Researchers at the Karlsruhe Institute of Technology (Toxicology and Genetics, Germany), the Experimental Urology Division of the Innsbruck Medical University (Austria) and the Institute of Biological Technology at the University of Tampere (Finalnd), have elucidated the previously unknown association of overexpressed Bag5 in prostate cancer.  Furthermore, they have confirmed the role of Bag5 in ER-stress induced apoptosis and discovered its interaction with GRP78/BiP.

The Bag family of proteins has been the subject of many studies this past decade.  Bag5 is unique in the family because of its 5 Bag domains found in its sequence.  Other Bag proteins have been associated with tumour growth and survival.  Although the specific role of Bag5 and associations were previously unknown, this remarkable study has shed light on this elusive member of the family.

The researchers examined prostate cancer patients to determine the levels of Bag5 mRNA and protein expression via real-time PCR and immunoblot analyses, as well as immunohistological studies to determine Bag5 expression in tissue arrays.  They showed that Bag5 is found in greater abundance in prostatic cancer cells than in benign samples.  ER-stress also affected Bag5, relocating it to the ER itself.  Bag5 was also found to potentiate the ATPase activity of GRP78/BiP.  Finally, it was shown that cells expressing high amounts Bag5 were less sensitive to apoptosis: indicating that Bag5 overexpression is associated with pro-tumour activity.

The original research paper was published in: BMC Cancer, March 2013

Bcl-2 associated athanogene 5 (Bag5) is overexpressed in prostate cancer and inhibits ER-stress induced apoptosis.