The histone deacetylase inhibitor trichostatin A downregulates human MDR1 (ABCB1) gene expression by a transcription-dependent mechanism in a drug-resistant small cell lung carcinoma cell line model

Tumour drug-resistant ABCB1 gene expression is regulated at the chromatin level through epigenetic mechanisms. We examined the effects of the histone deacetylase inhibitor trichostatin A (TSA) on ABCB1 gene expression in small cell lung carcinoma (SCLC) drug-sensitive (H69WT) or etoposide-resistant (H69VP) cells. We found that TSA induced an increase in ABCB1 expression in drug-sensitive cells, but strongly decreased it in drug-resistant cells. These up- and downregulations occurred at the transcriptional level. Protein synthesis inhibition reduced these modulations, but did not completely suppress them. Differential temporal patterns of histone acetylation were observed at the ABCB1 promoter: increase in H4 acetylation in both cell lines, but different H3 acetylation with a progressive increase in H69WT cells but a transient one in H69VP cells. ABCB1 regulations were not related with the methylation status of the promoter −50GC, −110GC, and Inr sites, and did not result in further changes to these methylation profiles. Trichostatin A treatment did not modify MBD1 binding to the ABCB1 promoter and similarly increased PCAF binding in both H69 cell lines. Our results suggest that in H69 drug-resistant SCLC cell line TSA induces downregulation of ABCB1 expression through a transcriptional mechanism, independently of promoter methylation, and MBD1 or PCAF recruitment

“Reference waters” in French laboratories involved in tritium monitoring: how tritium-free are they?

International audienc

3He mass spectrometry for very low-level measurement of organic tritium in environmental samples

International audienc

Métrologie du tritium dans différentes matrices: cas du tritium organiquement lié (TOL)

International audienceThe measurement of tritium in its various forms (mainly gas (HT), water (HTO) or solid (hydrides)), is an important key step for evaluating health and environmental risks and finally, dosimetry assessment. In vegetable or animal samples, tritium is often associated with the free water fraction, but may be included in the organic form as organically bound tritium (OBT). In this case, 2 forms exist: (i) a fraction called exchangeable or labile (E-OBT), bound to oxygen and nitrogen atoms, and (ii) a so-called non-exchangeable fraction (NE-OBT) bound to carbon atoms. The main technique for tritium analysis is liquid scintillation, which enables one to measure concentrations in the range of several Bq.L-1. The standards (AFNOR, ISO) published to date relate only to tritium analysis in water. Only one CETAMA method addresses OBT analysis in biological environments. This method has been tested since 2001 through intercomparison circuits on grass samples collected from the environment. Regarding tritium analysis in water, the strengths are reliability of this analysis at low concentrations (order of Bq.L-1), robustness and simplicity, and weaknesses are linked to problems of background, conservation and contamination of samples. Concerning OBT analysis, the analysis is reliable for values around 50 Bq.kg-1 of fresh sample. The weaknesses are problems of contamination, reproducibility, analysis time (2 to 6 days) and lack of reference materials. The difficulty to date is the separation between E-OBT and NE-OBT, that will need experimental validation. © 2010 EDP Sciences.La mesure du tritium sous ses différentes formes (gaz (HT), eau (HTO), ou solide (hydrures)), est une étape importante pour l’évaluation des risques sanitaires et environnementaux associés et in fine son estimation dosimétrique. Dans les échantillons du règne végétal ou animal, le tritium est associé à la fraction eau libre et est inclus dans les composés organiques sous forme de tritium organiquement lié (TOL). Dans ce cas, 2 formes existent : (i) la fraction dite échangeable ou labile (TOL-E) liée à des atomes d’oxygène et d’azote ; (ii) la fraction dite non échangeable (TOL-NE) liée aux atomes de carbones. La technique de référence pour l’analyse du tritium est la scintillation liquide permettant de mesurer des concentrations de l’ordre de quelques Bq.L-1. Les normes (AFNOR, ISO) publiées à ce jour ne concernent que l’analyse du tritium dans l’eau. Seule une méthode CETAMA aborde la mesure du TOL dans des milieux biologiques. Cette méthode a été testée depuis 2001 via des circuits d’intercomparaisons sur des échantillons d’herbe prélevés dans l’environnement. Concernant l’analyse du tritium dans les eaux, les principaux points forts sont la fiabilité de cette analyse pour des concentrations de l’ordre de 1 Bq.L-1, la robustesse et la simplicité de mise en œuvre. Les points faibles sont essentiellement liés à des problèmes de bruit de fond, de conservation et de contamination des échantillons. Concernant l’analyse du TOL, l’analyse est fiable pour des valeurs de l’ordre de 50 Bq.kg-1 d’échantillon frais. Les points faibles sont des problèmes de contamination, de reproductibilité, de temps d’analyse (2 à 6 jours) et l’absence de matériaux de référence. La difficulté à ce jour est la séparation entre TOL-E et TOL-NE qui doit être validée expérimentalement