Cell Surface Receptor Protein Research Articles

Lack of the architectural factor HMGA1 causes insulin resistance and diabetes in humans and mice

Type 2 diabetes mellitus is a widespread disease, affecting millions of people globally. Although genetics and environmental factors seem to have a role, the cause of this metabolic disorder is largely unknown. Here we report a genetic flaw that markedly reduced the intracellular expression of the high mobility group A1 (HMGA1) protein, and adversely affected insulin receptor expression in cells and tissues from four subjects with insulin resistance and type 2 diabetes. Restoration of HMGA1 protein expression in subjects' cells enhanced INSR gene transcription, and restored cell-surface insulin receptor protein expression and insulin-binding capacity. Loss of Hmga1 expression, induced in mice by disrupting the Hmga1 gene, considerably decreased insulin receptor expression in the major targets of insulin action, largely impaired insulin signaling and severely reduced insulin secretion, causing a phenotype characteristic of human type 2 diabetes.

Synthesis, in vitro, and in vivo characterization of an integrin αvβ3-targeted molecular probe for optical imaging of tumor

Integrin αvβ3 is a widely-recognized target for the development of targeted molecular probes for imaging pathological conditions. αvβ3 is a cell-surface receptor protein that is upregulated in various pathological conditions including osteoporosis, rheumatoid arthritis, macular degeneration, and cancer. The synthesis of an αvβ3-targeted optical probe 7 from compound 1, and its in vitro and in vivo characterization is described. A series of aliphatic carbamate derivatives of the potent non-peptide integrin antagonist 1 was synthesized and the binding affinity to αvβ3 was determined in both enzyme linked immunosorbent assay (ELISA) and cell adhesion inhibition assays. The hydrophobic carbamate-linked appendages improved the binding affinity of the parent compound for αvβ3 by 2–20 times. A Boc-protected neopentyl derivative in the series is shown to have the best binding affinity to αvβ3 (IC50=0.72nM) when compared to compound 1 as well as to c-RGDfV. Optical probe 7 utilizes the neopentyl linker and demonstrates increased binding affinity and significant tumor cell uptake in vitro as well as specific tumor accumulation and retention in vivo. These results illustrate the potential of employing integrin-targeted molecular probes based on 1 to image a multitude of diseases associated with αvβ3 overexpression.

Bison PRNP genotyping and potential association with Brucella spp. seroprevalence

The implication that host cellular prion protein (PrP(C)) may function as a cell surface receptor and/or portal protein for Brucella abortus in mice prompted an evaluation of nucleotide and amino acid variation within exon 3 of the prion protein gene (PRNP) for six US bison populations. A non-synonymous single nucleotide polymorphism (T50C), resulting in the predicted amino acid replacement M17T (Met --> Thr), was identified in each population. To date, no variation (T50; Met) has been detected at the corresponding exon 3 nucleotide and/or amino acid position for domestic cattle. Notably, 80% (20 of 25) of the Yellowstone National Park bison possessing the C/C genotype were Brucella spp. seropositive, representing a significant (P = 0.021) association between seropositivity and the C/C genotypic class. Moreover, significant differences in the distribution of PRNP exon 3 alleles and genotypes were detected between Yellowstone National Park bison and three bison populations that were either founded from seronegative stock or previously subjected to test-and-slaughter management to eradicate brucellosis. Unlike domestic cattle, no indel polymorphisms were detected within the corresponding regions of the putative bison PRNP promoter, intron 1, octapeptide repeat region or 3'-untranslated region for any population examined. This study provides the first evidence of a potential association between nucleotide variation within PRNP exon 3 and the presence of Brucella spp. antibodies in bison, implicating PrP(C) in the natural resistance of bison to brucellosis infection.

The Hrs/STAM Complex in the Downregulation of Receptor Tyrosine Kinases

Cell surface receptor proteins that have undergone endocytosis are transported to the endosome. From the endosome, ligand-activated receptor tyrosine kinases are further transported to the lysosome for degradation, a process called "receptor downregulation." By contrast, nutrient receptors, such as those for low-density lipoprotein and transferrin, are recycled back to the plasma membrane. Sorting of these two types of receptors occurs at the endosome, where ubiquitination of receptor proteins serves as the sorting signal. Namely, ubiquitinated receptors are incorporated into the lysosomal degradation pathway, whereas those that are not ubiquitinated are returned to the cell surface. Hrs and STAM are proteins that form a complex on the endosomal membrane. Recent studies have shown that the Hrs/STAM complex binds ubiquitin moieties and acts as sorting machinery that recognizes ubiquitinated receptors and transfers them to further sequential lysosomal sorting/trafficking processes.

Intracellular Hyaluronan in Arterial Smooth Muscle Cells: Association with Microtubules, RHAMM, and the Mitotic Spindle

Although considered a pericellular matrix component, hyaluronan was recently localized in the cytoplasm and nucleus of proliferating cells, supporting earlier reports that hyaluronan was present in locations such as the nucleus, rough endoplasmic reticulum, and caveolae. This suggests that it can play roles both inside and outside the cell. Hyaluronan metabolism is coupled to mitosis and cell motility, but it is not clear if intracellular hyaluronan associates with cytoskeletal elements or plays a structural role. Here we report the distribution of intracellular hyaluronan, microtubules, and RHAMM in arterial smooth muscle cells in vitro. The general distribution of intracellular hyaluronan more closely resembled microtubule staining rather than actin filaments. Hyaluronan was abundant in the perinuclear microtubule-rich areas and was present in lysosomes, other vesicular structures, and the nucleolus. Partially fragmented fluorescein-hyaluronan was preferentially translocated to the perinuclear area compared with high-molecular-weight hyaluronan. In the mitotic spindle, hyaluronan colocalized with tubulin and with the hyaladherin RHAMM, a cell surface receptor and microtubule-associated protein that interacts with dynein and maintains spindle pole stability. Internalized fluorescein-hyaluronan was also seen at the spindle. Following telophase, an abundance of hyaluronan near the midbody microtubules at the cleavage furrow was also noted. In permeabilized cells, fluorescein-hyaluronan bound to RHAMM-associated microtubules. These findings suggest novel functions for hyaluronan in cellular physiology.

Retroviral vector targeting through insertion of epidermal growth factor into receptor binding deficient influenza A hemagglutinin results in fusion defective particles

Targeting retroviral entry is a central theme in the development of vectors for gene therapy. The host range of a retrovirus is dependent upon the interaction of its envelope glycoprotein (Env) with a specific cell surface receptor protein, which allows viral entry. In contrast, the pH-dependent viruses enter cells through receptor-mediated endocytosis and the subsequent acidification produces conformational changes in the viral envelope protein(s) which lead to membrane fusion. We attempted to redirect retroviral vectors to epidermal growth factor (EGF) receptor expressing cells by using the pH-dependent influenza A virus hemagglutinin (HA). Wild type receptor binding was avoided either by point mutations or by deletion of the globular head structure of HA and also inserted EGF into HA. Replacement of the whole head domain was not tolerated. Two of the EGF-HA proteins bearing point mutations could be incorporated into retroviral particles, but unfortunately their fusion activity was lost. The data indicate that care must be taken when mutating multiple sites in HA, and that targeting HA requires further analysis of appropriate sites for the insertion of foreign sequences.

Boca-dependent maturation of beta-propeller/EGF modules in low-density lipoprotein receptor proteins.

The extracellular portions of cell surface receptor proteins are often comprised of independently folding protein domains. As they are translated into the endoplasmic reticulum (ER), some of these domains require protein chaperones to assist in their folding. Members of the low-density lipoprotein receptor (LDLR) family require the chaperone called Boca in Drosophila or its ortholog, Mesoderm development, in the mouse. All LDLRs have at least one six-bladed beta-propeller domain, which is immediately followed by an epidermal growth factor (EGF) repeat. We show here that Boca is specifically required for the maturation of these beta-propeller/EGF modules through the secretory pathway, but is not required for other LDLR domains. Protein interaction data suggest that as LDLRs are translated into the ER, Boca binds to the beta-propeller. Subsequently, once the EGF repeat is translated, the beta-propeller/EGF module achieves a more mature state that has lower affinity for Boca. We also show that Boca-dependent beta-propeller/EGF modules are found not only throughout the LDLR family but also in the precursor to the mammalian EGF ligand.

HIV-1 entry inhibitor entrances

BMS-378806 is a newly described small-molecule inhibitor of human immunodeficiency virus type 1 (HIV-1) replication. It acts by binding to the gp120 surface glycoprotein of the virus within, or very close to, the pocket normally occupied by the CD4 antigen, the primary cell-surface receptor protein of HIV-1. Consequently, BMS-378806 inhibits gp120–CD4 binding and the subsequent events of virus–cell attachment and fusion. Thus, BMS-378806 or a derivative could be highly suitable to treat HIV-1 infection, and perhaps also to prevent infection when used in combination with other inhibitors of HIV-1 entry.

CI-1033, an irreversible pan-erbB receptor inhibitor and its potential application for the treatment of breast cancer

The erbB family of cell surface receptor proteins consists of four members, all of which play a role in the development and growth of the normal breast. The activity of this signaling pathway is normally tightly controlled, and dysregulation has been shown to play a significant role in the pathogenesis and progression of breast and other cancers. The potent transforming potential of these receptors is further enhanced by the coexpression of multiple members of this receptor family, which worsens prognosis. Therapeutic blockade of erbB-2 receptor signaling has to date been shown to be effective in only a subset of chemotherapy-resistant breast cancer patients. CI-1033 is a highly potent and selective pan-erbB inhibitor that efficiently blocks signal transduction through all four members of the erbB receptor family. In addition, it covalently binds to these receptors, irreversibility inhibiting them, and thereby provides for prolonged suppression of erbB receptor-mediated signaling. Clinically, it has been shown to have an acceptable side effect profile at potentially therapeutic doses and schedules. Biomarker studies have shown target inhibition in patients, and evidence of antitumor activity has also been observed in phase I studies. Given the broad expression pattern of the erbB family of receptors in solid tumors, and the important proliferative effect of co-expression of multiple erbB receptors, CI-1033, as an irreversible, pan-erbB inhibitor, has the potential to have an important role in the future treatment of breast and other cancers.

Nonrandom intragenic variations in patterns of codon bias implicate a sequential interplay between transitional genetic drift and functional amino acid selection.

Although most codon third bases appear to be functionless, the synonymous codons so defined exhibit a strikingly nonrandom distribution (codon bias) within human and other genes. To examine this phenomenon further, we generated a database of DNA sequences encoding human transmembrane cell-surface receptor proteins. Using this database we show here that the guanine and cytosine content of codon third bases (GC3) varies intragenically with the nature of the specified receptor domains (transmembrane > extracellular > intracellular domains; p < 0.001), the phenotype of the encoded amino acids (hydrophobic > hydrophilic > neutral amino acids; p < 0.001), and the receptor affiliation of the transmembrane (G-protein-coupled receptors > receptor tyrosine kinases; p < 0.001). Within gene regions specifying transmembrane domains, GC3 declines as domain functionality becomes redundant with increasing hydrophobicity (p < 0.001). Codons containing the second-base cytosine (XCZ, which encodes neutral amino acids) are selectively depleted of third-base adenine content (A3: XCA codons) when encoding transmembrane domain residues, consistent with positive selection for transitional mutation of XCG to XTG (which encodes hydrophobic amino acids) rather than to the synonymous XCA. Supporting this XCG --> XTG mechanism of codon bias, the G3:A3 ratio of codons specifying the transmembrane amino acid glycine (GGZ) is intermediate between that of its functional homolog alanine (GCZ) and that of hydrophobic valine (GTZ), even though the C3:T3 ratios are similar. Conversely, nearest-neighbor analysis of third bases 5' to codons specifying valine and leucine (CTZ) confirms a significant difference in C3:T3 but not G3:A3 ratios (i.e., C3/G1 --> T3/G1 > C3/A1; p < 0.001), consistent with the functionally advantageous retention of hydrophobic residues. These data raise the possibility that patterns of intragenic codon bias reflect a balance between negative and positive selection, suggesting in turn that analysis of codon third-base usage may help to predict the functional significance of encoded products.

Prediction of the multimeric assembly of staphylococcal enterotoxin A with cell-surface protein receptors

Staphylococcal enterotoxin A (SEA) cross-links two class II major histocompatibility complex (MHC) molecules and forms a multimeric assembly with T-cell receptors (TcRs). The X-ray crystal structure of SEA has been solved, yet details describing molecular recognition and association remain unclear. We present a structural model for the interactions of SEA with cell-surface proteins. Molecular docking calculations predicting SEA association with the class II MHC molecule HLA-DR1 were performed by using a rigid-body docking method. Docked orientations were evaluated by a Poisson–Boltzmann model for the electrostatic free energy of binding and the hydrophobic effect calculated from molecular surface areas. We found that the best-scoring SEA conformers for the DR1α interface display a binding mode similar to that determined crystallographically for staphylococcal enterotoxin B bound to HLA-DR1. For the zinc-binding site of SEA, docking DR1β yielded several orientations exhibiting tetrahedral-like coordination geometries. Combining the two interfaces, tetramers were modeled by docking an αβ TcR with trimolecular complexes DR1β–SEA–DR1α and SEA–βDR1α–SEA. Our results indicate that the complex DR1β–SEA–DR1α provides a more favorable assembly for the engagement of TcRs, forming SEA molecular contacts that are in accord with reported mutagenesis studies. In contrast, the cooperative association of two SEA molecules on a single DR1 molecule sterically inhibits interactions with TcRs. We suggest that signal transduction stimulated by SEA through large-scale assembly is limited to four or five TcR–(DR1β–SEA–DR1α) tetramers and requires the dimerization of class II MHC molecules, while TcR dimerization is unlikely.

Bardet-Biedl syndrome and Usher syndrome.

Bardet-Biedl syndrome (BBS) and Usher syndrome (USH) are the most prevalent syndromic forms of retinitis pigmentosa (RP), together they make up almost a quarter of the patients with RP. BBS is defined by the association of retinopathy, obesity, hypogonadism, renal dysfunction, postaxial polydactyly and mental retardation. This clinically complex syndrome is genetically heterogeneous with linkage to more than 6 loci, and 4 genes have been cloned so far. Recent molecular data present evidence that, in some instances, the clinical manifestation of BBS requires recessive mutations in 1 of the 6 BBS loci plus one or two additional mutations in a second BBS locus (tri- or tetra-allelic inheritance). USH is characterized by the combination of congenital or early-onset sensorineural deafness, RP, and variable degrees of vestibular dysfunction. Each of the three clinical types is genetically heterogeneous: 7 loci have been mapped for type 1, three loci for type 2, and two loci for type 3. Currently, 6 USH genes (MYO7A, USH1C, CDH23, PCDH15, USH2A, USH3) have been identified. Pathogenetically, mutations of the USH1 genes seem to result in defects of auditory and retinal sensory cells, the USH 2 phenotype is caused by defects of extracellular matrix or cell surface receptor proteins, and USH3 may be due to synaptic disturbances. The considerable contribution of syndromic forms of RP requires interdisciplinary approaches to the clinical and diagnostic management of RP patients.

Siderophore-mediated cell signalling in Pseudomonas aeruginosa: divergent pathways regulate virulence factor production and siderophore receptor synthesis.

Under iron-limiting conditions, Pseudomonas aeruginosa produces a siderophore called pyoverdine. Pyoverdine is secreted into the extracellular environment where it chelates iron, and the resulting ferri-pyoverdine complexes are transported back into the bacteria by a cell surface receptor protein FpvA. Pyoverdine also acts as a signalling molecule inducing the production of three secreted virulence factors. Binding of ferri-pyoverdine to FpvA transduces a signal to the periplasmic part of the membrane-spanning antisigma factor FpvR. The signal is transmitted to the cytoplasmic part of FpvR, which controls the activity of an extracytoplasmic family (ECF) sigma factor protein PvdS. This results in the production of the virulence factors pyoverdine, exotoxin A and PrpL endoprotease. Here, we show that a second divergent branch of this signalling pathway regulates the production of the FpvA protein. FpvR negatively regulates the activity of a second ECF sigma factor, FpvI, which is required for the synthesis of FpvA, and the presence of ferri-pyoverdine greatly increases the activity of FpvI so that production of FpvA is induced. To the best of our knowledge, this is the first example of a branched signalling system of this sort and the first example of an antisigma factor protein (FpvR) that directly regulates the activities of two different ECF sigma factor proteins (PvdS and FpvI).

Review: Endotoxin in the environment — exposure and effects

This review deals with endotoxin in the environment and its relation to disease among exposed persons. Data are presented on levels of endotoxin in different environments with maximum values of several μg/m3. The cellular reactions of importance for inhalation exposure effects are attachment to lipopolysaccharide binding protein, CD14 cell surface protein and TLR-4 receptors. The internalisation of endotoxin in macrophages and endothelial cells results in local production of inflammatory cytokines with subsequent migration of inflammatory cells into the lung and the penetration of cytokines into the blood. These events orchestrate clinical effects in terms of toxic pneumonitis, airways' inflammation and systemic symptoms. Inhalation challenges with pure endotoxin and field studies confirm the relation between these effects and exposure to dusts containing endotoxin. It is possible that polymorphism in genes determining endotoxin reactivity, particularly TLR-4, influences the risk for disease after environmental exposures. Some data suggest that the inflammation caused by inhaled endotoxin may decrease the risk for atopic sensitisation among children and lung cancer among workers exposed to organic dust. Additional research is needed to clarify the role of other environmental agents that are present in connection with endotoxin, particularly (1→3)-β-D-glucan from mold cell walls.

Endotoxin in the environment--exposure and effects.

This review deals with endotoxin in the environment and its relation to disease among exposed persons. Data are presented on levels of endotoxin in different environments with maximum values of several microg/m(3). The cellular reactions of importance for inhalation exposure effects are attachment to lipopolysaccharide binding protein, CD14 cell surface protein and TLR-4 receptors. The internalisation of endotoxin in macrophages and endothelial cells results in local production of inflammatory cytokines with subsequent migration of inflammatory cells into the lung and the penetration of cytokines into the blood. These events orchestrate clinical effects in terms of toxic pneumonitis, airways' inflammation and systemic symptoms. Inhalation challenges with pure endotoxin and field studies confirm the relation between these effects and exposure to dusts containing endotoxin. It is possible that polymorphism in genes determining endotoxin reactivity, particularly TLR-4, influences the risk for disease after environmental exposures. Some data suggest that the inflammation caused by inhaled endotoxin may decrease the risk for atopic sensitisation among children and lung cancer among workers exposed to organic dust. Additional research is needed to clarify the role of other environmental agents that are present in connection with endotoxin, particularly (1-->3)-beta-D-glucan from mold cell walls.

Localization and expression of usherin: a novel basement membrane protein defective in people with Usher’s syndrome type IIa

People with Usher’s syndrome type IIa have mutations in a novel gene encoding a protein with domains commonly found in many types of extracellular matrix and cell surface receptor proteins. Here we report that this protein, which we refer to as usherin, is a new basement membrane protein. In the mouse, usherin has a broad, but not ubiquitous, tissue distribution. Usherin is found in all of the capillary and structural basement membranes of the human and mouse retina and in the murine inner ear at both post-natal day 0 and in the adult. High levels of usherin are also observed in tissues not affected in Usher’s syndrome type IIa, including spleen, testis, oviduct, epididymis, submaxillary gland, and large and small intestines. Many organs are completely devoid of usherin, including the brain, skin, kidney, lung, liver, and skeletal muscle. Expression was observed in the smooth muscle of the small intestine, colon, and oviduct, however, usherin is not present in cardiac smooth muscle. Usherin is critical for normal development and tissue homeostasis in the inner ear and retina, illustrating yet another example of the importance of basement membranes in the development and function of tissues.

Expression of HER-2/neu receptor protein in adrenal tumors.

The HER-2/neu protein is overexpressed in many human carcinomas obtained from different tissues and may represent a useful target for therapy with the commercially available monoclonal antibody trastuzumab (herceptin). Novel therapeutic options are needed for metastasized adrenocortical cancer. Therefore, we studied expression of the HER-2/neu cell surface receptor protein using three different antibodies in 12 adrenal adenomas, 17 adrenocortical carcinomas and 5 pheochromocytomas. Normal adrenals (n = 5) served as controls. One adenoma showed very weak membranous immunostaining with the Dako antibody, two others showed a nonspecific cytoplasmic staining pattern. A nonspecific reaction in the cytoplasm was demonstrable in seven carcinomas with the Novocastra antibody. In all pheochromocytomas, a granular intracytoplasmic and, rarely, slightly membranous immunostaining with the Dako antibody was found. From our data we conclude that specific and significant membranous immunostaining indicating strong overexpression (grade 3) of HER-2/neu protein is not present in adrenocortical tumors. The granular cytoplasmic immunostaining of the medulla may be helpful for differentiation of adrenocortical tumors from pheochromocytomas.

Hemodialysis Membranes

ABSTRACT. Maintenance hemodialysis patients display evidence of elevated interleukin-1 (IL-1) and tumor necrosis factor alpha release after stimulation either by contaminated dialysate, bioincompatible membrane material, or both. This release is followed by the stimulated secretion of a large number of other interleukins, particularly IL-6, the cytokine principally responsible for acute-phase protein synthesis. It has been shown that high levels of the circulating proinflammatory cytokines IL-1, tumor necrosis factor alpha, IL-6, and IL-13 are associated with mortality in hemodialysis patients. Essential functions of polymorphonuclear leukocytes—that is, phagocytosis, oxygen species production, upregulation of specific cell surface receptor proteins, or apoptosis—are disturbed in patients with end-stage renal disease. These are further altered as a result of complement activation by the hemodialysis procedure, particularly if bioincompatible dialyzers are used. Polymorphonuclear leukocyte degranulation occurring during extracorporeal circulation does not depend on complement activation but rather on intracellular calcium and the presence or absence of the degranulation inhibitory proteins angiogenin and complement factor D. Clinical signs and symptoms of end-stage renal disease patients are at least in part related to the accumulation of middle molecules such as β2-microglobulin, parathyroid hormone, advanced glycation end products, advanced lipoxidation end products, advanced oxidation protein products (formed as a result of oxidative stress, carbonyl stress, or both), granulocyte inhibitory proteins, or leptin. Currently available membrane materials do not provide long-lasting, effective reduction of middle molecules in patients who require maintenance hemodialysis.

Generation of monoclonal antibody CIBCgp185 against C-erbB-2 oncoprotein and its clinical evaluation

The C-erbB-2 proto-oncogene encodes the production of a cell surface receptor protein, with tyrosine kinase activity. Over expression of this gene either due to gene amplification and/or increased transcription has been observed and has been correlated with poor prognosis in patients with Breast (10-33%) and ovarian (20-33%) cancers. The very low levels of expression of C-erbB-2 by normal tissues makes this receptor a potential target for diagnosis and therapy with Monoclonal antibodies raised against its extracellular domain. One such monoclonal antibody designated as CIBCgp185 of IgG2a isotype has been generated in our laboratory using BT474 breast carcinoma cell line as immunogen. This monoclonal antibody immunoprecipitated a 185 KD glycoprotein. The specificity of this antibody was confirmed by the formation of a single discrete band and positive reaction with BT474 antigen in Western blot and Dot blot respectively. Flowcytometric analysis performed using various cancer cell lines revealed that this Monoclonal antibody exhibited high binding affinity with BT474 and SKBR3 cells whichoverexpresses C-erbB-2. By immunoperoxidase test, this antibody stained specifically the tumor cell membrane in frozen tissue sections of breast and ovarian tumors indicating overexpression of the C-erbB-2 product. All these results well correlated with those obtained using a control antibody ICR12, an anti-C-erbB-2 antibody. These studies clearly indicate that Monoclonal antibody CIBCgp185 might prove useful to identify tumors with over expression of C-erbB-2 which are often associated with poor prognosis and early recurrence.

KAI1, a prostate metastasis suppressor: prediction of solvated structure and interactions with binding partners; integrins, cadherins, and cell-surface receptor proteins.

The solution structure of the transmembrane-4 superfamily protein KAI1, a recently identified prostate cancer metastasis suppressor gene that encodes a 267-amino acid protein, was modeled. The structure of this four-helical transmembrane protein was developed by defining and modeling sections individually. A complete three-dimensional structure for the solvated protein was developed by combining the individually modeled sections. The four-helix transmembrane bundle structure was predicted combining information from several methods including Fourier transform analysis of residue variability for helix orientation. The structure of the KAI1 large extracellular domain was modeled based on the solved crystal structure of the extracellular domain of another tetraspanin superfamily protein member, CD81 (hepatitis C virus envelope E2 glycoprotein receptor). This is a novel protein fold consisting of five alpha helices held together by two disulfide bonds for which the CD81 protein is the first solved representative. Molecular dynamics studies were performed to test stability and to relax the total model KAI1 structure's solution. The resulting KAI1 structural model should be a useful tool for predicting modes of self-association and associations with other TM4SF proteins, integrins, cadherins, and other KAI1 binding partners. Mutations for probing the interactions of KAI1 with antibodies and with other binding partners are suggested. Published 2001 Wiley-Liss, Inc.