Issues

Tumor progression can be associated with Knudson-type loss of the normal alleles of certain ribosomal genes by cancer cells, making the continued expression of the mutant but antigenic ribosomal protein essential. Transfection of the genes for mutant (bottom left) or wild-type (bottom right) ribosomal protein L9 fused to the enhanced green fluorescent protein (EGFP) gene into cancer cells that have lost the normal allele leads to a cellular distribution of the fluorescent protein that is characteristic for a ribosomal protein (i.e., nucleoli are stained), while transfection of the unfused EGFP gene (top right) does not lead to specific localization. For comparison, untransfected cancer cells are shown in the top left panel. Introduction of the wild-type but not the mutant L9 fusion gene at comparable levels reverts the progressor phenotype of the cancer cells to that of a regressor phenotype in SCID mice. See related article in this issue by Beck-Engeser et al., pp. 285-299.