LICOS, a primordial costimulatory ligand?

In mammals, the classical B7 molecules expressed on antigen-presenting cells, B7-1 (CD80) and B7-2 (CD86), bind the structurally related glycoproteins CD28 and CTLA-4 (CD152), generating costimulatory signals that regulate the activation state of T cells. A recently identified human CD28-like protein, ICOS, also induces costimulatory signals in T cells when crosslinked with antibodies, but it is unclear whether ICOS is part of a B7-mediated regulatory pathway of previously unsuspected complexity, or whether it functions independently and in parallel. Here, we report that, rather than binding B7-1 or B7-2, ICOS binds a new B7-related molecule of previously unknown function that we call LICOS (for ligand of ICOS). At 37 degrees C, LICOS binds only to ICOS but, at lower, non-physiological temperatures, it also binds weakly to CD28 and CTLA-4. Sequence comparisons suggest that LICOS is the homologue of a molecule expressed by avian macrophages and of a murine protein whose expression is induced in non-lymphoid organs by tumour necrosis factor alpha (TNFalpha). Our results define the components of a distinct and novel costimulatory pathway and raise the possibility that LICOS, rather than B7-1 or B7-2, is the contemporary homologue of a primordial vertebrate costimulatory ligand.

Characterization and quantitation of the epidermal growth factor receptor in invasive and superficial bladder tumors.

Epidermal growth factor receptors (EGFr) have been measured on primary human bladder tumor membranes by 125I-EGF ligand binding. High affinity receptors were detected on both superficial (Kd 0.2-1.45 nM; mean, 0.86 nM; median, 0.88 nM) and invasive tumors (Kd 0.19-2.38 nM; mean, 0.9 nM, median, 0.79 nM). There was one class of binding sites and EGFr concentration was quantified by competitive binding and Scatchard analysis. The EGFr was further characterized and shown to be cleaved at the major autophosphorylation site by a calcium-activated mechanism. Thus the EGFr from primary bladder tumors exhibits similar biochemical characteristics to those in established cell lines. Tumors classified as invasive on the basis of muscle invasion had higher EGFr levels [EGF binding, 99 +/- 252 (SD) fmol/mg protein; median, 21; n = 24] than superficial tumors (12 +/- 12 fmol/mg protein; median, 11; n = 23) or normal bladder mucosa (9 +/- 12 fmol/mg protein; median, 6; n = 6) (P = 0.05). When the two largest subgroups of superficial and invasive tumors were compared (15 pTa, 16 T3), the invasive tumors had significantly higher EGFr levels (P less than 0.05). EGFr may therefore be involved in mechanisms of tumor progression. EGFr may be a target for selective therapy with EGF-linked drugs in a subset of invasive bladder cancers.

CD2F-10: a new member of the CD2 subset of the immunoglobulin superfamily.

The CD2 subset of the immunoglobulin superfamily consists of a rapidly expanding family of leukocyte cell surface receptors, at least five of which (CD2, CD48, CD58, CD150, and CD244) are involved in lymphocyte activation as either receptors or ligands. Completion of the draft sequence of the human genome offers the possibility of systematically identifying the full set of proteins and interactions of this important family. Here we describe the identification and characterization of the first new member of the subset, CD2F-10, found exclusively by genome searching.

Epidermal growth factor receptor in human bladder cancer: a comparison of immunohistochemistry and ligand binding.

Epidermal growth factor receptors were measured in biopsies from patients with newly diagnosed bladder cancer. Two methods to detect these receptors were compared: immunohistochemical staining of frozen sections, and a ligand binding study using radiolabeled epidermal growth factor and tumor cell membranes. We studied 101 patients by immunohistochemistry and 47 patients by both methods. An association was found between immunohistochemical positivity for epidermal growth factor receptors and high tumor stage (p less than 0.001). Thus, most of the muscle invasive tumors were positive (35 of 49, 71 per cent) and more stage pT1 tumors were positive (8 of 18, 44 per cent) than were stage pTa tumors (5 of 34, 15 per cent, p less than 0.05). The ligand binding study was slightly more sensitive in detecting receptors than immunohistochemistry (30 of 47, 64 per cent and 25 of 47, 53 per cent, respectively). Greater amounts of receptors were found in muscle invasive tumors compared to tumors not invading muscle (p less than 0.05). A significant association was found between the 2 methods in the detection of receptors (p less than 0.001) and no discrepancies were found between the 2 methods in tumors containing high levels of receptors. Immunohistochemistry provides a satisfactory method to detect receptors in tumors with high levels of receptors, although ligand binding is more sensitive in tumors with low levels of receptors.

Quantification of epidermal growth factor in human breast cyst fluids: correlation with dehydroepiandrosterone-sulphate and electrolyte concentrations.

Epidermal growth factor (EGF), dehydroepiandrosterone (DHA)-sulphate and [Na+] and [K+] were assayed in 78 cyst fluids from patients with a palpable breast cyst. Epidermal growth factor was detected in all but 2 cysts, the mean value +/- SEM being 506.2 +/- 39.3 ng/ml, with a range of 0-1,599 ng/ml. When the cyst fluids were sub-divided according to their [Na+]:[K+] ratio, group A cyst fluids ( [Na+]:[K+] less than 3) had a significantly higher (p less than 0.001) level of EGF than group B cyst fluids ([Na+]:[K+] greater than 3). Furthermore, the relationship between EGF and [Na+] and [K+] and between EGF and DHA-sulphate seemed to differ between the 2 cyst types and each cyst type was therefore analyzed separately.

Structure and dimerization of a soluble form of B7-1.

B7-1 (CD80) and B7-2 (CD86) are glycoproteins expressed on antigen-presenting cells. The binding of these molecules to the T cell homodimers CD28 and CTLA-4 (CD152) generates costimulatory and inhibitory signals in T cells, respectively. The crystal structure of the extracellular region of B7-1 (sB7-1), solved to 3 A resolution, consists of a novel combination of two Ig-like domains, one characteristic of adhesion molecules and the other previously seen only in antigen receptors. In the crystal lattice, sB7-1 unexpectedly forms parallel, 2-fold rotationally symmetric homodimers. Analytical ultracentrifugation reveals that sB7-1 also dimerizes in solution. The structural data suggest a mechanism whereby the avidity-enhanced binding of B7-1 and CTLA-4 homodimers, along with the relatively high affinity of these interactions, favors the formation of very stable inhibitory signaling complexes.

Crystallization and functional analysis of a soluble deglycosylated form of the human costimulatory molecule B7-1.

The interactions of B7-1 with CD28 and CTLA-4 modulate the course of human immune responses, making B7-1 an important target for developing structure-based therapeutics. B7-1 is, however, one of the most heavily glycosylated proteins found at the leukocyte cell surface, complicating the structural analysis of this molecule. Methods for the production, crystallization and selenomethionine labelling of a soluble deglycosylated form of this molecule are described. The protein readily forms both tetragonal plate and bipyramidal crystals belonging to space groups I4(1)22, with unit-cell parameters a = b = 56.9, c = 298.7 A, and P4(1)22 (or P4(3)22), with unit-cell parameters a = b = 89.0, c = 261.9 A, respectively. The I4(1)22 and primitive crystal forms diffract to 2.7 and 3.5 A, respectively. Surface plasmon resonance-based assays indicate that the ligand-binding properties of sB7-1 are unaffected by deglycosylation. Since none of the methods relied on any special structural properties of sB7-1, it is proposed that this novel combination of procedures could in principle be adapted to the systematic analysis of many other glycoproteins of structural or functional interest.

Signaling lymphocytic activation molecule (CDw150) is homophilic but self-associates with very low affinity.

Signaling lymphocytic activating molecule ((SLAM) CDw150) is a glycoprotein that belongs to the CD2 subset of the immunoglobulin superfamily and is expressed on the surface of activated T- and B-cells. It has been proposed that SLAM is homophilic and required for bidirectional signaling during T- and B-cell activation. Previous work has suggested that the affinity of SLAM self-association might be unusually high, undermining the concept that protein interactions mediating transient cell-cell contacts, such as those involving leukocytes, have to be weak in order that such contacts are readily reversible. Using surface plasmon resonance-based methods and analytical ultracentrifugation (AUC), we confirm that SLAM is homophilic. However, we also establish a new theoretical treatment of surface plasmon resonance-derived homophilic binding data, which indicates that SLAM-SLAM interactions (solution K(d) approximately 200 micrometer) are in fact considerably weaker than most other well characterized protein-protein interactions at the cell surface (solution K(d) approximately 0.4-20 micrometer), a conclusion that is supported by the AUC analysis. Whereas further analysis of the AUC data imply that SLAM could form "head to head" dimers spanning adjacent cells, the very low affinity raises important questions regarding the physiological role and/or properties of such interactions.