Small contribution of G1 checkpoint control manipulation to modulation of p53-mediated apoptosis

Canman, Christine E.; Kastan, Michael B.

doi:10.1038/sj.onc.1201612

Cited by 22 publications

(12 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Significantly, we did not observe an increased sensitivity to ionizing radiation in the HCT-116 ATR Ϫ/flox cell line, again showing the disparity between ATR and ATM because loss of ATM leads to classic radiosensitivity (30,31). It seems unlikely that this increased sensitivity to hypoxia/ reoxygenation is because of a failure in a checkpoint response (32,33); therefore, we suggest that during hypoxia exposure ATR acts to protect and stabilize stalled replication forks from collapse and hence DNA damage and that this is at least in part mediated via Chk1 activity. The consequences of damaged replication forks are numerous and include genomic instability and reproductive failure.…”

Section: Discussionmentioning

confidence: 65%

Inhibition of ATR Leads to Increased Sensitivity to Hypoxia/Reoxygenation

2004

View full text Add to dashboard Cite

The transient opening and closing of tumor vasculature result in periods of severe oxygen deprivation (hypoxia) followed by reoxygenation. This exerts a positive selective pressure for cells that have lost their sensitivity to killing by reduced oxygen levels. These cells are effectively resistant to hypoxia-induced apoptosis and conventional therapeutic approaches. Here we show hypoxia-induced S-phase arrest results in regions of single-stranded DNA in stalled replication forks and signals the activation of ATR. S-phase cells represent the most sensitive phase of the cell cycle to the stress of hypoxia/reoxygenation. Loss of ATR or inhibition of ATR kinase activity results in a further loss of reproductive viability in S-phase cells when exposed to hypoxic conditions followed by reoxygenation but has little effect on the inhibition of DNA synthesis. This is, at least in part, mediated via Chk1 signaling because loss of Chk1 also results in increased sensitivity to hypoxia/reoxygenation. The observed decrease in reproductive survival is in part because of the accumulation of DNA damage in S-phase cells during hypoxia exposure in the absence of full ATR activity. Therefore, ATR acts to protect stalled replication forks during hypoxia exposure. In conclusion, ATR and Chk1 play critical roles in the cellular response to hypoxia/reoxygenation, and inhibitors of ATR and Chk1 represent new hypoxic cell cytotoxins.

show abstract

Section: Discussionmentioning

confidence: 65%

Inhibition of ATR Leads to Increased Sensitivity to Hypoxia/Reoxygenation

2004

View full text Add to dashboard Cite

show abstract

“…At various time points, cells were harvested and fixed in 70% methanol. Cells were then stained for both DNA content and BrdUrd incorporation by the acid denaturation-protease method by using fluorescein isothiocyanate (FITC)-conjugated anti-BrdUrd (Becton Dickinson) as described previously (6).…”

Section: Methodsmentioning

confidence: 99%

Two Molecularly Distinct G₂/M Checkpoints Are Induced by Ionizing Irradiation

Kim

Lim

et al. 2002

Molecular and Cellular Biology

445

373

View full text Add to dashboard Cite

Cell cycle checkpoints are among the multiple mechanisms that eukaryotic cells possess to maintain genomic integrity and minimize tumorigenesis. Ionizing irradiation (IR) induces measurable arrests in the G 1 , S, and G 2 phases of the mammalian cell cycle, and the ATM (ataxia telangiectasia mutated) protein plays a role in initiating checkpoint pathways in all three of these cell cycle phases. However, cells lacking ATM function exhibit both a defective G 2 checkpoint and a prolonged G 2 arrest after IR, suggesting the existence of different types of G 2 arrest. Two molecularly distinct G 2 /M checkpoints were identified, and the critical importance of the choice of G 2 /M checkpoint assay was demonstrated. The first of these G 2 /M checkpoints occurs early after IR, is very transient, is ATM dependent and dose independent (between 1 and 10 Gy), and represents the failure of cells which had been in G 2 at the time of irradiation to progress into mitosis. Cell cycle assays that can distinguish mitotic cells from G 2 cells must be used to assess this arrest. In contrast, G 2 /M accumulation, typically assessed by propidium iodide staining, begins to be measurable only several hours after IR, is ATM independent, is dose dependent, and represents the accumulation of cells that had been in earlier phases of the cell cycle at the time of exposure to radiation. G 2 /M accumulation after IR is not affected by the early G 2 /M checkpoint and is enhanced in cells lacking the IR-induced S-phase checkpoint, such as those lacking Nbs1 or Brca1 function, because of a prolonged G 2 arrest of cells that had been in S phase at the time of irradiation. Finally, neither the S-phase checkpoint nor the G 2 checkpoints appear to affect survival following irradiation. Thus, two different G 2 arrest mechanisms are present in mammalian cells, and the type of cell cycle checkpoint assay to be used in experimental investigation must be thoughtfully selected.

show abstract

“…This 6-1 cell is a subline of interleukin 3-dependent mouse pro-B lymphoid cell line, BaF3, and stably co-expresses tTA and lacI (53,54). The BaF3 cell is reported to possess functional p53 and undergo p53-dependent apoptosis by DNA-damaging agents, such as X-irradiation and cisplatin (59,60). Upon transient trans- FIG.…”

Section: Fig 4 Mapping Of Protein Interaction Domains a In Vitro mentioning

confidence: 99%

Physical Interaction and Functional Antagonism between the RNA Polymerase II Elongation Factor ELL and p53

Shinobu

Maeda

Aso

et al. 1999

Journal of Biological Chemistry

View full text Add to dashboard Cite

ELL was originally identified as a gene that undergoes translocation with the trithorax-like MLL gene in acute myeloid leukemia. Recent studies have shown that the gene product, ELL, functions as an RNA polymerase II elongation factor that increases the rate of transcription by RNA polymerase II by suppressing transient pausing. Using yeast two-hybrid screening with ELL as bait, we isolated the p53 tumor suppressor protein as a specific interactor of ELL. The interaction involves respectively the transcription elongation activation domain of ELL and the C-terminal tail of p53. Through this interaction, ELL inhibits both sequence-specific transactivation and sequence-independent transrepression by p53. Thus, ELL acts as a negative regulator of p53 in transcription. Conversely, p53 inhibits the transcription elongation activity of ELL, suggesting that p53 is capable of regulating general transcription by RNA polymerase II through controlling the ELL activity. Elevated levels of ELL in cells resulted in the inhibition of p53-dependent induction of endogenous p21 and substantially protected cells from p53-mediated apoptosis that is induced by genotoxic stress. Our observations indicate the existence of a mutually inhibitory interaction between p53 and a general transcription elongation factor ELL and raise the possibility that an aberrant interaction between p53 and ELL may play a role in the genesis of leukemias carrying MLL-ELL gene translocations.The ELL gene (also known as MEN) was molecularly identified as a gene that was fused to the Drosophila trithorax-like MLL gene (also called ALL-1 or Hrx) in acute myeloid leukemia carrying the t(11;19)(q23;p13.1) chromosomal translocation (1, 2). The gene product, ELL, was recently demonstrated to function as an RNA polymerase II elongation factor that increases the overall rate of transcription elongation by RNA polymerase II via suppression of transient pausing by the polymerase at many sites along DNA (3).The connection between transcription elongation factors and oncogenesis was first provided by the finding that the product of VHL tumor suppressor gene, VHL, associates with the complex of the B and C regulatory subunits of another transcription elongation factor, elongin (4, 5). Binding of VHL to the elongin BC complex inhibits its ability to activate elongin A subunit in transcription elongation. The observation that many of the naturally occurring VHL mutants exhibit substantially reduced binding to the elongin BC complexes led to the suggestion that tumor suppression by VHL may involve negative regulation of elongin as a transcription elongation factor.ELL is the second transcription elongation factor found associated with human malignancy. The chimeric protein generated by MLL-ELL gene translocation contains an N-terminal AT-hook DNA binding domain and the methyltransferase-like domain of MLL that is fused to almost the entire ELL sequences (1, 2). Expression of the MLL portion of the fusion protein appears to be insufficient for inducing the leukemic phenotype ...

show abstract

Small contribution of G1 checkpoint control manipulation to modulation of p53-mediated apoptosis

Cited by 22 publications

References 46 publications

Inhibition of ATR Leads to Increased Sensitivity to Hypoxia/Reoxygenation

Inhibition of ATR Leads to Increased Sensitivity to Hypoxia/Reoxygenation

Two Molecularly Distinct G₂/M Checkpoints Are Induced by Ionizing Irradiation

Physical Interaction and Functional Antagonism between the RNA Polymerase II Elongation Factor ELL and p53

Contact Info

Product

Resources

About

Small contribution of G1 checkpoint control manipulation to modulation of p53-mediated apoptosis

Cited by 22 publications

References 46 publications

Inhibition of ATR Leads to Increased Sensitivity to Hypoxia/Reoxygenation

Inhibition of ATR Leads to Increased Sensitivity to Hypoxia/Reoxygenation

Two Molecularly Distinct G2/M Checkpoints Are Induced by Ionizing Irradiation

Physical Interaction and Functional Antagonism between the RNA Polymerase II Elongation Factor ELL and p53

Contact Info

Product

Resources

About

Two Molecularly Distinct G₂/M Checkpoints Are Induced by Ionizing Irradiation