Chunjing Bian

Upregulation of miR-22 Promotes Osteogenic Differentiation and Inhibits Adipogenic Differentiation of Human Adipose Tissue-Derived Mesenchymal Stem Cells by Repressing HDAC6 Protein Expression

Mesenchmal stem cells (MSCs) can be differentiated into either adipocytes or osteoblasts, and a reciprocal relationship exists between adipogenesis and osteogenesis. Multiple transcription factors and signaling pathways have been reported to regulate adipogenic or osteogenic differentiation, respectively, yet the molecular mechanism underlying the cell fate alteration between adipogenesis and osteogenesis still remains to be illustrated. MicroRNAs are important regulators in diverse biological processes by repressing protein expression of their targets. Here, miR-22 was found to regulate adipogenic and osteogenic differentiation of human adipose tissue-derived mesenchymal stem cells (hADMSCs) in opposite directions. Our data showed that miR-22 decreased during the process of adipogenic differentiation but increased during osteogenic differentiation. On one hand, overexpression of miR-22 in hADMSCs could inhibit lipid droplets accumulation and repress the expression of adipogenic transcription factors and adipogenic-specific genes. On the other hand, enhanced alkaline phosphatase activity and matrix mineralization, as well as increased expression of osteo-specific genes, indicated a positive role of miR-22 in regulating osteogenic differentiation. Target databases prediction and validation by Dual Luciferase Reporter Assay, western blot, and real-time polymerase chain reaction identified histone deacetylase 6 (HDAC6) as a direct downstream target of miR-22 in hADMSCs. Inhibition of endogenous HDAC6 by small-interfering RNAs suppressed adipogenesis and stimulated osteogenesis, consistent with the effect of miR-22 overexpression in hADMSCs. Together, our results suggested that miR-22 acted as a critical regulator of balance between adipogenic and osteogenic differentiation of hADMSCs by repressing its target HDAC6.

miR-17-5p promotes human breast cancer cell migration and invasion through suppression of HBP1

MicroRNAs have been implicated in regulating diverse cellular pathways. Emerging evidence indicate that the miR-17-92 cluster may have a causal role in breast cancer tumorigenesis as a novel class of oncogenes, but the role of these miRNAs in breast cancer invasion and migration remains unexplored. The aims of this study were to verify the effect of miR-17-5p (an important member of the miR-17-92 cluster) on the invasive and migratory ability of breast cancer cells. The matching of miR-17-5p and HMG box-containing protein 1 (HBP1) was predicted by TargetScan and confirmed by DNA constructs and luciferase target assay. The expression levels of miR-17-5p and its candidate target-HBP1 in MCF7 and MDA-MB-231 breast cancer cells were measured by real-time PCR and western blotting. Effects of miR-17-5p in cell cycle progression, proliferation, invasion and migration were evaluated by flow cytometry assay, 3-(4,-dimethy -lthiazol-2-yl)-2,-diphenyl -tetrazoliumbromide assay, soft-agar colony formation assay, and transwell invasive and migratory assay, respectively. The results showed that miR-17-5p was highly expressed in high-invasive MDA-MB-231 breast cancer cells but not in low-invasive MCF-7 breast cancer cells. Over-expression of miR-17-5p in MCF-7 cells rendered them the invasive and migratory abilities by targeting HBP1/β-catenin pathway. On the other hand, down-regulation of endogenous miR-17-5p suppressed the migration and invasion of MDA-MB-231 cells in vitro. These findings suggest that miR-17-5p plays an important role in breast cancer cell invasion and migration by suppressing HBP1 and subsequent activation of Wnt/β-catenin.

Overexpression of ΔNp63α induces a stem cell phenotype in MCF7 breast carcinoma cell line through the Notch pathway.

To elucidate a role of ΔNp63α in breast cancer, the expression levels of p63, estrogen receptor, progesterone receptor, p53, CK5, cerBb‐2, and Notch1 were assayed in 50 clinical breast cancer specimens using immunochemistry. P63 was highly expressed in a subset of breast cancer with basal‐like features. We then transfected MCF7 cells with ΔNp63α plasmid, and assayed its cancer stem cell‐like features after transfection. Overexpression of ΔNp63α in MCF7 cells increased the percentage of CD24−CD44+ subpopulation from 2.2 ± 0.2% to 25.1 ± 1.5% (P < 0.05) and led to increased cancer cell proliferation, clonogenicity, anchorage‐independent growth, and the incidence of xenograft grown in vivo. In addition, ΔNp63α overexpressing cancer cells were more drug resistant. Further studies suggested ΔNp63α‐induced activation of the Notch pathway may play a role in these effects. Chromatin immunoprecipitation confirmed that ΔNp63α could directly bind to Notch1. In clinical breast cancer specimens, the expression level of p63 was also found to positively correlate with the expression level of Notch1. Our results suggest that ΔNp63α might serve as a tumor initiating transcription factor in breast cancer. (Cancer Sci 2010; 101: 2417–2424)

Poly(ADP-ribose) polymerase-1 down-regulates BRCA2 expression through the BRCA2 promoter.

Expression of the BRCA2 tumor suppressor gene is tightly linked to its roles in DNA damage repair and maintenance of chromosomal stability and genomic integrity. Three transcription factors that activate (USF, NF-κB, and Elf1) and a single factor that represses (SLUG) BRCA2 promoter activity have been reported. In addition, a 67-bp region (–582 to–516) associated with inhibition of promoter activity has been identified. However, it remains unclear how the 67-bp region contributes to regulation of BRCA2 expression. Here, we describe the affinity purification of a 120-kDa protein that binds to a silencer-binding region within the 67-bp repression region of the BRCA2 promoter. Mass spectrometry revealed the identity of the protein as poly-(ADP-ribose) polymerase-1 (Parp-1). Gel shift, antibody super-shift, and chromatin immunoprecipitation (ChIP) assays demonstrated that Parp-1 is associated with the BRCA2 promoter both in vitro and in vivo. Furthermore, Parp-1 inhibitors (either 3-AB or NU1025) and Parp-1 gene specific siRNA resulted in increased levels of endogenous BRCA2 expression. Inhibition of Parp-1 activity (by 3-AB) reduced histone 3 lysine 9 acetylation and blocked Parp-1 binding to the BRCA2 promoter. These results indicate that Parp-1 down-regulates BRCA2 expression through an interaction with a repression region of the BRCA2 promoter.

TAp63α mediates chemotherapeutic agent-induced apoptosis in human bone marrow mesenchymal stem cells.

Human bone marrow-derived mesenchymal stem cells (MSCs) are currently widely used in cell therapy and tissue engineering. In vitro experiments have demonstrated that apoptosis of MSCs can be induced by hypoxia, serum deprivation, and chemotherapeutic agents, and the process is p53 independent. In this study, we investigated the role of p63 (a member of p53 family) in the regulation of apoptosis of MSCs. TAp63α, a subtype of p63, is highly similar to p53 and plays a crucial role in apoptosis. In vitro exposure of MSCs to either cisplatin or etoposide resulted in an increased TAp63α expression, which was time and dose dependent. Interference of TAp63α led to drug resistance and decreased apoptosis, accompanied by reduced expression of Bax, poly(ADP-ribose) polymerase, and caspase-3. However, downregulation of TAp63α did not influence the phenotype, proliferation capacity, and differentiation potential of MSCs. These results indicate that downregulation of TAp63α in MSCs is an attractive strategy to protect against apoptosis when MSCs are used to support hematopoiesis during bone marrow transplantation.