Gabriela Aust

Sticky Signaling—Adhesion Class G Protein–Coupled Receptors Take the Stage

Emerging insight on the structural and functional versatility of Adhesion-GPCRs draws a fascinating picture of the multiple signals these molecules transmit. Gloss Adhesion-type heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (Adhesion-GPCRs) comprise a class of noncanonical seven-transmembrane spanning (7TM) receptors present on almost any cell type. Despite their abundance, remarkable size, and intriguing two-unit structure facilitating cell-cell and cell-matrix contacts in various organ systems, Adhesion-GPCRs are by far the most poorly understood 7TM receptors. Data indicate that a juxtamembrane GPCR autoproteolysis-inducing domain containing the GPCR proteolysis site (GPS) figures prominently in the biological function of Adhesion-GPCRs. This review, which has five figures, five tables, and 216 references, discusses the currently available data regarding the major structural elements of Adhesion-GPCRs in the context of receptor function and signaling. Adhesion-type heterotrimeric guanine nucleotide–binding protein (G protein)–coupled receptors (Adhesion-GPCRs) comprise a class of widely distributed seven-transmembrane spanning (7TM) receptors with unusual layout and properties. The key to understanding the function of Adhesion-GPCRs appears to be their hybrid architecture: They have an extracellular domain containing an extended array of protein folds fit for interactions, and structural elements of GPCRs with a 7TM and an intracellular domain. If and how these distinct protein portions interact is currently under intense investigation. Intriguingly, all Adhesion-GPCRs have a juxtamembrane GPCR autoproteolysis-inducing domain that, in many homologs, facilitates the autocatalytic processing into an N-terminal fragment (NTF) and a C-terminal fragment (CTF), which subsequently remain attached at the cell surface. The NTF provides the ability for combinatorial engagement with cellular or matrix-associated molecules facilitating cell adhesion, orientation, and positioning during development, immune responses, and tumor growth. The CTF, like in canonical GPCRs, initiates interactions with different types of signaling molecules, including heterotrimeric G proteins, small guanosine triphosphatases, and transmembrane protein partners, yet the agonistic potential of most known Adhesion-GPCR ligands is uncertain. Studies with truncated receptors suggest that the NTF and CTF of Adhesion-GPCRs may function as autonomous adhesive and signaling units, respectively, but other studies in nonvertebrates demonstrating NTF-CTF interplay challenge this view. We discuss the available data concerning the main structural elements of Adhesion-GPCRs in the context of receptor function and signaling.

International Union of Basic and Clinical Pharmacology. XCIV. Adhesion G Protein–Coupled Receptors

The Adhesion family forms a large branch of the pharmacologically important superfamily of G protein–coupled receptors (GPCRs). As Adhesion GPCRs increasingly receive attention from a wide spectrum of biomedical fields, the Adhesion GPCR Consortium, together with the International Union of Basic and Clinical Pharmacology Committee on Receptor Nomenclature and Drug Classification, proposes a unified nomenclature for Adhesion GPCRs. The new names have ADGR as common dominator followed by a letter and a number to denote each subfamily and subtype, respectively. The new names, with old and alternative names within parentheses, are: ADGRA1 (GPR123), ADGRA2 (GPR124), ADGRA3 (GPR125), ADGRB1 (BAI1), ADGRB2 (BAI2), ADGRB3 (BAI3), ADGRC1 (CELSR1), ADGRC2 (CELSR2), ADGRC3 (CELSR3), ADGRD1 (GPR133), ADGRD2 (GPR144), ADGRE1 (EMR1, F4/80), ADGRE2 (EMR2), ADGRE3 (EMR3), ADGRE4 (EMR4), ADGRE5 (CD97), ADGRF1 (GPR110), ADGRF2 (GPR111), ADGRF3 (GPR113), ADGRF4 (GPR115), ADGRF5 (GPR116, Ig-Hepta), ADGRG1 (GPR56), ADGRG2 (GPR64, HE6), ADGRG3 (GPR97), ADGRG4 (GPR112), ADGRG5 (GPR114), ADGRG6 (GPR126), ADGRG7 (GPR128), ADGRL1 (latrophilin-1, CIRL-1, CL1), ADGRL2 (latrophilin-2, CIRL-2, CL2), ADGRL3 (latrophilin-3, CIRL-3, CL3), ADGRL4 (ELTD1, ETL), and ADGRV1 (VLGR1, GPR98). This review covers all major biologic aspects of Adhesion GPCRs, including evolutionary origins, interaction partners, signaling, expression, physiologic functions, and therapeutic potential.

A Comprehensive Model of the Spatio-Temporal Stem Cell and Tissue Organisation in the Intestinal Crypt

We introduce a novel dynamic model of stem cell and tissue organisation in murine intestinal crypts. Integrating the molecular, cellular and tissue level of description, this model links a broad spectrum of experimental observations encompassing spatially confined cell proliferation, directed cell migration, multiple cell lineage decisions and clonal competition. Using computational simulations we demonstrate that the model is capable of quantitatively describing and predicting the dynamic behaviour of the intestinal tissue during steady state as well as after cell damage and following selective gain or loss of gene function manipulations affecting Wnt- and Notch-signalling. Our simulation results suggest that reversibility and flexibility of cellular decisions are key elements of robust tissue organisation of the intestine. We predict that the tissue should be able to fully recover after complete elimination of cellular subpopulations including subpopulations deemed to be functional stem cells. This challenges current views of tissue stem cell organisation.

Expression and Regulation of CD97 in Colorectal Carcinoma Cell Lines and Tumor Tissues

The expression of CD97, a member of the EGF-TM7 family with adhesive properties, is proportional to the aggressiveness and lymph node involvement in thyroid tumors. CD97 has never been systematically investigated in other tumors. First, we examined colorectal carcinoma cell lines (n = 18) for CD97 expression and regulation. All cell lines were CD97-positive. The level of CD97 in each line correlated with migration and invasion in vitro. This result was confirmed in CD97-inducible Tet-off HT1080 cells. Transforming growth factor-beta, which inhibits proliferation in transforming growth factor-beta-sensitive LS513 and LS1034 cells, down-regulated CD97 in these cell lines. Examining CD97 during sodium butyrate-induced cell differentiation of Caco-2 cells, we could demonstrate a CD97-decreasing effect. Second, we screened 81 colorectal adenocarcinomas by immunohistology for expression of CD97. Normal colorectal epithelium is CD97-negative. Seventy-five of 81 of the carcinomas expressed CD97. The strongest staining for CD97 occurred in scattered tumor cells at the invasion front compared to cells located within solid tumor formations of the same tumor. Carcinomas with more strongly CD97-stained scattered tumor cells showed a poorer clinical stage as well as increased lymph vessel invasion compared to cases with uniform CD97 staining. In summary, CD97 expression correlates with dedifferentiation, migration, and invasion in colorectal tumor cell lines. Moreover, more strongly CD97-stained tumor cells at the invasion front of colorectal carcinomas indicate the involvement of the molecule in tumor migration and invasion.

Vaspin serum concentrations in patients with carotid stenosis

Obesity is associated with accelerated atherosclerosis. Adipokines may directly influence vessel wall homeostasis by influencing the function of endothelial cells, arterial smooth muscle cells, and modulating inflammation. Recently, visceral adipose tissue-derived serpin (vaspin) was identified as a novel adipokine related to obesity and its metabolic consequences. However, the regulation of vaspin serum concentrations in human atherosclerosis is unknown. We therefore assessed vaspin serum concentrations in 107 consecutive patients with carotid stenosis undergoing carotid endarterectomy (CEA) in relation to severity of atherosclerosis, measures of obesity and circulating markers of obesity and atherosclerosis. Vaspin serum concentrations were significantly lower in patients with carotid stenosis who experienced an ischemic event within 3 months before surgery compared to asymptomatic patients. However, circulating vaspin was not associated with measures of atherosclerosis severity as maximum percentage stenosis. Vaspin serum concentrations were indistinguishable before and after CEA. We found a significant correlation between vaspin and leptin serum concentrations supporting previous results that vaspin closely reflects body fat mass. In conclusion, our data show that low vaspin serum concentrations correlate with recently experienced ischemic events in patients with carotid stenosis despite the lack of an association between circulating vaspin and parameters of atherosclerosis severity.

From single cells to tissue architecture-a bottom-up approach to modelling the spatio-temporal organisation of complex multi-cellular systems.

Collective phenomena in multi-cellular assemblies can be approached on different levels of complexity. Here, we discuss a number of mathematical models which consider the dynamics of each individual cell, so-called agent-based or individual-based models (IBMs). As a special feature, these models allow to account for intracellular decision processes which are triggered by biomechanical cell–cell or cell–matrix interactions. We discuss their impact on the growth and homeostasis of multi-cellular systems as simulated by lattice-free models. Our results demonstrate that cell polarisation subsequent to cell–cell contact formation can be a source of stability in epithelial monolayers. Stroma contact-dependent regulation of tumour cell proliferation and migration is shown to result in invasion dynamics in accordance with the migrating cancer stem cell hypothesis. However, we demonstrate that different regulation mechanisms can equally well comply with present experimental results. Thus, we suggest a panel of experimental studies for the in-depth validation of the model assumptions.

Individual cell-based models of the spatial-temporal organization of multicellular systems--achievements and limitations.

Computational approaches of multicellular assemblies have reached a stage where they may contribute to unveil the processes that underlie the organization of tissues and multicellular aggregates. In this article, we briefly review and present some new results on a number of 3D lattice free individual cell‐based mathematical models of epithelial cell populations. The models we consider here are parameterized by bio‐physical and cell‐biological quantities on the level of an individual cell. Eventually, they aim at predicting the dynamics of the biological processes on the tissue level. We focus on a number of systems, the growth of cell populations in vitro, and the spatial‐temporal organization of regenerative tissues. For selected examples we compare different model approaches and show that the qualitative results are robust with respect to many model details. Hence, for the qualitative features and largely for the quantitative features many model details do not matter as long as characteristic biological features and mechanisms are correctly represented. For a quantitative prediction, the control of the bio‐physical and cell‐biological parameters on the molecular scale has to be known. At this point, slide‐based cytometry may contribute. It permits to track the fate of cells and other tissue subunits in time and validated the organization processes predicted by the mathematical models.

CD97, but not its closely related EGF-TM7 family member EMR2, is expressed on gastric, pancreatic, and esophageal carcinomas

CD97 expression is related closely to the dedifferentiation and tumor stage in thyroid carcinomas. We systematically examined the role of CD97 and its closest relative, EMR2, in normal and malignant gastric, esophageal, and pancreatic tissue. The normal tissues were EMR2-, whereas CD97 was expressed slightly in the parietal cells of gastric mucosa and in exocrine pancreatic cells. Interestingly, intralobular and interlobular pancreatic ducts were CD97+. All tumors were EMR2-. CD97 was expressed by 44 of 50 gastric, 14 of 18 pancreatic, and 10 of 13 esophageal carcinomas. Of the 44 gastric cancers, 27 showed disseminated or scattered tumor cells at the invasion front with stronger CD97 expression than tumor cells located in solid tumor formations. There was no correlation between CD97 levels in the tumors or soluble CD97 in the serum samples and the clinicopathologic features of the patients. Taken together, significant numbers of gastric, esophageal, and pancreatic carcinomas are CD97+, whereas its homolog, EMR2, does not have any role in such tumors.

Genetic variation in GPR133 is associated with height: genome wide association study in the self-contained population of Sorbs

Recently, associations of several common genetic variants with height have been reported in different populations. We attempted to identify further variants associated with adult height in a self-contained population (the Sorbs in Eastern Germany) as discovery set. We performed a genome wide association study (GWAS) (approximately 390,000 genetic polymorphisms, Affymetrix gene arrays) on adult height in 929 Sorbian individuals. Subsequently, the best SNPs (P < 0.001) were taken forward to a meta-analysis together with two independent cohorts [Diabetes Genetics Initiative, British 1958 Birth Cohort, (58BC, publicly available)]. Furthermore, we genotyped our best signal for replication in two additional German cohorts (Leipzig, n = 1044 and Berlin, n = 1728). In the primary Sorbian GWAS, we identified 5 loci with a P-value < 10(-5) and 455 SNPs with P-value < 0.001. In the meta-analysis on those 455 SNPs, only two variants in GPR133 (rs1569019 and rs1976930; in LD with each other) retained a P-value at or below 10(-6) and were associated with height in the three cohorts individually. Upon replication, the SNP rs1569019 showed significant effects on height in the Leipzig cohort (P = 0.004, beta = 1.166) and in 577 men of the Berlin cohort (P = 0.049, beta = 1.127) though not in women. The combined analysis of all five cohorts (n = 6,687) resulted in a P-value of 4.7 x 10(-8) (beta = 0.949). In conclusion, our GWAS suggests novel loci influencing height. In view of the robust replication in five different cohorts, we propose GPR133 to be a novel gene associated with adult height.

Analysis of CD97 Expression and Manipulation: Antibody Treatment but Not Gene Targeting Curtails Granulocyte Migration

The heptahelical receptor CD97 is a defining member of the EGF-TM7 family of adhesion class receptors. In both humans and mice, CD97 isoforms are expressed with variable numbers of tandemly arranged N-terminal epidermal growth factor-like domains that facilitate interactions with distinct cellular ligands. Results from treatment of mice with mAbs in various disease models have suggested a role for CD97 in leukocyte trafficking. Here, we aimed to thoroughly characterize the expression profile of CD97, and delineate its biological function. To this end, we applied a novel polyclonal Ab, which is the first antiserum suitable for immunohistochemistry, and combined this analysis with the study of Cd97-lacZ knock-in mice. We show that similar to the situation in humans, hematopoietic, epithelial, endothelial, muscle, and fat cells expressed CD97. Despite this broad expression pattern, the Cd97−/− mouse that we created had no overt phenotype, except for a mild granulocytosis. Furthermore, granulocyte accumulation at sites of inflammation was normal in the absence of CD97. Interestingly, application of CD97 mAbs blocked granulocyte trafficking after thioglycollate-induced peritonitis in wild-type but not in knock-out mice. Hence, we conclude that CD97 mAbs actively induce an inhibitory effect that disturbs normal granulocyte trafficking, which is not perturbed by the absence of the molecule.