Loss of intracisternal A-type retroviral particles in BL6 melanoma cells transfected with MHC class I genes

1 Pittsburgh Cancer Institute and Department of Pathology, University of Pittsburgh, Pittsburgh, PA 15213, USA 2 Division of Viral Products, Food and Drug Administration, Bethesda, MD 20892, USA 3,4 Laboratory of Cell Biology and Laboratory of Biochemistry, National Cancer Institute, NIH, Bethesda, MD 20892, USA Electron microscopy of B16 melanoma and its sublines revealed that these cells produce numerous intracisternal A-type retroviral particles (IAPs). To identify and sequence the melanoma-associated IAPs of C57BL/6 mice, a cDNA library was constructed from IAP-producing BL6-8 cell RNA and screened using MIA 14 IAP DNA as a probe. A 6.8 kb mRNA was identified that represents the full-length message for a new subfamily of IAP, termed MeIAP. The melanoma-derived IAP cDNA showed high similarity to MIA14 with major differences in the LTR. A nine base motif of the R region showed that this IAP differs from other previously sequenced IAPs. Analysis of the individual clones from BL6 melanoma revealed that IAPs were produced only in the clones that failed to express H-2K b molecules. No IAPs were found in the melanoma clones that expressed endogenous H-2K b . To analyse further the association between MHC class I genes and IAP production, the H-2K b -negative clones of BL6 melanoma were transfected with various H-2 genes. Transfection of the H-2K b or H-2K d , but not H-2D d or H-2L d genes resulted in the elimination of IAPs. Northern blot analysis revealed that loss of IAPs in the H-2K gene-transfected BL6 melanoma cells was due to lack of IAP transcripts. Elimination of IAPs in the H-2K b -positive BL6 melanoma cells was also accompanied by alterations in expression of various cellular genes and changes of their phenotypic properties. Received 11 April 1996; accepted 22 July 1996.