Interaction between the Adhesion Receptor, CD44, and the Oncogene Product, p185 HER2 , Promotes Human Ovarian Tumor Cell Activation*

In this study we have examined the interaction between CD44s (the standard form) and the p185 HER2 proto-oncogene in the ovarian carcinoma cell line. Surface biotinylation followed by wheat germ agglutinin column chromatography and anti-CD44-mediated immunoprecipitation indicate that both CD44s and p185 HER2 are expressed on the cell surface and most importantly, that these two molecules are physically linked to each other via interchain disulfide bonds. We have also determined that hyaluronic acid stimulates CD44s-associated p185 HER2 tyrosine kinase activity, leading to an increase in the ovarian carcinoma cell growth. After transfection of the ovarian carcinoma cell line with the adenovirus 5 E1A gene, which is known to repress p185 HER2 expression, we observed that both surface CD44s expression and CD44s-mediated cell adhesion to hyaluronic acid are significantly reduced in the transfectant cells compared with the control cells. These data suggest that down-regulation of p185 HER2 blocks CD44s expression and subsequent adhesion function. Our findings also indicate that the CD44s-p185 HER2 interaction is both functionally coupled and biosynthetically regulated. We believe that direct “cross-talk” between these two surface molecules (i.e. CD44s and the p185 HER2 ) may be one of the most important signaling events in human ovarian carcinoma development.