No abstract

Our previous studies showed that mouse β4-galactosyltransferase 5 (β4GalT5) is a lactosylceramide (Lac-Cer) synthase, and that its gene expression increases by 2- to 3-fold upon malignant transformation of cells. In the present study, we examined whether or not the tumorigenic and metastatic potentials of B16-F10 mouse melanoma cells can be suppressed by reducing the expression of the β4GalT5 gene. We isolated a stable clone named E5 whose β4GalT5 gene expression level was reduced to 35% that of a control clone C1 by transfection of its antisense cDNA. Thin-layer chromatography analysis of glycosphingolipids showed that the amounts of Lac-Cer and ganglioside GM3 are significantly less in clone E5 than in clone C1. Clone C1 and E5 cells were each transplanted subcutaneously or injected intravenously into C57BL/6 mice, and the sizes of tumors and numbers of colonies formed in the lungs were determined. The average tumor size and average number of colonies formed with clone E5 were decreased to 44 and 49%, respectively, of those formed with clone C1. Furthermore, the numbers and sizes of colonies formed in the soft agarose gels, and the volumes of tumors formed in athymic mice with fibroblasts from wild type, heterozygous and homozygous β4GalT5-knockout mouse embryos upon transformation with the polyoma virus oncogene correlated with the β4GalT5 gene dosage. These results strongly indicate that the amounts of Lac-Cer synthesized by β4GalT5 correlate with the tumorigenic potentials of malignantly transformed cells.

Altered N-glycosylation of membrane proteins is associated with malignant transformation of cells. We found that the expression of the β4-galactosyltransferase 2 (β4GalT2) gene is decreased markedly during the transformation. Here, we examined whether the tumor growth activity of B16-F10 mouse melanoma cells can be reduced by the enhanced expression of the β4GalT2 gene. We isolated a clone, B16-β4GalT2, showing its β4GalT2 transcript 2.5 times higher than a control clone, B16-mock, by transducing its cDNA, and transplanted them subcutaneously into C57BL/6 mice to examine their tumor growth activity. The results showed that the average size of tumors formed with B16-mock cells is 13.1±0.76 mm, whereas that of tumors formed with B16-β4GalT2 cells is 5.1±1.13 mm (P<0.01) 2 weeks after transplantation. Immunohistochemical analyses showed that the apoptosis and the suppression of angiogenesis are induced in the tumors upon transduction of the β4GalT2 gene. To pursue a clinical usefulness of the β4GalT2 gene for suppressing human tumor growth, we injected adenoviruses carrying the human β4GalT2 cDNA into HuH-7 human hepatocellular carcinomas developed in severe combined immunodeficient mice, and observed marked growth retardation of the tumors. The enhancement of the β4GalT2 gene expression in tumors is one of the promising approaches to suppress human tumor growth.