p190-A, a human tumor suppressor gene, maps to the chromosomal region 19q13.3 that is reportedly deleted in some gliomas

To date, two distinct genes coding for Ras GAP-binding phosphoproteins of 190kDa, p190-A and p190-B, have been cloned from mammalian cells. Rat p190-A of 1513 amino acids shares 50% sequence identity with human p190-B of 1499 amino acids. We have previously demonstrated, using rat p190-A cDNA, that full-length p190-A is a tumor suppressor, reversing v-Ha-Ras-induced malignancy of NIH 3T3 cells through both the N-terminal GTPase (residues 1-251) and the C-terminal Rho GAP (residues 1168-1441) domains. Here we report the cloning of the full-length human p190-A cDNA and its first exon covering more than 80% of this protein, as well as its chromosomal mapping. Human p190-A encodes a protein of 1514 amino acids, and shares overall 97% sequence identity with rat p190-A. Like the p190-B exon, the first exon of p190-A is extremely large (3.7 kb in length), encoding both the GTPase and middle domains (residues 1-1228), but not the remaining GAP domain, suggesting a high conservation of genomic structure between two p190 genes. Using a well characterized monochromosome somatic cell hybrid panel, fluorescent in situ hybridization (FISH) and other complementary approaches, we have mapped the p190-A gene between the markers D19S241E and STD (500 kb region) of human chromosome 19q13.3. Interestingly, this chromosomal region is known to be rearranged in a variety of human solid tumors including pancreatic carcinomas and gliomas. Moreover, at least 40% glioblastoma/astrocytoma cases with breakpoints in this region were previously reported to show loss of the chromosomal region encompassing p190-A, suggesting the possibility that loss or mutations of this gene might be in part responsible for the development of these tumors.

Characterization of mouse A33 antigen, a definitive marker for basolateral surfaces of intestinal epithelial cells

The murine A33 antigen is emerging as a definitive marker of intestinal epithelial cells. Cloning and sequence determination of cDNAs encoding mA33 antigen predict a novel type 1 transmembrane protein of 298 amino acids, comprising an extracellular domain with two immunoglobulin-like domains, a single-span transmembrane domain, and a highly acidic cytoplasmic domain. On the basis of conservation of amino acid sequence and genomic structure, the mA33 antigen is a member of a growing subfamily within the immunoglobulin superfamily, which includes transmembrane proteins CTX/ChT1, CTM/CTH, and CAR. During embryonic development, mA33 antigen expression is first observed in the inner cell mass of blastocysts before implantation. Intestinal expression of mA33 antigen is initiated in the hindgut at E14.5 and increases steadily throughout late embryonic and postnatal life into adulthood. The protein is specifically expressed on the basolateral surfaces of intestinal epithelial cells of all lineages, independent of their position along the rostrocaudal and crypt-villus axes. Thus the mA33 antigen appears to be a novel marker for both proliferating and differentiating intestinal epithelial cells.

Abnormal gastrointestinal development in PDGF-A and PDGFR-(alpha) deficient mice implicates a novel mesenchymal structure with putative instructive properties in villus morphogenesis

Development of the gastrointestinal (GI) tract depends on reciprocal epithelial-mesenchymal cell signaling. Here, we demonstrate a role for platelet-derived growth factor-A (PDGF-A) and its receptor, PDGFR-(alpha), in this process. Mice lacking PDGF-A or PDGFR-(alpha) were found to develop an abnormal GI mucosal lining, including fewer and misshapen villi and loss of pericryptal mesenchyme. Onset of villus morphogenesis correlated with the formation of clusters of PDGFR-(alpha) positive cells, ‘villus clusters’, which remained located at the tip of the mesenchymal core of the growing villus. Lack of PDGF-A or PDGFR-(alpha) resulted in progressive depletion of PDGFR-(alpha) positive mesenchymal cells, the formation of fewer villus clusters, and premature expression of smooth muscle actin (SMA) in the villus mesenchyme. We found that the villus clusters were postmitotic, expressed BMP-2 and BMP-4, and that their formation correlated with downregulated DNA synthesis in adjacent intestinal epithelium. We propose a model in which villus morphogenesis is initiated as a result of aggregation of PDGFR-(α) positive cells into cell clusters that subsequently function as mesenchymal centers of signaling to the epithelium. The role of PDGF-A seems to be to secure renewal of PDGFR-(alpha) positive cells when they are consumed in the initial rounds of cluster formation.

Crystal structure and functional dissection of the cytostatic cytokine oncostatin M

BACKGROUND

The cytokine oncostatin M (OSM) inhibits growth of certain tumour-derived cells, induces proliferation in other cell types (e.g. haemangioblasts) and is a mediator of inflammatory responses. Its mechanism of action is via specific binding to gp130 and either the leukaemia inhibitory factor receptor (LIFR) or oncostatin M receptor (OSMR) systems at the cell surface to form an active signalling complex.

RESULTS

We report here the crystal structure of human oncostatin M (hOSM) along with mutagenesis data which map the receptor-binding epitopes of the molecule. The structure was determined to a resolution of 2.2 A and conforms to the haematopoietin cytokine up-up-down-down four-helix bundle topology. The site 2 epitope, responsible for gp130 binding, is centred around Gly120 which forms a 'dimple' on the surface of the molecule located on helices A and C. The site 3 motif, responsible for LIFR and OSMR binding, consists of a protruding Phe160/Lys163 pair located at the start of helix D.

CONCLUSIONS

The data presented allow functional dissection of the receptor-binding interfaces to atomic resolution. Modelling suggests that the gp130 residue Phe169 packs into the site 2 dimple in an analogous fashion to structurally equivalent residues at the growth hormone-growth hormone receptor interface, implying that certain key features may underlie recognition across the whole cytokine/receptor superfamily. Conversely, detailed comparison of the available structures suggests that variations on a common theme dictate the specificity of receptor-ligand interactions within the gp130 family of cytokines.

Receptor recognition by gp130 cytokines

Cytokines of the gp130 family exert their diverse biological effects by formation of stable high affinity transmembrane receptor complexes that are characterized by the presence of the shared transmembrane signalling receptor gp130. Different gp130 ligands form signalling complexes that vary in both composition and stoichiometry. Analysis of the three-dimensional structure of selected ligands and receptor elements indicates that ligands display three topologically conserved receptor recognition epitopes that interact with complementary ligand recognition elements. The composition of the signalling complex and downstream biological responses is defined by the relative affinity of different receptor components for these epitopes. The detailed structure of receptor recognition epitopes indicates that the generation of small molecule cytokine mimetics may be a feasible objective.

Identification of three distinct receptor binding sites of murine interleukin-11

Interleukin-11 (IL-11) is a member of the gp130 family of cytokines. These cytokines drive the assembly of multisubunit receptor complexes, all of which contain at least one molecule of the transmembrane signaling receptor gp130. A complex of IL-11 and the IL-11 receptor (IL-11R) has been shown to interact with gp130, with high affinity, and to induce gp130- dependent signaling. In this study, we have identified residues crucial for the binding of murine IL-11 (mIL-11) to both the IL-11R and gp130 by examining the activities of mIL-11 mutants in receptor binding and cell proliferation assays. The location of these residues, as predicted from structural studies and a model of IL-11, reveals that mIL-11 has three distinct receptor binding sites. These are structurally and functionally analogous to the previously defined receptor binding sites I, II, and III of interleukin-6 (IL-6). This supports the hypothesis that IL-11 signals via the formation of a hexameric receptor complex and indicates that site III is a generic feature of cytokines that signal via association with gp130.

Defective oligodendrocyte development and severe hypomyelination in PDGF-A knockout mice

There is a class of oligodendrocyte progenitors, called O-2A progenitors, that is characterized by expression of platelet-derived growth factor α-receptors (PDGFR(α)). It is not known whether all oligodendrocytes are derived from these PDGFRalpha-progenitors or whether a subset(s) of oligodendrocytes develops from a different, PDGFR alpha-negative lineage(s). We investigated the relationship between PDGF and oligodendrogenesis by examining mice that lack either PDGF-A or PDGF-B. PDGF-A null mice had many fewer PDGFR alpha-progenitors than either wild-type or PDGF-B null mice, demonstrating that proliferation of these cells relies heavily (though not exclusively) on PDGF-AA homodimers. PDGF-A-deficient mice also had reduced numbers of oligodendrocytes and a dysmyelinating phenotype (tremor). Not all parts of the central nervous system (CNS) were equally affected in the knockout. For example, there were profound reductions in the numbers of PDGFR alpha-progenitors and oligodendrocytes in the spinal cord and cerebellum, but less severe reductions of both cell types in the medulla. This correlation suggests a close link between PDGFRalpha-progenitors and oligodendrogenesis in most or all parts of the CNS. We also provide evidence that myelin proteolipid protein (PLP/DM-20)-positive cells in the late embryonic brainstem are non-dividing cells, presumably immature oligodendrocytes, and not proliferating precursors.

Trophic effects of cardiotrophin-1 and interleukin-11 on rat dorsal root ganglion neurons in vitro

Cardiotrophin-1 (CT-1) was originally isolated for its hypertrophy inducing effects on cardiac myocytes whereas interleukin-11 (IL-11) was identified due to its ability to stimulate an interleukin-6 (IL-6) dependent plasmocytoma cell line. Both cytokines are structurally and functionally related to a group of factors called neuropoietic cytokines, which also includes IL-6, ciliary neurotrophic factor (CNTF), leukemia inhibitory factor (LIF), and oncostatin M. These factors have trophic effects on subsets of neurons. In the present study we examined the influence of CT-1 and IL-11 on newborn rat dorsal root ganglion neuron survival in vitro. Mouse CT-1 showed prominent trophic effects that were comparable to those of CNTF and LIF. Mouse IL-11 alone did not enhance neuronal survival, but soluble mouse IL-11 receptor alpha rendered neurons sensitive to IL-11. Surprisingly, soluble IL-11 receptor alpha even had slight neurotrophic effects by itself. These results suggest that CT-1 and IL-11 might also be involved in the physiological regulation of sensory neuron survival. Thus, they might, like CNTF, become tools for the therapeutic intervention in neurodegeneration due to disease, toxicity, and trauma.

CTX, a Xenopus thymocyte receptor, defines a molecular family conserved throughout vertebrates

CTX, a cortical thymocyte marker in Xenopus, is an immunoglobulin superfamily (Igsf) member comprising one variable and one constant C2-type Igsf domain, a transmembrane segment and a cytoplasmic tail. Although resembling that of the TCR and immunoglobulins, the variable domain is not encoded by somatic rearrangement of the gene but by splicing of two half-domain exons. The C2 domain, also encoded by two exons, has an extra pair of cysteines. The transmembrane segment is free of charged residues, and the cytoplasmic tail (70 amino acids) contains one tyrosine and many glutamic acid residues. ChT1, a chicken homologue of CTX, has the same structural and genetic features, and both molecules are expressed on the thymocyte surface. We cloned new mouse (CTM) and human (CTH) cDNA and genes which are highly homologous to CTX/ChT1 but not lymphocyte specific. Similarity with recently described human cell surface molecules, A33 antigen and CAR (coxsackie and adenovirus 5 receptor), and a number of expressed sequence tags leads us to propose that CTX defines a novel subset of the Igsf, conserved throughout vertebrates and extending beyond the immune system. Strong homologies within vertebrate sequences suggest that the V and C2 CTX domains are scions of a very ancient lineage.

The interactions of the cytokine-binding homology region and immunoglobulin-like domains of gp130 with oncostatin M: implications for receptor complex formation

The receptor gp130 is utilized by cytokines including interleukin 6, leukemia inhibitory factor, oncostatin M, cilary neurotrophic factor and cardiotrophin. It is essential for myocardial development and haematopoiesis during embryogenesis, and its role as a shared signal transducer among different cytokines explains their overlapping biological functions. Although gp130 contains a cytokine-binding homology region (CHR) analogous to the extracellular growth hormone receptor, the complexes that utilize gp130 are not simple dimerizations of receptors around a single cytokine but involve receptor interactions with additional sites on the ligand resulting in higher order complexes. Analysis by surface plasmon resonance of the binding of the immunoglobulin-like and CHR domains of the extracellular portion of gp130 to mutants of the cytokine oncostatin M reveal that the CHR forms the main binding site for oncostatin M by a classical site II interaction, but in addition a second interaction occurs involving the receptor's immunoglobulin-like domain and the cytokine's site III at the N-terminus of the D helix. The implications for complex formation are discussed.

Apert syndrome mutations in fibroblast growth factor receptor 2 exhibit increased affinity for FGF ligand

Dominantly acting mutations of the fibroblast growth factor (FGF) receptor 2 (FGFR2) gene have been implicated in various craniosynostosis syndromes. Apert syndrome, characterized in addition by syndactyly of the limbs, involves specific mutations at two adjacent residues, Ser252Trp and Pro253Arg, predicted to lie in the linker region between IgII and IgIII of the FGFR2 ligand-binding domain. We have analysed the interaction of FGF ligands with wild-type and Apert-type mutant FGFR2 ectodomains in solution. Wild-type and Apert-type receptors form a complex with FGF ligands with a stoichiometry of 2:2 (ligand:receptor). The kinetics and specificity of ligand binding to wild-type and Apert mutant receptors have been analysed using surface plasmon resonance techniques. This reveals that Apert mutations, compared with wild-type, exhibit a selective decrease in the dissociation kinetics of FGF2, but not of other FGF ligands examined. In contrast, the substitution Ser252Leu in FGFR2, previously observed in several asymptomatic individuals, exhibited wild-type kinetics. These findings indicate that Apert syndrome arises as a result of increased affinity of mutant receptors for specific FGF ligands which leads to activation of signalling under conditions where availability of ligand is limiting.

Oligodendrocyte population dynamics and the role of PDGF in vivo

Oligodendrocyte progenitors originate near the floor plate of the spinal cord, then proliferate and migrate throughout the cord before giving rise to oligodendrocytes. Progenitor cell proliferation stops before birth because the cell cycle slows down, linked to an increase in differentiation and death. Experiments with transgenic mice show that platelet-derived growth factor (PDGF) drives progenitor cell division and suggest that slowing of and exit from the cycle reflects a decline in PDGF signaling. Overexpressing PDGF induces hyperproliferation of progenitor cells and excessive, ectopic production of oligodendrocytes. However, the superfluous oligodendrocytes die at an immature stage of differentiation, leaving a normal complement of myelin-forming cells. Therefore, cell survival controls override proliferation controls for determining the final number and distribution of mature oligodendrocytes.

Targeted disruption of fibroblast growth factor (FGF) receptor 2 suggests a role for FGF signaling in pregastrulation mammalian development

We disrupted the fibroblast growth factor (FGF) receptor 2 (FGFR2) gene by introducing a neo cassette into the IIIc ligand binding exon and by deleting a genomic DNA fragment encoding its transmembrane domain and part of its kinase I domain. A recessive embryonic lethal mutation was obtained. Preimplantation development was normal until the blastocyst stage. Homozygous mutant embryos died a few hours after implantation at a random position in the uterine crypt, with collapsed yolk cavity. Mutant blastocysts hatched, adhered, and formed a layer of trophoblast giant cells in vitro, but after prolonged culture, the growth of the inner cell mass stopped, no visceral endoderm formed, and finally the egg cylinder disintegrated. It follows that FGFR2 is required for early postimplantation development between implantation and the formation of the egg cylinder. We suggest that FGFR2 contributes to the outgrowth, differentiation, and maintenance of the inner cell mass and raise the possibility that this activity is mediated by FGF4 signals transmitted by FGFR2. The role of early FGF signaling in pregastrulation development as a possible adaptation to mammalian (amniote) embryogenesis is discussed.

Conserved use of a non-canonical 5' splice site (/GA) in alternative splicing by fibroblast growth factor receptors 1, 2 and 3

The two classes of sequences for recognition and splicing of pre-mRNA in eukaryotes, GT-AG and AT-AC, are characterized by the nearly invariant dinucleotides present at the extreme 5' (donor) and 3' (acceptor) ends of the intron. Amongst GT-AG introns, which comprise the vast majority, the more extended consensus sequence at the 5' splice site isACAG/GTAGAGT (where / indicates the exon-intron boundary). This sequence is complementary to part of the U1 snRNA and is important in intron recognition. We have determined the genomic structure of the mouse fibroblast growth factor receptor 2 gene (Fgfr2) and identified a divergent 5' splice site (ACA/GAAAGT), conserved in FGFR1 , - 2 and - 3 from humans, mice and Xenopus that is used for alternative splicing of a hexanucleotide sequence, encoding Val-Thr, at the end of exon 10. This is the only example known of the use of /GA in vertebrate splicing. Similarities to a splice site in the Antennapedia gene of Drosophila suggest that this variant motif is involved in alternative splicing of short sequences at the 5' splice site. Inclusion or exclusion of the Val-Thr dipeptide may play an important role in controlling FGFR signalling through the Ras/MAPK pathway.

Crystal structure of a cytokine-binding region of gp130

The structure of the cytokine-binding homology region of the cell surface receptor gp130 has been determined by X-ray crystallography at 2.0 A resolution. The beta sandwich structure of the two domains conforms to the topology of the cytokine receptor superfamily. This first structure of an uncomplexed receptor exhibits a similar L-shaped quaternary structure to that of ligand-bound family members and suggests a limited flexibility in relative domain orientation of some 3 degrees. The putative ligand-binding loops are relatively rigid, with a phenylalanine side chain similarly positioned to exposed aromatic residues implicated in ligand binding for other such receptors. The positioning and structure of the N-terminal portion of the polypeptide chain have implications for the structure and function of cytokine receptors, such as gp130, which contain an additional N-terminal immunoglobulin-like domain.

Early posterior neural tissue is induced by FGF in the chick embryo

Signals that induce neural cell fate in amniote embryos emanate from a unique cell population found at the anterior end of the primitive streak. Cells in this region express a number of fibroblast growth factors (FGFs), a group of secreted proteins implicated in the induction and patterning of neural tissue in the amphibian embryo. Here we exploit the large size and accessibility of the early chick embryo to analyse the function of FGF signalling specifically during neural induction. Our results demonstrate that extraembryonic epiblast cells previously shown to be responsive to endogenous neural-inducing signals express early posterior neural genes in response to local, physiological levels of FGF signal. This neural tissue does not express anterior neural markers or undergo neuronal differentiation and forms in the absence of axial mesoderm. Prospective mesodermal tissue is, however, induced and we present evidence for both the direct and indirect action of FGFs on prospective posterior neural tissue. These findings suggest that FGF signalling underlies a specific aspect of neural induction, the initiation of the programme that leads to the generation of the posterior central nervous system.

An antagonist for the leukemia inhibitory factor receptor inhibits leukemia inhibitory factor, cardiotrophin-1, ciliary neurotrophic factor, and oncostatin M

The leukemia inhibitory factor receptor (LIF-R) is activated not only by LIF, but also by cardiotrophin-1, ciliary neurotrophic factor with its receptor, and oncostatin M (OSM). Each of these cytokines induces the hetero-oligomerization of LIF-R with gp130, a signal-transducing subunit shared with interleukin-6 and interleukin-11. The introduction of mutations into human LIF that reduced the affinity for gp130 while retaining affinity for LIF-R has generated antagonists for LIF. In the current study, a LIF antagonist that was free of detectable agonistic activity was tested for antagonism against the family of LIF-R ligands. On cells that express LIF-R and gp130, all LIF-R ligands were antagonized. On cells that also express OSM receptor, OSM was not antagonized, demonstrating that the antagonist is specific for LIF-R. Ligand-triggered tyrosine phosphorylation of both LIF-R and gp130 was blocked by the antagonist. The antagonist is therefore likely to work by preventing receptor oligomerization.

Alveogenesis failure in PDGF-A-deficient mice is coupled to lack of distal spreading of alveolar smooth muscle cell progenitors during lung development

PDGF-A(−/−) mice lack lung alveolar smooth muscle cells (SMC), exhibit reduced deposition of elastin fibres in the lung parenchyma, and develop lung emphysema due to complete failure of alveogenesis. We have mapped the expression of PDGF-A, PDGF receptor-alpha, tropoelastin, smooth muscle alpha-actin and desmin in developing lungs from wild type and PDGF-A(−/−) mice of pre- and postnatal ages in order to get insight into the mechanisms of PDGF-A-induced alveolar SMC formation and elastin deposition. PDGF-A was expressed by developing lung epithelium. Clusters of PDGF-Ralpha-positive (PDGF-Ralpha+) mesenchymal cells occurred at the distal epithelial branches until embryonic day (E) 15.5. Between E16.5 and E17.5, PDGF-Ralpha+ cells multiplied and spread to acquire positions as solitary cells in the terminal sac walls, where they remained until the onset of alveogenesis. In PDGF-A(−/−) lungs PDGF-Ralpha+ cells failed to multiply and spread and instead remained in prospective bronchiolar walls. Three phases of tropoelastin expression were seen in the developing lung, each phase characterized by a distinct pattern of expression. The third phase, tropoelastin expression by developing alveolar SMC in conjunction with alveogenesis, was specifically and completely absent in PDGF-A(−/−) lungs. We propose that lung PDGF-Ralpha+ cells are progenitors of the tropoelastin-positive alveolar SMC. We also propose that postnatal alveogenesis failure in PDGF-A(−/−) mice is due to a prenatal block in the distal spreading of PDGF-Ralpha+ cells along the tubular lung epithelium during the canalicular stage of lung development.

Fgfr2 and osteopontin domains in the developing skull vault are mutually exclusive and can be altered by locally applied FGF2

Mutations in the human fibroblast growth factor receptor type 2 (FGFR2) gene cause craniosynostosis, particularly affecting the coronal suture. We show here that, in the fetal mouse skull vault, Fgfr2 transcripts are most abundant at the periphery of the membrane bones; they are mutually exclusive with those of osteopontin (an early marker of osteogenic differentiation) but coincide with sites of rapid cell proliferation. Fibroblast growth factor type 2 (FGF2) protein, which has a high affinity for the FGFR2 splice variant associated with craniosynostosis, is locally abundant; immunohistochemical detection showed it to be present at low levels in Fgfr2 expression domains and at high levels in differentiated areas. Implantation of FGF2-soaked beads onto the fetal coronal suture by ex utero surgery resulted in ectopic osteopontin expression, encircled by Fgfr2 expression, after 48 hours. We suggest that increased FGF/FGFR signalling in the developing skull, whether due to FGFR2 mutation or to ectopic FGF2, shifts the cell proliferation/differentiation balance towards differentiation by enhancing the normal paracrine down-regulation of Fgfr2.

Aggressiveness, hypoalgesia and high blood pressure in mice lacking the adenosine A2a receptor

Adenosine is released from metabolically active cells by facilitated diffusion, and is generated extracellularly by degradation of released ATP. It is a potent biological mediator that modulates the activity of numerous cell types, including various neuronal populations, platelets, neutrophils and mast cells, and smooth muscle cells in bronchi and vasculature. Most of these effects help to protect cells and tissues during stress conditions such as ischaemia. Adenosine mediates its effects through four receptor subtypes: the A1, A2a, A2b and A3 receptors. The A2a receptor (A2aR) is abundant in basal ganglia, vasculature and platelets, and stimulates adenylyl cyclase. It is a major target of caffeine, the most widely used psychoactive drug. Here we investigate the role of the A2a receptor by disrupting the gene in mice. We found that A2aR-knockout (A2aR-/-) mice were viable and bred normally. Their exploratory activity was reduced, whereas caffeine, which normally stimulates exploratory behaviour, became a depressant of exploratory activity. Knockout animals scored higher in anxiety tests, and male mice were much more aggressive towards intruders. The response of A2aR-/- mice to acute pain stimuli was slower. Blood pressure and heart rate were increased, as well as platelet aggregation. The specific A2a agonist CGS 21680 lost its biological activity in all systems tested.

Characterization of posttranslational modifications of human A33 antigen, a novel palmitoylated surface glycoprotein of human gastrointestinal epithelium

Monoclonal antibody (mAb) A33 recognizes a differentiation antigen (A33) expressed in normal human gastrointestinal epithelium and in 95% of human colon cancers. Murine mAb A33 shows specific targeting of colon cancer in humans and a humanized A33 antibody is currently being evaluated in the clinic. The cDNA for the human A33 antigen has recently been cloned, and sequence comparison indicated that the A33 antigen is a novel human cell surface molecule of the immunoglobulin superfamily. Because mAb A33 recognizes a conformational epitope, only a partial characterization of the A33 antigen has been carried out to date. In this report we show that the A33 antigen is (I) N-glycosylated, containing approximately 8 K of N-linked carbohydrate and there is no evidence for O-glycosylation, sialylation or glycophosphatidylinositol, and (ii) S-acylated in vitro, incorporating [3H] palmitic acid linked through a hydroxylamine-sensitive thioester bond. The S-palmitoylation may be involved in regulating the internalization process initiated by binding of mAb A33 to cell surface A33 antigen.

Leukaemia inhibitory factor is retrogradely transported by a distinct population of adult rat sensory neurons: co-localization with trkA and other neurochemical markers

Sciatic sensory afferents that retrogradely transport and accumulate leukaemia inhibitory factor (LIF) within their soma were characterized in the adult rat in vivo. Twenty-four percent of neurons within the L4 and L5 dorsal root ganglia accumulated biotinylated LIF following intraneural injection of the cytokine into the sciatic nerve. Labelled cell bodies were predominantly of small diameter (20.1 +/- 0.5 microm). Retrograde transport was eliminated by excess unlabelled LIF but not by the related cytokines, ciliary-derived neurotrophic factor (CNTF) and interleukin-6 (IL-6). Double labelling revealed that the majority (81%) of LIF-accumulating neurons were immunopositive for CGRP and 34% were immunopositive for the cell surface glycoconjugate IB4. Sixty-two percent of LIF-accumulating neurons were immunopositive for trkA. Our results demonstrate a group of small-diameter sensory neurons that retrogradely transport LIF, comprising cells that constitutively express neuropeptides and those likely to be peptide-deficient. LIF-accumulating neurons expressing trkA are also potentially responsive to nerve growth factor. It is likely that the LIF-accumulating neurons described in this study are nociceptive in function.

Electrophoretic analysis of the novel antigen for the gastrointestinal-specific monoclonal antibody, A33

The murine monoclonal antibody A33 (mAbA33) recognises a human cell membrane-associated antigen selectively expressed in epithelial cells of the lower gastrointestinal tract and > 90% of colonic cancers, but is not detected in a wide range of other normal tissues by immunohistochemical analysis. In phase I/II clinical triasl, mAbA33 has been shown to target advanced colon cancers and the humanized version is currently being evaluated in therapy studies. Although the mAbA33 has been well characterised by immunohistochemical and clinical studies, until recently, the target antigen has remained poorly defined. This was largely attributable to the antigenic determinant recognised by mAbA33 being dependent on the native spatial conformation of the A33 antigen which impeded its identification by conventional two-dimensional electrophoresis (2-DE) and immunoblot analysis. We have developed an immunoblot method, based on nonreducing/non-urea precast 2-DE gels, that has facilitated the purification of the detergent (0.3% Triton X-100) solubilised A33 antigen from the human colon cancer cell lines LIM1215 and SW1222. Under these 2-DE conditions, the A33 antigen electrophoreses with an apparent M(r) approximately 41000 and pI 5.0-6.0. Attempts to isolate the A33 antigen from 2-DE gels for direct structural analysis were unsuccessful, due to its co-electrophoresis with actin and cytokeratin proteins. However, using Western blot and biosensor detection the A33 antigen has been purified chromatographically and N-terminal sequence analysis was possible. Using polyclonal antibodies raised against a synthetic peptide corresponding to the N-terminal region of the A33 antigen we have used Western blot analysis to localise the molecule in our master 2-DE protein database for normal human colon crypts and several colon carcinoma cell lines (URL address: http:(/)/www.ludwig.edu.au). Under reducing 2-DE conditions, the A33 antigen electrophoresis as 6 differentially charged isoforms (pI 4.6-4.8) with a single molecular weight species at M(r) approximately 55000.

cash4, a novel achaete-scute homolog induced by Hensen's node during generation of the posterior nervous system

In vertebrate embryos, the precursor cells of the central nervous system (CNS) are induced by signaling from the organizer region. Here we report the isolation of a novel vertebrate achaete-scute homolog, cash4, which is expressed in the presumptive posterior nervous system in response to such signaling. cash4 is first expressed in epiblast cells flanking the late-phase organizer (Hensen's node), which retains its ability to induce cash4 during regression to the caudal end of the embryo. We show that these node-derived signals can be mimicked in vivo by the activity of fibroblast growth factor (FGF). We demonstrate that cash4 can substitute for the achaete/scute genes in the fly and that it also has proneural activity in vertebrate embryos. Together these results suggest that cash4 functions as a proneural gene downstream of node-derived signals (including FGF) to promote the formation of the neural precursors that will give rise to the posterior CNS in the chick embryo.

The human A33 antigen is a transmembrane glycoprotein and a novel member of the immunoglobulin superfamily

The mAb A33 detects a membrane antigen that is expressed in normal human colonic and small bowel epithelium and > 95% of human colon cancers. It is absent from most other human tissues and tumor types. The murine A33 mAb has been shown to target colon cancer in clinical trials, and the therapeutic potential of a humanized antibody is currently being evaluated. Using detergent extracts of the human colon carcinoma cell lines LIM1215 and SW1222, in which the antigen is highly expressed, the molecule was purified, yielding a 43-kDa protein. The N-terminal sequence was determined and further internal peptide sequence obtained following enzymatic cleavage. Degenerate primers were used in PCRs to produce a probe to screen a LIM1215 cDNA library, yielding clones that enabled us to deduce the complete amino acid sequence of the A33 antigen and express the protein. The available data bases have been searched and reveal no overall sequence similarities with known proteins. Based on a hydrophilicity plot, the A33 protein has three distinct structural domains: an extracellular region of 213 amino acids (which, by sequence alignment of conserved residues, contains two putative immunoglobulin-like domains), a single hydrophobic transmembrane domain, and a highly polar intracellular tail containing four consecutive cysteine residues. These data indicate that the A33 antigen is a novel cell surface receptor or cell adhesion molecule in the immunoglobulin superfamily.