Ci-Xiang Zhou

Pathologically decreased miR-26a antagonizes apoptosis and facilitates carcinogenesis by targeting MTDH and EZH2 in breast cancer

The role of miR-26a in carcinogenesis appears to be a complicated one, in the sense that both oncogenic and tumor suppressive effects were reported in cancers such as glioblastoma and hepatocellular carcinoma, respectively. Here, we report for the first time that miR-26a is downregulated in breast cancer specimens and cell lines and its transient transfection initiates apoptosis of breast cancer cell line MCF7 cells. Furthermore, retrovirus-delivered miR-26a impairs the in vitro colony forming and in vivo tumor-loading ability of MCF7 cells. Subsequently, MTDH and EZH2 are identified as two direct targets of miR-26a and they are significantly upregulated in breast cancer. MCF7 xenografts with exogenous miR-26a show that a decrease in expression of both MTDH and EZH2 is accompanied by an increase in apoptosis. Moreover, knockdown of MTDH causes apoptosis while reexpression of MTDH partially reverses the proapoptotic effect of miR-26a in MCF7 cells. Our findings suggest that miR-26a functionally antagonizes human breast carcinogenesis by targeting MTDH and EZH2.

MiR-124 targets Slug to regulate epithelial-mesenchymal transition and metastasis of breast cancer.

MicroRNAs (miRNAs or miR) have been integrated into tumorigenic programs as either oncogenes or tumor suppressor genes. The miR-124 was reported to be attenuated in several tumors, such as glioma, medulloblastoma and hepatocellular carcinoma. However, its role in cancer remains greatly elusive. In this study, we show that the miR-124 expression is significantly suppressed in human breast cancer specimens, which is reversely correlated to histological grade of the cancer. More intriguingly, ectopic expression of miR-124 in aggressive breast cancer cell lines MDA-MB-231 and BT-549 strongly inhibits cell motility and invasive capacity, as well as the epithelial–mesenchymal transition process. Also, lentivirus-delivered miR-124 endows MDA-MB-231 cells with the ability to suppress cell colony formation in vitro and pulmonary metastasis in vivo. Further studies have identified the E-cadherin transcription repressor Slug as a direct target gene of miR-124; its downregulation by miR-124 increases the expression of E-cadherin, a hallmark of epithelial cells and a repressor of cell invasion and metastasis. Moreover, knockdown of Slug notably impairs the motility of MDA-MB-231 cells, whereas re-expression of Slug abrogates the reduction of motility and invasion ability induced by miR-124 in MDA-MB-231 cells. These findings highlight an important role for miR-124 in the regulation of invasive and metastatic potential of breast cancer and suggest a potential application of miR-124 in cancer treatment.

MicroRNA-26b is underexpressed in human breast cancer and induces cell apoptosis by targeting SLC7A11

MicroRNAs are widely dysregulated in various cancers and integrated into tumorigenic programs as either oncogenes or tumor suppressor genes. Here, we show that miR‐26b, which is down‐regulated in human breast cancer specimens and cell lines, impairs viability and triggers apoptosis of human breast cancer MCF7 cells. SLC7A11 is identified as a direct target of miR‐26b and its expression is remarkably increased in both breast cancer cell lines and clinical samples. Furthermore, SLC7A11 silence mimics miR‐26b‐aroused viability impairment and apoptosis in MCF7 cells. Our studies reveal a protective role of miR‐26b in the molecular etiology of human breast cancer by promoting apoptosis.

HIF-1α downregulates miR-17/20a directly targeting p21 and STAT3: a role in myeloid leukemic cell differentiation.

Hypoxia-inducible factor 1 (HIF-1) is a crucial transcription factor for the cellular adaptive response to hypoxia, which contributes to multiple events in cancer biology. MicroRNAs (miRNAs) are involved in almost all cellular activities such as differentiation, proliferation, and apoptosis. In this work, we use miRNA microarrays to profile miRNA expression in acute myeloid leukemia (AML) cells with inducible HIF-1α expression, and identify 19 differentially expressed miRNAs. Our study shows that HIF-1α represses the expression of miR-17 and miR-20a by downregulating c-Myc expression. These two miRNAs alleviate hypoxia and HIF-1α-induced differentiation of AML cells. More intriguingly, miR-17 and miR-20a directly inhibit the p21 and STAT3 (signal transducer and activator of transcription 3) expression, both of which can reverse miR-17/miR-20a-mediated abrogation of HIF-1α-induced differentiation. Moreover, we show in vivo that miR-20a contributes to HIF-1α-induced differentiation of leukemic cells. Taken together, our results suggest that HIF-1α regulates the miRNA network to interfere with AML cell differentiation, representing a novel molecular mechanism for HIF-1-mediated anti-leukemic action.

Antileukemic roles of human phospholipid scramblase 1 gene, evidence from inducible PLSCR1-expressing leukemic cells

Phospholipid scramblase 1 (PLSCR1) is a multiply palmitoylated protein which is localized in either the cell membrane or nucleus depending on its palmitoylated state. The increasing evidence showed the biological roles of PLSCR1 in cell signaling, maturation and apoptosis. To investigate the functions of PLSCR1 in leukemic cells, we generated an inducible PLSCR1-expressing cell line using myeloid leukemic U937 cells. In this cell line, PLSCR1 was tightly regulated and induced upon tetracycline withdrawal. Our results showed that inducible PLSCR1 expression arrested the proliferation of U937 cells at G1 phase. Meanwhile, PLSCR1-overexpressing U937 cells also underwent granulocyte-like differentiation with increased sensitivity to etoposide-induced apoptosis. Furthermore, we also found that PLSCR1 induction increased cyclin-dependent kinase inhibitors p27Kip1 and p21Cip1 proteins, together with downregulation of S phase kinase-associated protein 2 (SKP2), an F-box subunit of the ubiquitin-ligase complex that targets proteins for degradation. Additionally, PLSCR1 induction significantly decreased c-Myc protein and antiapoptotic Bcl-2 protein. Although the exact mechanism by which PLSCR1 regulates these cellular events and gene expression remains unresolved, our results suggest that PLSCR1 plays the antagonistic role regarding leukemia development. These data will shed new insights into understanding the biochemical and biological functions of PLSCR1 protein.

The downregulation of onzin expression by PKCε-ERK2 signaling and its potential role in AML cell differentiation

Onzin is a small, novel, and highly conserved protein with unique structure and tissue-restricted expression. The regulation of its expression and biological roles remain greatly elusive. Here, we provide the first demonstration that onzin expression is significantly downregulated during differentiation induction of acute myeloid leukemic (AML) cell lines and primary cells by all-trans retinoic acid (ATRA) and especially by phorbol 12-myristate 13-acetate (PMA). Applying chemical inhibitions, RNA interferences, and transfected expressions of dominant negative mutants or constitutive catalytic forms of the related kinases, we show that protein kinase C-ɛ (PKCɛ)-extracellular signal-regulated protein kinase 2 (ERK2) signaling axis is required for PMA-induced downregulation of onzin expression. The ectopic expression of onzin partially inhibits PMA-induced monocytic differentiation of AML cells, whereas suppression of onzin by specific short hairpin RNAs enhances PMA-induced differentiation to a degree. Furthermore, onzin partially inhibits the transcriptional activity of hematopoiesis-related important transcription factor PU.1 via their interaction. Taken together, our results show that PMA downregulates onzin expression through PKCɛ-ERK2 signaling pathway, which favors monocytic differentiation of leukemic cells.

MicroRNA-494 inhibits breast cancer progression by directly targeting PAK1.

MicroRNA (miRNA) is involved in the progression and metastasis of diverse human cancers, including breast cancer, as strong evidence has been found that miRNAs can act as oncogenes or tumor suppressor genes. Here, we show that miR-494 is decreased in human breast cancer specimens and breast cancer cell lines. Ectopic expression of miR-494 in basal-like breast cancer cell lines MDA-MB-231-LUC-D2H3LN and BT-549 inhibits clonogenic ability and metastasis-relevant traits in vitro. Moreover, ectopic expression of miR-494 suppresses neoplasm initiation as well as pulmonary metastasis in vivo. Further studies have identified PAK1, as a direct target gene of miR-494, contributes to the functions of miR-494. Remarkably, the expression of PAK1 is inversely correlated with the level of miR-494 in human breast cancer samples. Furthermore, re-expression of PAK1 partially reverses miR-494-mediated proliferative and clonogenic inhibition as well as migration and invasion suppression in breast cancer cells. Taken together, these findings highlight an important role for miR-494 in the regulation of progression and metastatic potential of breast cancer and suggest a potential application of miR-494 in breast cancer treatment.

MiR-630 suppresses breast cancer progression by targeting metadherin

MicroRNAs have been integrated into tumorigenic programs as either oncogenes or tumor suppressor genes. The miR-630 was reported to be deregulated and involved in tumor progression of several human malignancies. However, its expression regulation shows diversity in different kinds of cancers and its potential roles remain greatly elusive. Herein, we demonstrate that miR-630 is significantly suppressed in human breast cancer specimens, as well as in various breast cancer cell lines. In aggressive MDA-MB-231-luc and BT549 breast cancer cells, ectopic expression of miR-630 strongly inhibits cell motility and invasive capacity in vitro. Moreover, lentivirus delivered miR-630 bestows MDA-MB-231-luc cells with the ability to suppress cell colony formation in vitro and pulmonary metastasis in vivo. Further studies identify metadherin (MTDH) as a direct target gene of miR-630. Functional studies shows that MTDH contributes to miR-630-endowed effects including cell migration and invasion as well as colony formation in vitro. Taken together, these findings highlight an important role for miR-630 in the regulation of metastatic potential of breast cancer and suggest a potential application of miR-630 in breast cancer treatment.

Nuclear translocation of dihydrofolate reductase is not a pre-requisite for DNA damage induced apoptosis

Dihydrofolate reductase (DHFR) is a key enzyme for the synthesis of thymidylate, and therefore, of DNA. By applying subcellular proteomic analysis, we identified that the DHFR protein was translocated from cytoplasm into the nucleus when apoptosis was induced by NSC606985, a camptothecin analogue. The nuclear translocation of DHFR protein during apoptosis was independent of the cellular context, but it was more sensitive in cell death induction by DNA damaging agents such as doxorubicin, etoposide and ultraviolent radiation than endoplasmic reticulum stressors (brefeldin-A and tunicamycin) and anti-microtubule agents (paclitaxel and nocodozole). The addition of methotrexate almost completely blocked the nuclear translocation of DHFR protein. Further investigations showed that the nuclear translocation of DHFR was not a pre-requisite for DNA damage induced apoptosis. Therefore, its potential biological significance remains to be further explored.

MicroRNA-630 inhibits breast cancer progression by directly targeting BMI1

&NA; MicroRNAs (miRNAs) play critical roles in breast cancer cell biological processes, including proliferation and apoptosis by inhibiting the expression of their target genes. Herein, we reported that miR‐630 overexpression initiates apoptosis, blocks cell cycle progression and suppresses cell proliferation in breast cancer cells. Furthermore, BMI1, a member of polycomb group family, was identified as a direct target of miR‐630, and there was a negative correlation between the expression levels of BMI1 and miR‐630 in human breast cancer samples. With a series of biology approaches, subsequently, we proved that BMI1 was a functional downstream target of miR‐630 and mediated the property of miR‐630‐dependent inhibition of breast cancer progression. Taken together, these findings provide further evidence on the tumor‐suppression function of miR‐630 in breast cancer, and clarify BMI1 as a novel functional target gene of miR‐630.