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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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 6

let-7a expression regulated by CXCR4 signaling is partially mediated though YY1.

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let-7a expression regulated by CXCR4 signaling is partially mediated tho...
(A) qRT-PCR demonstrated that pri-let-7a-1, pri-let-7a-2, and pri-let-7a-3 were downregulated by SDF-1α and upregulated with POL6326 treatment. (B) qRT-PCR, Western blotting, and immunocytochemistry confirmed the upregulation of YY1 with SDF-1α treatment and its reduction by CXCR4 antagonist at the mRNA and protein levels. Expression level relative to control is shown below blots. Scale bars: 10 μm. (C) Specific primers were designed for let-7a DNA fragments that include the YY1 binding sites. ChIP assay further confirmed that the interaction between YY1 and the pri-let-7a-1, pri-let-7a-2, and pri-let-7a-3 DNA fragments was enhanced by SDF-1α treatment. (D) YY1 expression in OCI-AML3 cells was knocked down by shRNA, and the cells showed a significantly higher level of let-7a compared with NS-shRNA-OCI3 cells. Moreover, YY1-shRNA-OCI3 cells were more sensitive to Ara-C treatment. Expression level relative to parental OCI-AML3 cells is shown below blots. (E) ChIP assays were performed with control IgG or antibody to H3K27 on the chromatin obtained from cells transfected with either control or YY1 shRNA. The immunoprecipitated chromatin was analyzed by PCR using specific primers (see Methods). *P < 0.05, **P < 0.01.