Sladjana Gagrica

Cancer Research UK, Londinium, England, United Kingdom

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Publications (7)42.06 Total impact

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    ABSTRACT: Glioblastoma (GBM) is an aggressive brain tumor whose growth is driven by stem cell-like cells. BMP signaling triggers cell-cycle exit and differentiation of GBM stem cells (GSCs) and, therefore, might have therapeutic value. However, the epigenetic mechanisms that accompany differentiation remain poorly defined. It is also unclear whether cell-cycle arrest is terminal. Here we find only a subset of GSC cultures exhibit astrocyte differentiation in response to BMP. Although overtly differentiated non-cycling astrocytes are generated, they remain vulnerable to cell-cycle re-entry and fail to appropriately reconfigure DNA methylation patterns. Chromatin accessibility mapping identified loci that failed to alter in response to BMP and these were enriched in SOX transcription factor-binding motifs. SOX transcription factors , therefore, may limit differentiation commitment. A similar propensity for cell-cycle re-entry and de-differentiation was observed in GSC-derived oligodendrocyte-like cells. These findings highlight significant obstacles to BMP-induced differentiation as therapy for GBM.
    Full-text · Article · Nov 2015 · Stem Cell Reports
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    ABSTRACT: Cellular senescence, the stable cell cycle arrest elicited by various forms of stress, is an important facet of tumor suppression. Although much is known about the key players in the implementation of senescence, including the pRb and p53 axes and the cyclin dependent kinase inhibitors p16(INK4a) and p21(CIP1), many details remain unresolved. In studying conditional senescence in human fibroblasts that express a temperature sensitive SV40 large T-antigen (T-Ag), we uncovered an unexpected role for CDK4. At the permissive temperature, where pRb and p53 are functionally compromised by T-Ag, cyclin D-CDK4 complexes are disrupted by the high p16(INK4a) levels and reduced expression of p21(CIP1). In cells arrested at the non-permissive temperature, p21(CIP1) promotes reassembly of cyclin D-CDK4 yet pRb is in a hypo-phosphorylated state, consistent with cell cycle arrest. In exploring whether the reassembled cyclin D-CDK4-p21 complexes are functional, we found that shRNA-mediated knockdown or chemical inhibition of CDK4 prevented the increase in cell size associated with the senescent phenotype by allowing the cells to arrest in G1 rather than G2/M. The data point to a role for CDK4 kinase activity in a G2 checkpoint that contributes to senescence.
    Preview · Article · Feb 2015 · Cell cycle (Georgetown, Tex.)
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    ABSTRACT: Glioblastoma multiforme (GBM) is the most common primary brain cancer in adults and there are few effective treatments. GBMs contain cells with molecular and cellular characteristics of neural stem cells that drive tumour growth. Here we compare responses of human glioblastoma-derived neural stem (GNS) cells and genetically normal neural stem (NS) cells to a panel of 160 small molecule kinase inhibitors. We used live-cell imaging and high content image analysis tools and identified JNJ-10198409 (J101) as an agent that induces mitotic arrest at prometaphase in GNS cells but not NS cells. Antibody microarrays and kinase profiling suggested that J101 responses are triggered by suppression of the active phosphorylated form of polo-like kinase 1 (Plk1) (phospho T210), with resultant spindle defects and arrest at prometaphase. We found that potent and specific Plk1 inhibitors already in clinical development (BI 2536, BI 6727 and GSK 461364) phenocopied J101 and were selective against GNS cells. Using a porcine brain endothelial cell blood-brain barrier model we also observed that these compounds exhibited greater blood-brain barrier permeability in vitro than J101. Our analysis of mouse mutant NS cells (INK4a/ARF(-/-), or p53(-/-)), as well as the acute genetic deletion of p53 from a conditional p53 floxed NS cell line, suggests that the sensitivity of GNS cells to BI 2536 or J101 may be explained by the lack of a p53-mediated compensatory pathway. Together these data indicate that GBM stem cells are acutely susceptible to proliferative disruption by Plk1 inhibitors and that such agents may have immediate therapeutic value.
    Full-text · Article · Oct 2013 · PLoS ONE
  • Sladjana Gagrica · Sharon Brookes · Emma Anderton · Janice Rowe · Gordon Peters
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    ABSTRACT: The cyclin-dependent kinase (CDK) inhibitors, p18(INK4c) and p16(INK4a), both have the credentials of tumor suppressors in human cancers and mouse models. For p16(INK4a), the underlying rationale is its role in senescence, but the selective force for inactivation of p18(INK4c) in incipient cancer cells is less clear. Here, we show that in human fibroblasts undergoing replicative or oncogene-induced senescence, there is a marked decline in the levels of p18(INK4c) protein and RNA, which mirrors the accumulation of p16(INK4a). Downregulation of INK4c is not dependent on p16(INK4a), and RAS can promote the loss of INK4c without cell-cycle arrest. Downregulation of p18(INK4c) correlates with reduced expression of menin and E2F1 but is unaffected by acute cell-cycle arrest or inactivation of the retinoblastoma protein (pRb). Collectively, our data question the idea that p18(INK4c) acts as a backup for loss of p16(INK4a) and suggest that the apparent activation of p18(INK4c) in some settings represents delayed senescence rather than increased expression. We propose that the contrasting behavior of the two very similar INK4 proteins could reflect their respective roles in senescence versus differentiation.
    No preview · Article · Nov 2011 · Cancer Research
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    ABSTRACT: Here we report the identification of the LIN complex (LINC), a human multiprotein complex that is required for transcriptional activation of G2/M genes. LINC is related to the recently identified dREAM and DRM complexes of Drosophila and C. elegans that contain homologs of the mammalian retinoblastoma tumor suppressor protein. The LINC core complex consists of at least five subunits including the chromatin-associated LIN-9 and RbAp48 proteins. LINC dynamically associates with pocket proteins, E2F and B-MYB during the cell cycle. In quiescent cells, LINC binds to p130 and E2F4. During cell cycle entry, E2F4 and p130 dissociate and LINC switches to B-MYB and p107. Chromatin Immunoprecipitation experiments demonstrate that LINC associates with a large number of E2F-regulated promoters in quiescent cells. However, RNAi experiments reveal that LINC is not required for repression. In S-phase, LINC selectively binds to the promoters of G2/M genes whose products are required for mitosis and plays an important role in their cell cycle dependent activation.
    Full-text · Article · Sep 2007 · Cell cycle (Georgetown, Tex.)
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    ABSTRACT: Here we report the identification of the LIN complex (LINC), a human multiprotein complex that is required for transcriptional activation of G2/sub>/M genes. LINC is related to the recently identified dREAM and DRM complexes of Drosophila and C.elegans that contain homologues of the mammalian retinoblastoma tumor suppressor protein. The LINC core complex consists of at least five subunits including the chromatin-associated LIN-9 and RbAp48 proteins. LINC dynamically associates with pocket proteins, E2F and B-MYB during the cell cycle. In quiescent cells, LINC binds to p130 and E2F4. During cell cycle entry, E2F4 and p130 dissociate and LINC switches to B-MYB and p107. Chromatin Immunoprecipitation experiments demonstrate that LINC associates with a large number of E2F-regulated promoters in quiescent cells. However, RNAi experiments reveal that LINC is not required for repression. In S phase, LINC selectively binds to the promoters of G2/sub>/M genes whose products are required for mitosis and plays an important role in their cell cycle dependent activation.
    No preview · Article · Aug 2007 · Cell cycle (Georgetown, Tex.)
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    ABSTRACT: Genetic studies in Caenorhabditis elegans identified lin-9 to function together with the retinoblastoma homologue lin-35 in vulva differentiation. We have now identified a human homologue of Lin-9 (hLin-9) and provide evidence about its function in the mammalian pRB pathway. hLin-9 binds to pRB and cooperates with pRB in flat cell formation in Saos-2 cells. In addition, hLin-9 synergized with pRB and Cbfal to transactivate an osteoblast-specific reporter gene. In contrast, hLin-9 was not involved in pRB-mediated inhibition of cell cycle progression or repression of E2F-dependent transactivation. Consistent with these data, hLin-9 was able to associate with partially penetrant pRB mutants that do not bind to E2F, but retain the ability to activate transcription and to promote differentiation. hLin-9 can also inhibit oncogenic transformation, dependent on the presence of a functional pRB protein. RNAi-mediated knockdown of Lin-9 can substitute for the loss of pRB in transformation of human primary fibroblasts. These data suggest that hLin-9 has tumor-suppressing activities and that the ability of hLin-9 to inhibit transformation is mediated through its association with pRB.
    Full-text · Article · Nov 2004 · The EMBO Journal

Publication Stats

169 Citations
42.06 Total Impact Points

Institutions

  • 2015
    • Cancer Research UK
      Londinium, England, United Kingdom
  • 2013-2015
    • University College London
      • Department of Cancer Biology
      Londinium, England, United Kingdom
  • 2011
    • London Research Institute
      Londinium, England, United Kingdom
  • 2007
    • University of Wuerzburg
      • Department of Physiological Chemistry I
      Würzburg, Bavaria, Germany
  • 2004
    • Philipps University of Marburg
      Marburg, Hesse, Germany