Microenvironment Remodeling and Subsequent Clinical Implications in Diffuse Large B-Cell Histologic Variant of Richter Syndrome

International audienceIntroduction: Richter Syndrome (RS) is defined as the development of an aggressivelymphoma in the context of Chronic Lymphocytic Leukemia (CLL), with a Diffuse Large B-Cell Lymphoma (DLBCL) histology in 95% cases. RS genomic landscape shares only a few features with de novo DLBCLs and is marked by a wide spectrum of cytogenetic abnormalities. Little is known about RS microenvironment. Therapeutic options and efficacy are limited, leading to a 12 months median overall survival. The new targeted treatments usually effective in CLL fail to obtain long-term remissions in RS. Methods: We reviewed available PubMed literature about RS genomics, PD-1/PD-L1 (Programmed Death 1/Programmed Death Ligand 1) pathway triggering and subsequent new therapeutic options. Results: Data from about 207 patients from four landmark papers were compiled to build an overview of RS genomic lesions and point mutations. A number of these abnormalities may be involved in tumor microenvironment reshaping. T lymphocyte exhaustion through PD-L1 overexpression by tumor cells and subsequent PD-1/PD-L1 pathway triggering is frequently reported in solid cancers. This immune checkpoint inhibitor is also described in B lymphoid malignancies, particularly CLL: PD-1 expression is reported in a subset of prolymphocytes from the CLL lymph node proliferation centers. However, there is only few data about PD-1/PD-L1 pathway in RS. In RS, PD-1 expression is a hallmark of recently described « Regulatory B-cells », which interact with tumor microenvironment by producing inhibiting cytokines such as TGF-band IL-10, impairing T lymphocytes anti-tumoral function. Based upon the discovery of high PD-1 expression on tumoral Blymphocyte from RS, immune checkpoint blockade therapies such as anti-PD-1 antibodies have been tested on small RS cohorts and provided heterogeneous butencouraging results. Conclusion: RS genetic landscape and immune evasion mechanisms are being progressively unraveled. New protocols using targeted treatments such as checkpoint inhibitors as single agents or in combination with immunochemotherapy are currently being evaluated

A signaling cascade mediated by ceramide, src and PDGFRβ coordinates the activation of the redox-sensitive neutral sphingomyelinase-2 and sphingosine kinase-1.

International audienceStress-inducing agents, including oxidative stress, generate the sphingolipid mediators ceramide (Cer) and sphingosine-1-phosphate (S1P) that are involved in stress-induced cellular responses. The two redox-sensitive neutral sphingomyelinase-2 (nSMase2) and sphingosine kinase-1 (SK1) participate in transducing stress signaling to ceramide and S1P, respectively; however, whether these key enzymes are coordinately regulated is not known. We investigated whether a signaling link coordinates nSMase2 and SK1 activation by H2O2. In mesenchymal cells, H2O2 elicits a dose-dependent biphasic effect, mitogenic at low concentration (5μM), and anti-proliferative and toxic at high concentration (100μM). Low H2O2 concentration triggered activation of nSMase2 and SK1 through a nSMase2/Cer-dependent signaling pathway that acted upstream of activation of SK1. Further results implicated src and the trans-activation of PDGFRβ, as supported by the blocking effect of specific siRNAs, pharmacological inhibitors, and genetically deficient cells for nSMase2, src and SK1. The H2O2-induced src/PDGFRβ/SK1 signaling cascade was impaired in nSMase2-deficient fro/fro cells and was rescued by exogenous C2Cer that activated src/PDGFRβ/SK1. Thus, the results define a nSMase2/SK1 signaling pathway implicated in the mitogenic response to low oxidative stress. On the other hand, high oxidative stress induced inhibition of SK1. The results also showed that the toxicity of high H2O2 concentration was comparable in control and nSMase2-deficient cells. Taken together the results identify a tightly coordinated nSMase2/SK1 pathway that mediates the mitogenic effects of H2O2 and may sense the degree of oxidative stress

Integrin alpha(v)beta(3), metalloproteinases, and sphingomyelinase-2 mediate urokinase mitogenic effect.

International audiencePlasminogen activators are implicated in the pathogenesis of several diseases such as inflammatory diseases and cancer. Beside their serine-protease activity, these agents trigger signaling pathways involved in cell migration, adhesion and proliferation. We previously reported a role for the sphingolipid pathway in the mitogenic effect of plasminogen activators, but the signaling mechanisms involved in neutral sphingomyelinase-2 (NSMase-2) activation (the first step of the sphingolipid pathway) are poorly known. This study was carried out to investigate how urokinase plasminogen activator (uPA) activates NSMase-2. We report that uPA, as well as its catalytically inactive N-amino fragment ATF, triggers the sequential activation of MMP-2, NSMase-2 and ERK1/2 in ECV304 cells that are required for uPA-induced ECV304 proliferation, as assessed by the inhibitory effect of Marimastat (a MMP inhibitor), MMP-2-specific siRNA, MMP-2 defect, and NSMase-specific siRNA. Moreover, upon uPA stimulation, uPAR, MT1-MMP, MMP-2 and NSMase-2 interacted with integrin alpha(v)beta(3), evidenced by co-immunoprecipitation and immunocytochemistry experiments. Moreover, the alpha(v)beta(3) blocking antibody inhibited the uPA-triggered MMPs/uPAR/integrin alpha(v)beta(3) interaction, NSMase-2 activation, Ki67 expression and DNA synthesis in ECV304. In conclusion, uPA triggers interaction between integrin alpha(v)beta(3), uPAR and MMPs that leads to NSMase-2 and ERK1/2 activation and cell proliferation. These findings highlight a new signaling mechanism for uPA, and suggest that, upon uPA stimulation, uPAR, MMPs, integrin alpha(v)beta(3) and NSMase-2 form a signaling complex that take part in mitogenic signaling in ECV304 cells

The neutral sphingomyelinase-2 is involved in angiogenic signaling triggered by oxidized LDL

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Mesenchymal Stem Cells Promote Matrix Metalloproteinase Secretion By Cardiac Fibroblasts And Reduce Cardiac Ventricular Fibrosis After Myocardial Infarction.

International audienceRecent studies showed that mesenchymal stem cells (MSCs) transplantation significantly decreased cardiac fibrosis. However, the mechanisms involved in these effects are still poorly understood. In this work, we investigated whether the antifibrotic properties of MSCs involve the regulation of matrix metalloproteinases (MMPs) and matrix metalloproteinase endogenous inhibitor (TIMPs) production by cardiac fibroblasts.In vitro experiments showed that conditioned medium from MSCs decreased viability, alpha-SMA expression and collagen secretion of cardiac fibroblasts. These effects were concomitant to the stimulation of MMP-2/MMP-9 activities and MT1-MMP expression. Experiments performed with fibroblasts from MMP2-/- mice demonstrated that MMP2 plays a preponderant role in preventing collagen accumulation upon incubation with conditioned-medium from MSCs. Interestingly, we found that MSC-conditioned medium also decreased the expression of TIMP2 in cardiac fibroblasts. In vivo studies showed that intracardiac injection of MSCs in a rat model of post-ischemic heart failure induced a significant decrease in ventricular fibrosis. This effect was associated with the improvement of morphological and functional cardiac parameters.In conclusion, we showed that MSCs modulate the phenotype of cardiac fibroblasts and their ability to degrade extracellular matrix. These properties of MSCs open new perspective for understanding of the mechanisms of action of MSCs and anticipate their potential therapeutic or side effects