BIRC6 may be a suitable target for inhibition of autophagy-mediated cell survival and for treatment resistance in prostate cancer cells. Targeting autophagy has already been shown to sensitize a variety of cancers to treatment, including prostate cancer. Treatment of prostate cancer cells deficient in argininosuccinate synthetase with siRNAs targeting Beclin-1 or chloroquine, has been BAY 73-4506 reported to inhibit autophagy and increase the sensitivity of such cells to treatment with the anti-cancer agent ADI-PEG20, a pegylated arginine deiminase. In view of the above, it is proposed that targeting BIRC6 in prostate cancer can be used to inhibit autophagy, and thus, autophagy-mediated treatment resistance. This strategy represents a novel approach to sensitizing prostate cancer cells to therapy. However, further work is needed to determine the effectiveness of targeting BIRC6 as a strategy to control autophagy-mediated treatment resistance. The finding that treatment of LNCaP cells with doxorubicin results in a dramatic loss of BIRC6 expression, is consistent with a previous report demonstrating that apoptosis induced by topoisomerase inhibitors etoposide and camptothecin was associated with degradation of BIRC6 protein. The authors concluded that degradation of BIRC6 appears to be a general event during initiation of apoptosis. In the present study we further demonstrated that the doxorubicin-induced BIRC6 decline precedes PARP cleavage, suggesting that BIRC6 may play a causative role in apoptosis induction upon doxorubicin treatment. In addition, our finding that specific siRNAinduced reduction of BIRC6 protein expression in LNCaP cells leads to apoptosis, as indicated by marker expression, raises the possibility that the apoptotic effect of doxorubicin and perhaps of the topoisomerase inhibitors, is based, at least in part, on a reduction of BIRC6 protein expression. This suggests a novel mechanism by which doxorubicin may induce apoptosis by triggering loss of BIRC6. The increase in BIRC6 expression in Gleason 6�C8 clinical prostate cancers, including castration-resistant cancers, suggests an important role for this protein in the development and progression of the disease. In view of the prosurvival function of BIRC6 in prostate cancer cells and in other systems, elevations in the expression of BIRC6 are expected to provide a cytoprotective advantage to prostate cancer cells and promote prostate cancer development and progression. The anti-apoptotic role of BIRC6 could likely be involved in the development of castration-resistant prostate cancer and underlie therapy resistance in this advanced form of the disease. While the large majority of prostate cancer tissues exhibited BIRC6 protein elevations, not all stages of the disease expressed 
elevated levels of the protein. The expression of BIRC6 over the course of prostate cancer progression reached peak levels in Gleason score 7 cancers but had levels in Gleason score 9�C10 prostate cancers that were similar to those of benign tissues. Our finding is consistent with an earlier study focusing on IAP expressions in various stages of prostate cancer tissues, which demonstrated that increased expression of IAP. While BIRC6 expression may not be required in advanced stage prostate cancer, the resurge of BIRC6 in CRPC may LY2109761 suggest that cellular stress, e.g. castration, may trigger the overexpression of cytoprotective BIRC6.