title: Proteomic identification of E6AP as a molecular target of tamoxifen in MCF7 cells.
abstract: Tamoxifen (Tam) is most widely used selective estrogen receptor modulator (SERM) for treatment of hormone-responsive breast cancer. Despite being regularly used in clinical therapy for breast cancer since 1971, the mechanism of Tam action remains largely unclear. In order to gain insights into Tam-mediated antibreast cancer actions, we applied 2DE and MS based proteomics approach to identify target proteins of Tam. We identified E6-associated protein, i.e. E6AP (UBE3A) among others to be regulated by Tam that otherwise is upregulated in breast tumors. We confirmed our 2DE finding by immunoblotting and further show that Tam leads to inhibition of E6AP expression presumably by promoting its autoubiquitination, which is coupled with nuclear export and subsequent proteasome-mediated degradation. Furthermore, we show that Tam- and siE6AP-mediated inhibition of E6AP leads to enhanced G0-G1 growth arrest and apoptosis, which is also evident from significant upregulation of cytochrome-c, Bax, p21, and PARP cleavage. Taken together, our data suggest that, Tam-targeted E6AP inhibition is in fact required for Tam-mediated antibreast cancer actions. Thus, E6AP may be a therapeutic target in breast cancer.
authors.affiliation: DTDD Division, CSIR-Central Drug Research Institute, Lucknow, Uttar Pradesh, India.
authors.forename: Savita
authors.initials: S
authors.lastname: Lochab
authors.forename: Pooja
authors.initials: P
authors.lastname: Pal
authors.forename: Jitendra K
authors.initials: JK
authors.lastname: Kanaujiya
authors.forename: Shashi B
authors.initials: SB
authors.lastname: Tripathi
authors.forename: Isha
authors.initials: I
authors.lastname: Kapoor
authors.forename: Madan L B
authors.initials: ML
authors.lastname: Bhatt
authors.forename: Sabyasachi
authors.initials: S
authors.lastname: Sanyal
authors.forename: Gerhard
authors.initials: G
authors.lastname: Behre
authors.forename: Arun K
authors.initials: AK
authors.lastname: Trivedi
mesh_terms: D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D059447:Cell Cycle Checkpoints / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D003593:Cytoplasm / Q000378:metabolism; D015180:Electrophoresis, Gel, Two-Dimensional; D047628:Estrogen Receptor alpha / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D057809:HEK293 Cells; D006801:Humans; D013058:Mass Spectrometry; D058990:Molecular Targeted Therapy / Q000379:methods; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D011506:Proteins / Q000737:chemistry / Q000145:classification / Q000378:metabolism; D020543:Proteome / Q000032:analysis / Q000187:drug effects / Q000378:metabolism; D013629:Tamoxifen / Q000494:pharmacology*; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*
chemical_list: D018931:Antineoplastic Agents, Hormonal; D047628:Estrogen Receptor alpha; D011506:Proteins; D020543:Proteome; D025801:Ubiquitin; D013629:Tamoxifen; C471639:UBE3A protein, human; D044767:Ubiquitin-Protein Ligases; D046988:Proteasome Endopeptidase Complex