Abstract B11: Expression of microRNAs-135b and -196b in response to cellular stress in leukemia cells
Authors: Ho Tsui-Ting , He Xiaolong , Arslan Ahmet Dirim , Beck William T. 
Published: April 2013

Abstract
MicroRNAs are a class of non-coding small RNA molecules that have roles in important biological processes. Multidrug resistance is a key obstacle to successful cancer therapy in human cancers. To determine whether microRNAs have a role in the development or maintenance of multidrug resistance, we used the TaqMan™ Human MicroRNA Array to investigate the expression of microRNAs in multidrug resistant (MDR) CCRF-CEM human T-cell leukemia cells (CEM/VM-1-5) and drug-sensitive parental line, CCRF-CEM (CEM). The MDR line was selected for resistance to teniposide and is cross-resistant to etoposide and other drugs. Our profiling study of 365 microRNAs revealed that certain microRNAs are differentially expressed between CEM/VM-1-5 and CEM cells, and we focused our subsequent work on two of these: miR-135b and -196b. Since MDR cells were selected and developed by stepwise increases in concentrations of teniposide, we therefore asked whether these altered microRNAs in MDR CEM/VM-1-5 cells are associated with cellular responses to genotoxic agents. We observed substantial increases in miR-135b and -196b expression in drug-sensitive CEM cells following their short exposure (3 to 48 hours) with etoposide, doxorubicin and topotecan, but not in cells treated with vinblastine or paclitaxel, suggesting that the upregulation of these two microRNAs might be the consequence of DNA damage. We also found similar increases in miR-135b and -196b in other leukemia cell lines (RPMI 8226 [myeloma], HL-60 [acute promyelocytic leukemia], Jurkat and MOLT-4 [both acute T cell leukemia]), but not in solid tumor-derived cell lines (MCF7 breast cancer and A2780 ovarian cancer). This suggests that induction of expression of these microRNAs is histiotype-specific. To further confirm that upregulation of these two microRNAs is a consequence of DNA damage, we examined expression of miR-135b and -196b following ionizing radiation. When we treated CEM pairs with ionizing radiation, MDR CEM/VM-1-5 cells were more radioresistant compared to CEM cells. As expected, higher doses of radiation induced miR-135b and -196b expression in MDR CEM/VM-1-5 cells compared to CEM cells, in accordance with what we observed in cells treated with the DNA damaging agent etoposide. Moreover, time-course and dose-response studies showed that the elevation of miR-135b and -196b correlated positively with the exposure time and radiation dosage. Together, our results suggest that microRNAs might play a significant role in cellular response to genotoxic agents and upregulation of miR-135b and -196b appears to be a marker of DNA damage in leukemia cells.
(Supported in part by RO1CA40570 from NCI to WTB, and in part by UIC.)
Citation Format: Tsui-Ting Ho, Xiaolong He, Ahmet Dirim Arslan, William T. Beck. Expression of microRNAs-135b and -196b in response to cellular stress in leukemia cells [abstract]. In: Proceedings of the AACR Special Conference on Noncoding RNAs and Cancer; 2012 Jan 8-11; Miami Beach, FL. Philadelphia (PA): AACR; Cancer Res 2012;72(2 Suppl):Abstract nr B11.