Overexpression of laminin-5 γ2 chain in clear cell carcinoma of the ovary

One of the characteristic microscopic features of ovarian clear cell carcinoma (CCC) is the densely hyaline basement membrane material expanding the stroma. The biological significance of this material, however, has remained unclear. Recent studies have shown that laminin-5 (LN-5), a major component of the epithelial basement membrane, plays a more active role in cell migration or tumor invasion. In the present study, 20 CCCs and 5 borderline clear cell tumors were examined for LN-5 expression immunohistochemically, using an antibody against LN-5 γ2 chain. All of the 20 CCCs showed a focal or diffuse immunoreactivity with the LN-5 γ2 chain in the tumor stroma; whereas, borderline clear cell tumors rarely showed a stromal immunoreactivity. Cytoplasmic accumulation of the LN-5 γ2 chain was far less common than stromal accumulation, suggesting an accelerated secretion in CCC. In vitro, CCC cell lines showed a significant increase in cell migration over excessive LN-5, and the migration was blocked by an antibody against integrin α3. These results indicate that an interaction between CCC cells and extracellularly accumulated LN-5 is responsible for cell migration and the subsequent stromal invasion of CCC.