Deubiquitinating enzymes at the crossroads of lipid metabolism and cancer

Deregulated lipid metabolism has been recognized as a critical alteration that supports the development and growth of various types of tumors. Changes in lipid metabolism enable reprogramming of energetics and availability of synthetic intermediates and signaling mediators that can have pleiotropic effects in cellular physiology. The identification of critical factors that reshape lipid metabolism during oncogenesis can provide targets for the development of novel therapeutic protocols. Enzymes are an attractive class of molecules for the development of therapeutic compounds. This review focuses on deubiquitinating enzymes (DUBs) that have been implicated both in lipid and cellular homeostatic processes. In certain cases, a causative link between the two processes is mediated by the deubiquitinating enzyme whereas in other cases we present evidence that support a possible role for the DUB as the underlying linker of lipid content and cell growth deregulation. Collectively, our report highlights critical nodes of deubiquitination-dependent metabolic and growth regulatory processes that can be interrogated further for a detailed understanding of cancer promoting mechanisms and therapeutic exploitation

The Epstein-Barr virus transforming protein LMP1 engages signaling proteins for the tumor necrosis factor receptor family

AbstractThe cytoplasmic C-terminus of Epstein-Barr virus (EBV) latent infection membrane protein 1 (LMP1) is essential for B lymphocyte growth transformation and is now shown to interact with a novel human protein (LMP1-associated protein 1 [LAP1]). LAN is homologous to a murine protein, tumor necrosis factor receptor-associated factor 2 (TRAF2), implicated in growth signaling from the p80 TNFR. A second novel protein (EBI6), induced by EBV infection, is the human homolog of a second murine TNFR-associated protein (TRAF1). LMP1 expression causes LAPP and EBI6 to localize to LMP1 clusters in lymphoblast plasma membranes, and LMPI coimmunoprecipitates with these proteins. LAPI binds to the p80 TNFR, CD40, and the lymphotoxin-β receptor, while EBI6 associates with the p80 TNFR. The interaction of LMP1 with these TNFR family-associated proteins is further evidence for their role in signaling and links LMP1-mediated transformation to signal transduction from the TNFR family

The Tumor Suppressor CYLD Inhibits Mammary Epithelial to Mesenchymal Transition by the Coordinated Inhibition of YAP/TAZ and TGFβ Signaling

Downregulation of the cylindromatosis (CYLD) tumor suppressor has been associated with breast cancer development and progression. Here, we report a critical role for CYLD in maintaining the phenotype of mammary epithelial cells in vitro and in vivo. CYLD downregulation or inactivation induced an epithelial to mesenchymal transition of mammary epithelial cells that was dependent on the concomitant activation of the transcription factors Yes-associated protein (YAP)/transcriptional coactivator with PDZ-binding motif (TAZ) and transforming growth factor beta (TGF�)signaling. CYLD inactivation enhanced the nuclear localization of YAP/TAZ and the phosphorylation of Small Mothers Against Decapentaplegic (SMAD)2/3 proteins in confluent cell culture conditions. Consistent with these findings were the hyperplastic alterations of CYLD-deficient mouse mammary epithelia, which were associated with enhanced nuclear expression of the YAP/TAZ transcription factors. Furthermore, in human breast cancer samples, downregulation of CYLD expression correlates with enhanced YAP/TAZ-regulated target gene expression. Our results identify CYLD as a critical regulator of a signaling node that prevents the coordinated activation of YAP/TAZ and the TGF� pathway in mammary epithelial cells, in order to maintain their phenotypic identity and homeostasis. Consequently, they provide a novel conceptual framework that supports and explains a causal implication of deficient CYLD expression in aggressive human breast cancers

Truncation of the Deubiquitinating Domain of CYLD in Myelomonocytic Cells Attenuates Inflammatory Responses

The cylindromatosis tumor suppressor (CYLD) is a deubiquitinating enzyme that has been implicated in various aspects of adaptive and innate immune responses. Nevertheless, the role of CYLD in the function of specific types of immune cells remains elusive. In this report we have used conditional gene targeting in mice to address the role of the deubiquitinating activity of CYLD in the myelomonocytic lineage. Truncation of the deubiquitinating domain of CYLD specifically in myelomonocytic cells impaired the development of lethal LPS-induced endotoxic shock and the accumulation of thioglycollate-elicited peritoneal macrophages. Our data establish CYLD as a regulator of monocyte-macrophage activation in response to inflammatory stimuli and identify it as a potential target for therapeutic intervention in relevant inflammatory disorders in humans

The LMP1 Promoter Can Be Transactivated Directly by NF-κB▿

A bioinformatic analysis identified two putative NF-κB binding sites in the Epstein-Barr virus (EBV) latent membrane protein 1 (LMP1) promoter. The ability of p65RelA to interact with the LMP1 promoter was shown by in vitro and in vivo assays. Using an EBV-transformed lymphoblastoid cell line as a reporter system for the activity of the +40/−328 LMP1 promoter region, the functional importance of NF-κB and other transcription factor binding sites was demonstrated. p65RelA could also induce LMP1 expression from the EBV genome in Daudi and P3HR1 Burkitt's lymphoma cell lines. Finally, it was shown that p65RelA could cooperate with EBNA2 or the aryl hydrocarbon receptor in the transactivation of the LMP1 promoter. Our study established the importance of NF-κB and several cis-acting elements in the regulation of the LMP1 promoter in a latency III environment and highlighted a complex interplay between NF-κB and other transcription factors in this process

Induction of Apoptosis by Rewiring the Signal Transduction of Epstein-Barr Virus Oncoprotein LMP1 toward Caspase Activation

The Epstein-Barr virus latent membrane protein 1 (LMP1) is an oncoprotein which mimics activated tumor necrosis factor receptor family members. Here we demonstrate the principle that an inducible association of the LMP1 cytoplasmic carboxyl terminus with caspase-8 by a heterodimerizing agent causes apoptosis. This process depends on the catalytic activity of caspase-8 and the ability of LMP1 to oligomerize constitutively at the plasma membrane. Our data indicate that chemical inducers of the association of the LMP1 carboxyl terminus with caspase-8 can kill LMP1-expressing cells selectively. Such compounds could be used as chemotherapeutic agents for LMP1-associated malignancies

Comparative Analysis of Signal Transduction by CD40 and the Epstein-Barr Virus Oncoprotein LMP1 In Vivo

There is much evidence, based primarily on in vitro studies, indicating that the Epstein-Barr virus oncoprotein latent membrane protein 1 (LMP1) mimics an activated CD40 receptor. In order to investigate the extent of similarity between LMP1 and CD40 functions in vivo, we analyzed the cytoplasmic signaling properties of LMP1 and CD40 in B cells in a directly comparable manner. For this purpose, we generated transgenic mice expressing either LMP1 or a chimeric LMP1CD40 molecule, which constitutively activates the CD40 pathway, under the control of the CD19 promoter. LMP1 and LMP1CD40 were expressed at similar levels in a B-lymphocyte-specific manner. Similar to LMP1, LMP1CD40 suppressed germinal center (GC) formation and antibody production in response to thymus-dependent antigens, albeit to a greater extent than LMP1. Furthermore, the avidity of the antibodies produced against thymus-dependent antigens was lower for LMP1CD40 transgenic mice than for wild-type and LMP1 transgenic mice. GC suppression was linked to the ability of LMP1CD40 and LMP1 to downregulate mRNA and protein levels of BCL6 and to suppress the activity of the BCL6 promoter. In contrast to LMP1, LMP1CD40 caused an upregulation of CD69, CD80, and CD86 in B cells and a dramatic increase in serum immunoglobulin M. In addition, LMP1CD40 but not LMP1 transgenic mice had elevated numbers of marginal-zone B cells and increased populations of polymorphonuclear cells and/or neutrophils. Consistent with these findings, LMP1CD40 but not LMP1 transgenic mice showed signs of spontaneous inflammatory reactions and the potential for autoimmunity

Normal hematopoietic development in <i>M-Cyld^Δ9</i> mice.

<p>A) Enumeration of the indicated hematopoietic lineage cells (lower panel) by flow cytometric analysis of bone marrow cells for the expression of Ly6c and CD31 surface markers at steady state conditions (upper left panel) and after 72 h of thioglycollate treatment (upper right panel). In the first case 5 control and 3 <i>M-Cyld^Δ9</i> mice were evaluated whereas in the second case 7 control and 5 <i>M-Cyld^Δ9</i> mice were evaluated. B) Monocyte lineage populations in spleen. Enumeration of cells in the spleen that were collected from control (<i>M-Cyld⁺</i>) and mutant (<i>M-Cyld^Δ9</i>) mice 72 hours after thioglycollate injection. Data are depicted as mean absolute numbers (±SEM) from n = 7 control and 5 <i>M-Cyld^Δ9</i> mice at 8 weeks of age. The statistically significant difference in the macrophage populations (Mac1⁺ Gr1⁻) of control and mutant mice is depicted by two stars (p<0,001, Student's unpaired t test).</p

Attenuation of LPS-induced endotoxic shock in <i>M-Cyld^Δ9</i> mice.

<p>A) Ten control (4 <i>Cyld ^flx9/+</i> and 6 <i>Cyld ^flx9/+ LysMcre</i>) and eight <i>M-Cyld^Δ9</i> mice were subjected to LPS induced endotoxic shock (32 mg LPS/kg) and survival was monitored for the next 5 days. <i>M-Cyld^Δ9</i> mice exhibited increased resistance to endotoxemia in comparison to control mice. Data are depicted as mean absolute numbers (±SEM) from n = 10 control and 8 <i>M-Cyld^Δ9</i> mice at 8 weeks of age. (p value = 0,02 as assessed by Student's unpaired t test). B) Concentrations of TNFα were measured by enzyme-linked immunosorbent assay in supernatants from control and <i>M-Cyld^Δ9</i> BMDMs before and 24 h after treatment with 100 ng/mL LPS. The results shown are the means (±S.D.) of triplicate measurements. Control BMDMs were isolated from 3 wild type and 4 <i>Cyld^flx9/+LysMCre</i> mice and <i>M-Cyld^Δ9</i> BMDMs were isolated from 4 mice.</p