Autonomous metabolic reprogramming and oxidative stress characterize endothelial dysfunction in acute myocardial infarction

Compelling evidence has accumulated on the role of oxidative stress on the endothelial cell (EC) dysfunction in acute coronary syndrome. Unveiling the underlying metabolic determinants has been hampered by the scarcity of appropriate cell models to address cell-autonomous mechanisms of EC dysfunction. We have generated endothelial cells derived from thrombectomy specimens from patients affected with acute myocardial infarction (AMI) and conducted phenotypical and metabolic characterizations. AMI-derived endothelial cells (AMIECs) display impaired growth, migration, and tubulogenesis. Metabolically, AMIECs displayed augmented ROS and glutathione intracellular content, with a diminished glucose consumption coupled to high lactate production. In AMIECs, while PFKFB3 protein levels of were downregulated, PFKFB4 levels were upregulated, suggesting a shunting of glycolysis towards the pentose phosphate pathway, supported by upregulation of G6PD. Furthermore, the glutaminolytic enzyme GLS was upregulated in AMIECs, providing an explanation for the increase in glutathione content. Finally, AMIECs displayed a significantly higher mitochondrial membrane potential than control ECs, which, together with high ROS levels, suggests a coupled mitochondrial activity. We suggest that high mitochondrial proton coupling underlies the high production of ROS, balanced by PPP- and glutaminolysis-driven synthesis of glutathione, as a primary, cell-autonomous abnormality driving EC dysfunction in AMI.

Autochthonous Peruvian Natural Plants as Potential SARS-CoV-2 Mpro Main Protease Inhibitors

Over 750 million cases of COVID-19, caused by the Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), have been reported since the onset of the global outbreak. The need for effective treatments has spurred intensive research for therapeutic agents based on pharmaceutical repositioning or natural products. In light of prior studies asserting the bioactivity of natural compounds of the autochthonous Peruvian flora, the present study focuses on the identification SARS-CoV-2 M^pro main protease dimer inhibitors. To this end, a target-based virtual screening was performed over a representative set of Peruvian flora-derived natural compounds. The best poses obtained from the ensemble molecular docking process were selected. These structures were subjected to extensive molecular dynamics steps for the computation of binding free energies along the trajectory and evaluation of the stability of the complexes. The compounds exhibiting the best free energy behaviors were selected for in vitro testing, confirming the inhibitory activity of Hyperoside against M^pro, with a K_i value lower than 20 µM, presumably through allosteric modulation.

A novel gene signature unveils three distinct immune-metabolic rewiring patterns conserved across diverse tumor types and associated with outcomes

Existing immune signatures and tumor mutational burden have only modest predictive capacity for the efficacy of immune check point inhibitors. In this study, we developed an immune-metabolic signature suitable for personalized ICI therapies. A classifier using an immune-metabolic signature (IMMETCOLS) was developed on a training set of 77 metastatic colorectal cancer (mCRC) samples and validated on 4,200 tumors from the TCGA database belonging to 11 types. Here, we reveal that the IMMETCOLS signature classifies tumors into three distinct immune-metabolic clusters. Cluster 1 displays markers of enhanced glycolisis, hexosamine byosinthesis and epithelial-to-mesenchymal transition. On multivariate analysis, cluster 1 tumors were enriched in pro-immune signature but not in immunophenoscore and were associated with the poorest median survival. Its predicted tumor metabolic features suggest an acidic-lactate-rich tumor microenvironment (TME) geared to an immunosuppressive setting, enriched in fibroblasts. Cluster 2 displays features of gluconeogenesis ability, which is needed for glucose-independent survival and preferential use of alternative carbon sources, including glutamine and lipid uptake/β-oxidation. Its metabolic features suggest a hypoxic and hypoglycemic TME, associated with poor tumor-associated antigen presentation. Finally, cluster 3 is highly glycolytic but also has a solid mitochondrial function, with concomitant upregulation of glutamine and essential amino acid transporters and the pentose phosphate pathway leading to glucose exhaustion in the TME and immunosuppression. Together, these findings suggest that the IMMETCOLS signature provides a classifier of tumors from diverse origins, yielding three clusters with distinct immune-metabolic profiles, representing a new predictive tool for patient selection for specific immune-metabolic therapeutic approaches.

Recovery of serum testosterone levels is an accurate predictor of survival from COVID-19 in male patients

BACKGROUND

SARS-CoV-2 infection portends a broad range of outcomes, from a majority of asymptomatic cases to a lethal disease. Robust correlates of severe COVID-19 include old age, male sex, poverty, and co-morbidities such as obesity, diabetes, and cardiovascular disease. A precise knowledge of the molecular and biological mechanisms that may explain the association of severe disease with male sex is still lacking. Here, we analyzed the relationship of serum testosterone levels and the immune cell skewing with disease severity in male COVID-19 patients.

METHODS

Biochemical and hematological parameters of admission samples in 497 hospitalized male and female COVID-19 patients, analyzed for associations with outcome and sex. Longitudinal (in-hospital course) analyses of a subcohort of 114 male patients were analyzed for associations with outcome. Longitudinal analyses of immune populations by flow cytometry in 24 male patients were studied for associations with outcome.

RESULTS

We have found quantitative differences in biochemical predictors of disease outcome in male vs. female patients. Longitudinal analyses in a subcohort of male COVID-19 patients identified serum testosterone trajectories as the strongest predictor of survival (AUC of ROC = 92.8%, p < 0.0001) in these patients among all biochemical parameters studied, including single-point admission serum testosterone values. In lethal cases, longitudinal determinations of serum luteinizing hormone (LH) and androstenedione levels did not follow physiological feedback patterns. Failure to reinstate physiological testosterone levels was associated with evidence of impaired T helper differentiation and augmented circulating classical monocytes.

CONCLUSIONS

Recovery or failure to reinstate testosterone levels is strongly associated with survival or death, respectively, from COVID-19 in male patients. Our data suggest an early inhibition of the central LH-androgen biosynthesis axis in a majority of patients, followed by full recovery in survivors or a peripheral failure in lethal cases. These observations are suggestive of a significant role of testosterone status in the immune responses to COVID-19 and warrant future experimental explorations of mechanistic relationships between testosterone status and SARS-CoV-2 infection outcomes, with potential prophylactic or therapeutic implications.

Discovery of Diverse Natural Products as Inhibitors of SARS-CoV-2 Mpro Protease through Virtual Screening

SARS-CoV-2 is a type of coronavirus responsible for the international outbreak of respiratory illness termed COVID-19 that forced the World Health Organization to declare a pandemic infectious disease situation of international concern at the beginning of 2020. The need for a swift response against COVID-19 prompted to consider different sources to identify bioactive compounds that can be used as therapeutic agents, including available drugs and natural products. Accordingly, this work reports the results of a virtual screening process aimed at identifying antiviral natural product inhibitors of the SARS-CoV-2 M^pro viral protease. For this purpose, ca. 2000 compounds of the Selleck database of Natural Compounds were the subject of an ensemble docking process targeting the M^pro protease. Molecules that showed binding to most of the protein conformations were retained for a further step that involved the computation of the binding free energy of the ligand-M^pro complex along a molecular dynamics trajectory. The compounds that showed a smooth binding free energy behavior were selected for in vitro testing. From the resulting set of compounds, five compounds exhibited an antiviral profile, and they are disclosed in the present work.

Potential Protective Effect from COVID-19 Conferred by Altitude: A Longitudinal Analysis in Peru During Full Lockdown

Thomson, Timothy M., Fresia Casas, Harold Andre Guerrero, Rómulo Figueroa-Mujíca, Francisco C. Villafuerte, and Claudia Machicado. Potential protective effect from COVID-19 conferred by altitude: A longitudinal analysis in Peru during full lockdown. High Alt Med Biol. 22: 209-224, 2021. Background: The COVID-19 pandemic had a delayed onset in America. Despite the time advantage for the implementation of preventative measures to contain its spread, the pandemic followed growth rates that paralleled those observed before in Europe. Objectives: To analyze the temporal and geographical distribution of the COVID-19 pandemic at district-level in Perú during the full lockdown period in 2020. Methods: Analysis of publicly available data sets, stratified by altitude and geographical localization. Correlation tests of COVID-19 case and death rates to population prevalence of comorbidities. Results: We observe a strong protective effect of altitude from COVID-19 mortality in populations located above 2,500 m. We provide evidence that internal migration through a specific land route is a significant factor progressively overriding the protection from COVID-19 afforded by high altitude. This protection is independent of poverty indexes and is inversely correlated with the prevalence of hypertension and hypercholesterolemia. Discussion: Long-term adaptation to residency at high altitude may be the third general protective factor from COVID-19 severity and death, after young age and female sex. Multisystemic adaptive traits or acclimatization processes in response to chronic hypobaric hypoxia may explain the apparent protective effect of high altitude from COVID-19 death.

C1 esterase inhibitor and the contact system in COVID-19

Coronavirus disease 2019 (COVID-19) is frequently associated with severe systemic consequences, including vasculitis, a hyperinflammatory state and hypercoagulation. The mechanisms leading to these life-threatening abnormalities are multifactorial. Based on the analysis of publicly available interactomes, we propose that severe acute respiratory syndrome coronavirus-2 infection directly causes a deficiency in C1 esterase inhibitor, a pathogen-specific mechanism that may help explain significant systemic abnormalities in patients with COVID-19.

Metabolic Alterations in Cardiopulmonary Vascular Dysfunction

Cardiovascular diseases (CVD) are the leading cause of death worldwide. CVD comprise a range of diseases affecting the functionality of the heart and blood vessels, including acute myocardial infarction (AMI) and pulmonary hypertension (PH). Despite their different causative mechanisms, both AMI and PH involve narrowed or blocked blood vessels, hypoxia, and tissue infarction. The endothelium plays a pivotal role in the development of CVD. Disruption of the normal homeostasis of endothelia, alterations in the blood vessel structure, and abnormal functionality are essential factors in the onset and progression of both AMI and PH. An emerging theory proposes that pathological blood vessel responses and endothelial dysfunction develop as a result of an abnormal endothelial metabolism. It has been suggested that, in CVD, endothelial cell metabolism switches to higher glycolysis, rather than oxidative phosphorylation, as the main source of ATP, a process designated as the Warburg effect. The evidence of these alterations suggests that understanding endothelial metabolism and mitochondrial function may be central to unveiling fundamental mechanisms underlying cardiovascular pathogenesis and to identifying novel critical metabolic biomarkers and therapeutic targets. Here, we review the role of the endothelium in the regulation of vascular homeostasis and we detail key aspects of endothelial cell metabolism. We also describe recent findings concerning metabolic endothelial cell alterations in acute myocardial infarction and pulmonary hypertension, their relationship with disease pathogenesis and we discuss the future potential of pharmacological modulation of cellular metabolism in the treatment of cardiopulmonary vascular dysfunction. Although targeting endothelial cell metabolism is still in its infancy, it is a promising strategy to restore normal endothelial functions and thus forestall or revert the development of CVD in personalized multi-hit interventions at the metabolic level.

Untargeted metabolomics reveals distinct metabolic reprogramming in endothelial cells co-cultured with CSC and non-CSC prostate cancer cell subpopulations

Tumour angiogenesis is an important hallmark of cancer and the study of its metabolic adaptations, downstream to any cellular change, can reveal attractive targets for inhibiting cancer growth. In the tumour microenvironment, endothelial cells (ECs) interact with heterogeneous tumour cell types that drive angiogenesis and metastasis. In this study we aim to characterize the metabolic alterations in ECs influenced by the presence of tumour cells with extreme metastatic abilities. Human umbilical vein endothelial cells (HUVECs) were subjected to different microenvironmental conditions, such as the presence of highly metastatic PC-3M and highly invasive PC-3S prostate cancer cell lines, in addition to the angiogenic activator vascular endothelial growth factor (VEGF), under normoxia. Untargeted high resolution liquid chromatography-mass spectrometry (LC-MS) based metabolomics revealed significant metabolite differences among the various conditions and a total of 25 significantly altered metabolites were identified including acetyl L-carnitine, NAD+, hypoxanthine, guanine and oleamide, with profile changes unique to each of the experimental conditions. Biochemical pathway analysis revealed the importance of fatty acid oxidation and nucleotide salvage pathways. These results provide a global metabolic preview that could help in selectively targeting the ECs aiding in either cancer cell invasion or metastasis in the heterogeneous tumour microenvironment.

Model-driven discovery of long-chain fatty acid metabolic reprogramming in heterogeneous prostate cancer cells

Epithelial-mesenchymal-transition promotes intra-tumoral heterogeneity, by enhancing tumor cell invasiveness and promoting drug resistance. We integrated transcriptomic data for two clonal subpopulations from a prostate cancer cell line (PC-3) into a genome-scale metabolic network model to explore their metabolic differences and potential vulnerabilities. In this dual cell model, PC-3/S cells express Epithelial-mesenchymal-transition markers and display high invasiveness and low metastatic potential, while PC-3/M cells present the opposite phenotype and higher proliferative rate. Model-driven analysis and experimental validations unveiled a marked metabolic reprogramming in long-chain fatty acids metabolism. While PC-3/M cells showed an enhanced entry of long-chain fatty acids into the mitochondria, PC-3/S cells used long-chain fatty acids as precursors of eicosanoid metabolism. We suggest that this metabolic reprogramming endows PC-3/M cells with augmented energy metabolism for fast proliferation and PC-3/S cells with increased eicosanoid production impacting angiogenesis, cell adhesion and invasion. PC-3/S metabolism also promotes the accumulation of docosahexaenoic acid, a long-chain fatty acid with antiproliferative effects. The potential therapeutic significance of our model was supported by a differential sensitivity of PC-3/M cells to etomoxir, an inhibitor of long-chain fatty acid transport to the mitochondria.

The coexistence within the same tumor of a variety of subpopulations, featuring different phenotypes (intra-tumoral heterogeneity) represents a challenge for diagnosis, prognosis and targeted therapies. In this work, we have explored the metabolic differences underlying tumor heterogeneity by building cell-type-specific genome-scale metabolic models that integrate transcriptome and metabolome data of two clonal subpopulations derived from the same prostate cancer cell line (PC-3). These subpopulations display either highly proliferative, cancer stem cell (PC-3/M) or highly invasive, epithelial-mesenchymal-transition-like phenotypes (PC-3/S). Our model-driven analysis and experimental validations have unveiled a differential utilization of the long-chain fatty acids pool in both subpopulations. More specifically, our findings show an enhanced entry of long-chain fatty acids into the mitochondria in PC-3/M cells, while in PC-3/S cells, long-chain fatty acids are used as precursors of eicosanoid metabolism. The different utilization of long-chain fatty acids between subpopulations endows PC-3/M cells with a highly proliferative phenotype while enhances PC-3/S invasive phenotype. The present work provides a tool to unveil key metabolic nodes associated with tumor heterogeneity and highlights potential subpopulation-specific targets with important therapeutic implications.

De novo MYC addiction as an adaptive response of cancer cells to CDK4/6 inhibition

Cyclin‐dependent kinases (CDK) are rational cancer therapeutic targets fraught with the development of acquired resistance by tumor cells. Through metabolic and transcriptomic analyses, we show that the inhibition of CDK4/6 leads to a metabolic reprogramming associated with gene networks orchestrated by the MYC transcription factor. Upon inhibition of CDK4/6, an accumulation of MYC protein ensues which explains an increased glutamine metabolism, activation of the mTOR pathway and blunting of HIF‐1α‐mediated responses to hypoxia. These MYC‐driven adaptations to CDK4/6 inhibition render cancer cells highly sensitive to inhibitors of MYC, glutaminase or mTOR and to hypoxia, demonstrating that metabolic adaptations to antiproliferative drugs unveil new vulnerabilities that can be exploited to overcome acquired drug tolerance and resistance by cancer cells.

Metabolic Reprogramming and Dependencies Associated with Epithelial Cancer Stem Cells Independent of the Epithelial-Mesenchymal Transition Program

In solid tumors, cancer stem cells (CSCs) can arise independently of epithelial-mesenchymal transition (EMT). In spite of recent efforts, the metabolic reprogramming associated with CSC phenotypes uncoupled from EMT is poorly understood. Here, by using metabolomic and fluxomic approaches, we identify major metabolic profiles that differentiate metastatic prostate epithelial CSCs (e-CSCs) from non-CSCs expressing a stable EMT. We have found that the e-CSC program in our cellular model is characterized by a high plasticity in energy substrate metabolism, including an enhanced Warburg effect, a greater carbon and energy source flexibility driven by fatty acids and amino acid metabolism and an essential reliance on the proton buffering capacity conferred by glutamine metabolism. An analysis of transcriptomic data yielded a metabolic gene signature for our e-CSCs consistent with the metabolomics and fluxomics analyses that correlated with tumor progression and metastasis in prostate cancer and in 11 additional cancer types. Interestingly, an integrated metabolomics, fluxomics, and transcriptomics analysis allowed us to identify key metabolic players regulated at the post-transcriptional level, suggesting potential biomarkers and therapeutic targets to effectively forestall metastasis. Stem Cells 2016;34:1163-1176.

SPARC mediates metastatic cooperation between CSC and non-CSC prostate cancer cell subpopulations

Background

Tumor cell subpopulations can either compete with each other for nutrients and physical space within the tumor niche, or co-operate for enhanced survival, or replicative or metastatic capacities. Recently, we have described co-operative interactions between two clonal subpopulations derived from the PC-3 prostate cancer cell line, in which the invasiveness of a cancer stem cell (CSC)-enriched subpopulation (PC-3M, or M) is enhanced by a non-CSC subpopulation (PC-3S, or S), resulting in their accelerated metastatic dissemination.

Methods

M and S secretomes were compared by SILAC (Stable Isotope Labeling by Aminoacids in Cell Culture). Invasive potential in vitro of M cells was analyzed by Transwell-Matrigel assays. M cells were co-injected with S cells in the dorsal prostate of immunodeficient mice and monitored by bioluminescence for tumor growth and metastatic dissemination. SPARC levels were determined by immunohistochemistry and real-time RT-PCR in tumors and by ELISA in plasma from patients with metastatic or non-metastatic prostate cancer.

Results

Comparative secretome analysis yielded 213 proteins differentially secreted between M and S cells. Of these, the protein most abundantly secreted in S relative to M cells was SPARC. Immunodepletion of SPARC inhibited the enhanced invasiveness of M induced by S conditioned medium. Knock down of SPARC in S cells abrogated the capacity of its conditioned medium to enhance the in vitro invasiveness of M cells and compromised their potential to boost the metastatic behavior of M cells in vivo. In most primary human prostate cancer samples, SPARC was expressed in the epithelial tumoral compartment of metastatic cases.

Conclusions

The matricellular protein SPARC, secreted by a prostate cancer clonal tumor cell subpopulation displaying non-CSC properties, is a critical mediator of paracrine effects exerted on a distinct tumor cell subpopulation enriched in CSC. This paracrine interaction results in an enhanced metastatic behavior of the CSC-enriched tumor subpopulation. SPARC is expressed in the neoplastic cells of primary prostate cancer samples from metastatic cases, and could thus constitute a tumor progression biomarker and a therapeutic target in advanced prostate cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/1476-4598-13-237) contains supplementary material, which is available to authorized users.

Prostate tumor OVerexpressed-1 (PTOV1) down-regulates HES1 and HEY1 notch targets genes and promotes prostate cancer progression

BACKGROUND

PTOV1 is an adaptor protein with functions in diverse processes, including gene transcription and protein translation, whose overexpression is associated with a higher proliferation index and tumor grade in prostate cancer (PC) and other neoplasms. Here we report its interaction with the Notch pathway and its involvement in PC progression.

METHODS

Stable PTOV1 knockdown or overexpression were performed by lentiviral transduction. Protein interactions were analyzed by co-immunoprecipitation, pull-down and/or immunofluorescence. Endogenous gene expression was analyzed by real time RT-PCR and/or Western blotting. Exogenous promoter activities were studied by luciferase assays. Gene promoter interactions were analyzed by chromatin immunoprecipitation assays (ChIP). In vivo studies were performed in the Drosophila melanogaster wing, the SCID-Beige mouse model, and human prostate cancer tissues and metastasis. The Excel package was used for statistical analysis.

RESULTS

Knockdown of PTOV1 in prostate epithelial cells and HaCaT skin keratinocytes caused the upregulation, and overexpression of PTOV1 the downregulation, of the Notch target genes HEY1 and HES1, suggesting that PTOV1 counteracts Notch signaling. Under conditions of inactive Notch signaling, endogenous PTOV1 associated with the HEY1 and HES1 promoters, together with components of the Notch repressor complex. Conversely, expression of active Notch1 provoked the dismissal of PTOV1 from these promoters. The antagonist role of PTOV1 on Notch activity was corroborated in the Drosophila melanogaster wing, where human PTOV1 exacerbated Notch deletion mutant phenotypes and suppressed the effects of constitutively active Notch. PTOV1 was required for optimal in vitro invasiveness and anchorage-independent growth of PC-3 cells, activities counteracted by Notch, and for their efficient growth and metastatic spread in vivo. In prostate tumors, the overexpression of PTOV1 was associated with decreased expression of HEY1 and HES1, and this correlation was significant in metastatic lesions.

CONCLUSIONS

High levels of the adaptor protein PTOV1 counteract the transcriptional activity of Notch. Our evidences link the pro-oncogenic and pro-metastatic effects of PTOV1 in prostate cancer to its inhibitory activity on Notch signaling and are supportive of a tumor suppressor role of Notch in prostate cancer progression.

Infrequent loss of luminal differentiation in ductal breast cancer metastasis

Lymph node involvement is a major prognostic variable in breast cancer. Whether the molecular mechanisms that drive breast cancer cells to colonize lymph nodes are shared with their capacity to form distant metastases is yet to be established. In a transcriptomic survey aimed at identifying molecular factors associated with lymph node involvement of ductal breast cancer, we found that luminal differentiation, assessed by the expression of estrogen receptor (ER) and/or progesterone receptor (PR) and GATA3, was only infrequently lost in node-positive primary tumors and in matched lymph node metastases. The transcription factor GATA3 critically determines luminal lineage specification of mammary epithelium and is widely considered a tumor and metastasis suppressor in breast cancer. Strong expression of GATA3 and ER in a majority of primary node-positive ductal breast cancer was corroborated by quantitative RT-PCR and immunohistochemistry in the initial sample set, and by immunohistochemistry in an additional set from 167 patients diagnosed of node-negative and –positive primary infiltrating ductal breast cancer, including 102 samples from loco-regional lymph node metastases matched to their primary tumors, as well as 37 distant metastases. These observations suggest that loss of luminal differentiation is not a major factor driving the ability of breast cancer cells to colonize regional lymph nodes.

Stem cells in prostate cancer

Tumors constitute complex ecosystems with multiple interactions among neoplastic cells displaying various phenotypes and functions and where the tumoral niche is built with an active participation of the host environment that also impacts the malignant progression of the tumor cells. Irrespective of the cell of origin of prostate adenocarcinoma, mounting evidences support the existence of a hierarchy within neoplastic prostate cells that contributes to the heterogeneity of these tumors. At the origin of this hierarchy are small populations of tumor cells with high self-renewal potential and also capable of generating progeny tumor cells that lose self-renewal properties as they acquire more differentiated phenotypes. These cancer stem cells (CSC) depend on active gene networks that confer them with their self-renewal capacity through symmetrical divisions whereas they can also undergo asymmetrical division and differentiation either as stochastic events or in response to environmental cues. Although new experimental evidences indicate that this is can be a reversible process, thus blurring the distinction between CSCs and non-CSCs, the former are considered as the drivers of tumor growth and evolution, and thus a prime target for therapeutic intervention. Of particular importance in prostate cancer, CSCs may constitute the repository population of androgen-insensitive and chemotherapy-resistant tumor cells responsible for castration-resistant and chemotherapy-insensitive tumors, thus their identification and quantification in primary and metastatic neoplasms could play important roles in the management of this disease.

Acid ceramidase as a therapeutic target in metastatic prostate cancer

Acid ceramidase (AC) catalyzes the hydrolysis of ceramide into sphingosine, in turn a substrate of sphingosine kinases that catalyze its conversion into the mitogenic sphingosine-1-phosphate. AC is expressed at high levels in several tumor types and has been proposed as a cancer therapeutic target. Using a model derived from PC-3 prostate cancer cells, the highly tumorigenic, metastatic, and chemoresistant clone PC-3/Mc expressed higher levels of the AC ASAH1 than the nonmetastatic clone PC-3/S. Stable knockdown of ASAH1 in PC-3/Mc cells caused an accumulation of ceramides, inhibition of clonogenic potential, increased requirement for growth factors, and inhibition of tumorigenesis and lung metastases. We developed de novo ASAH1 inhibitors, which also caused a dose-dependent accumulation of ceramides in PC-3/Mc cells and inhibited their growth and clonogenicity. Finally, immunohistochemical analysis of primary prostate cancer samples showed that higher levels of ASAH1 were associated with more advanced stages of this neoplasia. These observations confirm ASAH1 as a therapeutic target in advanced and chemoresistant forms of prostate cancer and suggest that our new potent and specific AC inhibitors could act by counteracting critical growth properties of these highly aggressive tumor cells.

Identification of RNF8 as a ubiquitin ligase involved in targeting the p12 subunit of DNA polymerase δ for degradation in response to DNA damage

DNA polymerase δ consists of four subunits, one of which, p12, is degraded in response to DNA damage through the ubiquitin-proteasome pathway. However, the identities of the ubiquitin ligase(s) that are responsible for the proximal biochemical events in triggering proteasomal degradation of p12 are unknown. We employed a classical approach to identifying a ubiquitin ligase that is involved in p12 degradation. Using UbcH5c as ubiquitin-conjugating enzyme, a ubiquitin ligase activity that polyubiquitinates p12 was purified from HeLa cells. Proteomic analysis revealed that RNF8, a RING finger ubiquitin ligase that plays an important role in the DNA damage response, was the only ubiquitin ligase present in the purified preparation. In vivo, DNA damage-induced p12 degradation was significantly reduced by shRNA knockdown of RNF8 in cultured human cells and in RNF8(-/-) mouse epithelial cells. These studies provide the first identification of a ubiquitin ligase activity that is involved in the DNA damage-induced destruction of p12. The identification of RNF8 allows new insights into the integration of the control of p12 degradation by different DNA damage signaling pathways.

Epithelial-mesenchymal transition can suppress major attributes of human epithelial tumor-initiating cells

Malignant progression in cancer requires populations of tumor-initiating cells (TICs) endowed with unlimited self renewal, survival under stress, and establishment of distant metastases. Additionally, the acquisition of invasive properties driven by epithelial-mesenchymal transition (EMT) is critical for the evolution of neoplastic cells into fully metastatic populations. Here, we characterize 2 human cellular models derived from prostate and bladder cancer cell lines to better understand the relationship between TIC and EMT programs in local invasiveness and distant metastasis. The model tumor subpopulations that expressed a strong epithelial gene program were enriched in highly metastatic TICs, while a second subpopulation with stable mesenchymal traits was impoverished in TICs. Constitutive overexpression of the transcription factor Snai1 in the epithelial/TIC-enriched populations engaged a mesenchymal gene program and suppressed their self renewal and metastatic phenotypes. Conversely, knockdown of EMT factors in the mesenchymal-like prostate cancer cell subpopulation caused a gain in epithelial features and properties of TICs. Both tumor cell subpopulations cooperated so that the nonmetastatic mesenchymal-like prostate cancer subpopulation enhanced the in vitro invasiveness of the metastatic epithelial subpopulation and, in vivo, promoted the escape of the latter from primary implantation sites and accelerated their metastatic colonization. Our models provide new insights into how dynamic interactions among epithelial, self-renewal, and mesenchymal gene programs determine the plasticity of epithelial TICs.

Highly sensitive molecular diagnosis of prostate cancer using surplus material washed off from biopsy needles

Introduction:

Currently, final diagnosis of prostate cancer (PCa) is based on histopathological analysis of needle biopsies, but this process often bears uncertainties due to small sample size, tumour focality and pathologist's subjective assessment.

Methods:

Prostate cancer diagnostic signatures were generated by applying linear discriminant analysis to microarray and real-time RT–PCR (qRT–PCR) data from normal and tumoural prostate tissue samples. Additionally, after removal of biopsy tissues, material washed off from transrectal biopsy needles was used for molecular profiling and discriminant analysis.

Results:

Linear discriminant analysis applied to microarray data for a set of 318 genes differentially expressed between non-tumoural and tumoural prostate samples produced 26 gene signatures, which classified the 84 samples used with 100% accuracy. To identify signatures potentially useful for the diagnosis of prostate biopsies, surplus material washed off from routine biopsy needles from 53 patients was used to generate qRT–PCR data for a subset of 11 genes. This analysis identified a six-gene signature that correctly assigned the biopsies as benign or tumoural in 92.6% of the cases, with 88.8% sensitivity and 96.1% specificity.

Conclusion:

Surplus material from prostate needle biopsies can be used for minimal-size gene signature analysis for sensitive and accurate discrimination between non-tumoural and tumoural prostates, without interference with current diagnostic procedures. This approach could be a useful adjunct to current procedures in PCa diagnosis.

Differential regulation of RNF8-mediated Lys48- and Lys63-based poly-ubiquitylation

Pairing of a given E3 ubiquitin ligase with different E2s allows synthesis of ubiquitin conjugates of different topologies. While this phenomenon contributes to functional diversity, it remains largely unknown how a single E3 ubiquitin ligase recognizes multiple E2s, and whether identical structural requirements determine their respective interactions. The E3 ubiquitin ligase RNF8 that plays a critically important role in transducing DNA damage signals, interacts with E2s UBCH8 and UBC13, and catalyzes both K48- and K63-linked ubiquitin chains. Interestingly, we report here that a single-point mutation (I405A) on the RNF8 polypeptide uncouples its ability in catalyzing K48- and K63-linked ubiquitin chain formation. Accordingly, while RNF8 interacted with E2s UBCH8 and UBC13, its I405A mutation selectively disrupted its functional interaction with UBCH8, and impaired K48-based poly-ubiquitylation reactions. In contrast, RNF8 I405A preserved its interaction with UBC13, synthesized K63-linked ubiquitin chains, and assembled BRCA1 and 53BP1 at sites of DNA breaks. Together, our data suggest that RNF8 regulates K48- and K63-linked poly-ubiquitylation via differential RING-dependent interactions with its E2s UBCH8 and UBC13, respectively.

Protein-protein interaction antagonists as novel inhibitors of non-canonical polyubiquitylation

BACKGROUND

Several pathways that control cell survival under stress, namely RNF8-dependent DNA damage recognition and repair, PCNA-dependent DNA damage tolerance and activation of NF-kappaB by extrinsic signals, are regulated by the tagging of key proteins with lysine 63-based polyubiquitylated chains, catalyzed by the conserved ubiquitin conjugating heterodimeric enzyme Ubc13-Uev.

METHODOLOGY/PRINCIPAL FINDINGS

By applying a selection based on in vivo protein-protein interaction assays of compounds from a combinatorial chemical library followed by virtual screening, we have developed small molecules that efficiently antagonize the Ubc13-Uev1 protein-protein interaction, inhibiting the enzymatic activity of the heterodimer. In mammalian cells, they inhibit lysine 63-type polyubiquitylation of PCNA, inhibit activation of NF-kappaB by TNF-alpha and sensitize tumor cells to chemotherapeutic agents. One of these compounds significantly inhibited invasiveness, clonogenicity and tumor growth of prostate cancer cells.

CONCLUSIONS/SIGNIFICANCE

This is the first development of pharmacological inhibitors of non-canonical polyubiquitylation that show that these compounds produce selective biological effects with potential therapeutic applications.

Monoubiquitination of RPN10 regulates substrate recruitment to the proteasome

The proteasome recognizes its substrates via a diverse set of ubiquitin receptors, including subunits Rpn10/S5a and Rpn13. In addition, shuttling factors, such as Rad23, recruit substrates to the proteasome by delivering ubiquitinated proteins. Despite the increasing understanding of the factors involved in this process, the regulation of substrate delivery remains largely unexplored. Here we report that Rpn10 is monoubiquitinated in vivo and that this modification has profound effects on proteasome function. Monoubiquitination regulates the capacity of Rpn10 to interact with substrates by inhibiting Rpn10's ubiquitin-interacting motif (UIM). We show that Rsp5, a member of NEDD4 ubiquitin-protein ligase family, and Ubp2, a deubiquitinating enzyme, control the levels of Rpn10 monoubiquitination in vivo. Notably, monoubiquitination of Rpn10 is decreased under stress conditions, suggesting a mechanism of control of receptor availability mediated by the Rsp5-Ubp2 system. Our results reveal an unanticipated link between monoubiquitination signal and regulation of proteasome function.

Regulation of aurora B kinase by the lipid raft protein flotillin-1

The lipid raft protein Flotillin-1 was previously shown to be required for cell proliferation. Here we show that it is critical for the maintenance of the levels of the mitotic regulator Aurora B. Knockdown of Flotillin-1 induced aberrant mitotic events similar to those produced by Aurora B depletion and led to a marked decline in Aurora B levels and activity. Transfection of wild-type full-length Flotillin-1 or forms directed to the nucleus increased Aurora B levels and activity. Flotillin-1 interacted with Aurora B directly through its SPFH domain in a complex distinct from the chromosomal passenger protein complex, and the two proteins co-purified in nuclear, non-raft fractions. These observations are the first evidence for a function of Flotillin-1 outside of lipid rafts and suggest its critical role in the maintenance of a pool of active Aurora B.

HER3 is required for the maintenance of neuregulin-dependent and -independent attributes of malignant progression in prostate cancer cells

HER3 (ERBB3) is a catalytically inactive pseudokinase of the HER receptor tyrosine kinase family, frequently overexpressed in prostate and other cancers. Aberrant expression and mutations of 2 other members of the family, EGFR and HER2, are key carcinogenic events in several types of tumors, and both are well- validated therapeutic targets. In this study, we show that HER3 is required to maintain the motile and invasive phenotypes of prostate (DU-145) and breast (MCF-7) cancer cells in response to the HER3 ligand neuregulin-1 (NRG-1), epidermal growth factor (EGF) and fetal bovine serum. Although MCF-7 breast cancer cells appeared to require HER3 as part of an autocrine response induced by EGF and FBS, the response of DU-145 prostate cancer cells to these stimuli, while requiring HER3, did not appear to involve autocrine stimulation of the receptor. DU-145 cells required the expression of HER3 for efficient clonogenicity in vitro in standard growth medium and for tumorigenicity in immunodeficient mice. These observations suggest that prostate cancer cells derived from tumors that overexpress HER3 are dependent on its expression for the maintenance of major attributes of neoplastic aggressiveness, with or without cognate ligand stimulation.

Analysis of electrostatic contributions to the selectivity of interactions between RING-finger domains and ubiquitin-conjugating enzymes

The zinc-coordinated protein motifs known as RING-finger domains, present on a class of ubiquitin ligases (E3's), recruit ubiquitin-conjugating enzymes (E2s), tethering them to substrate proteins for covalent modification with ubiquitin. Each RING-finger domain can recruit different E2s, and these interactions are frequently selective, in that certain RING-finger domains associate preferentially with certain E2s. This selectivity acquires particular biological relevance when the recruited E2s exert specialized functions. We have explored the determinants that specify the presence or absence of experimentally detectable interaction between two RING-finger domains, those on RNF11 and RNF103, and two E2s, UBC13, a specialized E2 that catalyzes ubiquitin chain elongation through Lys63 of ubiquitin, and UbcH7, which mediates polyubiquitylation through Lys48. Through the iterative use of computational predictive tools and experimental validations, we have found that these interactions and their selectivity are partly governed by the combinations of electrostatic interactions linking specific residues of the contact interfaces. Our analysis also predicts that the main determinants of selectivity of these interactions reside on the RING-finger domains, rather than on the E2s. The application of some of these rules of interaction selectivity has permitted us to experimentally manipulate the selectivity of interaction of the RING-finger domain-E2 pairs under study.

The Alpha Project: a model system for systems biology research

One goal of systems biology is to understand how genome-encoded parts interact to produce quantitative phenotypes. The Alpha Project is a medium-scale, interdisciplinary systems biology effort that aims to achieve this goal by understanding fundamental quantitative behaviours of a prototypic signal transduction pathway, the yeast pheromone response system from Saccharomyces cerevisiae. The Alpha Project distinguishes itself from many other systems biology projects by studying a tightly bounded and well-characterised system that is easily modified by genetic means, and by focusing on deep understanding of a discrete number of important and accessible quantitative behaviours. During the project, the authors have developed tools to measure the appropriate data and develop models at appropriate levels of detail to study a number of these quantitative behaviours. The authors have also developed transportable experimental tools and conceptual frameworks for understanding other signalling systems. In particular, the authors have begun to interpret system behaviours and their underlying molecular mechanisms through the lens of information transmission, a principal function of signalling systems. The Alpha Project demonstrates that interdisciplinary studies that identify key quantitative behaviours and measure important quantities, in the context of well-articulated abstractions of system function and appropriate analytical frameworks, can lead to deeper biological understanding. The authors' experience may provide a productive template for systems biology investigations of other cellular systems.

Co-regulation analysis of closely linked genes identifies a highly recurrent gain on chromosome 17q25.3 in prostate cancer

Background

Transcriptional profiling of prostate cancer (PC) has unveiled new markers of neoplasia and allowed insights into mechanisms underlying this disease. Genomewide analyses have also identified new chromosomal abnormalities associated with PC. The combination of both classes of data for the same sample cohort might provide better criteria for identifying relevant factors involved in neoplasia. Here we describe transcriptional signatures identifying distinct normal and tumoral prostate tissue compartments, and the inference and demonstration of a new, highly recurrent copy number gain on chromosome 17q25.3.

Methods

We have applied transcriptional profiling to tumoral and non-tumoral prostate samples with relatively homogeneous epithelial representations as well as pure stromal tissue from peripheral prostate and cultured cell lines, followed by quantitative RT-PCR validations and immunohistochemical analysis. In addition, we have performed in silico colocalization analysis of co-regulated genes and validation by fluorescent in situ hybridization (FISH).

Results

The transcriptomic analysis has allowed us to identify signatures corresponding to non-tumoral luminal and tumoral epithelium, basal epithelial cells, and prostate stromal tissue. In addition, in silico analysis of co-regulated expression of physically linked genes has allowed us to predict the occurrence of a copy number gain at chromosomal region 17q25.3. This computational inference was validated by fluorescent in situ hybridization, which showed gains in this region in over 65% of primary and metastatic tumoral samples.

Conclusion

Our approach permits to directly link gene copy number variations with transcript co-regulation in association with neoplastic states. Therefore, transcriptomic studies of carefully selected samples can unveil new diagnostic markers and transcriptional signatures highly specific of PC, and lead to the discovery of novel genomic abnormalities that may provide additional insights into the causes and mechanisms of prostate cancer.

Orchestration of the DNA-damage response by the RNF8 ubiquitin ligase

Cells respond to DNA double-strand breaks by recruiting factors such as the DNA-damage mediator protein MDC1, the p53-binding protein 1 (53BP1), and the breast cancer susceptibility protein BRCA1 to sites of damaged DNA. Here, we reveal that the ubiquitin ligase RNF8 mediates ubiquitin conjugation and 53BP1 and BRCA1 focal accumulation at sites of DNA lesions. Moreover, we establish that MDC1 recruits RNF8 through phosphodependent interactions between the RNF8 forkhead-associated domain and motifs in MDC1 that are phosphorylated by the DNA-damage activated protein kinase ataxia telangiectasia mutated (ATM). We also show that depletion of the E2 enzyme UBC13 impairs 53BP1 recruitment to sites of damage, which suggests that it cooperates with RNF8. Finally, we reveal that RNF8 promotes the G2/M DNA damage checkpoint and resistance to ionizing radiation. These results demonstrate how the DNA-damage response is orchestrated by ATM-dependent phosphorylation of MDC1 and RNF8-mediated ubiquitination.

Regulation of mitotic exit by the RNF8 ubiquitin ligase

RNF8 is a ubiquitin ligase with a FHA domain near its N terminus, and a RING-finger domain at its C terminus, through which it recruits several ubiquitin-conjugating enzymes. In metazoans, only the mitotic checkpoint regulator CHFR shares this domain architecture. Here we show that RNF8 is a nuclear protein that follows a cell-cycle-dependent turnover, reaching its highest levels in mitosis, followed by a strong decline in late mitotic stages. Overexpression of RNF8 caused a delay in cytokinesis and the frequent appearance of aberrant mitotic figures. These effects were dependent on the ubiquitin ligase activity of RNF8, since they were significantly attenuated when a RING-finger mutant, inactive as an E3, was overexpressed. Depletion of RNF8 also caused a delay in the exit from the mitotic arrest induced by nocodazole, associated with a reduced turnover of the APC/C substrate cyclin B1. These observations suggest that RNF8 regulates the rate of exit from mitosis and cytokinesis.

Activation of the epidermal growth factor signalling pathway by tissue plasminogen activator in pancreas cancer cells

BACKGROUND

Tissue plasminogen activator (tPA) is the major activator of plasminogen in plasma. This serine protease is overexpressed by exocrine pancreas tumour cells, where it promotes tumour cell proliferation, growth, and invasion. Here we have explored the signalling pathways used by tPA to activate the proliferation of pancreatic cancer cells.

METHODS

Transcriptional profiling on cDNA micro arrays was used to analyse the pattern of gene expression in response to tPA compared to the response to epidermal growth factor (EGF) and platelet derived growth factor (PDGF). Results were confirmed using different biochemical assays in which specific kinase inhibitors or RNA interference were used.

RESULTS

Transcriptional profiling showed that tPA modulates the expression of a set of genes commonly regulated by EGF, but distinct from the major set of genes modulated by PDGF. This suggested that tPA and EGF share common signalling pathways, a conclusion supported by further experimental evidence. Firstly, we found that tPA induced a rapid and transient phosphorylation of the EGFR. Secondly, specific EGFR kinase inhibitors, but not PDGFR kinase inhibitors, abolished the tPA induced phosphorylation of the ERK1/2 kinases and cell proliferation. The mitogenic activity of tPA was also inhibited by siRNA depletion of EGFR, thus confirming the involvement of this receptor in tPA triggered signalling. Thirdly, we show that the signalling and mitogenic effects of tPA require its proteolytic activity, the activity of the metalloprotease-9 and active hb-EGF.

CONCLUSION

Our results suggest that tPA induces proliferation by triggering a proteolytic cascade that sequentially activates plasmin, metalloprotease-9 (MMP-9) and hb-EGF. These events are required to activate the EGFR signalling pathway and cell proliferation.

The RING finger protein RNF8 recruits UBC13 for lysine 63-based self polyubiquitylation

The heterodimeric ubiquitin conjugating enzyme (E2) UBC13-UEV mediates polyubiquitylation through lysine 63 of ubiquitin (K63), rather than lysine 48 (K48). This modification does not target proteins for proteasome-dependent degradation. Searching for potential regulators of this variant polyubiquitylation we have identified four proteins, namely RNF8, KIA00675, KF1, and ZNRF2, that interact with UBC13 through their RING finger domains. These domains can recruit, in addition to UBC13, other E2s that mediate canonical (K48) polyubiquitylation. None of these RING finger proteins were known previously to recruit UBC13. For one of these proteins, RNF8, we show its activity as a ubiquitin ligase that elongates chains through either K48 or K63 of ubiquitin, and its nuclear co-localization with UBC13. Thus, our screening reveals new potential regulators of non-canonical polyubiquitylation.

Tandem chimerism as a means to increase protein complexity in the human genome

The "one-gene, one-protein" rule, coined by Beadle and Tatum, has been fundamental to molecular biology. The rule implies that the genetic complexity of an organism depends essentially on its gene number. The discovery, however, that alternative gene splicing and transcription are widespread phenomena dramatically altered our understanding of the genetic complexity of higher eukaryotic organisms; in these, a limited number of genes may potentially encode a much larger number of proteins. Here we investigate yet another phenomenon that may contribute to generate additional protein diversity. Indeed, by relying on both computational and experimental analysis, we estimate that at least 4%-5% of the tandem gene pairs in the human genome can be eventually transcribed into a single RNA sequence encoding a putative chimeric protein. While the functional significance of most of these chimeric transcripts remains to be determined, we provide strong evidence that this phenomenon does not correspond to mere technical artifacts and that it is a common mechanism with the potential of generating hundreds of additional proteins in the human genome.

Dual activation of pathways regulated by steroid receptors and peptide growth factors in primary prostate cancer revealed by Factor Analysis of microarray data

Background

We use an approach based on Factor Analysis to analyze datasets generated for transcriptional profiling. The method groups samples into biologically relevant categories, and enables the identification of genes and pathways most significantly associated to each phenotypic group, while allowing for the participation of a given gene in more than one cluster. Genes assigned to each cluster are used for the detection of pathways predominantly activated in that cluster by finding statistically significant associated GO terms. We tested the approach with a published dataset of microarray experiments in yeast. Upon validation with the yeast dataset, we applied the technique to a prostate cancer dataset.

Results

Two major pathways are shown to be activated in organ-confined, non-metastatic prostate cancer: those regulated by the androgen receptor and by receptor tyrosine kinases. A number of gene markers (HER3, IQGAP2 and POR1) highlighted by the software and related to the later pathway have been validated experimentally a posteriori on independent samples.

Conclusion

Using a new microarray analysis tool followed by a posteriori experimental validation of the results, we have confirmed several putative markers of malignancy associated with peptide growth factor signalling in prostate cancer and revealed others, most notably ERRB3 (HER3). Our study suggest that, in primary prostate cancer, HER3, together or not with HER4, rather than in receptor complexes involving HER2, could play an important role in the biology of these tumors. These results provide new evidence for the role of receptor tyrosine kinases in the establishment and progression of prostate cancer.

PTOV1 enables the nuclear translocation and mitogenic activity of flotillin-1, a major protein of lipid rafts

PTOV1 is a mitogenic protein that shuttles between the nucleus and the cytoplasm in a cell cycle-dependent manner. It consists of two homologous domains arranged in tandem that constitute a new class of protein modules. We show here that PTOV1 interacts with the lipid raft protein flotillin-1, with which it copurifies in detergent-insoluble floating fractions. Flotillin-1 colocalized with PTOV1 not only at the plasma membrane but, unexpectedly, also in the nucleus, as demonstrated by immunocytochemistry and subcellular fractionation of endogenous and exogenous flotillin-1. Flotillin-1 entered the nucleus concomitant with PTOV1, shortly before the initiation of the S phase. Protein levels of PTOV1 and flotillin-1 oscillated during the cell cycle, with a peak in S. Depletion of PTOV1 significantly inhibited nuclear localization of flotillin-1, whereas depletion of flotillin-1 did not affect nuclear localization of PTOV1. Depletion of either protein markedly inhibited cell proliferation under basal conditions. Overexpression of PTOV1 or flotillin-1 strongly induced proliferation, which required their localization to the nucleus, and was dependent on the reciprocal protein. These observations suggest that PTOV1 assists flotillin-1 in its translocation to the nucleus and that both proteins are required for cell proliferation.

A Differential Gene Expression Profile Reveals Overexpression of RUNX1/AML1 in Invasive Endometrioid Carcinoma

Endometrial carcinoma is the most common gynecological malignant disease in industrialized countries. Two clinicopathological types of endometrial carcinoma have been described, based on estrogen relation and grade: endometrioid carcinoma (EEC) and non-EEC (NEEC). Some of the molecular events that occur during the development of endometrial carcinoma have been characterized, showing a dualistic genetic model for EEC and NEEC. However, the molecular bases for endometrial tumorigenesis are not clearly elucidated. In the present work, we attempted to identify new genes that could trigger cell transformation in EEC. We analyzed the differential gene expression profile between tumoral and nontumoral endometrial specimens with cDNA array hybridization. Among the 53 genes for which expression was found to be altered in EEC, the acute myeloid leukemia proto-oncogene, RUNX1/AML1, was one of the most highly up-regulated. The gene expression levels of RUNX1/AML1 were quantified by real-time quantitative PCR, and protein levels were characterized by tissue array immunohistochemistry. Real-time quantitative PCR validated RUNX1/AML1 up-regulation in EEC and demonstrated a specific and significantly stronger up-regulation in those tumor stages associated with myometrial invasion. Furthermore, tissue array immunohistochemistry showed that RUNX1/AML1 up-regulation correlates to the process of tumorigenesis, from normal atrophic endometrium to simple and complex hyperplasia and then, on to carcinoma. These results demonstrate for the first time the up-regulation of RUNX1/AML1 in EEC correlating with the initial steps of myometrial infiltration.

Specific interaction of tissue-type plasminogen activator (t-PA) with annexin II on the membrane of pancreatic cancer cells activates plasminogen and promotes invasion in vitro

BACKGROUND

Overexpression of tissue plasminogen activator (t-PA) in pancreatic cancer cells promotes invasion and proliferation in vitro and tumour growth and angiogenesis in vivo.

AIMS

To understand the mechanisms by which t-PA favours cancer progression, we analysed the surface membrane proteins responsible for binding specifically t-PA and studied the contribution of this interaction to the t-PA promoted invasion of pancreatic cancer cells.

METHODS

The ability of t-PA to activate plasmin and a fluorogenic plasmin substrate was used to analyse the nature of the binding of active t-PA to cell surfaces. Specific binding was determined in two pancreatic cancer cell lines (SK-PC-1 and PANC-1), and complex formation analysed by co-immunoprecipitation experiments and co-immunolocalisation in tumours. The functional role of the interaction was studied in Matrigel invasion assays.

RESULTS

t-PA bound to PANC-1 and SK-PC-1 cells in a specific and saturable manner while maintaining its activity. This binding was competitively inhibited by specific peptides interfering with the interaction of t-PA with annexin II. The t-PA/annexin II interaction on pancreatic cancer cells was also supported by co-immunoprecipitation assays using anti-t-PA antibodies and, reciprocally, with antiannexin II antibodies. In addition, confocal microscopy showed t-PA and annexin II colocalisation in tumour tissues. Finally, disruption of the t-PA/annexin II interaction by a specific hexapeptide significantly decreased the invasive capacity of SK-PC-1 cells in vitro.

CONCLUSION

t-PA specifically binds to annexin II on the extracellular membrane of pancreatic cancer cells where it activates local plasmin production and tumour cell invasion. These findings may be clinically relevant for future therapeutic strategies based on specific drugs that counteract the activity of t-PA or its receptor annexin II, or their interaction at the surface level.

PTOV-1, a novel protein overexpressed in prostate cancer, shuttles between the cytoplasm and the nucleus and promotes entry into the S phase of the cell division cycle

PTOV1 was recently identified as a novel gene and protein during a differential display screening for genes overexpressed in prostate cancer. The PTOV1 protein consists of two novel protein domains arranged in tandem, without significant similarities to known protein motifs. By immunohistochemical analysis, we have found that PTOV1 is overexpressed in 71% of 38 prostate carcinomas and in 80% of samples with prostate intraepithelial neoplasia. High levels of PTOV1 in tumors correlated significantly with proliferative index, as assessed by Ki67 immunoreactivity, and associated with a nuclear localization of the protein, suggesting a functional relationship between PTOV1 overexpression, proliferative status, and nuclear localization. In quiescent cultured prostate tumor cells, PTOV1 localized to the cytoplasm, being excluded from nuclei. After serum stimulation, PTOV1 partially translocated to the nucleus at the beginning of the S phase. At the end of mitosis, PTOV1 exited the nucleus. Transient transfection of chimeric green fluorescent protein-PTOV1 forced the entry of cells into the S phase of the cell cycle, as shown by double fluorescent imaging for green fluorescent protein and for Ki67, and also by flow cytometry. This was accompanied by greatly increased levels of cyclin D1 protein in the transfected cells. These observations suggest that overexpression of PTOV1 can contribute to the proliferative status of prostate tumor cells and thus to their biological behavior.

Expression and regulation of the transcriptional repressor ZNF43 in Ewing sarcoma cells

In vitro, cells derived from Ewing sarcoma (ES) with the characteristic somatic rearrangement between the genes EWS and FLII can be induced to differentiate toward a neuronal phenotype by exposure to agents such as dibutyryl cyclic AMP (db cAMP) or retinoic acid. Therefore, expression of the chimeric Ews-Flil protein does not irreversibly block the capacity of Ewing cells to engage in the neuronal differentiation program initiated by these agents. To identify genes that might be involved in the maintenance of Ewing cells in their undifferentiated state, a PCR-based differential display method was used to compare gene expression patterns in Ewing cell lines with those induced to differentiate toward a neuronal phenotype. A cDNA was expressed at high levels in proliferating Ewing-derived EW-1 cells and downregulated in EW-1 cells induced to differentiate, which corresponds to ZNF43, a multi-zinc finger protein containing the Krüppel-associated box (KRAB) transcriptional repression domain. Treatment of EW-1 cells with antisense oligonucleotides complementary to ZNF43 mRNA induces morphological differentiation and growth arrest. These findings suggest a role for ZNF43 in the maintenance of ES cells in an undifferentiated state, and that ZNF43 could be a primary target for differentiation stimuli in Ewing cells.

Tissue plasminogen activator is required for the growth, invasion, and angiogenesis of pancreatic tumor cells

BACKGROUND & AIMS

Overexpression of tissue-type plasminogen activator (t-PA) in exocrine pancreatic tumors might be a determinant of the aggressive biological behavior of these tumors.

METHODS

Endogenous t-PA production was suppressed by antisense oligonucleotides or transcripts in CAPAN-1 and RWP-1 cell lines. Reciprocally, the t-PA non-expressing BxPC-3 and PANC-1 cells were stably transfected to overexpress t-PA. Recombinant t-PA and chemical inhibitors were also used on these cells. Clones were assayed for invasion and growth in vitro and in vivo.

RESULTS

In vitro, specific inhibition of t-PA expression or activity significantly inhibited the proliferation of t-PA-producing RWP-1, CAPAN-1, and SK-PC-1 cells. Antisense constructs were used to generate RWP-1 clones stably suppressed for t-PA expression (AS clones). These clones had a significantly reduced invasion and proliferation on plastic and in soft agar. The addition of recombinant t-PA rescued the growth of the AS clones to parental levels and was mitogenic for other independent pancreas cell lines. This effect did not require plasmin activity. In athymic mice, RWP-1 AS clones produced tumors fivefold smaller than control clones. AS tumors contained a significantly reduced number of Ki67-positive nuclei, fewer mitotic cells, and a remarkably reduced angiogenic network. Finally, the generation of tetracycline-repressed t-PA transfectants in PANC-1 cells confirmed the activity of t-PA in invasion and proliferation in vitro and in vivo.

CONCLUSIONS

t-PA, in addition to its known role in invasion, plays other critical roles in pancreas tumor progression, stimulating cancer cell proliferation and tumor-associated angiogenesis.

PTOV1, a novel protein overexpressed in prostate cancer containing a new class of protein homology blocks

In a search for molecular markers of progression in prostate cancer by means of differential display, we have identified a new gene, which we have designated PTOV1. Semiquantitative RT-PCR has established that nine out of 11 tumors overexpress PTOV1 at levels significantly higher than benign prostatic hyperplasia or normal prostate tissue. The human PTOV1 protein consists almost entirely of two repeated blocks of homology of 151 and 147 amino acids, joined by a short linker peptide, and is encoded by a 12-exon gene localized in chromosome 19q13.3. A Drosophila melanogaster PTOV1 homolog also contains two tandemly arranged PTOV blocks. A second gene, PTOV2, was identified in humans and Drosophila, coding for proteins with a single PTOV homology block and unrelated amino- and carboxyl-terminal extensions. A 1.8-Kb PTOV1 transcript was detected abundantly in normal human brain, heart, skeletal muscle, kidney and liver, and at low levels in normal prostate. Immunocytochemical analysis and expression of chimeric GFP-PTOV1 proteins in cultured cells showed a predominantly perinuclear localization of PTOV1. In normal prostate tissue and in prostate adenomas, PTOV1 was undetectable or expressed at low levels, whereas nine out of 11 prostate adenocarcinomas showed a strong immunoreactivity, with a focal distribution in areas of carcinoma and prostatic intraepithelial neoplasia. Therefore, PTOV1 is a previously unknown gene, overexpressed in early and late stages of prostate cancer. The PTOV homology block represents a new class of conserved sequence blocks present in human, rodent and fly proteins.

Fusion of the human gene for the polyubiquitination coeffector UEV1 with Kua, a newly identified gene

UEV proteins are enzymatically inactive variants of the E2 ubiquitin-conjugating enzymes that regulate noncanonical elongation of ubiquitin chains. In Saccharomyces cerevisiae, UEV is part of the RAD6-mediated error-free DNA repair pathway. In mammalian cells, UEV proteins can modulate c-FOS transcription and the G2-M transition of the cell cycle. Here we show that the UEV genes from phylogenetically distant organisms present a remarkable conservation in their exon-intron structure. We also show that the human UEV1 gene is fused with the previously unknown gene Kua. In Caenorhabditis elegans and Drosophila melanogaster, Kua and UEV are in separated loci, and are expressed as independent transcripts and proteins. In humans, Kua and UEV1 are adjacent genes, expressed either as separate transcripts encoding independent Kua and UEV1 proteins, or as a hybrid Kua-UEV transcript, encoding a two-domain protein. Kua proteins represent a novel class of conserved proteins with juxtamembrane histidine-rich motifs. Experiments with epitope-tagged proteins show that UEV1A is a nuclear protein, whereas both Kua and Kua-UEV localize to cytoplasmic structures, indicating that the Kua domain determines the cytoplasmic localization of Kua-UEV. Therefore, the addition of a Kua domain to UEV in the fused Kua-UEV protein confers new biological properties to this regulator of variant polyubiquitination.

N-Ras induces alterations in Golgi complex architecture and in constitutive protein transport

Aberrant glycosylation of proteins and lipids is a common feature of many tumor cell types, and is often accompanied by alterations in membrane traffic and an anomalous localization of Golgi-resident proteins and glycans. These observations suggest that the Golgi complex is a key organelle for at least some of the functional changes associated with malignant transformation. To gain insight into this possibility, we have analyzed changes in the structure and function of the Golgi complex induced by the conditional expression of the transforming N-Ras(K61) mutant in the NRK cell line. A remarkable and specific effect associated with this N-Ras-induced transformation was a conspicuous rearrangement of the Golgi complex into a collapsed morphology. Ultrastructural and stereological analyses demonstrated that the Golgi complex was extensively fragmented. The collapse of the Golgi complex was also accompanied by a disruption of the actin cytoskeleton. Functionally, N-Ras-transformed KT8 cells showed an increase in the constitutive protein transport from the trans-Golgi network to the cell surface, and did not induce the appearance of aberrant cell surface glycans. The Golgi complex collapse, the actin disassembly, and the increased constitutive secretion were all partially inhibited by the phospholipase A2 inhibitor 4-bromophenylacyl bromide. The results thus suggest the involvement of the actin cytoskeleton in the shape of the Golgi complex, and intracellular phospholipase A2 in its architecture and secretory function.

Role of UEV-1A, a homologue of the tumor suppressor protein TSG101, in protection from DNA damage

The open reading frame YGL087c in the budding yeast Saccharomyces cerevisiae genome encodes a polypeptide highly similar to the human UEV (ubiquitin-conjugating E2 enzyme variant) proteins, which have been proposed to belong to a family of putative dominant negative ubiquitin regulators. Deletion of the YGL087c open reading frame yields viable cells which are sensitive to UV irradiation or methyl methanesulfonate, but not to hydroxyurea. This phenotype is reminiscent of that of rad mutants and suggests that the YGL087c-encoded protein functions in a process related to tolerance to DNA damage. We also show that the mutant phenotype is fully complemented by expression of the human UEV-1A cDNA and we propose that UEV-1 proteins could also have a role in protecting higher eukaryotic cells from DNA damaging agents.