GLOBOTRIAOSYL CERAMIDE (GB(3)) EXPRESSION IN HUMAN TUMOR-CELLS - INTRACELLULAR TRAFFICKING DEFINES A NEW RETROGRADE TRANSPORT PATHWAY FROM THE CELL-SURFACE TO THE NUCLEUS, WHICH CORRELATES WITH SENSITIVITY TO VEROTOXIN

The verotoxin receptor globotriaosyl ceramide (Gb3) is overexpressed i n an ovarian tumour resistant to chemotherapy. An overlay of frozen tu mour sections shows extensive staining of the tumour cells with veroto xin B subunit. In addition, blood vessels within the tumour mass are s tained. The sensitivity of ovarian tumour cells in vitro to verotoxin can be modulated by culturing the cells in sodium butyrate to obtain a n approximatly 5000-fold increase in susceptibility. This increased su sceptibility is correlated with the intracellular targeting of verotox in as monitored by using FITC-VT B subunit, in that prior to sodium bu tyrate treatment the toxin is internalized to a juxtanuclear (likely) Golgi location whereas, following butyrate treatment the intracellular toxin is distributed around the nucleus, consistent with endoplasmic reticulum and nuclear envelope location. This perinuclear location is similar to that found for drug-resistant variants of ovarian tumour ce ll lines. These results suggest that intracellular targeting of veroto xin to the perinuclear area results in increased cytotoxicity. Potenti ally such targeting may also occur in other human tumours.