Sevenspan transmembrane molecules: novel receptors involved in leukocyte adhesion

Adhesion GPCRs as a paradigm for understanding polycystin-1 G protein regulation

Polycystin-1, whose mutation is the most frequent cause of autosomal dominant polycystic kidney disease, is an extremely large and multi-faceted membrane protein whose primary or proximal cyst-preventing function remains undetermined. Accumulating evidence supports the idea that modulation of cellular signaling by heterotrimeric G proteins is a critical function of polycystin-1. The presence of a cis-autocatalyzed, G protein-coupled receptor (GPCR) proteolytic cleavage site, or GPS, in its extracellular N-terminal domain immediately preceding the first transmembrane domain is one of the notable conserved features of the polycystin-1-like protein family, and also of the family of cell adhesion GPCRs. Adhesion GPCRs are one of five families within the GPCR superfamily and are distinguished by a large N-terminal extracellular region consisting of multiple adhesion modules with a GPS-containing GAIN domain and bimodal functions in cell adhesion and signal transduction. Recent advances from studies of adhesion GPCRs provide a new paradigm for unraveling the mechanisms by which polycystin-1-associated G protein signaling contributes to the pathogenesis of polycystic kidney disease. This review highlights the structural and functional features shared by polycystin-1 and the adhesion GPCRs and discusses the implications of such similarities for our further understanding of the functions of this complicated protein.

The invasion and metastasis promotion role of CD97 small isoform in gastric carcinoma

CD97 is over-expressed in the majority of gastric adenocarcinomas and is associated with its dedifferentiation and aggressiveness. Our previous results demonstrated that out of three CD97 isoforms tested, only the small one was able to promote increased invasiveness in vitro. Based on these data we further aimed to investigate the role of CD97 small isoform in gastric cancer progression in vivo by employing the cells with a stable CD97 small isoform knock-down and an orthotopic gastric cancer mouse model. We could demonstrate that the knock down of CD97/EGF1,2,5, led to a significant decrease in the number of cells penetrating the gelatin coated membrane as compared with control cells. In the gastric cancer mouse model, both the hypodermic and the orthotopic yielded tumor masses of the CD97/EGF1,2,5kd group and were significantly smaller than the control. Metastatic tumor cell number in early metastatic regional lymph nodes on post-operative day 42 was distinctly decreased in the CD97/EGF1,2,5kd group as compared with the SGC-NS group, and was accompanied with the downregulation of CD44, VEGFR, CD31 and CD97. We concluded in this study that CD97 small isoform not only supported gastric cancer local growth, but also promoted metastatic spread in orthotopically implanted mouse model suggesting involvement of the CD97 small isoform in the preparation of (pre)metastatic niche.

Pathogenesis of Afa/Dr diffusely adhering Escherichia coli

Over the last few years, dramatic increases in our knowledge about diffusely adhering Escherichia coli (DAEC) pathogenesis have taken place. The typical class of DAEC includes E. coli strains harboring AfaE-I, AfaE-II, AfaE-III, AfaE-V, Dr, Dr-II, F1845, and NFA-I adhesins (Afa/Dr DAEC); these strains (i) have an identical genetic organization and (ii) allow binding to human decay-accelerating factor (DAF) (Afa/Dr(DAF) subclass) or carcinoembryonic antigen (CEA) (Afa/Dr(CEA) subclass). The atypical class of DAEC includes two subclasses of strains; the atypical subclass 1 includes E. coli strains that express AfaE-VII, AfaE-VIII, AAF-I, AAF-II, and AAF-III adhesins, which (i) have an identical genetic organization and (ii) do not bind to human DAF, and the atypical subclass 2 includes E. coli strains that harbor Afa/Dr adhesins or others adhesins promoting diffuse adhesion, together with pathogenicity islands such as the LEE pathogenicity island (DA-EPEC). In this review, the focus is on Afa/Dr DAEC strains that have been found to be associated with urinary tract infections and with enteric infection. The review aims to provide a broad overview and update of the virulence aspects of these intriguing pathogens. Epidemiological studies, diagnostic techniques, characteristic molecular features of Afa/Dr operons, and the respective role of Afa/Dr adhesins and invasins in pathogenesis are described. Following the recognition of membrane-bound receptors, including type IV collagen, DAF, CEACAM1, CEA, and CEACAM6, by Afa/Dr adhesins, activation of signal transduction pathways leads to structural and functional injuries at brush border and junctional domains and to proinflammatory responses in polarized intestinal cells. In addition, uropathogenic Afa/Dr DAEC strains, following recognition of beta(1) integrin as a receptor, enter epithelial cells by a zipper-like, raft- and microtubule-dependent mechanism. Finally, the presence of other, unknown virulence factors and the way that an Afa/Dr DAEC strain emerges from the human intestinal microbiota as a "silent pathogen" are discussed.

Expression of the Epidermal Growth Factor Seven-Transmembrane Member CD97 Correlates with Grading and Staging in Human Oral Squamous Cell Carcinomas

Introduction: The oral squamous cell carcinoma (OSCC) is the sixth most common malignant tumor worldwide. No significant better progress has been made in the treatment of OSCCs during the last decades. The heterodimeric CD97 protein is a epidermal growth factor seven-transmembrane family member and was identified as a dedifferentiation marker in thyroid carcinomas. Nothing is known about CD97 in OSCCs.

Material and Methods: Employing UV-laser microdissection, CD97 and its ligand CD55 were investigated in normal oral mucosa and OSCCs (n = 78) by multiplex reverse transcription-PCR. Frozen sections were investigated by immunohistochemistry. The effects of retinoic acid and sodium butyrate on the CD97/CD55 expression in OSCC cell lines were determined by quantitative PCR, immunocytochemistry, and flow cytometry.

Results: Weak CD97 transcripts were expressed in normal mucosa and normal basal epithelial cells revealed specific CD97 immunostaining. Strong CD97 transcripts were detected in pT3/T4 and G3/G4 OSCC tissues, whereas pT1/T2 and G1/G2 carcinomas revealed weak CD97 transcript levels. A weak CD97 immunostaining was observed in pT1/T2 and G1/G2 tumors. By contrast, intensive CD97 immunostaining was detected in pT3/T4 OSCCs and G3/G4 lesions. CD55 gene expression was low in normal mucosa. All OSCCs, irrespective of stage and grading, displayed strong CD55 immunostaining. Sodium butyrate and retinoic acid inhibited CD97 mRNA and protein in OSCC cell lines. Interestingly, CD55 was up-regulated by both substances.

Conclusion: We identified CD97 as a novel marker of dedifferentiated OSCC. Interaction of CD97 and CD55 may facilitate adhesion of OSCC cells to surrounding surfaces that would result in metastases and bad prognosis.

Molecular proximity of complement receptor type 3 (CR3) and the glycosylphosphatidylinositol-linked protein GPI-80 on neutrophils: effects of cell adherence, exogenous saccharides, and lipid raft disrupting agents

GPI-80, a novel glycosylphosphatidylinositol (GPI)-anchored protein on polymorphonuclear leukocytes, has been reported to cooperate with CR3 in several aspects of cell function including cell activation, adhesion and migration. The present study investigates the physical proximity of CR3 and GPI-80 on living cells using resonance energy transfer (RET) techniques, which gives positive results when the separation distance is < or = 7 nm. RET from donor-labeled anti-CR3 to acceptor-labeled anti-GPI-80 was detected on adherent neutrophils, but not observed for non-adherent cells. Furthermore, RET was not observed on cells treated with cell adhesion inhibitors 4-bromophenacyl bromide (BPB), N-ethylmaleimide (NEM) or cytochalasin D, suggesting dynamic interactions between CR3 and GPI-80. CR3-to-GPI-80 proximity was blocked by N-acetyl-D-glucosamine (NADG), but not by other monosaccharides such as D-mannose, fructose, fucose, glucose, sorbitol, or galactose; molecular proximity was also disrupted by the glycolipid raft depleting agents 2-OH-propyl-betaCD and MbetaCD. Thus, lipid rafts may be important for the physical and functional cooperation of CR3 and GPI-80.

The Epidermal Growth Factor-Seven Transmembrane (EGF-TM7) Receptor CD97 Is Required for Neutrophil Migration and Host Defense

The epidermal growth factor-seven transmembrane (EGF-TM7) family is a group of seven-span transmembrane receptors predominantly expressed by cells of the immune system. Family members CD97, EGF module-containing mucin-like receptor (EMR) 1, EMR2, EMR3, EMR4, and EGF-TM7-latrophilin-related protein are characterized by an extended extracellular region with a variable number of N-terminal EGF-like domains. EGF-TM7 receptors bind cellular ligands as demonstrated by the interaction of CD97 with decay accelerating factor (CD55) and dermatan sulfate. Investigating the effect of newly generated mAb on the migration of neutrophilic granulocytes, we here report for the first time in vivo data on the function of CD97. In dextran sulfate sodium-induced experimental colitis, we show that homing of adoptively transferred neutrophils to the colon was significantly delayed when cells were preincubated with CD97 mAb. The consequences of this defect in neutrophil migration for host defense are demonstrated in a murine model of Streptococcus pneumoniae-induced pneumonia. Mice treated with CD97 mAb to EGF domain 1 (1B2) and EGF domain 3 (1C5) displayed a reduced granulocytic inflammatory infiltrate at 20 h after inoculation. This was associated with a significantly enhanced outgrowth of bacteria in the lungs at 44 h and a strongly diminished survival. Together, these findings indicate an essential role for CD97 in the migration of neutrophils.

Ligand recognition in multiallelic pheromone receptors from the basidiomycete Schizophyllum commune studied in yeast

The homobasidiomycete Schizophyllum commune encodes a multiallelic pheromone receptor system that distinguishes more than 20 nonself from at least 2 self pheromones. The well-investigated pheromone response system of the yeast Saccharomyces cerevisiae was used to link the FUS1::lacZ reporter system to the heterologous pheromone receptors from S. commune. To investigate yeast G-protein binding, the unchanged heterologous receptor was compared to constructs carrying an exchange of the 3rd cytoplasmatic loop for the Ste2 sequence. A better coupling could be achieved with the altered constructs. In order to examine activation by single pheromones, an artificial peptide based on the sequence of a new putative pheromone gene, bap2(1), in the Balpha2 mating-type locus encoding the shortest pheromone found so far in fungal mating types was used. Thus, we have reassembled the pheromone recognition of the basidiomycete S. commune and constructed a system ideal for specificity analysis in the yeast S. cerevisiae.

TM7XN1, a novel human EGF-TM7-like cDNA, detected with mRNA differential display using human melanoma cell lines with different metastatic potential

We have identified a novel 3845 bp cDNA differentially expressed in a human melanoma metastasis model. Northern blot analysis showed expression in the poorly and intermediately metastasizing cell lines and a marked downregulation in the highly metastatic cell lines. Using RT-PCR expression was also seen in several other tumor cell lines and normal cell types of human origin. cDNA sequence analysis revealed an ORF of 687 amino acids containing seven putative transmembrane domains C-terminally and a long N-terminus. The gene was mapped to 16q13. Highest homology was observed with members of the EGF-TM7 subfamily of the secretin/calcitonin receptor family. We propose the delineation of a subfamily of TM7 proteins, LN-TM7, containing seven transmembrane proteins with a long N-terminal extracellular part.