Abstract. Several studies have addressed the interaction of the HIV Tat protein with the cell surface. Our analysis of the cell attachment-promoting activity of Tat and peptides derived from it revealed that the basic domain of Tat, not the arg-gly-asp (RGD) sequence, is required for cell attachment to Tat. Affinity chromatography with Tat peptides and immunoprecipitation with various anti-integrin antibodies suggest that the vitronectin-binding integrin, cxv/35, is the cell surface protein that binds to the basic domain of Tat. The Tat basic domain contains the sequence RKKRRQRRR. A related sequence, KKQRFRHRNRKG, present in the heparin-binding domain of an aviS5 ligand, vitronectin, also bound c~,/35 in affinity chromatography and, in combination with an RGD peptide, was an inhibitor of cell attachment to vitronectin. The a~/35 interaction with these peptides was not solely due to high content of basic amino acids in the ligand sequences; tXv/35 did not bind substantially to peptides consisting entirely of arginine or lysine, whereas a/3t integrin did bind to these peptides. The interaction of c~v/35 with Tat is atypical for integrins in that the binding to Tat is divalent cation independent, whereas the binding of the same integrin to an RGD-containing peptide or to vitronectin requires divalent cations. These data define an auxiliary integrin binding specificity for basic amino acid sequences. These basic domain binding sites may function synergistically with the binding sites that recognize RGD or equivalent sequences. TH~ tripeptide arg-gly-asp (RGD) 1 is required for cell adhesion to a number of proteins, including fibronectin, vitronectin, and fibrinogen (Pierschbacher and Ruoslahti, 1984;Ruoslahti and Pierschbacher, 1987). This adhesion is mediated by integrins, a family oftransmembrane receptors composed of two subunits, ot and/3 (Hemler, 1990;Ruoslahti, 1991;Hynes, 1992).The Tat protein of human immunodeficiency virus (HIV-1) contains an RGD sequence and can mediate cell attachment in an RGD-dependent manner (Brake et al., 1990). Extracellular Tat is internalized by cells and transported to the nucleus, where it retains the ability to transactivate the HIV promoter (Frankel and Pabo, 1988). Furthermore, extracellular Tat has been shown to modulate cell proliferation, both in the suppression of proliferation of antigen-activated T-cells (Viscidi et al., 1989) and in the stimulation of proliferation of Kaposi's sarcoma (KS)-derived cells (Ensoli et al., 1990 We felt that the possibility of an RGD-binding integrin mediating some of the interactions of Tat with cell surfaces was of a considerable interest and set out to identify such an integrin. We found that the otvl3~ integrin bound to the Tat protein, but that this interaction was not significant in the uptake of Tat by cells. Surprisingly, our results indicate that the binding of this integrin to Tat requires the basic region, whereas the RGD sequence is silent. We also provide evidence that a basic sequence in vitronectin can serve as a binding site...

CD97 is an activation-induced antigen on leukocytes which belongs to a new group of seven-span transmembrane (7-TM) molecules, designated EGF-TM7 family. Family members, including EMR1 and F4/80, are characterized by an extended extracellular region with several N-terminal epidermal growth factor-like (EGF) domains. Alternative splicing of CD97 results in isoforms possessing either three (EGF1, 2, 5), four (EGF1, 2, 3, 5) or five EGF domains (EGF1, 2, 3, 4, 5). We recently identified decay accelerating factor (DAF, CD55), a regulatory protein of the complement cascade, as a cellular ligand of the smallest isoform. Employing mutants of CD97(EGF1, 2, 5) in which the EGF domains have been systematically deleted, we here demonstrate the necessity of at least three tandemly linked EGF domains for the interaction with CD55. Consistent with the involvement of different EGF domains, monoclonal antibodies directed against the first EGF domain as well as the removal of Ca2+, for which binding sites exist in the second and fifth EGF domain, blocked binding to CD55. Compared to CD97(EGF1, 2 ,5) the larger isoforms CD97(EGF1, 2, 3, 5) and CD97(EGF1, 2, 3, 4, 5) have a significantly lower affinity for CD55. Thus, alternative splicing may regulate the ligand specificity of CD97 and probably other members of the EGF-TM7 family.

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SummaryCD97 is an activation-induced antigen on leukocytes with a seven-span transmembrane (7-TM) region homologous to the secretin receptor superfamily. However, in contrast to this group of peptide hormone receptors, CD97 has an extended extracellular region with three EGF domains at the NH2 terminus, two of them with a calcium binding site. By demonstrating that lymphocytes and erythrocytes specifically adhere to CD97-transfected COS cells we here show that CD97 in parallel with its molecular evolution has acquired the ability to bind cellular ligands. A mAb selected on its capacity to block the adhesion between CD97 transfectants and red cells was found to be directed to the NHz-terminal short consensus repeat (SCR) of decay accelerating factor (DAF, CD55), a regulatory protein of the complement cascade. The specificity of the interaction of CD97 with CD55 was established by the observation that erythrocytes that lack CD55, obtained from patients with paroxysmal nocturnal hemoglobinuria (PNH) or the CD55-phenotype Inab, failed to adhere to CD97 transfectants. This is the first demonstration of a cellular ligand for a 7-TM receptor. CD97 is an antigen which becomes immediately upregulated on most leukocytes during activation (1). We recently identified CD97 as a 7-TM molecule whose membrane-spanning region is homologous to the secretin receptor superfamily (2). CD97 is different from this group of mammalian and insect peptide hormone receptors (3, 4), in that it has an extended extracellular region with three EGF domains at the NH 2 terminus. The finding of a highly similar architecture in EMR1 (5), which possesses six EGF domains, and its probable murine homologue F4/80 (6) indicates the existence of a new group of 7-TM receptors characterized by several NH2-terminal EGF domains. We have demonstrated that this new type of 7-TM molecule has recently evolved by exon shuffling to the upstream region of an ancestral gene from the secretin receptor superfamily (7).All EGF domains in CD97 and EMR1, except the most NH2-terminal ones, possess a calcium binding site. The Ca 2+ in this subgroup of EGF domains stabilizes the conformation of the domain and can mediate contact to other proteins (8). The rather recent acquisition of EGF domains Bj6m Vogel is on leave from the Institute

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CD97 is an EGF-TM7 receptor found on various carcinomas where expression levels correlate with dedifferentiation and tumor stage, smooth muscle cells and leukocytes. CD97 acts as an adhesion molecule by binding to its cellular ligand, CD55. In this study, we demonstrate that 2 immunodominant CD97 epitopes are not equally present in the various cell types. Differences were apparent in gastrointestinal tumors and smooth muscle cells where monoclonal antibodies (mAbs) to the first epidermal growth factor (EGF) domain (CD97 EGF ) showed a more restricted staining pattern than mAbs to the stalk region (CD97 stalk ). This discrepancy was not detectable in cultured gastrointestinal tumor cell lines. In fact, the selection of the CD97 mAb influences the result of clinical studies. Thus, we clarified the reason(s) for these differences in CD97 mAb staining on various cell types. We provide evidence that epitope accessibility for CD97 EGF Key words: CD97; colorectal cancer; smooth muscle cell; epitope accessibility; glycosylation CD97 is a member of a subfamily of 7-span transmembrane (TM7) receptors referred to as EGF-TM7 proteins. 1,2 In normal tissues, CD97 is abundantly expressed in smooth muscle cells, macrophages, granulocytes, dendritic cells and in some T and B cells. 3 Carcinomas of different origin showed higher CD97 expression compared to the corresponding normal cell types. 4 -7 CD97 consists of an extended extracellular region with several N-terminal epidermal growth factor (EGF) domains coupled to the TM7 domain by a stalk. 1,8 Various CD97 isoforms exist possessing 3 (EGF 1,2,5), 4 (EGF 1,2,3,5), or 5 (EGF 1,2,3,4,5) EGF domains. CD97 binds to membrane receptor CD55. 9 This interaction is mediated by the first 2 CD97 EGF domains. 9 -11 Chondroitin sulfate glycosaminoglycan, present in cell membranes and the extracellular matrix, is a new ligand to the longest CD97 isoform (EGF 1,2,3,4,5). 12 The ability of CD97 EGF domains to interact with cellular and/or extracellular matrix ligands suggests that the molecule is involved in cell-cell or cell-matrix interactions. Various lines of evidence have shown an important role for CD97 in tumor dedifferentiation, migration, invasiveness and metastasis. CD97 levels correlate with the in vitro migration and invasion capacity of colorectal tumor cell lines and CD97-transfected cells. 6 Colorectal carcinomas with more strongly CD97-stained, scattered tumor cells at the invasion front showed a poorer clinical stage as well as increased lymph vessel invasion compared to cases with uniform CD97 staining. 6 In thyroid cancers, CD97 expression parallels the aggressiveness and lymph node involvement of these tumors. 4,5 Our previous data revealed that CD97 has prognostic and therapeutic potential in cancer. However, analyzing CD97 expression brings up the phenomenon that different staining patterns, depending on which CD97 monoclonal antibody (mAb) has been used for immunohistology, can be readily observed in pancreatic tissues. 7,13 Based on this observation, one aim of ...

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This contribution describes how Security Enhanced Linux (SELinux) is enabled on a Nokia 770 Internet Tablet. It will refer to a procedure done under a Debian [1] Testing (Etch) Environment. The procedure will also be possible under other Linux distributions but since Maemo is built upon Debian, this approach is the most preferrable way to extend Maemo Linux. An SELinux enabled device will provide the possibility of a convenient configuration of the device. Different stakeholders can define detailled access control to the components they maintain. This ensures the interests of the stakeholders by providing the benefits of a Linux based embedded device.