Human procathepsin B interacts with the annexin II tetramer on the surfaceof tumor cells

To study potential roles of plasma membrane-associated extracellular cathep sin B in tumor cell invasion and metastasis, we used the yeast two-hybrid s ystem to screen for proteins that interact with human procathepsin B. The a nnexin II light chain (p11), one of the two subunits of the annexin II tetr amer, was one of the proteins identified. We have confirmed that recombinan t human procathepsin B interacts with pll as well as with the annexin II te tramer in vitro. Furthermore, procathepsin B could interact with the annexi n II tetramer in vivo as demonstrated by coimmunoprecipitation. Cathepsin B and the annexin II tetramer were shown by immunofluorescent staining to co localize on the surface of human breast carcinoma and glioma cells. Taken t ogether, our results indicate that the annexin II tetramer can serve as a b inding protein for procathepsin B on the surface of tumor cells, an interac tion that may facilitate tumor invasion and metastasis.