Biomedical subjects

Laure Crabbe

Publications and source records attributed to Laure Crabbe.

4 recordsLinked to original sources

PubMed2005

Functional human telomeres are recognized as DNA damage in G2 of the cell cycle.

Telomeres have to be distinguished from DNA breaks that initiate a DNA damage response. Proteins involved in the DNA damage response have previously been found at telomeres in transformed cells; however, the importance of these factors for telomere function has not been understood. Here, we show that telomeres of telomerase-negative primary cells recruit Mre11, phosphorylated NBS1, and ATM in every G2 phase of the cell cycle. This recruitment correlates with a partial release of telomeric POT1; moreover, telomeres were found to be accessible to modifying enzymes at this time in the cell cycle, suggesting that they are unprotected. Degradation of the MRN complex, as well as inhibition of ATM, led to telomere dysfunction. Consequentially, we propose that a localized DNA damage response at telomeres after replication is essential for recruiting the processing machinery that promotes formation of a chromosome end protection complex.

Cell Line↗

PubMed2005

In the end, it's all structure.

Chromosome end protection is essential for all organisms with linear genomes. Specialized structures, called telomeres, accomplish this protection by forming DNA-protein complexes that hide the natural chromosome ends from the DNA damage machinery. In mammalian cells protection takes place on several levels. Telomeric DNA forms large duplex loops with the help of telomeric proteins, consequently hiding the very tip of the telomere. Telomeric proteins play additional roles in protecting the end from degradation, regulating telomere length, and suppressing the DNA damage response machinery. Here we summarize the current knowledge about telomere structure, and discuss the future directions of the field.

Animals↗

PubMed2004

Defective telomere lagging strand synthesis in cells lacking WRN helicase activity.

Cells from Werner syndrome patients are characterized by slow growth rates, premature senescence, accelerated telomere shortening rates, and genome instability. The syndrome is caused by the loss of the RecQ helicase WRN, but the underlying molecular mechanism is unclear. Here we report that cells lacking WRN exhibit deletion of telomeres from single sister chromatids. Only telomeres replicated by lagging strand synthesis were affected, and prevention of loss of individual telomeres was dependent on the helicase activity of WRN. Telomere loss could be counteracted by telomerase activity. We propose that WRN is necessary for efficient replication of G-rich telomeric DNA, preventing telomere dysfunction and consequent genomic instability.

Alleles↗

PubMed2004

Oxaliplatin-induced mitochondrial apoptotic response of colon carcinoma cells does not require nuclear DNA.

We previously established a model of acquired oxaliplatin resistance derived from the HCT116 oxaliplatin-sensitive cell line (HCT116S) and consisting in two resistant clones (HCT116R1, HCT116R2) and their total or partial revertants (HCT116Rev1 and HCT116Rev2, respectively). Using this cellular model, we explored the contribution of mitochondrial apoptosis and nuclear DNA to oxaliplatin-mediated apoptosis induction and oxaliplatin resistance. We showed that the activity of oxaliplatin is mediated by the induction of Bax/Bak-dependent mitochondrial apoptosis and that oxaliplatin resistance is mediated by a defect in Bax/Bak activation correlating with a reduced loss of the mitochondrial transmembrane potential (DeltaPsim). In addition, we observed that p53 only contributed marginally to oxaliplatin-induced cytotoxicity and was not involved in oxaliplatin resistance. Moreover and surprisingly, depletion of the nucleus in HCT116S cells did not abolish the oxaliplatin-induced DeltaPsim loss indicative of imminent apoptosis. Enucleation abolished the oxaliplatin resistance of HCT116R1 cells, while HCT116R2 cytoplasts conserved their resistant phenotype. Altogether, these data demonstrate that oxaliplatin exerts its cytotoxic effects by inducing mitochondrial apoptosis and that these effects can be initiated by interacting on other cellular structures than nuclear DNA. Resistance to oxaliplatin may imply both nuclear and cytoplasmic compartments.

Antineoplastic Agents↗