Characterization of MM-TRAG, a mitochondrial protein associated with MDR1 expression and the multidrug resistant phenotype in vitro
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Proc Amer Assoc Cancer Res, Volume 45, 2004 596 cDNA array analyses evaluating relative gene expression in paclitaxel resistant breast and ovarian resistant cell lines and their drug naïve parental lines have identified the unique gene MM-TRAG (MDR1 and Mitochondrial Taxol® (paclitaxel) Resistance Associated Gene). Overexpression of this gene is linked to overexpression of MDR1, and the MM-TRAG protein appears to be localized to the mitochondria. MM-TRAG is expressed as a 447 bp transcript that is predicted to encode a 118 amino acid protein. Northern analysis demonstrates that the MM-TRAG gene is overexpressed in a large collection of paclitaxel and doxorubicin resistant cell lines compared to their corresponding drug sensitive parent lines and that its expression pattern correlates with MDR1 expression in several drug resistant cell lines. The gene is located on chromosome 7q21 near the MDR1 gene. Southern blot analysis demonstrates that a single copy of MM-TRAG is present in the genomic DNA of the resistant cell lines suggesting that MM-TRAG overexpression is not due to genomic amplification or gene rearrangement. Cellular localization analysis of exogenously expressed enhanced green fluorescent protein (EGFP) tagged MM-TRAG in U-2OS cells demonstrates that the fluorescent protein is detected in the perinuclear region and localized with a coexpressed fluorescent protein that targets to mitochondria. The Cancer Profiling Array (Clontech) demonstrated that MM-TRAG is ubiquitously expressed in various normal tissues and their corresponding tumors. The Cancer Cell Line Profiling Array (Clontech), which contains cDNA samples generated from 26 human cancer cell lines treated with 26 different chemical agents, demonstrated that MM-TRAG is overexpressed 1.2 to 12.3 fold (average 4.4 fold) after 48 hours of paclitaxel exposure and 0.65 to 6.5 fold (average 2.2 fold) after doxorubicin exposure in various tumor cell lines. Manipulation of MDR1 expression using siRNA technology does not alter MM-TRAG expression suggesting that MM-TRAG expression is not dependent on MDR1 transcript levels.
author list (cited authors)
Duan, Z., Brakora, K. A., Foster, R., & Seiden, M. V.