title: Bim, a proapoptotic protein, up-regulated via transcription factor E2F1-dependent mechanism, functions as a prosurvival molecule in cancer.
abstract: Proapoptotic Bcl-2 homology 3-only protein Bim plays an important role in Bax/Bak-mediated cytochrome c release and apoptosis. Here, we provide evidence for a novel prosurvival function of Bim in cancer cells. Bim was constitutively overexpressed in multiple prostate and breast cancer cells as well as in primary tumor cells. Quantitative real time PCR analysis showed that Bim was transcriptionally up-regulated. We have identified eight endogenous E2F1-binding sites on the Bim promoter using in silico analysis. Luciferase assay demonstrated that Bim expression was E2F1-dependent as mutation of the E2F1-binding sites on the Bim promoter inhibited luciferase activities. In support, E2F1 silencing led to the loss of Bim expression in cancer cells. Bim primarily localized to mitochondrial and cytoskeleton-associated fractions. Bim silencing or microinjection of anti-Bim antibodies into the cell cytoplasm resulted in cell rounding, detachment, and subsequent apoptosis. We observed up-regulation of prosurvival proteins Bcl-xL and Mcl-1, which sequester Bim in cancer cells. In addition, a phosphorylated form of Bim was also elevated in cancer cells. These findings suggest that the constitutively overexpressed Bim may function as a prosurvival molecule in epithelial cancer cells, and phosphorylation and association with Bcl-xL/Mcl-1 block its proapoptotic functions.
authors.affiliation: Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, New York 14263, USA.
authors.forename: Raghu
authors.initials: R
authors.lastname: Gogada
authors.forename: Neelu
authors.initials: N
authors.lastname: Yadav
authors.forename: Junwei
authors.initials: J
authors.lastname: Liu
authors.forename: Shaohua
authors.initials: S
authors.lastname: Tang
authors.forename: Dianmu
authors.initials: D
authors.lastname: Zhang
authors.forename: Andrea
authors.initials: A
authors.lastname: Schneider
authors.forename: Athul
authors.initials: A
authors.lastname: Seshadri
authors.forename: Leimin
authors.initials: L
authors.lastname: Sun
authors.forename: C Marcelo
authors.initials: CM
authors.lastname: Aldaz
authors.forename: Dean G
authors.initials: DG
authors.lastname: Tang
authors.forename: Dhyan
authors.initials: D
authors.lastname: Chandra
mesh_terms: D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism*; D000072224:Bcl-2-Like Protein 11; D045744:Cell Line, Tumor; D002470:Cell Survival; D050687:E2F1 Transcription Factor / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D007150:Immunohistochemistry / Q000379:methods; D008565:Membrane Proteins / Q000378:metabolism*; D008870:Microtubules / Q000378:metabolism; D008928:Mitochondria / Q000378:metabolism; D009369:Neoplasms / Q000378:metabolism*; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D015398:Signal Transduction; D015854:Up-Regulation
chemical_list: D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; D000072224:Bcl-2-Like Protein 11; D050687:E2F1 Transcription Factor; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D012333:RNA, Messenger