title: Mitofusin 1 degradation is induced by a disruptor of mitochondrial calcium homeostasis, CGP37157: a role in apoptosis in prostate cancer cells.
abstract: 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.
authors.affiliation: Charlie Norwood VA Medical Center, Augusta, GA, USA.
authors.forename: Vivek
authors.initials: V
authors.lastname: Choudhary
authors.affiliation: Charlie Norwood VA Medical Center, Augusta, GA, USA.
authors.forename: Ismail
authors.initials: I
authors.lastname: Kaddour-Djebbar
authors.affiliation: Department of Physiology, Medical College of Georgia at Georgia Regents University, Augusta, GA, USA.
authors.forename: Rabei
authors.initials: R
authors.lastname: Alaisami
authors.affiliation: Charlie Norwood VA Medical Center, Augusta, GA, USA.
authors.forename: M Vijay
authors.initials: MV
authors.lastname: Kumar
authors.affiliation: Charlie Norwood VA Medical Center, Augusta, GA, USA.
authors.forename: Wendy B
authors.initials: WB
authors.lastname: Bollag
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D002998:Clonazepam / Q000031:analogs & derivatives* / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008297:Male; D008928:Mitochondria / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000378:metabolism; D011471:Prostatic Neoplasms / Q000378:metabolism / Q000473:pathology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013841:Thiazepines / Q000494:pharmacology*; D054875:Ubiquitination
chemical_list: D033681:Mitochondrial Membrane Transport Proteins; D024101:Mitochondrial Proteins; D013841:Thiazepines; D002998:Clonazepam; C079032:CGP 37157; D003513:Cycloheximide; D046988:Proteasome Endopeptidase Complex; D020558:GTP Phosphohydrolases; C470017:Mfn1 protein, human; D002118:Calcium