• Conserved sequence-specific lincRNA-steroid receptor interactions drive transcriptional repression and direct cell fate

      Hudson, William H.; Pickard, Mark R.; de Vera, Ian M.; Kuiper, Emily G.; Mourtada-Maarabouni, Mirna; Conn, Graeme L.; Kojetin, Douglas J.; Williams, Gwyn T.; Ortlund, Eric A.; Emory University School of Medicine; Keele University; Scripps Research Institute (Nature Publishing Group, 2014-11-07)
      The majority of the eukaryotic genome is transcribed, generating a significant number of long intergenic noncoding RNAs (lincRNAs). Although lincRNAs represent the most poorly understood product of transcription, recent work has shown lincRNAs fulfill important cellular functions. In addition to low sequence conservation, poor understanding of structural mechanisms driving lincRNA biology hinders systematic prediction of their function. Here we report the molecular requirements for the recognition of steroid receptors (SRs) by the lincRNA growth arrest-specific 5 (Gas5), which regulates steroid-mediated transcriptional regulation, growth arrest and apoptosis. We identify the functional Gas5-SR interface and generate point mutations that ablate the SR-Gas5 lincRNA interaction, altering Gas5-driven apoptosis in cancer cell lines. Further, we find that the Gas5 SR-recognition sequence is conserved among haplorhines, with its evolutionary origin as a splice acceptor site. This study demonstrates that lincRNAs can recognize protein targets in a conserved, sequence-specific manner in order to affect critical cell functions.
    • Interactions between PP4 and PEA-15 in the regulation of cell proliferation and apoptosis of breast cancer cells

      Mohammed, Hiba N.; Pickard, Mark R.; Mourtada-Maarabouni, Mirna; Keele University, United Kingdom (NCRI Cancer Conference 2015 Abstracts, 2015)
      Background The serine/threonine protein phosphatase 4 (PP4) is recognised to regulate a variety of cellular functions. Our previous work has shown that the catalytic subunit of PP4 (PP4c) promotes cell death and inhibits proliferation in breast cancer cells, suggestive of a role of PP4c as tumour suppressor gene. Phosphoprotein enriched in astrocytes 15 (PEA-15), a member of the death effector domain protein family known to control cell survival, is reported to be regulated by PP4c. The aims of this study were to investigate the involvement of PEA-15 in mediating the effects of PP4c on breast cancer cells. Method PEA-15 phosphorylation was examined by western blot analysis on proteins extracted from MCF7 and MDA-MB-231 cells over-expressing PP4 and PP4 knock down cells. To investigate the role of PEA-15 in mediating the effects of PP4c, MCF7 and MDA-MB-231 were transfected with control (-) siRNA or with three different PEA-15 specific siRNAs. 48 h post-transfection, control cells (transfected with negative control siRNA) and cells transfected with PEA-15 siRNAs were transiently transfected with pcDNA3.1-PP4c expression construct or pcDNA3.1. Cell viability and apoptosis level were assessed post transfection. Results In MCF7 and MDA-MB-231 cells, the phosphorylation state of PEA-15 increased when PP4c expression was suppressed and decreased when PP4c was over-expressed. Over-expression of PP4c in cells transfected with (-) siRNA caused 50% reduction in viability compared to cells transfected with empty vector. Cells transfected with PEA-15 siRNAs showed a decrease in viable cell number and long term survival. However, over-expression of PP4c in these cells did not have any additional effect on the decrease in cell viability. Conclusion These observations suggest that the induction of apoptosis by over-expression of PP4c is mediated, at least in part, by the dephosphorylation of PEA-15. The interactions between PEA-15 and PP4c may therefore be critical in breast cancer tumorigenesis.
    • The long non-coding RNA NEAT1 regulates cell survival in breast cancer cell lines

      Almnaseer, Zainab; Pickard, Mark R.; Mourtada-Maarabouni, Mirna; Keele University, United Kingdom (NCRI Cancer Conference 2015 Abstracts, 2015)
      Background Nuclear long non-coding RNAs (LncRNAs) regulate various cellular processes including the organization of nuclear sub-structures, the alteration of chromatin state, and the regulation of gene expression. Nuclear Enriched Abundant Transcript 1 (NEAT1) is a nuclear lncRNA transcribed from chromosome 11q13. Two transcripts are produced from the NEAT1 gene, 3.7-kb NEAT1_v1 and 23-kb NEAT1_v2. Both isoforms participate in the formation of the nuclear paraspeckles . NEAT1 is reported to be overexpressed in prostate cancer and a direct transcriptional target of hypoxia-inducible factor in many breast cancer cell lines. The aims of this study were to determine the effects of silencing NEAT1 on breast cancer cell survival. Method MCF7 and MDA-MB 231 cells were transfected with siRNAs to different NEAT1 sequences or NEAT1 antisense oligonucleotides (ASO). Controls received scrambled siRNA or scrambled oligonucleotide, as appropriate. In some experiments, cells were exposed to ultraviolet-C (UV-C) light post-transfection to induce apoptosis, and then culture viability and apoptosis were assessed. NEAT1 expression was evaluated by qRT-PCR TaqMan® analysis. Results In MCF7 and MDA-MB-231 cells, siRNA-mediated silencing of NEAT1 reduced basal survival and after UV-C irradiation and decreased their colony forming ability. NEAT1 ASOs were more effective in silencing NEAT1 and caused a greater reduction in cell viability. NEAT1 silencing also affected cell cycle profile by enhancing the proportion of cells in G0/G1 phase. Conclusion NEAT1 regulates the survival of Breast cells. Down regulation of NEAT1 expression decreased cell survival, proliferation and modulated cell cycle progression of breast cancer cells, indicating a link between the NEAT1 expression levels and carcinogenesis of breast cancer.
    • The protein phosphatase 4 - PEA15 axis regulates the survival of breast cancer cells

      Mohammed, Hiba N.; Pickard, Mark R.; Mourtada-Maarabouni, Mirna; Keele University; University of Chester (Elsevier, 2016-06-15)
      BACKGROUND: The control of breast cell survival is of critical importance for preventing breast cancer initiation and progression. The activity of many proteins which regulate cell survival is controlled by reversible phosphorylation, so that the relevant kinases and phosphatases play crucial roles in determining cell fate. Several protein kinases act as oncoproteins in breast cancer and changes in their activities contribute to the process of transformation. Through counteracting the activity of oncogenic kinases, the protein phosphatases are also likely to be important players in breast cancer development, but this class of molecules is relatively poorly understood. Here we have investigated the role of the serine/threonine protein phosphatase 4 in the control of cell survival of breast cancer cells. METHODS: The breast cancer cell lines, MCF7 and MDA-MB-231, were transfected with expression vectors encoding the catalytic subunit of protein phosphatase 4 (PP4c) or with PP4c siRNAs. Culture viability, apoptosis, cell migration and cell cycle were assessed. The involvement of phosphoprotein enriched in astrocytes 15kDa (PEA15) in PP4c action was investigated by immunoblotting approaches and by siRNA-mediated silencing of PEA15. RESULTS: In this study we showed that PP4c over-expression inhibited cell proliferation, enhanced spontaneous apoptosis and decreased the migratory and colony forming abilities of breast cancer cells. Moreover, PP4c down-regulation produced complementary effects. PP4c is demonstrated to regulate the phosphorylation of PEA15, and PEA15 itself regulates the apoptosis of breast cancer cells. The inhibitory effects of PP4c on breast cancer cell survival and growth were lost in PEA15 knockdown cells, confirming that PP4c action is mediated, at least in part, through the de-phosphorylation of apoptosis regulator PEA15. CONCLUSION: Our work shows that PP4 regulates breast cancer cell survival and identifies a novel PP4c-PEA15 signalling axis in the control of breast cancer cell survival. The dysfunction of this axis may be important in the development and progression of breast cancer.
    • Regulation of the cell cycle and cell death by protein phosphatase 4 in breast cancer cell lines

      Mohammed, Hiba N.; Pickard, Mark R.; Williams, Gwyn T.; Mourtada-Maarabouni, Mirna; Keele University, United Kingdom (NCRI Cancer Conference 2014 Abstracts, 2014)
      Background At the molecular level, cell death is often regulated by the level of phosphorylation of particular proteins, i.e. by the balance of between opposing kinase and phosphatase activities on those proteins. Protein phosphatase 4 (PP4) is a PP2A-related serine/threonine phosphatase. PP2A has already been implicated in the control of cell proliferation, cell cycle and tumorigenesis. Using a functional expression cloning strategy, we have previously identified the catalytic subunit of PP4 (PP4c) as an important gene influencing the regulation of both apoptosis and cell proliferation in human leukaemic cell lines and in normal lymphocytes. The aims of this study were to examine the effects of PP4c overexpression and silencing on the cell death and survival of breast cancer cell lines. Method MCF7 and MDA-MB-231 cells were transfected with pcDNA3.1 encoding PP4c (pcDNA3-PP4c) or siRNAs to different PP4c sequences. Cells transfected with scrambled siRNA or empty vector were considered as controls. Culture viability, apoptosis and cell cycle were assessed post transfection. Results In MCF7 and metastatic MDA-MB-231 cells, PP4c over-expression exerted an inhibitory effect on cell proliferation, enhanced spontaneous apoptosis and decreased their colony forming ability. Conversely, siRNA mediated silencing of PP4 enhanced the proliferation and survival of MCF7 and MDA-MB-231 cells, affected cell cycle kinetics by enhancing the proportion of cells in S and G2/M phases, increased the colony forming ability and stimulated the anchorage independent growth. Conclusion PP4c promotes cell death and inhibits proliferation in breast cells, suggestive of a role of PP4c as tumour suppressor gene. Down regulation of PP4c expression increases cell survival, proliferation and anchorage independent growth of breast cancer cells, indicating a potential link between the PP4c expression levels, tumorigenesis and metastasis.