The adhesion of tumour cells to the hyaluronan (HA) pericellular coat of mesothelial cells is an important step in the peritoneal spread of ovarian cancer. Previously, we have shown that the cell surface molecule CD44 is involved in this process. Paradoxically, the degree of adhesion does not appear to be related to the amount of CD44 expressed. In order to explain this observation we have examined the in vitro adhesion to HA of four high CD44-expressing ovarian cancer lines in relation to their CD44 spliced variant content and the CD44 glycosylation. Adhesion was measured in multiwell plates coated with different concentrations of HA in order to determine both the avidity and the maximum adhesion. Two lines had high adhesion and two lines had low adhesion. The avidity for HA was different for each line, but in all cases this could be totally blocked by treatment with an anti-CD44 antibody. The standard form of CD44 was the major species detected by RT/PCR in all lines and spliced variants were present in low amounts. Neuraminidase treatment increased the adhesion of the ‘low-adhesion’ lines at all HA coating concentrations; but only substantially increased the adhesion of the ‘high-adhesion’ lines at the lower HA coating concentrations. Tunicamycin treatment decreased the adhesion of the ‘high-adhesion lines’ at all HA coating concentrations and only substantially decreased the adhesion of one of the ‘low-adhesion’ lines when the plates were coated with a low concentration of HA. The adhesion of the remaining ‘low-adhesion’ line was slightly increased after tunicamycin treatment. It is concluded that glycosylation and not spliced variant content of CD44 affects the adhesive properties of ovarian tumour cells. This conclusion may have important consequences for developing new therapies in ovarian cancer
