Maspin (SERPINB5) was discovered as a mammary tumor suppressor that is expressed in normal mammary epithelium but lost in most breast cancer cell lines (1). While maspin is related to the serpin family of serine protease inhibitors, it may not function as a protease inhibitor (2). It plays an essential role in embryonic development through critical roles in cell adhesion (3). While the precise mechanism of maspin signaling is unclear (4), the tumor suppressing activity of maspin has been attributed to its ability to inhibit cell invasion/metastasis (5,6) and angiogenesis (7), while promoting apoptosis (8). Nuclear translocation of active IKKα has been shown to repress maspin transcription and promote prostate cancer metastasis (9).
