title: Hrk mediates 2-methoxyestradiol-induced mitochondrial apoptotic signaling in prostate cancer cells.
abstract: Prostate cancer is one of the most prevalent cancers in males and ranks as the second most common cause of cancer-related deaths. 2-methoxyestradiol (2-ME), an endogenous estrogen metabolite, is a promising anticancer agent for various types of cancers. Although 2-ME has been shown to activate c-Jun-NH2-kinase (JNK) and mitochondrial-dependent apoptotic signaling pathways, the underlying mechanisms, including downstream effectors, remain unclear. Here, we report that the human Bcl-2 homology 3 (BH3)-only protein harakiri (Hrk) is a critical effector of 2-ME-induced JNK/mitochondria-dependent apoptosis in prostate cancer cells. Hrk mRNA and protein are preferentially upregulated by 2-ME, and Hrk induction is dependent on the JNK activation of c-Jun. Hrk knockdown prevents 2-ME-mediated apoptosis by attenuating the decrease in mitochondrial membrane potential, subsequent cytochrome c (cyt c) release, and caspase activation. Involvement of the proapoptotic protein Bak in this process suggested the possible interaction between Hrk and Bak. Thus, Hrk activation by 2-ME or its overexpression displaced Bak from the complex with antiapoptotic protein Bcl-xL, whereas deletion of the Hrk BH3 domain abolished its interaction with Bcl-xL, reducing the proapoptotic function of Hrk. Finally, Hrk is also involved in the 2-ME-mediated reduction of X-linked inhibitor of apoptosis through Bak activation in prostate cancer cells. Together, our findings suggest that induction of the BH3-only protein Hrk is a critical step in 2-ME activation of the JNK-induced apoptotic pathway, targeting mitochondria by liberating proapoptotic protein Bak.
authors.affiliation: Department of Urology, San Francisco Veterans Affairs Medical Center and University of California San Francisco, San Francisco, CA 94121, USA.
authors.forename: Inik
authors.initials: I
authors.lastname: Chang
authors.forename: Shahana
authors.initials: S
authors.lastname: Majid
authors.forename: Sharanjot
authors.initials: S
authors.lastname: Saini
authors.forename: Mohd S
authors.initials: MS
authors.lastname: Zaman
authors.forename: Soichiro
authors.initials: S
authors.lastname: Yamamura
authors.forename: Takeshi
authors.initials: T
authors.lastname: Chiyomaru
authors.forename: Varahram
authors.initials: V
authors.lastname: Shahryari
authors.forename: Shinichiro
authors.initials: S
authors.lastname: Fukuhara
authors.forename: Guoren
authors.initials: G
authors.lastname: Deng
authors.forename: Rajvir
authors.initials: R
authors.lastname: Dahiya
authors.forename: Yuichiro
authors.initials: Y
authors.lastname: Tanaka
mesh_terms: D000077584:2-Methoxyestradiol; D017209:Apoptosis / Q000187:drug effects / Q000235:genetics*; D051017:Apoptosis Regulatory Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D045744:Cell Line, Tumor; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004967:Estrogens / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D055785:Gene Knockdown Techniques; D006801:Humans; D048670:MAP Kinase Kinase 4 / Q000378:metabolism; D008297:Male; D008928:Mitochondria / Q000378:metabolism / Q000473:pathology; D011471:Prostatic Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D015398:Signal Transduction / Q000187:drug effects; D050998:bcl-2 Homologous Antagonist-Killer Protein / Q000096:biosynthesis / Q000378:metabolism*
chemical_list: D051017:Apoptosis Regulatory Proteins; C494772:BAK1 protein, human; D004967:Estrogens; C484586:HRK protein, human; D050998:bcl-2 Homologous Antagonist-Killer Protein; D004958:Estradiol; D000077584:2-Methoxyestradiol; D048670:MAP Kinase Kinase 4