The protein MIA (melanoma inhibitory activity) is highly expressed in malignant melanomas but not in melanocytes. Furthermore, expression of MIA correlates with tumor progression in vivo. Here, MIA-dependent changes of gene expression after long-term inhibition of MIA expression in the human melanoma cell line HMB2 were investigated. Primarily, we observed characteristic changes in cell morphology, and also found re-established cell-cell contacts in MIA-deficient cell clones grown in monolayer culture. Real-time reverse transcription-polymerase chain reaction (RT-PCR) showed a downregulation of N-cadherin expression and a reinduction of E-cadherin expression in the MIA-deficient cell clones. Further, both cancer cDNA array and protein arrays verified a marked downregulation of several other melanoma-associated genes (e.g. membrane-type 1 matrix metalloproteinase tissue-type plasminogen activator integrin b3, secreted protein acidic and rich in cysteins and fibronectin) in the MIA-deficient melanoma cells, confirmed by real-time RT-PCR and Western blotting. As all these molecules are associated with migration, the effect of MIA on migration of human primary melanocytes was analysed. In the presence of MIA, we observed enhanced migratory ability of melanocytic cells, induction of melanoma-associated genes as well as inhibition of apoptosis due to anoikis. These results suggest that expression of MIA promotes melanoma progression by inducing further melanoma-associated genes.

Here we present a comprehensive molecular mapping of virus-induced autoimmune B cell responses obtained by serological identification of antigens by recombinant expression cloning analysis. Immunoscreening of cDNA expression libraries of various organs (lung, liver, and spleen) using sera from mice infected with cytopathic (vaccinia virus [VV]) or noncytopathic (lymphocytic choriomeningitis virus [LCMV]) viruses revealed a broad specificity of the elicited autoantibody response. Interestingly, the majority of the identified autoantigens have been previously described as autoantigens in humans. We found that induction of virus-induced autoantibodies of the immunoglobulin G class largely depends on the CD40–CD40L-mediated interaction between T and B cells. Furthermore, antibody titers against a number of autoantigens were comparable to the concomitantly induced antiviral antibody response. Comparison of serum reactivity against a selected panel of autoantigens after infection with VV, LCMV, or vesicular stomatitis virus showed that the different virus infections triggered distinct autoantibody responses, suggesting that virus infections may leave specific “autoantibody fingerprints” in the infected host.

The secreted protein melanoma inhibitory activity (MIA) is highly expressed in malignant melanoma but not in melanocytes and is associated with tumor progression in vivo. Here, we further investigated the functional role of MIA by inhibiting MIA expression of the human melanoma cell line HMB2 via stable antisense MIA cDNA transfection, and subsequent analysis of the cell clones. MIA-deficient cell clones showed several changes in cell morphology and growth pattern. In monolayer and three-dimensional culture enhanced cell-cell contacts were formed. Furthermore, a re-induction of pigment synthesis in comparison with the amelanotic parental cell line HMB2 was observed. Molecular analyses revealed a re-expression of tyrosinase-related protein 1 (Trp-1) and tyrosinase in the MIA-deficient cell clones necessary for melanin synthesis. In accordance, re-expression of MIA in the MIA-deficient melanoma cell clones resulted in downregulation of Trp-1. To identify the molecular mechanisms of MIA regulating pigmentation, MITF and PAX3, two positive regulators of Trp-1 and tyrosinase transcription, and PIAS3, a negative regulator of MITF activity, were analyzed. Only in MIA-deficient cells, expression of PAX3 mRNA and MITF protein was found. In contrast, strong expression of PIAS3 was detected in HMB2 but not in the MIA-deficient cells. To our knowledge this is the first report demonstrating a correlation between MIA expression and pigmentation and morphology of melanocytic cells.