Search

Background. The C-terminal-binding protein 1/brefeldin A ADP-ribosylation substrate (CtBP1/BARS) acts both as an oncogenic transcriptional co-repressor and as a fission inducing protein required for membrane trafficking and Golgi complex partitioning during mitosis, hence for mitotic entry. CtBP1/BARS overexpression, in multiple cancers, has pro-tumorigenic functions regulating gene networks associated with “cancer hallmarks” and malignant behavior including: increased cell survival, proliferation, migration/invasion, epithelial-mesenchymal transition (EMT). Structurally, CtBP1/BARS belongs to the hydroxyacid-dehydrogenase family and possesses a NAD(H)-binding Rossmann fold, which, depending on ligands bound, controls the oligomerization of CtBP1/BARS and, in turn, its cellular functions. Here, we proposed to target the CtBP1/BARS Rossmann fold with small molecules as selective inhibitors of mitotic entry and pro-tumoral transcriptional activities. Methods. Structured-based screening of drug databases at different development stages was applied to discover novel ligands targeting the Rossmann fold. Among these identified ligands, N-(3,4-dichlorophenyl)-4-{[(4-nitrophenyl)carbamoyl]amino}benzenesulfonamide, called Comp.11, was selected for further analysis. Fluorescence spectroscopy, isothermal calorimetry, computational modelling and site-directed mutagenesis were employed to define the binding of Comp.11 to the Rossmann fold. Effects of Comp.11 on the oligomerization state, protein partners binding and pro-tumoral activities were evaluated by size-exclusion chromatography, pull-down, membrane transport and mitotic entry assays, Flow cytometry, quantitative real-time PCR, motility/invasion, and colony assays in A375MM and B16F10 melanoma cell lines. Effects of Comp.11 on tumor growth in vivo were analyzed in mouse tumor model. Results. We identify Comp.11 as a new, potent and selective inhibitor of CtBP1/BARS (but not CtBP2). Comp.11 directly binds to the CtBP1/BARS Rossmann fold affecting the oligomerization state of the protein (unlike other known CtBPs inhibitors), which, in turn, hinders interactions with relevant partners, resulting in the inhibition of both CtBP1/BARS cellular functions: i) membrane fission, with block of mitotic entry and cellular secretion; and ii) transcriptional pro-tumoral effects with significantly hampered proliferation, EMT, migration/invasion, and colony-forming capabilities. The combination of these effects impairs melanoma tumor growth in mouse models. Conclusions. This study identifies a potent and selective inhibitor of CtBP1/BARS active in cellular and melanoma animal models revealing new opportunities to study the role of CtBP1/BARS in tumor biology and to develop novel melanoma treatments.

The GTPase Rab14 is localized at the trans-Golgi network and at the intermediate compartment associated to sorting/recycling endosomes-like structures of the transferrin-recycling pathway: as other Rab family members, it is involved in the regulation of intracellular vesicle trafficking, though its role and functional relationship with effector/endosomal proteins is still incomplete.We have analysed whether post-translational modifications could affect Rab14 activity: the results obtained define mono-ADP-ribosylation (MARylation) as the yet-unknown Rab14 modification, catalysed by the ADP-ribosyltransferase PARP12, which specifically modifies glutamic acid residues in position 159/162. This modification is essential for the Rab14-dependent endosome progression. Accordingly, recycling of the transferrin receptor is inhibited when MARylation of Rab14 is prevented by PARP12 knocking-down or inhibition, or by overexpression of Rab14 ADP-ribosylation-defective mutant. Under these conditions, Rab14 and transferrin receptors are withheld at the cell periphery at the level of the Rab4-RUFY1-positive sorting endosomes, indicating that the interaction of Rab14 with the dual effectors RUFY and then FIP1c (which specifically binds both Rab11 and Rab14) determines the progression between the Rab4-RUFY- and Rab11-FIP1c-specific vesicles. Therefore Rab14-MARylation determines the sequential binding of this GTPase to RUFY and FIP1c, thus controlling endosome progression (i.e., transferrin receptors recycling) through the Rab4-, Rab14- and Rab11-specific vesicles. This identifies a Rab14-specific compartment of the recycling pathway and a crucial enzymatic reaction amenable to pharmacological control.

Cancer is a disease resulting from aberrant communication between cells of a multicellular organism. The glycan coat that surrounds the cells is an important player in cellular communication. While altered cell surface glycans are known biomarkers for cancer, glycan biosynthesis itself has not been considered a potential oncogenic pathway. So, to understand the oncogenic potential of the glycan biosynthetic pathways we have analyzed the copy number alterations (CNA) of genes encoding for glycosylation regulators (glycogenes) in cancer genome datasets and identify novel glyco-oncogenes and glyco-tumor suppressor genes (TSGs). CNA of oncogenes and TSGs is an important cancer-associated genetic alteration that associates with worst prognosis. Nevertheless, identity of the driver genes in the copy number altered segments of the genome remains obscure in most cases. We developed a prioritization pipeline based on bioinformatic and experimental criteria to identify putative driver genes. In addition to correctly identifying several well-established oncogenes/TSGs, this pipeline discerns several novel oncogenes and TSGs, some of which are glycogenes. Further, among glyco-oncogenes there is an enrichment for glycosphingolipid biosynthetic pathway and trans-Golgi associated lysosomal sorting machinery and among glyco-TSGs there is an enrichment for early N-glycan biosynthetic enzymes. As a proof-of-principle we show that one of the identified glycooncogene B4GALT5, encoding a key enzyme in the glycosphingolipid pathway exhibits oncogenic property of promoting increased growth of hepatocellular carcinoma cells. Thus, this study identifies glycosylation pathways with oncoregulatory properties and opens up a new group of enzymes as potential therapeutic targets for cancer.

Significance Proteins are modified by many posttranslational modifications (PTMs) with crucial regulatory functions. A PTM attracting increasing interest is ADP-ribosylation, capable of altering crucial cellular targets. We show that mono-ADP-ribosylation by PARP12 of the protein Golgin-97 regulates transport to the plasma membrane of a specific group of functionally crucial cargo proteins. PARP12 is shown to be part of a regulatory cascade initiated by PKD and involving the direct phosphorylation and activation of PARP12. These events define, through Golgin-97 mono-ADP-ribosylation, a Golgi sorting mechanism for specific basolateral cargoes, including E-cadherin. Defects in this cascade impair E-cadherin transport and formation of cell–cell contacts, with potential consequences for the formation of adherens junctions, polarization of epithelial cells, and development of epithelial–mesenchymal transformation., Adenosine diphosphate (ADP)-ribosylation is a posttranslational modification involved in key regulatory events catalyzed by ADP-ribosyltransferases (ARTs). Substrate identification and localization of the mono-ADP-ribosyltransferase PARP12 at the trans-Golgi network (TGN) hinted at the involvement of ARTs in intracellular traffic. We find that Golgin-97, a TGN protein required for the formation and transport of a specific class of basolateral cargoes (e.g., E-cadherin and vesicular stomatitis virus G protein [VSVG]), is a PARP12 substrate. PARP12 targets an acidic cluster in the Golgin-97 coiled-coil domain essential for function. Its mutation or PARP12 depletion, delays E-cadherin and VSVG export and leads to a defect in carrier fission, hence in transport, with consequent accumulation of cargoes in a trans-Golgi/Rab11–positive intermediate compartment. In contrast, PARP12 does not control the Golgin-245–dependent traffic of cargoes such as tumor necrosis factor alpha (TNFα). Thus, the transport of different basolateral proteins to the plasma membrane is differentially regulated by Golgin-97 mono-ADP-ribosylation by PARP12. This identifies a selective regulatory mechanism acting on the transport of Golgin-97– vs. Golgin-245–dependent cargoes. Of note, PARP12 enzymatic activity, and consequently Golgin-97 mono-ADP-ribosylation, depends on the activation of protein kinase D (PKD) at the TGN during traffic. PARP12 is directly phosphorylated by PKD, and this is essential to stimulate PARP12 catalytic activity. PARP12 is therefore a component of the PKD-driven regulatory cascade that selectively controls a major branch of the basolateral transport pathway. We propose that through this mechanism, PARP12 contributes to the maintenance of E-cadherin–mediated cell polarity and cell–cell junctions.

Background: Shp1, a tyrosine-phosphatase-1 containing the Src-homology 2 (SH2) domain, is involved in inflammatory and immune reactions, where it regulates diverse signalling pathways, usually by limiting cell responses through dephosphorylation of target molecules. Moreover, Shp1 regulates actin dynamics. One Shp1 target is Src, which controls many cellular functions including actin dynamics. Src has been previously shown to be activated by a signalling cascade initiated by the cytosolic-phospholipase A2 (cPLA2) metabolite glycerophosphoinositol 4-phosphate (GroPIns4P), which enhances actin polymerisation and motility. While the signalling cascade downstream Src has been fully defined, the mechanism by which GroPIns4P activates Src remains unknown. Methods: Affinity chromatography, mass spectrometry and co-immunoprecipitation studies were employed to identify the GroPIns4P-interactors; among these Shp1 was selected for further analysis. The specific Shp1 residues interacting with GroPIns4P were revealed by NMR and validated by site-directed mutagenesis and biophysical methods such as circular dichroism, isothermal calorimetry, fluorescence spectroscopy, surface plasmon resonance and computational modelling. Morphological and motility assays were performed in NIH3T3 fibroblasts. Results: We find that Shp1 is the direct cellular target of GroPIns4P. GroPIns4P directly binds to the Shp1-SH2 domain region (with the crucial residues being Ser 118, Arg 138 and Ser 140) and thereby promotes the association between Shp1 and Src, and the dephosphorylation of the Src-inhibitory phosphotyrosine in position 530, resulting in Src activation. As a consequence, fibroblast cells exposed to GroPIns4P show significantly enhanced wound healing capability, indicating that GroPIns4P has a stimulatory role to activate fibroblast migration. GroPIns4P is produced by cPLA2 upon stimulation by diverse receptors, including the EGF receptor. Indeed, endogenously-produced GroPIns4P was shown to mediate the EGF-induced cell motility. Conclusions: This study identifies a so-far undescribed mechanism of Shp1/Src modulation that promotes cell motility and that is dependent on the cPLA2 metabolite GroPIns4P. We show that GroPIns4P is required for EGF-induced fibroblast migration and that it is part of a cPLA2/GroPIns4P/Shp1/Src cascade that might have broad implications for studies of immune-inflammatory response and cancer. [Figure not available: see fulltext.]

ADP-ribosylation is a post-translational modification involved in physiological and pathological events catalyzed by Poly-ADP-Ribosyl-Polymerase (PARP) enzymes. Substrates of this reaction have been identified by mass-spectrometry, but the definition of PARPs-regulated cellular functions remains scarce. Here, we have analyzed the control of intracellular membrane traffic by the mono-ADP-ribosyl-transferase PARP12, motivated by its localization at thetrans-Golgi network. By using bioinformatics, mutagenesis and cell biology approaches we identified Golgin-97, a protein regulating exocytosis, as a PARP12-specific substrate. Mono-ADP-ribosylation of Golgin-97 residues E558-E559-E565 is required for supporting traffic from thetrans-Golgi network to the plasma membrane. This step is halted when PARP12 is deleted or when the Golgin-97 ADP-ribosylation-defective mutant is expressed. Under these conditions E-cadherin, whose transport is controlled by Golgin-97, does not reach the plasma membrane but accumulates in atrans-Golgi proximal compartment. Thus, we demonstrate that the ADP-ribosylation of Golgin-97 is required for E-cadherin exocytosis and thus this event may regulate the sorting of exocytic carriers as well as epithelial-to-mesenchymal transition.

Motivation ADP-ribosylation is a post-translational modification (PTM) implicated in several crucial cellular processes, ranging from regulation of DNA repair and chromatin structure to cell metabolism and stress responses. To date, a complete understanding of ADP-ribosylation targets and their modification sites in different tissues and disease states is still lacking. Identification of ADP-ribosylation sites is required to discern the molecular mechanisms regulated by this modification. This motivated us to develop a computational tool for the prediction of ADP-ribosylated sites. Results Here, we present ADPredict, the first dedicated computational tool for the prediction of ADP-ribosylated aspartic and glutamic acids. This predictive algorithm is based on (i) physicochemical properties, (ii) in-house designed secondary structure-related descriptors and (iii) three-dimensional features of a set of human ADP-ribosylated proteins that have been reported in the literature. ADPredict was developed using principal component analysis and machine learning techniques; its performance was evaluated both internally via intensive bootstrapping and in predicting two external experimental datasets. It outperformed the only other available ADP-ribosylation prediction tool, ModPred. Moreover, a novel secondary structure descriptor, HM-ratio, was introduced and successfully contributed to the model development, thus representing a promising tool for bioinformatics studies, such as PTM prediction. Availability and implementation ADPredict is freely available at www.ADPredict.net. Supplementary information Supplementary data are available at Bioinformatics online.

Poly-ADP-ribose-polymerases (PARPs) 1 and 2 are nuclear enzymes that catalyze the poly-ADP-ribosylation of nuclear proteins transferring poly-ADP-ribose (PAR) polymers to specific residues. PARPs and PAR intervene in diverse functions, including DNA repair in the nucleus and stress granule assembly in the cytoplasm. Stress granules contribute to the regulation of translation by clustering and stabilizing mRNAs as well as several cytosolic PARPs and signaling proteins to modulate cell metabolism and survival. Our study is focused on one of these PARPs, PARP12, a Golgi-localized mono-ADP-ribosyltransferase that under stress challenge reversibly translocates from the Golgi complex to stress granules. PARP1 activation and release of nuclear PAR drive this translocation by direct PAR binding to the PARP12-WWE domain. Thus, PAR formation functionally links the activity of the nuclear and cytosolic PARPs during stress response, determining the release of PARP12 from the Golgi complex and the disassembly of the Golgi membranes, followed by a block in anterograde-membrane traffic. Notably, these functions can be rescued by reverting the stress condition (by drug wash-out). Altogether these data point at a novel, reversible nuclear signaling that senses stress to then act on cytosolic PARP12, which in turn converts the stress response into a reversible block in intracellular-membrane traffic.

Transient receptor potential melastatin 8 (TRPM8), a nonselective cation channel, is the predominant mammalian cold temperature thermosensor and it is activated by cold temperatures and cooling compounds, such as menthol and icilin. Because of its role in cold allodynia, cold hyperalgesia and painful syndromes TRPM8 antagonists are currently being pursued as potential therapeutic agents for the treatment of pain hypersensitivity. Recently TRPM8 has been found in subsets of bladder sensory nerve fibres, providing an opportunity to understand and treat chronic hypersensitivity. However, most of the known TRPM8 inhibitors lack selectivity, and only three selective compounds have reached clinical trials to date. Here, we applied two virtual screening strategies to find new, clinics suitable, TRPM8 inhibitors. This strategy enabled us to identify naphthyl derivatives as a novel class of potent and selective TRPM8 inhibitors. Further characterization of the pharmacologic properties of the most potent compound identified, compound 1, confirmed that it is a selective, competitive antagonist inhibitor of TRPM8. Compound 1 also proved itself active in a overreactive bladder model in vivo. Thus, the novel naphthyl derivative compound identified here could be optimized for clinical treatment of pain hypersensitivity in bladder disorders but also in different other pathologies.

Maintaining the optimal performance of cell processes and organelles is the task of auto-regulatory systems. Here we describe an auto-regulatory device that helps to maintain homeostasis of the endoplasmic reticulum (ER) by adjusting the secretory flux to the cargo load. The cargo-recruiting subunit of the coatomer protein II (COPII) coat, Sec24, doubles as a sensor of folded cargo and, upon cargo binding, acts as a guanine nucleotide exchange factor to activate the signaling protein G?12 at the ER exit sites (ERESs). This step, in turn, activates a complex signaling network that activates and coordinates the ER export machinery and attenuates proteins synthesis, thus preventing large fluctuations of folded and potentially active cargo that could be harmful to the cell or the organism. We call this mechanism AREX (autoregulation of ER export) and expect that its identification will aid our understanding of human physiology and diseases that develop from secretory dysfunction. By sensing the load of folded ER lumenal proteins, the COPII subunit Sec24 directs a signaling cascade that allows secretory pathway flux to respond to the abundance of cargo.

Background Shp1, a tyrosine-phosphatase-1 containing the Src-homology 2 (SH2) domain, is involved in inflammatory and immune reactions, where it regulates diverse signalling pathways, usually by limiting cell responses through dephosphorylation of target molecules. Moreover, Shp1 regulates actin dynamics. One Shp1 target is Src, which controls many cellular functions including actin dynamics. Src has been previously shown to be activated by a signalling cascade initiated by the cytosolic-phospholipase A2 (cPLA2) metabolite glycerophosphoinositol 4-phosphate (GroPIns4P), which enhances actin polymerisation and motility. While the signalling cascade downstream Src has been fully defined, the mechanism by which GroPIns4P activates Src remains unknown. Methods Affinity chromatography, mass spectrometry and co-immunoprecipitation studies were employed to identify the GroPIns4P-interactors; among these Shp1 was selected for further analysis. The specific Shp1 residues interacting with GroPIns4P were revealed by NMR and validated by site-directed mutagenesis and biophysical methods such as circular dichroism, isothermal calorimetry, fluorescence spectroscopy, surface plasmon resonance and computational modelling. Morphological and motility assays were performed in NIH3T3 fibroblasts. Results We find that Shp1 is the direct cellular target of GroPIns4P. GroPIns4P directly binds to the Shp1-SH2 domain region (with the crucial residues being Ser 118, Arg 138 and Ser 140) and thereby promotes the association between Shp1 and Src, and the dephosphorylation of the Src-inhibitory phosphotyrosine in position 530, resulting in Src activation. As a consequence, fibroblast cells exposed to GroPIns4P show significantly enhanced wound healing capability, indicating that GroPIns4P has a stimulatory role to activate fibroblast migration. GroPIns4P is produced by cPLA2 upon stimulation by diverse receptors, including the EGF receptor. Indeed, endogenously-produced GroPIns4P was shown to mediate the EGF-induced cell motility. Conclusions This study identifies a so-far undescribed mechanism of Shp1/Src modulation that promotes cell motility and that is dependent on the cPLA2 metabolite GroPIns4P. We show that GroPIns4P is required for EGF-induced fibroblast migration and that it is part of a cPLA2/GroPIns4P/Shp1/Src cascade that might have broad implications for studies of immune-inflammatory response and cancer. Electronic supplementary material The online version of this article (10.1186/s12964-019-0329-3) contains supplementary material, which is available to authorized users.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has been fixed in the paper.

Intracellular membrane trafficking among organelles occurs through vesicular or tubular intermediates that selectively deliver proteins and lipids from one compartment to another. The Rab proteins are small GTPases that function as master regulators of this process. All Rabs localize at specific subcellular compartments and their distribution is crucial for the specificity and directionality of membrane traffic (i.e. secretion, endocytosis, recycling etc.). In particular, Rab14, one of the recently discovered members of the Rab family is localized at the Golgi/trans-Golgi network (TGN) and endosomes and has been associated with different steps of the endosomal recycling pathway. Here we have identified Rab14 as a novel substrate of PARP12, a mono-ADP-ribosyl transferase mainly localized at the Golgi complex. The physiological functions of PARP12 are not yet completely elucidated. With this study we demonstrate that PARP12 is able to interact and modify Rab14 and that its depletion impairs Rab14 functions. Inhibition of ADP-ribosylation alters Rab14 localization, which in turn affects membrane flow through the recycling endosomes. Using bioinformatics and mutagenesis approaches, we have generated a Rab14 mutant that cannot be ADP-ribosylated by PARP12. The analysis of the mutant suggests that Rab14 participates in a cascade of events controlling the maturation of recycling endosomes and that the ADP-ribosylation of Rab14 is essential for this step. Overall our data identify mono-ADP-ribosylation as a novel post-translation modification of the small GTPase Rab14 that may be used to modulate the spatial-temporal regulation of the Rab14-GTPase activation cycle. In addition our data highlight a novel role of PARP12 in the progression of intracellular membrane traffic.

Poly-ADP-ribose-polymerases (PARPs) and the reaction product poly-ADP-ribose (PAR) intervene in diverse cellular functions, including DNA-damage repair in the nucleus and stress granule assembly in the cytoplasm. Stress granules contribute to the regulation of translation by clustering and stabilizing mRNAs as well as several cytosolic PARPs and signaling proteins to modulate cell metabolism and survival. Herein, we describe the behaviour of one of these PARPs -PARP12- and show that this enzyme contributes to cell response to oxidative stress, by translocating from the Golgi complex to the newly-formed stress granules, preventing in this way intracellular-membrane transport progression. PARP12 translocation to stress granules requires PARP1 activation and release of nuclear PAR that, in turn, is directly recognized by PARP12 through its WWE domain. Thus, PAR formation functionally links the activity of the nuclear and cytosolic PARPs during stress response, determining the release of PARP12 from the Golgi complex and, as a consequence, the disassembly of the Golgi membranes, followed by a block in the anterograde membrane traffic. Notably, Golgi complex organization and membrane traffic can be rescued by reverting the stress condition (by drug wash-out) as well as by inhibiting the nuclear signal. Altogether these data highlight a novel, reversible nuclear signaling that senses stress to then act on cytosolic PARP12, which in turn converts the stress response into a reversible block in intracellular membrane traffic.

This work aims to elucidate the mechanism by which N-methylpyrrolidone (NMP) enhances the skin permeation of a compound by combining experimental data with molecular dynamic (MD) simulations. The addition of 10% NMP significantly increased the propranolol (PR) permeation through the human epidermis (∼ 15 μg/cm(2) vs ∼ 30 μg/cm(2)) while resulting inefficacious on hydrocortisone (HC) diffusion. No significant alterations in the stratum corneum structure were found after the in vitro treatment of human epidermis with NMP dispersed in mineral oil or water by attenuated total reflectance Fourier transform infrared (ATR-FTIR) analyses. MD simulations revealed the formation of a complex by H-bonds and the π-π stacking interactions between the NMP's amido group and the drug's aromatic systems. The size of the depicted NMP/PR clusters was in line with the hydrodynamic radius derived by dynamic light scattering analyses (∼ 2.00 nm). Conversely, no interaction, and consequently cluster formation, between NMP and HC occurred. These results suggest that NMP is effective in enhancing the drug permeation through human epidermis by a cotransport mechanism when NMP/drug interaction occurs.

Modulation of the transient receptor potential melastatin type-8 (TRPM8), the receptor for menthol acting as the major sensor for peripheral innocuous cool temperatures, has several important applications in pharmaceutical, food and cosmetic industries. In the present study, we designed 12 isoxazole derivatives and tested their pharmacological properties both in F11 sensory neurons in vitro , and in an in vivo model of cold allodynia. In F11 sensory neurons, single-cell Ca 2+ -imaging experiments revealed that, when compared to menthol, some newly-synthesized compounds were up to 200-fold more potent, though none of them showed an increased efficacy. Some isoxazole derivatives potentiated allodynic responses elicited by acetone when administered to rats subjected to sciatic nerve ligation; when compared to menthol, these compounds were efficacious at earlier (0–2 min) but not later (7–9 or 14–16 min) time points. Docking experiments performed in a human TRPM8 receptor model revealed that newly-synthesized compounds might adopt two possible conformations, thereby allowing to distinguish “menthol-like” compounds (characterized by high efficacy/low potency), and “icillin-like” compounds (with high potency/low efficacy). Collectively, these data provide rationale structure–activity relationships for isoxazole derivatives acting as TRPM8 agonists, and suggest their potential usefulness for cold-evoked analgesia.