Biomedical subjects

Audrey Kauffmann

Publications and source records attributed to Audrey Kauffmann.

4 recordsLinked to original sources

PubMed2006

Interrelation between polyploidization and megakaryocyte differentiation: a gene profiling approach.

Polyploidization is a part of the normal developmental process leading to platelet production during megakaryocyte (MK) differentiation. Ploidization is mainly involved in cell enlargement, but it is not clear whether gene expression is modified during MK ploidization. In this study, human MKs were grown from CD34(+) cells in the presence of thrombopoietin and sorted according to their ploidy level. A pangenomic microarray technique was applied to compare gene expression in 2N-, 4N-, 8N-, and 16N-sorted MKs. Using hierarchical clustering, we demonstrated that 2N and 4N MKs or 8N and 16N MKs are 2 different close populations with 105 discriminating genes. In the second approach, we determined the profile of genes that were continuously down- and up-regulated during polyploidization. Among the 100 down-regulated genes, 24 corresponded to genes involved in DNA replication and repair. The great majority of up-regulated genes corresponded to genes directly involved in platelet functions, such as genes encoding specific platelet glycoproteins and alpha-granule proteins, actin and microtubule cytoskeleton, factors involved in signaling, and transport proteins. Together, these results suggest that MK polyploidization per se does not regulate gene expression but is intrinsically included in the differentiation process.

Antigens, CD34↗

PubMed2006

Apoptosis regulation in tetraploid cancer cells.

Tetraploidy can result in cancer-associated aneuploidy. As shown here, freshly generated tetraploid cells arising due to mitotic slippage or failed cytokinesis are prone to undergo Bax-dependent mitochondrial membrane permeabilization and subsequent apoptosis. Knockout of Bax or overexpression of Bcl-2 facilitated the survival of tetraploid cells at least as efficiently as the p53 or p21 knockout. When tetraploid cells were derived from diploid p53 and Bax-proficient precursors, such cells exhibited an enhanced transcription of p53 target genes. Tetraploid cells exhibited an enhanced rate of spontaneous apoptosis that could be suppressed by inhibition of p53 or by knockdown of proapoptotic p53 target genes such as BBC3/Puma, GADD45A and ferredoxin reductase. Unexpectedly, tetraploid cells were more resistant to DNA damaging agents (cisplatin, oxaliplatin and camptothecin) than their diploid counterparts, and this difference disappeared upon inhibition of p53 or knockdown of p53-inducible ribonucleotide reductase. Tetraploid cells were also more resistant against UVC and gamma-irradiation. These data indicate the existence of p53-dependent alterations in apoptosis regulation in tetraploid cells.

Animals↗

PubMed2006

Identification of target actin content and polymerization status as a mechanism of tumor resistance after cytolytic T lymphocyte pressure.

To investigate tumor resistance to T cell lysis, a resistant variant was selected after specific cytolytic T lymphocytes (CTL) selection pressure. Although the resistant variant triggered perforin and granzyme B transcription in specific CTLs, as well as their degranulation, it exhibited a dramatic resistance to cytotoxic T cell killing. It also displayed strong morphological changes with alterations of the actin cytoskeleton. Electron microscopy analysis revealed a loosen interaction between CTLs and the resistant variant despite the formation of apparently normal conjugates. Transcriptional profiling identified a gene expression signature that distinguished sensitive from resistant tumor targets. More notably, we found that actin-related genes ephrin-A1 and scinderin were overexpressed in resistant target. Silencing of these genes using RNA interference resulted in a restoration of normal cell morphology and a significant attenuation of variant resistance to CTL killing. Our present study shows that a shift in cytoskeletal organization can be used, by tumor cells, as a strategy to promote their resistance after CTL selection pressure.

Actins↗

PubMed2003

Excitability of the Clay model for squid giant axon.

The squid giant axon is the canonical experimental membrane prototype for the study of action potential generation. This work is concerned with Clay's model for this preparation, which implements the nonlinear dependence of sodium and potassium currents on voltage, a multicompartmental description of sodium channel kinetics that takes into account the dependence between activation and inactivation, revised potassium activation function, and potassium accumulation in the axoplasm and its uptake by glial cells. This model accounts better than the standard Hodgkin-Huxley (HH) model for the response of squid giant axons to various stimuli. We systematically compare the responses of the Clay model and the standard HH model to pulse-like and constant current stimuli. We also analyze hybrid models that combine features from both models. These studies reveal that the differences between the sodium currents account for the main difference between the two models, namely the lower excitability of the Clay model.

Action Potentials↗