We investigated whether breast tumor cells can modulate the function of mesenchymal stromal cells (MSCs) with a special emphasis on their chemoattractive activity towards hematopoietic stem and progenitor cells (HSPCs). Primary MSCs as well as a MSC line (SCP-1) were cocultured with primary breast cancer cells, MCF-7, MDA-MB231 breast carcinoma or MCF-10A non-malignant breast epithelial cells or their conditioned medium. In addition, the frequency of circulating clonogenic hematopoietic progenitors was determined in 78 patients with breast cancer and compared with healthy controls. Gene expression analysis of SCP-1 cells cultured with MCF-7 medium revealed CXCL12 (SDF-1) as one of the most significantly downregulated genes. Supernatant from both MCF-7 and MDA-MB231 reduced the CXCL12 promoter activity in SCP-1 cells to 77% and 47%, respectively. Moreover, the CXCL12 mRNA and protein levels were significantly reduced. As functional consequence of lower CXCL12 levels, we detected a decreased transwell migration of HSPCs towards MSC/tumor cell cocultures or conditioned medium. The specificity of this effect was confirmed by blocking studies with the CXCR4 antagonist AMD3100. Downregulation of SP1 and increased miR-23a levels in MSCs after contact with tumor cell medium as well as enhanced TGFb1 expression were identified as potential molecular regulators of CXCL12 activity in MSCs. Moreover, we observed a significantly higher frequency of circulating colony-forming hematopoietic progenitors in patients with breast cancer compared with healthy controls. Our in vitro results propose a potential new mechanism by which disseminated tumor cells in the bone marrow may interfere with hematopoiesis by modulating CXCL12 in protected niches.
The chemokine CXCL12 regulates the interaction between hematopoietic stem and progenitor cells and bone marrow stromal cells. Although its relevance in the bone marrow niche is well recognized, the regulation of CXCL12 by microRNA is not completely understood. We transfected a library of 486 microRNA in the bone marrow stromal cell line SCP-1 and studied the expression of CXCL12. Twenty-seven microRNA were shown to downregulate expression of CXCL12. Eight microRNA (miR-23a, 130b, 135, 200b, 200c, 216, 222, and 602) interacted directly with the 3´UTR of CXCL12. Next, we determined that only miR-23a is predicted to bind to the 3´UTR and is strongly expressed in primary bone marrow stromal cells. Modulation of miR-23a changes the migratory potential of hematopoietic progenitor cells in co-culture experiments. We discovered that TGFB1 mediates its inhibitory effect on CXCL12 levels by upregulation of miR-23a. This process was partly reversed by miR-23a molecules. Finally, we determined an inverse expression of CXCL12 and miR-23a in stromal cells from patients with myelodysplastic syndrome indicating that the interaction has a pathophysiological role. Here, we show for the first time that CXCL12-targeting miR23a regulates the functional properties of the hematopoietic niche. MicroRNA-23a mediates post-transcriptional regulation of CXCL12 in bone marrow stromal cells ABSTRACT © F e r r a t a S t o r t i F o u n d a t i o nproteases. 11,12 Furthermore, CXCL12 expression can be transcriptionally modulated by a variety of cytokines and growth factors, namely transforming growth factor-beta 1 (TGFB1). TGFB1 has a negative growth effect on HSPC which is mediated, in part, by the regulation of CXCL12 arising from stromal cells. 13 Thus, engraftment and response to cytotoxic drugs may vary according to CXCL12 levels provided by niche cells. 14,15 Recently, Pillai et al. suggested that CXCL12 can also be regulated by microRNA (miRNA) in human marrow stromal cells. 16 There are more than 1000 miRNA which form 1-2% of the human genome. Approximately half of human structural genes are predicted to be under miRNA control. In animals, miRNA act by targeting the 3ú ntranslated region (UTR) of genes with the consequence of repressing output of the respective protein. A classical switch interaction is used to avoid protein expression in a particular cell type, whereas tuning interactions are needed to supply the cell with the optimal level of protein. 17 In the hematopoietic system, CXCL12 must be fine-tuned in response to differing physiological requirements.We, therefore, decided to study the interaction of CXCL12 and miRNA by applying a strategy of overexpression of a library to reveal the various miRNA responsible for CXCL12 regulation in primary human bone marrow stromal cells (hBMSC). Moreover, we mapped expression of candidate miRNA in primary hBMSC to understand their physiological function in fine tuning CXCL12 expression in the hematopoietic niche. Methods Cell linesHS5, HS27, HL60, K562, KG1a, and HeLa cell lines were ob...
(2016) Epigenetic silencing of miR-26A1 in chronic lymphocytic leukemia and mantle cell lymphoma: Impact on EZH2 expression, Epigenetics, 11:5, 335-343, DOI: 10.1080/15592294.2016 ABSTRACT Downregulation of miR26A1 has been reported in various B-cell malignancies; however, the mechanism behind its deregulation remains largely unknown. We investigated miR26A1 methylation and expression levels in a well-characterized series of chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL). From 450K methylation arrays, we first observed miR26A1 (cg26054057) as uniformly hypermethylated in MCL (n D 24) (all >75%), while CLL (n D 18) showed differential methylation between prognostic subgroups. Extended analysis using pyrosequencing confirmed our findings and real-time quantitative PCR verified low miR26A1 expression in both CLL (n D 70) and MCL (n D 38) compared to normal B-cells. Notably, the level of miR26A1 methylation predicted outcome in CLL, with higher levels seen in poor-prognostic, IGHV-unmutated CLL. Since EZH2 was recently reported as a target for miR26A1, we analyzed the expression levels of both miR26A1 and EZH2 in primary CLL samples and observed an inverse correlation. By overexpression of miR26A1 in CLL and MCL cell lines, reduced EZH2 protein levels were observed using both Western blot and flow cytometry. In contrast, methyl-inhibitor treatment led to upregulated miR26A1 expression with a parallel decrease of EZH2 expression. Finally, increased levels of apoptosis were observed in miR26A1-overexpressing cell lines, further underscoring the functional relevance of miR26A1. In summary, we propose that epigenetic silencing of miR26A1 is required for the maintenance of increased levels of EZH2, which in turn translate into a worse outcome, as shown in CLL, highlighting miR26A1 as a tumor suppressor miRNA.
The composition of the hematopoietic stem cell (HSC) niche within the bone marrow is highly dynamic, tightly regulated, and of importance for various HSC properties. Integrins are important molecules within this niche that influence those properties through the interactions of HSCs and mesenchymal stem cells (MSCs). Here we investigated the function of miR-134 in integrin regulation in MSCs. In MSCs, miR-134 post-transcriptionally regulated β1 integrin expression. This negative regulation of β1 integrin was mediated by the binding of miR-134 to its 3' untranslated region, which contains two conserved binding sites for miR-134. The miR-134-mediated silencing of β1 integrin in MSCs was shown by atomic force microscopy to decrease the adhesion of 32D cells to MSCs transfected with miR-134. Furthermore, the adhesion of MSCs to fibronectin was reduced after transfection with miR-134. MSCs from patients with myelodysplastic syndrome (MDS) revealed highly significant miR-134 overexpression compared with MSCs from healthy bone marrow donors. MSCs from MDS patients showed lower β1 integrin protein, but not lower mRNA, expression, suggesting post-transcriptional regulation. The present study demonstrates miR-134-mediated negative regulation of β1 integrin that influences cell adhesion to and of MSCs. These results further contribute to our understanding of the complexity of MDS.
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