Identification of the Axis ß-Catenin-BTK in the Dynamic Adhesion of Chronic Lymphocytic Leukemia Cells to Their Microenvironment.

In the microenvironment, cell interactions are established between different cell types to regulate their migration, survival and activation. ß-Catenin is a multifunctional protein that stabilizes cell-cell interactions and regulates cell survival through its transcriptional activity. We used chronic lymphocytic leukemia (CLL) cells as a cellular model to study the role of ß-catenin in regulating the adhesion of tumor cells to their microenvironment, which is necessary for tumor cell survival and accumulation. When co-cultured with a stromal cell line (HS-5), a fraction of the CLL cells adhere to stromal cells in a dynamic fashion regulated by the different levels of ß-catenin expression. In non-adherent cells, ß-catenin is stabilized in the cytosol and translocates into the nucleus, increasing the expression of cyclin D1. In adherent cells, the level of cytosolic ß-catenin is low but membrane ß-catenin helps to stabilize the adhesion of CLL to stromal cells. Indeed, the overexpression of ß-catenin enhances the interaction of CLL with HS-5 cells, suggesting that this protein behaves as a regulator of cell adhesion to the stromal component and of the transcriptional regulation of cell survival. Inhibitors that block the stabilization of ß-catenin alter this equilibrium and effectively disrupt the support that CLL cells receive from the cross-talk with the stroma.

Stabilization of ß-catenin upon B-cell receptor signaling promotes NF-kB target genes transcription in mantle cell lymphoma.

B-cell receptor (BCR) signaling pathways and interactions with the tumor microenvironment account for mantle cell lymphoma (MCL) cells survival in lymphoid organs. In several MCL cases, the WNT/ß-catenin canonical pathway is activated and ß-catenin accumulates into the nucleus. As both BCR and ß-catenin are important mediators of cell survival and interaction with the microenvironment, we investigated the crosstalk between BCR and WNT/ß-catenin signaling and analyzed their impact on cellular homeostasis as well as their targeting by specific inhibitors. ß-catenin was detected in all leukemic MCL samples and its level of expression rapidly increased upon BCR stimulation. This stabilization was hampered by the BCR-pathway inhibitor Ibrutinib, supporting ß-catenin as an effector of the BCR signaling. In parallel, MCL cells as compared with normal B cells expressed elevated levels of WNT16, a NF-κB target gene. Its expression increased further upon BCR stimulation to participate to the stabilization of ß-catenin. Upon BCR stimulation, ß-catenin translocated into the nucleus but did not induce a Wnt-like transcriptional response, i.e., TCF/LEF dependent. ß-catenin rather participated to the regulation of NF-κB transcriptional targets, such as IL6, IL8, and IL1. Oligo pull down and chromatin immunoprecipitation experiments demonstrated that ß-catenin is part of a protein complex that binds the NF-κB DNA consensus sequence, strengthening the idea of an association between the two proteins. An inhibitor targeting ß-catenin transcriptional interactions hindered both NF-κB DNA recruitment and induced primary MCL cells apoptosis. Thus, ß-catenin likely represents another player through which BCR signaling impacts on MCL cell survival.

Intraspecific variability of carbon isotope discrimination and its correlation with grain yield in safflower: prospects for selection in a Mediterranean climate.

The goals of the present study were to obtain a first estimate of intraspecific variability of carbon isotope discrimination (Δ) in safflower, a thistle-like herbaceous plant, and to determine the statistical relationship between Δ and grain yield as well as its components in a collection of 45 accessions of different origins. Grain yield and aboveground biomass, harvest index, average grain weight, and Δ (measured on the bulk leaf organic matter) were investigated in experimental field conditions. A large variability was noted for all traits but a principal component analysis (PCA) allowed to identify several homogeneous groups of accessions. Average grain yield per plant varied between 1 and 39 g. Δ varied between 21.3 and 25.2 ‰, i.e. a large variation of 3.9 ‰. In our experiment, the variation of Δ was not significantly related to that of grain yield in the whole accession sample. However, we found contrasting trends for this relation within accession groups. These initial results motivate further experiments to assess more in depth correlation between Δ and yield in safflower and are encouraging regarding the possibility of using Δ as an effective selection index in safflower to obtain genotypes that efficiently consume water. This study also highlighted one accession that combines the two characters required in the Mediterranean regions, i.e. high yield performance and high water-use efficiency.