Phenotypic changes and loss of melanoma-specific endogenous C-type retroviruses in BL6 melanoma cells transfected with the H-2K(b) gene

The murine B16 melanoma and its sublines are low or totally deficient in expression of the H-2K(b) class I major histocompatibility complex (MHC) gene. In clones derived from the B16F10BL6 subline, expression of the transfected or endogenous H-2K(b) gene resulted in alterations of various phenotypic properties of these melanoma cells, among which was the loss of melanoma-associated antigen (MAA) expression. Because our previous immunoelectron microscopy studies showed that MAA was associated with a C-type ecotropic retrovirus specific for melanomas of C57BL/6 origin, we examined the effect of class I H-2K(b) as well as class II H-21A(k) gene expression on retrovirus production in subclones of BL6 melanoma cells, Here we have shown that expression of the transfected or endogenous H-2K(b) gene resulted in the loss of production of budding, MAA-specific, C-type retrovirus particles. Northern blot analysis demonstrated expression of ecotropic retroviral mRNAs in both particle-producing and non-producing BL6 melanoma clones. Southern blot analysis of high-molecular-weight cellular DNAs using an ecotropic env-specific DNA probe indicated that the parental BL6-8 melanoma cells contained the C57BL/6 endogenous ecotropic MuLV (Emv-2) and at least three additional, novel ecotropic retroviral DNAs. Restriction enzyme analysis of the proviral DNA suggests that the loss of retrovirus production in the H-2K(b)-expressing melanoma clones is the result of multiple rearrangements in the novel proviral DNAs. Thus, phenotypic changes observed in the H-2K(b) gene-transfected BL6 melanoma cells were associated with loss of endogenous melanoma-specific ecotropic retrovirus production.