CXCR4 downregulation of let-7a drives chemoresistance in acute myeloid leukemia
Ye Chen, … , Carlo Croce, Michael Andreeff
Ye Chen, … , Carlo Croce, Michael Andreeff
Published May 8, 2013
Citation Information: J Clin Invest. 2013;123(6):2395-2407. https://doi.org/10.1172/JCI66553.
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Research Article Oncology

CXCR4 downregulation of let-7a drives chemoresistance in acute myeloid leukemia

Abstract

We examined the role of microRNAs (miRNAs) in targeting the stromal-derived factor 1α/CXCR4 (SDF-1α/CXCR4) axis to overcome chemoresistance of AML cells. Microarray analysis of OCI-AML3 cells revealed that the miRNA let-7a was downregulated by SDF-1α–mediated CXCR4 activation and increased by CXCR4 inhibition. Overexpression of let-7a in AML cell lines was associated with decreased c-Myc and BCL-XL protein expression and enhanced chemosensitivity, both in vitro and in vivo. We identified the transcription factor Yin Yang 1 (YY1) as a link between SDF-1α/CXCR4 signaling and let-7a, as YY1 was upregulated by SDF-1α and downregulated by treatment with a CXCR4 antagonist. ChIP assay confirmed the binding of YY1 to unprocessed let-7a DNA fragments, and treatment with YY1 shRNA increased let-7a expression. In primary human AML samples, high CXCR4 expression was associated with low let-7a levels. Xenografts of primary human AML cells engineered to overexpress let-7a exhibited enhanced sensitivity to cytarabine, resulting in greatly extended survival of immunodeficient mice. Based on these data, we propose that CXCR4 induces chemoresistance by downregulating let-7a to promote YY1-mediated transcriptional activation of MYC and BCLXL in AML cells.

Authors

Ye Chen, Rodrigo Jacamo, Marina Konopleva, Ramiro Garzon, Carlo Croce, Michael Andreeff

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Figure 2

Transfection of synthetic let-7a sensitizes OCI-AML3 cells to Ara-C treatment.

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Transfection of synthetic let-7a sensitizes OCI-AML3 cells to Ara-C trea...
Mimic let-7a or negative control oligonucleotide was transfected into OCI-AML3 cells by electroporation. (A) qRT-PCR showed that cells transfected with mimic had an approximately 3.5-fold increase of let-7a compared with control. (B) Western blots showed cells with mimic let-7a transfection had low expression of let-7a targets such as ITGB3, c-Myc, and BCL-XL. Lane 1, normal culture; lane 2, negative control oligonucleotide; lane 3, mimic let-7a. Expression level relative to normal culture (lane 1) is shown below blots. (C) When exposed to Ara-C (2.5 μM, 48 hours), the mimic let-7a–transfected cells exhibited >2-fold increased apoptosis (69.8% ± 9.4% vs. 23.2% ± 2.7% annexin V+; P < 0.01) and significantly lower numbers of viable cells (27,715 ± 6025 vs. 166,878 ± 12,405 cells; P < 0.01) compared with negative controls. **P < 0.01.