Cisplatin-resistant cells in malignant pleural mesothelioma cell lines show ALDH(high)CD44(+) phenotype and sphere-forming capacity

BACKGROUND Conventional chemotherapy in malignant pleural mesothelioma (MPM) has minimal impact on patient survival due to the supposed chemoresistance of cancer stem cells (CSCs). We sought to identify a sub-population of chemoresistant cells by using putative CSC markers, aldehyde dehydrogenase (ALDH) and CD44 in three MPM cell lines; H28, H2052 and Meso4. METHODS The Aldefluor assay was used to measure ALDH activity and sort ALDH(high) and ALDH(low) cells. Drug-resistance was evaluated by cell viability, anchorage-independent sphere formation, flow-cytometry and qRT-PCR analyses. RESULTS The ALDH(high) - and ALDH(low) -sorted fractions were able to demonstrate phenotypic heterogeneity and generate spheres, the latter being less efficient, and both showed an association with CD44. Cis- diamminedichloroplatinum (II) (cisplatin) treatment failed to reduce ALDH activity and conferred only a short-term inhibition of sphere generation in both ALDH(high) and ALDH(low) fractions of the three MPM cell lines. Induction of drug sensitivity by an ALDH inhibitor, diethylaminobenzaldehyde (DEAB) resulted in significant reductions in cell viability but not a complete elimination of the sphere-forming cells, suggestive of the presence of a drug-resistant subpopulation. At the transcript level, the cisplatin + DEAB-resistant cells showed upregulated mRNA expression levels for ALDH1A2, ALDH1A3 isozymes and CD44 indicating the involvement of these markers in conferring chemoresistance in both ALDH(high) and ALDH(low) fractions of the three MPM cell lines. CONCLUSIONS Our study shows that ALDH(high) CD44(+) cells are implicated in conveying tolerance to cisplatin in the three MPM cell lines. The combined use of CD44 and ALDH widens the window for identification and targeting of a drug-resistant population which may improve the current treatment modalities in mesothelioma.

Givenness, procedural meaning and connectives: The case of French puisque

I argue that the communication of given information is part of the procedural instructions conveyed by some connectives like the French puisque. I submit in addition that the encoding of givenness has cognitive implications that are visible during online processing. I assess this hypothesis empirically by comparing the way the clauses introduced by two French causal connectives, puisque and parce que, are processed during online reading when the following segment is ‘given’ or ‘new’. I complement these results by an acceptability judgement task using the same sentences. These experiments confirm that introducing a clause conveying given information is a core feature characterizing puisque, as the segment following it is read faster when it contains given rather than new information, and puisque is rated as more acceptable than parce que in such contexts. I discuss the implications of these results for future research on the description of the meaning of connectives.

The intracellular parasite Theileria parva protects infected T cells from apoptosis.

Parasites have evolved a plethora of strategies to ensure their survival. The intracellular parasite Theileria parva secures its propagation and spreads through the infected animal by infecting and transforming T cells, inducing their continuous proliferation and rendering them metastatic. In previous work, we have shown that the parasite induces constitutive activation of the transcription factor NF-kappaB, by inducing the constitutive degradation of its cytoplasmic inhibitors. The biological significance of NF-kappaB activation in T. parva-infected cells, however, has not yet been defined. Cells that have been transformed by viruses or oncogenes can persist only if they manage to avoid destruction by the apoptotic mechanisms that are activated on transformation and that contribute to maintain cellular homeostasis. We now demonstrate that parasite-induced NF-kappaB activation plays a crucial role in the survival of T. parva-transformed T cells by conveying protection against an apoptotic signal that accompanies parasite-mediated transformation. Consequently, inhibition of NF-kappaB nuclear translocation and the expression of dominant negative mutant forms of components of the NF-kappaB activation pathway, such as IkappaBalpha or p65, prompt rapid apoptosis of T. parva-transformed T cells. Our findings offer important insights into parasite survival strategies and demonstrate that parasite-induced constitutive NF-kappaB activation is an essential step in maintaining the transformed phenotype of the infected cells.