Identification of cis- and trans-acting elements regulating calretinin expression in mesothelioma cells
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Jelena Kresoja-Rakic1, Esra Kapaklikaya1, Gabriela Ziltener1, Damian Dalcher2, Raffaella Santoro2, Brock C. Christensen3, Kevin C. Johnson3, Beat Schwaller4, Walter Weder5, Rolf A. Stahel1, Emanuela Felley-Bosco1
1Laboratory of Molecular Oncology, Clinic of Oncology, University Hospital Zürich, Zürich, Switzerland
2Institute of Veterinary Biochemistry and Molecular Biology, University of Zürich, Zürich, Switzerland
3Departments of Epidemiology, Pharmacology and Toxicology and Community and Family Medicine, Geisel School of Medicine at Dartmouth, Hanover, NH, USA
4Anatomy, Department of Medicine, University of Fribourg, Fribourg, Switzerland
5Division of Thoracic Surgery, University Hospital Zürich, Zürich, Switzerland
Emanuela Felley-Bosco, e-mail: [email protected]
Keywords: malignant pleural mesothelioma, calretinin, promoter, NRF-1, cell-cycle regulated expression
Received: September 08, 2015 Accepted: January 18, 2016 Published: February 01, 2016
Calretinin (CALB2) is a diagnostic marker for epithelioid mesothelioma. It is also a prognostic marker since patients with tumors expressing high calretinin levels have better overall survival. Silencing of calretinin decreases viability of epithelioid mesothelioma cells. Our aim was to elucidate mechanisms regulating calretinin expression in mesothelioma. Analysis of calretinin transcript and protein suggested a control at the mRNA level. Treatment with 5-aza-2′-deoxycytidine and analysis of TCGA data indicated that promoter methylation is not likely to be involved. Therefore, we investigated CALB2 promoter by analyzing ~1kb of genomic sequence surrounding the transcription start site (TSS) + 1 using promoter reporter assay. Deletion analysis of CALB2 proximal promoter showed that sequence spanning the –161/+80bp region sustained transcriptional activity. Site-directed analysis identified important cis-regulatory elements within this –161/+80bp CALB2 promoter. EMSA and ChIP assays confirmed binding of NRF-1 and E2F2 to the CALB2 promoter and siRNA knockdown of NRF-1 led to decreased expression of calretinin. Cell synchronization experiment showed that calretinin expression was cell cycle regulated with a peak of expression at G1/S phase. This study provides the first insight in the regulation of CALB2 expression in mesothelioma cells.
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