encode the melanocyte-stimulating hormone receptor (MC1-R), and functionally variant alleles have been demonstrated to cause a broad range of pigmentation phenotypes. To test for MC1-R allelic variation in man, genomic DNA was extracted from skin samples collected from patients with different skin types (I-VI), and eye and hair color. A PCR-based approach was used to amplify the full-length coding sequence of the MC1-R and the resulting products were sequenced. Two polymorphic alleles were identified with single point mutations in the coding sequence: a valine-to-methionine substitution at position 92 (V92M), and an aspartic acid-to-glutamic acid substitution at position 84 (D84E). RFLP analysis demonstrated the presence of the V92M allele in 4 out of 60 (6.6%) of individuals examined, predominantly those with blue eyes and blond hair. This polymorphism was found in both heterozygous and homozygous states in individuals with type I skin. The D84E allele was found in one individual with skin type I; this person also has the V92 M allele and thus is a compound heterozygote.

Melanoma-derived interleukin 6 inhibits in vivo melanoma growth.

Malignant melanomas are capable of producing a wide range of cytokines with multiple biologic functions, including interleukin 6 (IL-6). We have observed an inverse relationship between IL-6 production of three B16-derived murine melanoma cell lines (NP133, HFH18, and HFH(M)) and the tumorigenicity of these melanoma cells in syngeneic mice. To further test the effect of IL-6 on melanoma growth, a non-IL-6-producing murine B16-derived melanoma cell line (HFH18) was transfected with a murine IL-6 expression vector, resulting in stable transfectants (HFH18/IL-6(+)) that expressed significant amounts of IL-6 mRNA and secreted high levels of bioactive IL-6. Syngeneic C57BL/6 mice inoculated subcutaneously with HFH18/IL-6(+) cells developed tumors that reached a final mean diameter of less than half the size of tumors that developed in mice inoculated with either HFH18 parental or HFH18 cells transfected with the IL-6 cDNA in the non-coding 3'-5' orientation (HFH18/IL-6(-) cells). In addition, mice bearing IL-6-producing HFH18/IL-6(+) tumors survived twice as long as mice bearing HFH18 parental or HFH18/IL-6(-) tumors. The specificity of melanoma growth inhibition by IL-6 was confirmed by the reversal of the slow-growing phenotype of HFH18/IL-6(+) cells by local peritumoral administration of neutralizing alpha-murine IL-6 antibody. IL-6-producing melanoma cells exerted a growth-inhibitory effect on distant parental tumors in a dose-dependent manner. The growth of HFH18/IL-6(+) melanomas was also decreased in nude mice, suggesting that melanoma-derived IL-6 may mediate this anti-tumor effect independently of a normal host B- and T-cell immune response. Thus, melanoma-derived IL-6 exerts a significant inhibitory effect on cutaneous melanoma growth and progression. These results indicate that melanoma cytokines may have a profound effect on tumor pathogenesis.