Ángel García

A Comprehensive Proteomics and Genomics Analysis Reveals Novel Transmembrane Proteins in Human Platelets and Mouse Megakaryocytes Including G6b-B, a Novel Immunoreceptor Tyrosine-based Inhibitory Motif Protein

The platelet surface is poorly characterized due to the low abundance of many membrane proteins and the lack of specialist tools for their investigation. In this study we identified novel human platelet and mouse megakaryocyte membrane proteins using specialist proteomics and genomics approaches. Three separate methods were used to enrich platelet surface proteins prior to identification by liquid chromatography and tandem mass spectrometry: lectin affinity chromatography, biotin/NeutrAvidin affinity chromatography, and free flow electrophoresis. Many known, abundant platelet surface transmembrane proteins and several novel proteins were identified using each receptor enrichment strategy. In total, two or more unique peptides were identified for 46, 68, and 22 surface membrane, intracellular membrane, and membrane proteins of unknown subcellular localization, respectively. The majority of these were single transmembrane proteins. To complement the proteomics studies, we analyzed the transcriptome of a highly purified preparation of mature primary mouse megakaryocytes using serial analysis of gene expression in view of the increasing importance of mutant mouse models in establishing protein function in platelets. This approach identified all of the major classes of platelet transmembrane receptors, including multitransmembrane proteins. Strikingly 17 of the 25 most megakaryocyte-specific genes (relative to 30 other serial analysis of gene expression libraries) were transmembrane proteins, illustrating the unique nature of the megakaryocyte/platelet surface. The list of novel plasma membrane proteins identified using proteomics includes the immunoglobulin superfamily member G6b, which undergoes extensive alternate splicing. Specific antibodies were used to demonstrate expression of the G6b-B isoform, which contains an immunoreceptor tyrosine-based inhibition motif. G6b-B undergoes tyrosine phosphorylation and association with the SH2 domain-containing phosphatase, SHP-1, in stimulated platelets suggesting that it may play a novel role in limiting platelet activation.

Immunohistochemical staining for p16 and p53 in premalignant and malignant epithelial lesions of the vulva.

Summary:Two distinct types of vulvar squamous cell carcinomas and their precursors, vulvar intraepithelial neoplasias (VIN), which differ in terms of clinical presentation and behavior, have been delineated. Human papillomavirus (HPV)-associated carcinomas are of basaloid or warty type, whereas tumors unrelated to HPV are usually keratinizing and differentiated. Thus, the major stratifying factor for vulvar carcinomas and VIN is their etiopathogenetic relationship with HPV. However, because of technical difficulties in confidently detecting HPV in tissues, this diagnosis is usually based on purely morphologic criteria, even though some overlap exists between these histologic types. Recently, the tumor suppressor protein p16 has been shown to be specifically overexpressed in HPV-related carcinomas and premalignant lesions of the uterine cervix, oral cavity, and anus, but the presence of p16 vulvar squamous lesions has not been examined. We have evaluated the immunohistochemical expression of p16 in a series of formalin-fixed, paraffin-embedded vulvar carcinomas and their putative precursors. p16 was strongly positive in all cases of basaloid/condylomatous VIN3 (30/30) and basaloid (7/7) and warty (3/3) carcinomas. In contrast, p16 was almost consistently negative in normal skin, squamous cell hyperplasia (0/20), lichen sclerosus (0/19), differentiated (simplex) VIN3 (0/11), verrucous carcinoma (0/2), and keratinizing squamous cell carcinoma (3/33, 9%). One of the keratinizing squamous cell carcinomas positive for p16 occurred in a 25-year-old woman and the other two were associated with small foci of basaloid VIN3 adjacent to the tumor, suggesting a probable relationship with HPV. p16 was positive in 6 of 10 of basal cell carcinomas. In conclusion, p16 immunostaining is a good discriminator between HPV-associated and HPV-unrelated vulvar carcinomas and VIN, although it cannot differentiate basaloid squamous and basal cell carcinoma.

A Microtubule Interactome: Complexes with Roles in Cell Cycle and Mitosis

The microtubule (MT) cytoskeleton is required for many aspects of cell function, including the transport of intracellular materials, the maintenance of cell polarity, and the regulation of mitosis. These functions are coordinated by MT-associated proteins (MAPs), which work in concert with each other, binding MTs and altering their properties. We have used a MT cosedimentation assay, combined with 1D and 2D PAGE and mass spectrometry, to identify over 250 MAPs from early Drosophila embryos. We have taken two complementary approaches to analyse the cellular function of novel MAPs isolated using this approach. First, we have carried out an RNA interference (RNAi) screen, identifying 21 previously uncharacterised genes involved in MT organisation. Second, we have undertaken a bioinformatics analysis based on binary protein interaction data to produce putative interaction networks of MAPs. By combining both approaches, we have identified and validated MAP complexes with potentially important roles in cell cycle regulation and mitosis. This study therefore demonstrates that biologically relevant data can be harvested using such a multidisciplinary approach, and identifies new MAPs, many of which appear to be important in cell division.

Expression of HLA G in human tumors is not a frequent event

Expression of HLA G may be a way for tumor cells to escape immuno‐surveillance. HLA G is selectively expressed by extravillous trophoblast in the human placenta, a tissue that does not express HLA A or B molecules. It is tempting to propose that tumor cells resemble this unique HLA class I phenotype as they frequently lose classical HLA A, B and C class I expression. Such peculiar HLA class I distribution would in theory allow tumor cells to escape from T‐ and NK‐cell cytotoxicity. To determine whether HLA G is expressed on tumor cells, we studied HLA G mRNA levels using RT‐PCR and HLA G cell‐surface expression by immuno‐histological techniques in a panel of 50 human solid tumor tissues, 31 tumor cell lines of different origin, 4 autologous mucosa samples and 3 peripheral white cell samples. We found mRNA transcripts of different HLA G isoforms in most of the samples studied. However, we did not detect cell‐surface expression of HLA G using 3 specific monoclonal antibodies (MAbs; 87G, 01G and G223). HLA G was detected only in the U937 myelomonocytic cell line after stimulation with IFN‐γ. We favor the hypothesis that HLA G plays a minor role, if any, in providing an inhibitory signal to NK cells to escape immunosurveillance. We cannot, however, exclude the possibility that some other HLA G isoforms may be expressed in some tumors. Int. J. Cancer 81:512–518, 1999.

Characterization of muscarinic receptor subtypes in human tissues

The affinities of selective, pirenzepine and AF-DX 116, and classical, N-methylscopolamine and atropine, muscarinic cholinergic receptor antagonists were investigated in displacement binding experiments with [3H]Pirenzepine and [3H]N-methylscopolamine in membranes from human autoptic tissues (forebrain, cerebellum, atria, ventricle and submaxillary salivary glands). Affinity estimates of N-methylscopolamine and atropine indicated a non-selective profile. Pirenzepine showed differentiation between the M1 neuronal receptor of the forebrain and the receptors in other tissues while AF-DX 116 clearly discriminated between muscarinic receptors of heart and glands. The results in human tissues confirm the previously described selectivity profiles of pirenzepine and AF-DX 116 in rat tissues. These findings thus reveal the presence also in man of three distinct muscarinic receptor subtypes: the neuronal M1, the cardiac M2 and the glandular M3.

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.

Proteins Involved in Platelet Signaling Are Differentially Regulated in Acute Coronary Syndrome: A Proteomic Study

Background Platelets play a fundamental role in pathological events underlying acute coronary syndrome (ACS). Because platelets do not have a nucleus, proteomics constitutes an optimal approach to follow platelet molecular events associated with the onset of the acute episode. Methodology/Principal Findings We performed the first high-resolution two-dimensional gel electrophoresis-based proteome analysis of circulating platelets from patients with non-ST segment elevation ACS (NSTE-ACS). Proteins were identified by mass spectrometry and validations were by western blotting. Forty protein features (corresponding to 22 unique genes) were found to be differentially regulated between NSTE-ACS patients and matched controls with chronic ischemic cardiopathy. The number of differences decreased at day 5 (28) and 6 months after the acute event (5). Interestingly, a systems biology approach demonstrated that 16 of the 22 differentially regulated proteins identified are interconnected as part of a common network related to cell assembly and organization and cell morphology, processes very related to platelet activation. Indeed, 14 of those proteins are either signaling or cytoskeletal, and nine of them are known to participate in platelet activation by αIIbβ3 and/or GPVI receptors. Several of the proteins identified participate in platelet activation through post-translational modifications, as shown here for ILK, Src and Talin. Interestingly, the platelet-secreted glycoprotein SPARC was down-regulated in NSTE-ACS patients compared to stable controls, which is consistent with a secretion process from activated platelets. Conclusions/Significance The present study provides novel information on platelet proteome changes associated with platelet activation in NSTE-ACS, highlighting the presence of proteins involved in platelet signaling. This investigation paves the way for future studies in the search for novel platelet-related biomarkers and drug targets in ACS.

The EMT signaling pathways in endometrial carcinoma.

Endometrial cancer (EC) is the most common gynecologic malignancy of the female genital tract and the fourth most common neoplasia in women. In EC, myometrial invasion is considered one of the most important prognostic factors. For this process to occur, epithelial tumor cells need to undergo an epithelial to mesenchymal transition (EMT), either transiently or stably, and to differing degrees. This process has been extensively described in other types of cancer but has been poorly studied in EC. In this review, several features of EMT and the main molecular pathways responsible for triggering this process are investigated in relation to EC. The most common hallmarks of EMT have been found in EC, either at the level of E-cadherin loss or at the induction of its repressors, as well as other molecular alterations consistent with the mesenchymal phenotype-like L1CAM and BMI-1 up-regulation. Pathways including progesterone receptor, TGFβ, ETV5 and microRNAs are deeply related to the EMT process in EC.

Proteomic analysis of integrin alphaIIbbeta3 outside-in signaling reveals Src-kinase-independent phosphorylation of Dok-1 and Dok-3 leading to SHIP-1 interactions.

Summary.  Background and Objectives: Outside‐in integrin αIIbβ3 signaling involves a series of tyrosine kinase reactions that culminate in platelet spreading on fibrinogen. The aim of this study was to identify novel tyrosine phosphorylated signaling proteins downstream of αIIbβ3, and explore their role in platelet signaling. Methods and Results: Utilizing proteomics to search for novel platelet proteins that contribute to outside‐in signaling by the integrin αIIbβ3, we identified 27 proteins, 17 of which were not previously shown to be part of a tyrosine phosphorylation‐based signaling complex downstream of αIIbβ3. The proteins identified include the novel immunoreceptors G6f and G6b‐B, and two members of the Dok family of adapters, Dok‐1 and Dok‐3, which underwent increased tyrosine phosphorylation following platelet spreading on fibrinogen. Dok‐3 was also inducibly phosphorylated in response to the GPVI‐specific agonist collagen‐related peptide (CRP) and the PAR‐1 and ‐4 agonist thrombin, independently of the integrin αIIbβ3. Tyrosine phosphorylation of Dok‐1 and Dok‐3 was primarily Src kinase‐independent downstream of the integrin, whereas it was Src kinase‐dependent downstream of GPVI. Moreover, both proteins inducibly interacted with Grb‐2 and SHIP‐1 in fibrinogen‐spread platelets. Conclusions: This study provides new insights into the molecular mechanism regulating αIIbβ3‐mediated platelet spreading on fibrinogen. The novel platelet adapter Dok‐3 and the structurally related Dok‐1 are tyrosine phosphorylated in an Src kinase‐independent manner downstream of αIIbβ3 in human platelets, leading to an interaction with Grb2 and SHIP‐1.

The clinicopathological significance of K-RAS point mutation and gene amplification in endometrial cancer

The aim of this study was to examine the prevalence and clinicopathological significance of K-RAS oncogene activation in endometrial carcinoma and atypical hyperplasia. We analysed K-RAS point mutation and gene amplification in 55 endometrial carcinomas using polymerase chain reaction associated with restriction fragment length polymorphism and genomic differential polymerase chain reaction. Point mutations at codon 12 of K-RAS oncogene were identified in 8 of 55 (14.5%) tumour specimens. In addition, we were unable to detect any K-RAS gene amplification in any of the endometrial carcinomas studied. No correlation was found between K-RAS gene mutation and age at onset, histological subtype, grade of differentiation, clinical stage or current patient status. We conclude that K-RAS mutation is a relatively common event in endometrial carcinomas, but with no clear prognostic value.