The presence of scattered tumor cells at the invading front of several carcinomas has clinical significance. These cells differ in their protein expression from cells in central tumor regions as recently shown for the EGF-TM7 receptor CD97. To understand the impact of such heterogeneity on tumor invasion, we investigated tumor cells with modified CD97 expression in vitro and in vivo. Applying an individual cellbased computer model approach, we linked specific cell properties of these cells to tumor invasion characteristics. CD97 overexpression promoted tumor growth in scid mice, stimulated single cell motility, increased proteolytic activity of matrix metalloproteinases, and secretion of chemokines in vitro in an isoform-specific manner. We demonstrated by computer simulation studies that these effects of CD97 can increase the invasion capacity of tumors. Furthermore, they can cause the appearance of scattered tumor cells at the invasion front. We identified local tumor environment interactions as triggers of these multiple capabilities. Experimentally, our simulation results are supported by the finding that CD97 expression in tumor cells is regulated by their environment. The progression of carcinomas is associated with a loss of epithelial differentiation and gain of mesenchyme-like capabilities of scattered tumor cells at the invasive front. This transition is associated with alterations of the expression of molecules involved in cell-cell and/or cell-extracellular matrix interactions, such as motility-promoting molecules.1-3 Furthermore, the secretion of cytokines and extracellular matrix-degrading proteinases are altered.4,5 For colorectal carcinomas it has been shown that in metastases such alterations are reversed and the molecules show a similar expression pattern or level compared with the central region of the primary tumor. 6,7 Consequently, Brabletz and co-workers 6,7 suggested an active role of the tumor environment in malignant tumor progression. A tumor microenvironment invasion model was suggested by Condeelis and co-workers. 8 It is a challenge to understand how the complex tumor invasion behavior emerges from collective interactions on the molecular and cellular level. Although the effects of molecular changes on the individual cell behavior can be quantified directly in experiments, dynamic links between the changes at the cellular level and the characteristics of the tumor invasion process are hard to assess. Here, we exclusively focus on that problem. A major insight into the link between individual cell behavior and tissue dynamics can be gained by computer modeling approaches. They permit investigation of the potential role of generic organization principles in specific tissues. We chose Supported by the Deutsche Forschungsgemeinschaft (DFG; project AU 132/3-1 and grant BIZ-6 1/1 to J.G.) and by the

Leukocyte recruitment in response to inflammatory signals is governed, in part, by binding to Thy-1 (CD90) on activated endothelial cells (EC). In this study, we characterized the adhesion G-protein coupled receptor CD97, present on peripheral myeloid cells, as a novel interacting partner for Thy-1. CD97 was upregulated on polymorphonuclear cells (PMNC) of patients with psoriasis. In psoriatic skin lesions, CD97+ myeloid cells colocalized with Thy-1+ EC of small vessels in microabscesses, suggesting an interaction between CD97 and Thy-1 that was further examined by adhesion and protein-binding assays. PMNC and cell lines stably overexpressing CD97 adhered specifically to Thy-1+–activated human dermal EC, Thy-1+ CHO cells, and immobilized Thy-1 protein. Binding of the CD97+ CHO clones correlated with their CD97 expression level. Soluble CD97 bound specifically to immobilized Thy-1 protein, as well as Thy-1+–activated EC and CHO cells. In all assays, cellular adhesion or protein binding was blocked partially by CD97 and Thy-1–blocking mAb. Our data suggested that CD97 interacts via its stalk with Thy-1 because mAb directed to the stalk of CD97 showed stronger blocking compared with mAb to its epidermal growth factor-like domains, and binding was calcium independent. Moreover, soluble CD97 without the stalk and soluble EMR2, containing highly homologous epidermal growth factor-like domains but a different stalk, failed to bind. In summary, binding of leukocytes to activated endothelium mediated by the interaction of CD97 with Thy-1 is involved in firm adhesion of PMNC during inflammation and may play a role in the regulation of leukocyte trafficking to inflammatory sites.

Objective: Graves' disease (GD) and Hashimoto's thyroiditis (HT) are characterized by lymphocytic infiltrates partly resembling secondary lymphoid follicles in the thyroid. CXCR5 and its ligand CXCL13 regulate compartmentalization of B-and T-cells in secondary lymphoid organs. The aim of the study was to elucidate the role of this chemokine receptor -ligand pair in thyroid autoimmunity. Methods: Peripheral blood and thyroid-derived lymphocyte subpopulations were examined by flow cytometry for CXCR5. CXCR5 and CXCL13 cDNA were quantified in thyroid tissues by real-time RT-PCR. Results: We found no differences between the percentages of peripheral blood CXCR5þ T-and B-cells in GD patients (n ¼ 10) and healthy controls (n ¼ 10). In GD patients, the number of memory CD4 þ cells expressing CXCR5 which are functionally characterized as follicular B helper T-cells is higher in thyroidderived (18^3%) compared with peripheral blood T-lymphocytes (8^2%). The highest CXCL13 mRNA levels were found in HT (n ¼ 2, 86.1^1.2 zmol (10 221 mol) cDNA/PCR) followed by GD tissues (n ¼ 16, 9.6^3.5). Only low amounts were determined in thyroid autonomy (TA) (n ¼ 11) thyroid tissues, irrespective of whether the autonomous nodule (0.5^0.1) or the surrounding normal tissue (1.8^0.7) had been analyzed. The same differences were found for CXCR5 (HT: 179.1^6.8; GD: 17.4^10.6; TA nodule : 0.8^0.5; TA normal : 4.4^3.6). In GD, there is a correlation between CXCL13 and CXCR5 mRNA levels and the number of focal lymphocytic infiltrates and germinal centers as well as anti-thyroperoxidase but not anti-TSH receptor autoantibodies. Conclusions: CXCR5 and CXCL13 play an essential role in maintaining B-and T-cells in lymphocytic infiltrates and ectopic follicles in thyroid tissue from patients affected by autoimmunity. 150 225-234 European Journal of Endocrinology

Cells respond to mechanical stimuli with altered signaling networks. Here, we show that mechanical forces rapidly induce phosphorylation of CD97/ADGRE5 (pCD97) at its intracellular C-terminal PDZ-binding motif (PBM). Biochemically, this phosphorylation disrupts CD97 binding to PDZ domains of the scaffold protein DLG1. In shear-stressed cells, pCD97 appears not only in junctions, retracting fibers, and the attachment area but also in lost membrane patches, demonstrating (intra)cellular detachment at the CD97 PBM. This motif is critical for the CD97-dependent mechanoresponse. Cells expressing CD97 without the PBM are more deformable, and under shear stress, these cells lose cell contacts faster and show changes in the actin cytoskeleton when compared with cells expressing full-length CD97. Our data indicate CD97 linkage to the cytoskeleton. Consistently, CD97 knockout phenocopies CD97 without the PBM, and membranous CD97 is organized in an F-actin-dependent manner. In summary, CD97 shapes the cellular mechanoresponse through signaling modulation via its PBM.

The adhesion G-protein-coupled receptor CD97 is present in normal colonic enterocytes but overexpressed in colorectal carcinoma. To investigate the function of CD97 in colorectal carcinogenesis, transgenic Tg(villin-CD97) mice overexpressing CD97 in enterocytes were generated and subjected to azoxymethane (AOM)/dextran sodium sulfate (DSS)-induced colitis-associated tumorigenesis. Unexpectedly, we found a CD97 cDNA copy number-dependent reduction of DSS-induced colitis in Tg compared to wild-type (WT) mice that was confirmed by applying a simple DSS protocol. Ultrastructural analysis revealed that overexpression of CD97 strengthened lateral cell-cell contacts between enterocytes, which, in contrast, were weakened in CD97 knockout (Ko) mice. Transepithelial resistance was not altered in Tg and Ko mice, indicating that tight junctions were not affected. In Tg murine and normal human colonic enterocytes as well as in colorectal cell lines CD97 was localized preferentially in E-cadherin-based adherens junctions. CD97 overexpression upregulated membrane-bound but not cytoplasmic or nuclear β-catenin and reduced phospho-β-catenin, labeled for degradation. This was associated with inactivation of glycogen synthase kinase-3β (GSK-3β) and activation of Akt. In summary, CD97 increases the structural integrity of enterocytic adherens junctions by increasing and stabilizing junctional β-catenin, thereby regulating intestinal epithelial strength and attenuating experimental colitis.