title: Functional characterization of the human translocator protein (18kDa) gene promoter in human breast cancer cell lines.
abstract: The translocator protein (18kDa; TSPO) is a mitochondrial drug- and cholesterol-binding protein that has been implicated in several processes, including steroidogenesis, cell proliferation, and apoptosis. Expression of the human TSPO gene is elevated in several cancers. To understand the molecular mechanisms that regulate TSPO expression in human breast cancer cells, the TSPO promoter was identified, cloned, and functionally characterized in poor-in-TSPO hormone-dependent, non-aggressive MCF-7 cells and rich-in-TSPO hormone-independent, aggressive, and metastatic MDA-MB-231 breast cancer cells. RNA ligase-mediated 5'-rapid amplification of cDNA ends analysis indicated transcription initiated at multiple sites downstream of a GC-rich promoter that lacks functional TATA and CCAAT boxes. Deletion analysis indicated that the region from -121 to +66, which contains five putative regulatory sites known as GC boxes, was sufficient to induce reporter activity up to 24-fold in MCF-7 and nearly 120-fold in MDA-MB-231 cells. Electrophoretic mobility shift and chromatin immunoprecipitation assays indicated that Sp1, Sp3 and Sp4 bind to these GC boxes in vitro and to the endogenous TSPO promoter. Silencing of Sp1, Sp3 and Sp4 gene expression reduced TSPO levels. In addition, TSPO expression was epigenetically regulated at one or more of the identified GC boxes. Disruption of the sequence downstream of the main start site of TSPO differentially regulated TSPO promoter activity in MCF-7 and MDA-MB-231 cells, indicating that essential elements contribute to its differential expression in these cells. Taken together, these experiments constitute the first in-depth functional analysis of the human TSPO gene promoter and its transcriptional regulation.
authors.affiliation: The Research Institute of the McGill University Health Centre and the Department of Medicine, McGill University, Montreal, Quebec, Canada H3G 1A4. amani.batarseh@childrens.harvard.edu
authors.forename: Amani
authors.initials: A
authors.lastname: Batarseh
authors.forename: Keith D
authors.initials: KD
authors.lastname: Barlow
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Martinez-Arguelles
authors.forename: Vassilios
authors.initials: V
authors.lastname: Papadopoulos
mesh_terms: D001483:Base Sequence; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology*; D045744:Cell Line, Tumor; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D020868:Gene Silencing; D006801:Humans; D008969:Molecular Sequence Data; D009361:Neoplasm Invasiveness; D009362:Neoplasm Metastasis; D009376:Neoplasms, Hormone-Dependent / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D011401:Promoter Regions, Genetic / Q000235:genetics*; D034741:RNA, Small Interfering / Q000235:genetics; D018079:Receptors, GABA / Q000235:genetics* / Q000378:metabolism*; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism; D051705:Sp3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D051706:Sp4 Transcription Factor / Q000235:genetics / Q000378:metabolism
chemical_list: D034741:RNA, Small Interfering; D018079:Receptors, GABA; C497121:SP3 protein, human; C497124:SP4 protein, human; D016329:Sp1 Transcription Factor; D051706:Sp4 Transcription Factor; C499229:TSPO protein, human; D051705:Sp3 Transcription Factor