Mitochondria constantly divide (mitochondrial fission) and fuse (mitochondrial fusion) in a normal cell. Disturbances in the balance between these two physiological processes may lead to cell dysfunction or to cell death. Induction of cell death is the prime goal of
prostate cancer chemotherapy. Our previous study demonstrated that
androgens increase the expression of a
mitochondrial protein involved in fission and facilitate an apoptotic response to
CGP37157 (CGP), an inhibitor of mitochondrial
calcium efflux, in
prostate cancer cells. However, the regulation and role of mitochondrial fusion
proteins in the death of these cells have not been examined. Therefore, our objective was to investigate the effect of CGP on a key mitochondrial fusion
protein, mitofusin 1 (Mfn1), and the role of Mfn1 in
prostate cancer cell apoptosis. We used various
prostate cancer cell lines and western blot analysis, qRT-PCR,
siRNA, M30 apoptosis assay and immunoprecipitation techniques to determine mechanisms regulating Mfn1. Treatment of
prostate cancer cells with CGP resulted in selective degradation of Mfn1. Mfn1 ubiquitination was detected following immunoprecipitation of overexpressed Myc-tagged Mfn1
protein from CGP-treated cells, and treatment with the proteasomal inhibitor
lactacystin, as well as
siRNA-mediated knockdown of the
E3 ubiquitin ligase March5, protected Mfn1 from CGP-induced degradation. These data indicate the involvement of the
ubiquitin-
proteasome pathway in CGP-induced degradation of Mfn1. We also demonstrated that downregulation of Mfn1 by
siRNA enhanced the apoptotic response of LNCaP cells to CGP, suggesting a likely pro-survival role for Mfn1 in these cells. Our results suggest that manipulation of mitofusins may provide a novel therapeutic advantage in treating
prostate cancer.