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Results for “Polycomb Repressive Complex 1”

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PubMed2002

The Bmi-1 oncogene induces telomerase activity and immortalizes human mammary epithelial cells.

The vast majority of breast cancers are carcinomas that arise from mammary epithelial cells (MECs). One of the key early events in tumorigenic transformation is the ability of cells to overcome replicative senescence. However, the precise genetic changes that are responsible for this event in MECs is largely unknown. Here, we report that Bmi-1, originally identified as a c-Myc cooperating oncoprotein, can bypass senescence, extend the replicative life span, and immortalize MECs. Furthermore, Bmi-1 was overexpressed in immortal MECs and several breast cancer cell lines. Overexpression of Bmi-1 in MECs led to activation of human telomerase reverse transcriptase (hTERT) transcription and induction of telomerase activity. Telomerase induction by Bmi-1 was an early event in the extension of the replicative life span and immortalization. Bmi-1 was not overexpressed in hTERT-immortalized MECs, suggesting that Bmi-1 functions upstream of hTERT. Although, c-Myc has been reported to induce telomerase in MECs, Bmi-1 appeared to act independently of c-Myc binding sequences in the hTERT promoter. Deletion analysis of the Bmi-1 protein suggested that the RING finger, as well as a conserved helix-turn-helix-turn domain, were required for its ability to induce telomerase and immortalize MECs. These data suggest that Bmi-1 regulates telomerase expression in MECs and plays a role in the development of human breast cancer.

Binding Sites↗
PubMed2004

[Cancer stem cells in pediatric brain tumors].

Cancers are formed by heterogeneous cell types from immature highly proliferative cells to lineage-committed differentiated cells. Transplantation studies have suggested the existence of "cancer stem cells", individual cells capable of producing an entire tumor. Recent advances in stem cell research have allowed for the demonstration of the existence of cancer stem cells in acute myeloid leukemia, breast cancer, and, most recently, in pediatric brain tumors. Each of these has some similarities with the normal stem cells in the corresponding organs. For example, leukemia stem cells express some, but not all, markers of hematopoietic stem cells. Regarding pediatric brain tumors, putative cancer stem cells were identified from medulloblastoma and also from glioma. These tumor-derived cells self-renew under clonal conditions, and differentiate into neurons and glia as well as into abnormal cells with mixed phenotypes. Interestingly, the tumor stem/progenitors, enriched in culture, maintained proliferation after 4 weeks from transplantation into neonatal rat brain. In this review, we discuss the difference as well as the similarity between tumor and normal stem cells, and also the possible clinical implication of cancer stem cells.

Animals↗
PubMed2005

Hematopoietic stem cells, leukemic stem cells and chronic myelogenous leukemia.

Blood-related cancers, or leukemias, have been shown to arise from a rare subset of cells that escape normal regulation and drive the formation and growth of the tumor. The finding that these so-called cancer stem cells, or leukemic stem cells (LSC), can be purified away from the other cells in the tumor allows their precise analysis to identify candidate molecules and regulatory pathways that play a role in progression, maintenance, and spreading of leukemias. The analyses of the other, numerically dominant, cells in the tumor, while also interesting, do not directly interrogate these key properties of malignancies. Mouse models of human myeloproliferative disorder and acute myelogenous leukemia have highlighted the remarkable conservation of disease mechanisms between both species. They can now be used to identify the LSC for each type of human leukemia and understand how they escape normal regulation and become malignant. Given the clinical importance of LSC identification, the insights gained through these approaches will quickly translate into clinical applications and lead to improved treatments for human leukemias.

Animals↗
PubMed2005

Construction of antisense Bmi-1 expression plasmid and its inhibitory effect on K562 cells proliferation.

BACKGROUND: Bmi-1 gene determines the proliferative capacity of normal and leukemia stem cells. Expression of Bmi-1 has been found in all types of myeloid leukemia cells in both humans and mice. This study aimed at assessing the effect of antisense Bmi-1 expression on K562 cells proliferation and p16 protein (p16) expression. METHODS: A transcriptional repressor, Bmi-1 cDNA was cloned by reverse transcriptase polymerase chain reaction (RT-PCR) of its mRNA from K562 cells. A plasmid expressing antisense Bmi-1 mRNA was then constructed by reverse design of PCR primers and cloned to the plasmid pLNCX2; G418 was added to the medium after the plasmid was successfully introduced in K562 cells by lipofectin-mediated DNA transfection. The effects of the antisense expression on the proliferation of K562 cells were analyzed by using microculture tetrazolium and colony forming. Cell cycle was analyzed by using flow cytometry. The p16 expression of K562 cells was observed by immunofluorescence histochemical stain. RESULTS: K562 cells transfected with antisense Bmi-1 plasmid grew significantly slower than that of controls (the parental K562 and cells transfected with empty plasmid). The colony forming ability of antisense Bmi-1 plasmid transfected cells decreased significantly (P < 0.01) compared with controls. The p16 expression of cells transfected with antisense Bmi-1 was upgraded more apparently than that of controls. CONCLUSION: The antisense Bmi-1 gene can inhibit the growth of K562 cell and upgrade expression of p16 in K562 cells.

Cell Cycle↗
PubMed2005

[Inhibition effect of antisense Bmi-1 on Jurkat cells].

OBJECTIVES: To investigate whether antisense Bmi-1 plasmid could inhibit the proliferation of Jurkat cells. METHODS: The antisense plasmid was constructed by PCR amplification of a 171 bp segment spanning Bmi-1 start codon and zinc finger structure and the PCR product was subsequently inserted reversely to plasmid pLNCX2. The final construct was confirmed through restriction enzyme digestion. G418 was added into the medium after the plasmid was successfully introduced into Jurkat cells by using lipofectin-mediated DNA transfection. The proliferation of Jurkat cells were determined by MTT and colony formation assays. Cell cycle was determined by flow cytometry. The p16 expression of Jurkat cells was studied by immunofluorescent histochemistry. RESULTS: The growth rate of antisense Bmi-1 transfected Jurkat cells was significantly lower than that of the controls, and the colony forming capacity of the transfected cells decreased significantly (P < 0.01), the colony numbers being (90.7 +/- 9.07)/10(3) cells, (83.3 +/- 6.11)/10(3) cells and (56.0 +/- 5.56)/10(3) cells for control cells, empty plasmid transfected Jurkat cells and antisense Bmi-1 transfected Jurkat cells, respectively. The percentage of G, phase cells was increased and the p16 expression of antisense Bmi-1 transfected cells was significantly upregulated than that of control cells. CONCLUSION: Antisense Bmi-1 can inhibit the growth and upregulate the expression of p16 of Jurkat cells in vitro.

Cell Cycle↗
PubMed2006

[Regulatory effects of Bmi-1 gene on self-renewal of hematopoietic stem cells--review].

Self-renewal of hematopoietic stem cells is vital for the sustained daily production of blood cells. The Bmi-1 gene is a putative oncogene belonging to the Polycomb group family. Recent studies have shown that the Polycomb-group gene Bmi-1 is indispensable for regulation of self-renewal of normal and leukemic stem cells. The research progress on structure and function of Bmi-1 gene, and its role in self-renewal of hematopoietic stem cells was reviewed.

Cell Differentiation↗
PubMed2006

[Cloning of Bmi1 cDNA from mouse testis and its expression in E. coli BL21].

OBJECTIVE: To produce BMI1 polyclonal antibody, mouse Bmi1 cDNA was cloned from mouse testis and expressed in E. coli BL21. METHODS: Bmi1 gene was amplified from mouse testis by RT-PCR and inserted into the prokaryotic expression vector pET-28c(+). Subsequently the recombined vector was transformed and expressed in E. coli BL21 (DE3) and the immunogenicity of recombined protein BMI1 (rBMI1) was tested by Western blot. RESULTS: Mouse Bmi1 cDNA of 975 bp was successfully cloned and recombined. E. coli BL21 strains expressed rBMI1 were screened. The expression protein amounted to 12% of the total bacterial protein after induced with IPTG, which included inclusion body and soluble protein. Inclusion body was the major pattern of the expression that amounted to 71% of the insoluble protein. Western blot analysis showed that rBMI1 could be specially recognized by mouse monoclonal IgG1 anti-BMI1 and His-tag antibody. CONCLUSION: There was expression of Bmi1 gene in mouse testis. Mouse Bmi1 cDNA was successfully cloned and expressed prokaryoticly.

Animals↗
PubMed2006

Temporal and spatial expression of homeotic genes is important for segment-specific neuroblast 6-4 lineage formation in Drosophila.

Different proliferation of neuroblast 6-4 (NB6-4) in the thorax and abdomen produces segmental specific expression pattern of several neuroblast marker genes. NB6-4 is divided to form four medialmost cell body glia (MM-CBG) per segment in thorax and two MM-CBG per segment in abdomen. As homeotic genes determine the identities of embryonic segments along theA/P axis, we investigated if temporal and specific expression of homeotic genes affects MM-CBG patterns in thorax and abdomen. A Ubx loss-of-function mutation was found to hardly affect MM-CBG formation, whereas abd-A and Abd-B caused the transformation of abdominal MM-CBG to their thoracic counterparts. On the other hand, gain-of-function mutants of Ubx, abd-A and Abd-B genes reduced the number of thoracic MM-CBG, indicating that thoracic MM-CBG resembled abdominal MM-CBG. However, mutations in Polycomb group (PcG) genes, which are negative transregulators of homeotic genes, did not cause the thoracic to abdominal MM-CBG pattern transformation although the number of MM-CBG in a few per-cent of embryos were partially reduced or abnormally patterned. Our results indicate that temporal and spa-tial expression of the homeotic genes is important to determine segmental-specificity of NB6-4 daughter cells along the anterior-posterior (A/P) axis.

Abdomen↗
PubMed2006

Histological type of oncogenity and expression of cell cycle genes in tumor cells from human mesenchymal stem cells.

In previous experiments, a novel tumor cell line, which was characterized by dominated F6 mutated from human mesenchymal stem cells (hMSCs), was developed. The mechanism and biological characteristics of this mutation are still unclear. In this study, the histological type of F6 cells was investigated by immunohistochemistry with specific markers: vimentin, CD117, desmin, NSE and vWF. The characteristics of proliferation and metastasis were shown by PCNA (proliferating cell nuclear antigen), and nm23 and cell cycle-related genes, such as p16, p21, p53 and pRb, were analyzed by RT-PCR and immunohistochemistry. The expression of hTRAP and BMI-1 were detected by real-time PCR and Western blotting. The activity of telomerase was analyzed by TRAP (telomerase repeat amplification protocol) assay. The results showed that multi-directional differentiation occurred in F6 cells, i.e., special markers of muscle, endothelial cell and nerve system were co-expressed in F6 cells, while hardly expressed in hMSCs. F6 cells maintained the same properties as of MSCs, such as negativity for both CD117 and vimentin. F6 cells exhibited strong positivity for PCNA and negativity for nm23. The cell cycle-related genes, such as p16, p21, p53 and pRb, were not detected in F6 cells, while the expression of hTRAP and BMI-1 was significantly higher. The activity of telomerase was also significantly higher in F6 cells than that in hMSCs. These findings indicated that multi-directional differentiation occurred during the transformation of hMSCs into F6 cells, and that the genes of cell cycle and cell senescence may also be associated with the neoplasia of adult stem cells.

Acid Phosphatase↗
PubMed1990

Expression of novel DNA-binding protein with zinc finger structure in various tumor cells.

We have isolated from B16 mouse melanoma cells a complementary DNA (Mel-18), whose deduced amino acid sequence possesses a characteristic zinc finger structure. Immunostaining with antibodies raised against partial Mel-18 peptide sequences demonstrated nuclear localization of the gene product. We have also demonstrated that this protein has DNA-binding capacity, and the zinc finger is responsible for the DNA binding. At the transcriptional level the Mel-18 mRNA was detected in all tumor cells examined as well as melanoma cells (ontogenically of neural origin) but was scarcely present in normal tissues except neural organs. The transcript is developmentally regulated. These data suggest that Mel-18 may play a role in transcriptional regulation and also in control of cell proliferation and/or neural cell development.

Amino Acid Sequence↗
PubMed1993

flvi-2, a target of retroviral insertional mutagenesis in feline thymic lymphosarcomas, encodes bmi-1.

LC-FeLV is a myc-containing strain of feline leukemia virus which induces thymic lymphosarcoma in the domestic cat with short latency. A locus in feline DNA, termed flvi-2, is commonly interrupted in naturally occurring and experimentally induced thymic lymphosarcomas containing LC-FeLV; thus, interruption of a gene encoded by flvi-2 may cooperate with the myc oncogene in the induction of T-cell tumors by LC-FeLV. Clones homologous to flvi-2 have been isolated from a normal human thymus cDNA library. Nucleotide sequence analysis of the cDNA clones demonstrates that flvi-2 encodes bmi-1, a gene previously identified as a target for MoMuLV integration and as a myc-collaborator in retrovirally-induced B-cell lymphomas in E mu-myc transgenic mice. In feline thymic lymphomas, retroviral integrations occur downstream of the gene, and result in enhanced expression of a bmi-1 transcript of normal size. These findings demonstrate the interruption of bmi-1 in natural as well as experimentally induced tumors, implicate the activation of bmi-1 in the induction of T-cell as well as B-cell lymphoma, and support the premise that bmi-1 functions as a myc collaborator.

Amino Acid Sequence↗
PubMed1996

Probes of chromatin accessibility in the Drosophila bithorax complex respond differently to Polycomb-mediated repression.

The Polycomb group (PcG) of genes are required for maintenance of the repressed state of the homeotic genes in Drosophila. There are similarities between the PcG repression and mating-type silencing in yeast or heterochromatic position effect in Drosophila, which suggest that PcG repression may involve a highly compacted chromatin structure. To test for such a structure, heterologous DNA- binding proteins were used as probes for DNA accessibility in Drosophila embryos. Binding sites for the yeast transcriptional activator GAL4 and for bacteriophage T7 RNA polymerase were inserted into the bithorax (bx) regulatory region of the endogenous Ultrabithorax (Ubx) gene, which is regulated by the PcG. Ubiquitously expressed GAL4 protein directs transcription through its binding sites only in the posterior segments where the bx region is active. The block to GAL4 activation in the more anterior segments is dependent on Polycomb (Pc) function. In contrast, T7 RNA polymerase can transcribe from its target promoter in all segments of the embryo. Thus, Pc-mediated repression blocks activated polymerase II transcription, but does not simply exclude all proteins.

Animals↗
PubMed2006

Bmi1 cooperates with Dnmt1-associated protein 1 in gene silencing.

Polycomb group (PcG) proteins are involved in gene silencing through chromatin modifications. Among polycomb repressive complexes (PRCs), PRC1 exhibits H2A-K119 ubiquitin E3 ligase activity. However, the molecular mechanisms underlying PRC1-mediated gene silencing remain largely obscure. In this study, we found that Bmi1 directly interacts with Dnmt-associated protein 1 (Dmap1), which has been characterized to associate with the maintenance DNA methyltransferase, Dnmt1. Bmi1 was demonstrated to form a ternary complex with Dmap1 and Dnmt1 with Dmap1 in the central position. Chromatin immunoprecipitations confirmed the ternary complex formation within the context of the PRC1 at the Bmi1 target loci. Loss of Dmap1 binding to the Bmi1 target loci was tightly associated with derepressed gene expression in Bmi1-/- cells. Dmap1 knockdown exhibited the same impact as Bmi1 knockout did on the expression of Bmi1 targets, including Hox genes. Collectively, our findings suggest that Bmi1 incorporates Dmap1 in polycomb gene silencing.

Animals↗
PubMed2005

Mammalian polycomb-mediated repression of Hox genes requires the essential spliceosomal protein Sf3b1.

Polycomb group (PcG) proteins are responsible for the stable repression of homeotic (Hox) genes by forming multimeric protein complexes. We show (1) physical interaction between components of the U2 small nuclear ribonucleoprotein particle (U2 snRNP), including Sf3b1 and PcG proteins Zfp144 and Rnf2; and (2) that Sf3b1 heterozygous mice exhibit skeletal transformations concomitant with ectopic Hox expressions. These alterations are enhanced by Zfp144 mutation but repressed by Mll mutation (a trithorax-group gene). Importantly, the levels of Sf3b1 in PcG complexes were decreased in Sf3b1-heterozygous embryos. These findings suggest that Sf3b1-PcG protein interaction is essential for true PcG-mediated repression of Hox genes.

Animals↗