Anticoagulants used in plasma collection affect adipokine multiplexed measurements.

Obesity is an important health problem worldwide. Adipose tissue acts as an endocrine organ that secretes various bioactive substances, called adipokines, including pro-inflammatory biomarkers such as TNF-α, IL-6, leptin and C-reactive protein (CRP) and anti-inflammatory molecules such as adiponectin. The deregulated production of adipokines in obesity is linked to the pathogenesis of various disease processes and monitoring their variation is critical to understand metabolic diseases. The aim of this study was to determine the plasma concentration of adipokines in healthy subjects by multiplexed measurements and the effect of anticoagulants on their levels. Plasma samples from 10 healthy donors were collected in two different anticoagulants (sodium citrate or heparin). All markers, excluding TNF-α, showed significantly higher concentrations in heparinized compared to citrate plasma. However, levels of adipokines in different plasma samples were highly correlated for most of these markers. We reported that different anticoagulants used in the preparation of the plasma samples affected the measurements of some adipokines. The importance of the present results in epidemiology is relevant when comparing different studies in which blood samples were collected with different anticoagulants.

The cellular apoptosis susceptibility CAS/CSE1L gene protects ovarian cancer cells from death by suppressing RASSF1C.

The cellular apoptosis susceptibility gene CAS/CSE1L is overexpressed in cancer, although it was originally identified as a gene that renders cells vulnerable to apoptotic stimuli. CAS/CSE1L has roles in the nucleocytoplasmic recycling of importin-α and in the regulation of gene expression, cell migration, and secretion. We identified CAS/CSE1L as a survival factor for ovarian cancer cells in vitro and in vivo. In 3/3 ovarian cancer cell lines, CAS/CSE1L was down-modulated by the unorthodox proapoptotic signaling of the MET receptor. CAS/CSE1L knockdown with RNA interference committed the ovarian cancer cells to death, but not immortalized normal cells and breast and colon cancer cells. In 70 and 95% of these latter cells, respectively, CAS/CSE1L was localized in the cytoplasm, while it accumulated in the nucleus in >90% of ovarian cancer cells. Nuclear localization depended on AKT, which was constitutively active in ovarian cancer cells. In the nucleus, CAS/CSE1L regulated the expression of the proapoptotic Ras-association domain family 1 gene products RASSF1C and RASSF1A, which mediated death signals evoked by depletion of CAS/CSE1L. Our data show that CAS/CSE1L protects ovarian cancer cells from death through transcriptional suppression of a proapoptotic gene and suggest that the localization of CAS/CSE1L dictates its function.

Mono-ADP-ribosylation of the G protein betagamma dimer is modulated by hormones and inhibited by Arf6.

Mono-ADP-ribosylation is a reversible post-translational modification that can modulate the functions of target proteins. We have previously demonstrated that the ß subunit of heterotrimeric G proteins is endogenously mono-ADP-ribosylated, and once modified, the ßγ dimer is inactive toward its effector enzymes. To better understand the physiological relevance of this post-translational modification, we have studied its hormonal regulation. Here, we report that Gß subunit mono-ADP-ribosylation is differentially modulated by G protein-coupled receptors. In intact cells, hormone stimulation of the thrombin receptor induces Gß subunit mono-ADP-ribosylation, which can affect G protein signaling. Conversely, hormone stimulation of the gonadotropin-releasing hormone receptor (GnRHR) inhibits Gß subunit mono-ADP-ribosylation. We also provide the first demonstration that activation of the GnRHR can activate the ADP-ribosylation factor Arf6, which in turn inhibits Gß subunit mono-ADP-ribosylation. Indeed, removal of Arf6 from purified plasma membranes results in loss of GnRHR-mediated inhibition of Gß subunit mono-ADP-ribosylation, which is fully restored by re-addition of purified, myristoylated Arf6. We show that Arf6 acts as a competitive inhibitor of the endogenous ADP-ribosyltransferase and is itself modified by this enzyme. These data provide further understanding of the mechanisms that regulate endogenous ADP-ribosylation of the Gß subunit, and they demonstrate a novel role for Arf6 in hormone regulation of Gß subunit mono-ADP-ribosylation.

Combining affinity purification by ADP-ribose-binding macro domains with mass spectrometry to define the mammalian ADP-ribosyl proteome.

Mono-ADP-ribosylation is a reversible posttranslational modification that modulates the function of target proteins. The enzymes that catalyze this reaction in mammalian cells are either bacterial pathogenic toxins or endogenous cellular ADP-ribosyltransferases. For the latter, both the enzymes and their targets have largely remained elusive, mainly due to the lack of specific techniques to study this reaction. The recent discovery of the macro domain, a protein module that interacts selectively with ADP-ribose, prompted us to investigate whether this interaction can be extended to the identification of ADP-ribosylated proteins. Here, we report that macro domains can indeed be used as selective baits for high-affinity purification of mono-ADP-ribosylated proteins, which can then be identified by mass spectrometry. Using this approach, we have identified a series of cellular targets of ADP-ribosylation reactions catalyzed by cellular ADP-ribosyltransferases and toxins. These proteins include most of the known targets of ADP-ribosylation, indicating the validity of this method, and a large number of other proteins, which now need to be individually validated. This represents an important step toward the discovery of new ADP-ribosyltransferase targets and an understanding of the physiological role and the pharmacological potential of this protein modification.

Physiological relevance of the endogenous mono(ADP-ribosyl)ation of cellular proteins.

The mono(ADP-ribosyl)ation reaction is a post-translational modification that is catalysed by both bacterial toxins and eukaryotic enzymes, and that results in the transfer of ADP-ribose from betaNAD+ to various acceptor proteins. In mammals, both intracellular and extracellular reactions have been described; the latter are due to glycosylphosphatidylinositol-anchored or secreted enzymes that are able to modify their targets, which include the purinergic receptor P2X7, the defensins and the integrins. Intracellular mono(ADP-ribosyl)ation modifies proteins that have roles in cell signalling and metabolism, such as the chaperone GRP78/BiP, the beta-subunit of heterotrimeric G-proteins and glutamate dehydrogenase. The molecular identification of the intracellular enzymes, however, is still missing. A better molecular understanding of this reaction will help in the full definition of its role in cell physiology and pathology.

Minimal Residual Disease Detection by Droplet Digital PCR in Multiple Myeloma, Mantle Cell Lymphoma, and Follicular Lymphoma: A Comparison with Real-Time PCR.

Real-time quantitative PCR (qPCR) is a well-established tool for minimal residual disease (MRD) detection in mature lymphoid malignancies. Despite remarkable sensitivity and specificity, qPCR has some limitations, particularly in the need for a reference standard curve, based on target serial dilutions. In this study, we established droplet digital PCR (ddPCR) for MRD monitoring in multiple myeloma, mantle cell lymphoma, and follicular lymphoma and compared it head-to-head with qPCR. We observed that ddPCR has sensitivity, accuracy, and reproducibility comparable with qPCR. We then compared the two approaches in 69 patients with a documented molecular marker at diagnosis (18 multiple myelomas, 21 mantle cell lymphomas assessed with the immunoglobulin gene rearrangement, and 30 follicular lymphomas with the use of the BCL2/immunoglobulin gene major breakpoint region rearrangement). ddPCR was successful in 100% of cases, whereas qPCR failed to provide a reliable standard curve in three patients. Overall, 222 of 225 samples were evaluable by both methods. The comparison highlighted a good concordance (r = 0.94, P < 0.0001) with 189 of 222 samples (85.1%; 95% CI, 80.4%-89.8%) being fully concordant. We found that ddPCR is a reliable tool for MRD detection with greater applicability and reduced labor intensiveness than qPCR. It will be necessary to authorize ddPCR as an outcome predictor tool in controlled clinical settings and multilaboratory standardization programs.

ADP-ribosylated proteins as old and new drug targets for anticancer therapy: the example of ARF6.

Post-translational modifications of cellular proteins by mono- or poly-ADP-ribosylation are associated with numerous cellular processes. ADP-ribosylation reactions are important in the nucleus, and in mitochondrial activity, stress response signaling, intracellular trafficking, and cell senescence and apoptosis decisions. These reversible reactions add ADP-ribose to target proteins via specific enzymes to form the ADP-ribosylated protein; the cleaveage of this covalent bond is performed via hydrolases. Deficiencies in these enzymatic activities lead to cell death or tumor formation, thus defining their functional roles and impact on human disease. Unlike mono- ADP-ribosyltransferases, poly-ADP-ribose polymerases (PARPs) have been at the frontline of drug discovery since the 1980s. PARP1 is a valuable therapeutic target, with a central role in responses to DNA damage. With mono-ADP-ribosylation now linked to human diseases, such as inflammation, diabetes, neurodegeneration and cancer metastasis, novel and equally important functions of mono-ADPribosylation in cell signaling pathways can now be defined. Recently, we reported mono-ADP-ribosylation of ADP-ribosylation factor 6 (ARF6), a small G-protein of the Ras superfamily. In addition to its involvement in actin remodeling, plasma membrane reorganization and vesicular transport, ARF6 contributes to cancer progression through activation of cell motility and invasion. Consequently, targeting this modification will counteract the pro-invasive effects of ARF6, providing innovative anti-tumor therapy. This review summarizes our present knowledge of the enzymes and targets involved in ADP-ribosylation reactions, and describes in silico approaches to visualize their site of interaction and to identify the precise site for ADP-ribosylation. This should ultimately improve pharmacological strategies to enhance both anti-tumor efficacy and treatment of a number of inflammatory and neurodegenerative disorders.

The MET oncogene transforms human primary bone-derived cells into osteosarcomas by targeting committed osteo-progenitors.

The MET oncogene is aberrantly overexpressed in human osteosarcomas. We have previously converted primary cultures of human bone-derived cells into osteosarcoma cells by overexpressing MET. To determine whether MET transforms mesenchymal stem cells or committed progenitor cells, here we characterize distinct MET overexpressing osteosarcoma (MET-OS) clones using genome-wide expression profiling, cytometric analysis, and functional assays. All the MET-OS clones consistently display mesenchymal and stemness markers, but not most of the mesenchymal­stem cell-specific markers. Conversely, the MET-OS clones express genes characteristic of early osteoblastic differentiation phases, but not those of late phases. Profiling of mesenchymal stem cells induced to differentiate along osteoblast, adipocyte, and chondrocyte lineages confirms that MET-OS cells are similar to cells at an initial phase of osteoblastic differentiation. Accordingly, MET-OS cells cannot differentiate into adipocytes or chondrocytes, but can partially differentiate into osteogenic-matrix-producing cells. Moreover, in vitro MET-OS cells form self-renewing spheres enriched in cells that can initiate tumors in vivo. MET kinase inhibition abrogates the self-renewal capacity of MET-OS cells and allows them to progress toward osteoblastic differentiation. These data show that MET initiates the transformation of a cell population that has features of osteo-progenitors and suggest that MET regulates self-renewal and lineage differentiation of osteosarcoma cells.

Characterisation of a novel glycosylphosphatidylinositol-anchored mono-ADP-ribosyltransferase isoform in ovary cells.

The mammalian mono-ADP-ribosyltransferases are a family of enzymes related to bacterial toxins that can catalyse both intracellular and extracellular mono-ADP-ribosylation of target proteins involved in different cellular processes, such as cell migration, signalling and inflammation. Here, we report the molecular cloning and functional characterisation of a novel glycosylphosphatidylinositol (GPI)-anchored mono-ADP-ribosyltransferase isoform from Chinese hamster ovary (CHO) cells (cARTC2.1) that has both NAD-glycohydrolase and arginine-specific ADP-ribosyltransferase activities. cARTC2.1 has the R-S-EXE active-site motif that is typical of arginine-specific ADP-ribosyltransferases, with Glu209 as the predicted catalytic amino acid. When over-expressed in CHO cells, the E209G single point mutant of cARTC2.1 cannot hydrolyse NAD(+), although it retains low arginine-specific ADP-ribosyltransferase activity. This ADP-ribosyltransferase activity was abolished only with an additional mutation in the R-S-EXE active-site motif, with both of the glutamate residues of the EKE sequence of cARTC2.1 mutated to glycine (E207/209G). These glutamate-mutated proteins localise to the plasma membrane, as does wild-type cARTC2.1. Thus, the partial or total loss of enzymatic activity of cARTC2.1 that arises from these mutations does not affect its cellular localisation. Importantly, an endogenous ADP-ribosyltransferase is indeed expressed and active in a subset of CHO cells, while a similar activity cannot be detected in ovarian cancer cells. With respect to this endogenous ecto-ART activity, we have identified two cell populations: ART-positive and ART-negative CHO cells. The subset of ART-positive cells, which represented 5% of the total cells, is tightly maintained in the CHO cell population.

Endogenous mono-ADP-ribosylation of the free Gbetagamma prevents stimulation of phosphoinositide 3-kinase-gamma and phospholipase C-beta2 and is activated by G-protein-coupled receptors.

We have recently demonstrated that the beta subunit of the heterotrimeric G-proteins is endogenously mono-ADP-ribosylated in intact cells. The modified betagamma heterodimer loses its ability to inhibit calmodulin-stimulated type 1 adenylate cyclase and, remarkably, is de-ADP-ribosylated by a cytosolic hydrolase that completes an ADP-/de-ADP-ribosylation cycle of potential physiological relevance. In the present study, we show that this ADP-ribosylation might indeed be a general mechanism for termination of betagamma signalling, since the ADP-ribosylated betagamma subunit is also unable to activate both phosphoinositide 3-kinase-gamma and phospholipase C-beta2. Moreover, we show that beta subunit ADP-ribosylation is induced by G-protein-coupled receptor activation, since hormone stimulation of Chinese-hamster ovary plasma membranes leads to increases in beta subunit labelling. This occurs when betagamma is in its active heterodimeric conformation, since full inhibition of this modification can be achieved by binding of GDP-alphai3 to the betagamma heterodimer. Taken together, these findings delineate a pathway that arises from the activation of a G-protein-coupled receptor and leads to the inhibition of betagamma activity through its reversible mono-ADP-ribosylation.