Project description:Non mitotic tumor cells are resistant to conventional chemotherapeutic drugs. However, the mechanisms underlying this phenomenon remain unclear. Here, we found a population that is viable but remains in the G1 phase for an extended period of time (up to 48 h) by Long-term time-lapse observations in Fucci-HCT116 cells and then we conducted DNA microarray-based comparative analyses between the RR (the long-term G1-arrested cells) and R (the G1-arrested cells) fractions, to determine the molecular basis of the G1 arrest/maintenance mechanism. This study is related to GSE34940.
Project description:Non mitotic tumor cells are resistant to conventional chemotherapeutic drugs. However, the mechanisms underlying this phenomenon remain unclear. Here, we found a population that is viable but remains in the G1 phase for an extended period of time (up to 48 h) by Long-term time-lapse observations in Fucci-HCT116 cells and then we conducted DNA microarray-based comparative analyses between the RR (the long-term G1-arrested cells) and R (the G1-arrested cells) fractions, to determine the molecular basis of the G1 arrest/maintenance mechanism. This study is related to GSE34940. The labeled cRNAs were hybridized on 4X44K v2 Agilent Whole Human Genome dual color Microarrays (G4845A) in two dye swap experiments, resulting in four individual microarrays.
Project description:<p>Cell size and the cell cycle are intrinsically coupled and abnormal increases in cell size are associated with senescence and permanent cell cycle arrest. The mechanism by which overgrowth primes cells to withdraw from the cell cycle remains unknown. We investigate this here using CDK4/6 inhibitors that arrest cell cycle progression during G0/G1 and are used in the clinic to treat ER+/HER2- metastatic breast cancer. We demonstrate that CDK4/6 inhibition promotes cellular overgrowth during G0/G1, causing p38MAPK-p53-p21-dependent cell cycle withdrawal. We find that cell cycle withdrawal is triggered by two waves of p21 induction. First, overgrowth during a long-term G0/G1 arrest induces an osmotic stress response. This stress response produces the first wave of p21 induction. Second, when CDK4/6 inhibitors are removed, a fraction of cells escape long term G0/G1 arrest and enter S-phase where overgrowth-driven replication stress results in a second wave of p21 induction that causes cell cycle withdrawal from G2, or the subsequent G1. We propose a model whereby both waves of p21 induction contribute to promote permanent cell cycle arrest. This model could explain why cellular hypertrophy is associated with senescence and why CDK4/6 inhibitors have long-lasting effects in patients.</p>
Project description:Cell size and the cell cycle are intrinsically coupled and abnormal increases in cell size are associated with senescence and permanent cell cycle arrest. The mechanism by which overgrowth primes cells to withdraw from the cell cycle remains unknown. We investigate this here using CDK4/6 inhibitors that arrest cell cycle progression during G0/G1 and are used in the clinic to treat ER+/HER2- metastatic breast cancer. We demonstrate that CDK4/6 inhibition promotes cellular overgrowth during G0/G1, causing p38MAPK-p53-p21-dependent cell cycle withdrawal. We find that cell cycle withdrawal is triggered by two waves of p21 induction. First, overgrowth during a long-term G0/G1 arrest induces an osmotic stress response. This stress response produces the first wave of p21 induction. Second, when CDK4/6 inhibitors are removed, a fraction of cells escape long term G0/G1 arrest and enter S-phase where overgrowth-driven replication stress results in a second wave of p21 induction that causes cell cycle withdrawal from G2, or the subsequent G1. We propose a model whereby both waves of p21 induction contribute to promote permanent cell cycle arrest. This model could explain why cellular hypertrophy is associated with senescence and why CDK4/6 inhibitors have long-lasting effects in patients.
Project description:Immuno-histochemistry for RelA in breast tumors revealed a range of staining intensity and negative correlation between RelA levels and proliferation-index in estrogen receptor-positive tumors. Conditional expression of RelA arrested proliferation in primary mammary and fallopian tube epithelial cells. RelA dependent CDK4 downregulation was responsible for activating the G1/S checkpoint and cell cycle arrest. RelA target genes, including Interferon Response Factors (IRF), were up-regulated in the arrested cells. Among the IRFs, IRF1 expression correlates with RelA expression. Suppressing IRF1 restored CDK4 levels and rescued RelA-dependent proliferation arrest analogous to abrogating the G1/S checkpoint or restoring CDK4 levels. Apart from cyclins, regulation of CDK4 by the RelA-IRF1 transcriptional network controls proliferation of breast tumors and predicts sensitivity to a CDK4/6 inhibitor.
