BAG‐1, An Anti‐Apoptotic Tumour Marker

BAG‐1 is a multifunctional and anti‐apoptotic or anti‐cell death protein that interacts with a variety of cellular proteins and affects their functions. On the cell surface, it binds to the cytosolic domain of the growth factor receptors and enhances the protection from cell death triggered by growth factor receptors. In the cytosol, it binds to Bcl‐2 and heat shock protein, and modulates their functions. In the nucleus, it binds to a variety of nuclear hormone receptors and inhibits hormone‐induced apoptosis. BAG‐1 is widely overexpressed in a variety of tumour cell lines and cancer tissues. In addition, differential expression of BAG‐1 isoforms has been observed. Preclinical studies indicate that overexpression of BAG‐1, especially its nuclear and cytoplasmic isoforms, may be useful as a prognostic and/or predictive biomarker. Pilot clinical studies have demonstrated that overexpression of nuclear BAG‐1 may be associated with a shorter survival in breast and laryngeal carcinomas. Conversely, overexpression of cytoplasmic BAG‐1 may be associated with a better clinical outcome in early stage breast cancer and in non‐small cell lung cancer. Further large‐scale clinical studies are warranted to establish the role of BAG‐1 as a novel prognostic and/or predictive biomarker in the clinical management of these common malignancies.