Expression of cysteine peptidase cathepsin L and its inhibitors stefins A and B in relation to tumorigenicity of breast cancer cell lines.

The in vitro invasiveness of human breast cancer cell lines was compared with their reported tumorigenicity in vivo, increasing from MCF7, MDA-MB468, MDA-MB231 to MDA-MB435 cells. The invasiveness roughly corresponded to the tumorigenicity of the cell lines. The levels of cathepsin L mRNA and protein correlated with the invasiveness of the cells. Stefin A protein decreased with the invasiveness and the reported tumorigenicity, whereas stefin B protein was significantly lower in all MDA-MB lines compared with the least invasive and tumorigenic MCF7 line. Our results suggest that the imbalance between cathepsin L and the stefins contributes to the development of a malignant cell phenotype.