The SH2-containing tyrosine phosphatase corkscrew is required during signaling by sevenless, Ras1 and Raf

The sevenless gene encodes a receptor tyrosine kinase which is required for the development of the R7 photoreceptor cell in each ommatidium of the Drosophila eye. We have previously used a sensitized genetic screen to identify mutations, designated Enhancers of sevenless (E(sev)), which affect genes that encode components of the sevenless signaling pathway. Here, we report that one of these mutations, E(sev)1Ae0P is a dominantly inhibiting allele of corkscrew, which encodes an SH2 domain-containing protein tyrosine phosphatase (Perkins et al., 1992). We show that corkscrew function is essential for sevenless signaling and that expression of a membrane-targeted form of corkscrew can drive R7 photoreceptor development in the absence of sevenless function. Furthermore, we have used the dominantly inhibiting corkscrew allele to examine the role of corkscrew during signaling by activated forms of Ras1 and Raf. Our analysis indicates that corkscrew function is still required during signaling by activated forms Ras1 and Raf proteins. These results define a function for corkscrew that is either downstream of Ras1 activation or in a parallel pathway that acts with activated Ras1/Raf to specify R7 photoreceptor development.

Lisofylline as a modifier of radiation therapy

Lisofylline is a new methylxanthine. The potential of lisofylline to enhance the response to ionizing radiation of the EMT-6 murine mammary carcinoma in vitro and in vivo was assessed and compared with pentoxifylline. Addition of lisofylline (100 microM) or pentoxifylline (100 microM) from the time of radiation exposure and throughout the time of colony formation did not alter the response of normally oxygenated EMT-6 cells to gamma-radiation delivered at 0.76 Gy/min or 12.3 Gy/min. The dose modifying factor for hypoxic EMT-6 cells by lisofylline or pentoxifylline and radiation delivered at 0.76 Gy/min was 2.3. Higher dose rate radiation (12.3 Gy/min) was more cytotoxic toward hypoxic EMT-6 cells than lower dose rate radiation. The dose modifying factor produced by lisofylline in the high dose rate radiation setting was 1.2. In vivo, using the tumor cell survival assay, lisofylline decreased the shoulder of the radiation survival curve (0.76 Gy/min) by a factor of 1.7 +/- 0.2 while pentoxifylline did not. In the tumor growth delay assay, administration of multiple doses of lisofylline or pentoxifylline along with single dose radiation (0.76 Gy/min) was 1.3, while the radiation dose modifying factor for lisofylline or pentoxifylline administered by continuous infusion was 1.5. Overall, lisofylline was a more effective modifier of gamma-radiation therapy than pentoxifylline, and further investigation of lisofylline in this setting is warranted.

The adhesion molecule E-cadherin and a surface antigen recognized by the antibody 9C4 are selectively expressed on erythroid cells of defined maturational stages

The antigen expression of immature erythroid bone marrow cells was studied using two recently generated monoclonal antibodies (mAb), mAb 67A4 and 9C4, with specificities for the epithelial cell adhesion molecule E-cadherin (E-cad; mAb 67A4), and a novel 110 kDa differentiation antigen (mAb 9C4) with unknown molecular structure. Pappenheim staining of FACS-purified cells labeled with mAb 9C4 and anti-glycophorin A (GA) revealed that the majority of the 9C4+GA- and 9C4+GA+ cells consisted of erythroblasts. In contrast, the E-cad-positive population comprised normoblasts and erythroblasts. While the E-cad+GA- fraction contained mainly erythroblasts and basophilic normoblasts, the E-Cad+GA+ population was enriched in orthochromatic and polychromatophilic normoblasts. By colony assays of affinity column-purified cells it could be shown that erythroid colony forming units (CFU-E) were enriched and erythroid burst forming units (BFU-E) were depleted in the 9C4- and E-cad-positive fractions. Flow cytometric analysis of bone marrow cells double-labeled with mAb 67A4 and anti-CD71, anti-CD117, anti-CD34, or anti-GA revealed that about 90% of the E-cad-positive cells coexpressed CD71, about 70% were positive for CD117, about 50% for GA, and only about 5% coexpressed CD34. The expression pattern of 9C4 antigen was similar to that of E-Cad with the exception that only a minority of the 9C4-positive cells coexpressed GA. Lymphoid and myeloid markers were negative on both the E-Cad- and 9C4-positive populations. In these studies we describe the identification of a new mAb-defined antigen which is specifically expressed on erythroblasts and CFU-E(9C4) and demonstrate that E-Cad is not only expressed on epithelial cells but also on erythropoietic cells of defined maturational stages.

Formation of signal transfer complexes between stem cell and platelet-derived growth factor receptors and SH2 domain proteins in vitro

Cellular growth and differentiation signals are generated and defined by the interaction of specific phosphotyrosine residues of activated receptor tyrosine kinases (RTKs) and src homology-2 (SH2) domain-containing intracellular signal transducers. This appears to involve for both the p145c-kit and beta platelet-derived growth factor receptor (PDGF-R) cytoplasmic domains the formation of multiprotein signal transfer complexes, which include combinations of noncatalytic and enzymatically active subunits of phosphatidylinositol 3'-kinase (PI3'-K), phospholipase C-gamma (PLC gamma), and guanosine trisphosphatase activating protein (GAP). In vitro association experiments indicate that PLC gamma and PI3'-K bind the beta PDGF-R simultaneously, while these two SH2 proteins compete for association to p145c-kit binding sites, with p85/PI3'-K exhibiting higher affinity. Interestingly, GAP and p85/PI3'-K binding to distinct p145c-kit phosphotyrosines is cooperative, enhancing formation of a heterotetrameric signaling complex, which may include different combinations of p85 alpha and p85 beta with p110, p112, and p116 by interaction with the same tyrosine 721 docking site. The diversity of molecular interactions observed for PDGF-R and p145c-kit suggests a new mode of signal definition and modulation.

Oncogenic activation of v-kit involves deletion of a putative tyrosine-substrate interaction site

The transforming gene of the Hardy-Zuckerman-4 strain of feline sarcoma virus, v-kit, arose by transduction of the cellular c-kit gene, which encodes the receptor tyrosine kinase (RTK) p145c-kit. To gain insight into the molecular basis of the v-kit transforming potential, we characterized the feline c-kit by cDNA cloning. Comparison of the feline v-kit and c-kit sequences revealed, in addition to deletions of the extracellular and transmembrane domains, three additional mutations in the v-kit oncogene product: deletion of tyrosine-569 and valine-570, the exchange of aspartate at position 761 to glycine, and replacement of the C-terminal 50 amino acids by five unrelated residues. Examinations of individual v-kit mutations in the context of chimeric receptors yielded inhibitory effects for some mutants on both autophosphorylation and substrate phosphorylation functions. In contrast, deletion of tyrosine-569 and valine-570 significantly enhanced transforming and mitogenic activities of p145c-kit, while the other mutations had no significant effects. Conservation in subclass III RTKs and the identification of the corresponding residue in beta PDGF-R, Y579, as a binding site for src family tyrosine kinases suggests an important role for Y568 in kit signal regulation and the definition of its oncogenic potential. Repositioning of Y571 by an inframe two codon deletion may be the crucial alteration resulting in enhancement of v-kit oncogenic activity.

Analysis of the protein kinase activity of moss phytochrome expressed in fibroblast cell culture

In the moss Ceratodon purpureus a phytochrome gene encodes a phytochrome type (PhyCer) which has a C-terminal domain homologous to the catalytic domain of eukaryotic protein kinases (PKs). PhyCer exhibits sequence conservation to serine/threonine as well to tyrosine kinases. Since PhyCer is expressed very weakly to moss cells, to investigate the proposed PK activity of PhyCer, we overexpressed PhyCer transiently in fibroblast cells. For this purpose we made a chimeric receptor, EC-R, which consists of the extracellular, the membrane-spanning and the juxtamembrane domains of the human epidermal growth-factor receptor (EGF-R) linked to the PK catalytic domain of PhyCer (CerKin). The expression of EC-R in transiently transfected cells was confirmed with antibodies directed against the extracellular domain of EGF-R or against CerKin. Both EGF-R and EC-R were immunoprecipitated from lysates of overexpressing cells with antibodies against the extracellular domain of EGF-R. Phosphorylation experiments were performed with the immunoprecipitates and the phosphorylation products were subjected to phosphoamino acid analysis. Phosphorylation products specifically obtained with EC-R-transfected cells exhibit phosphorylation on serine and threonine residues. In EC-R transfected cells the endogenous EGF-R showed enhanced phosphorylation of serine and threonine residues compared to EGF-R immunoprecipitated from control cells. Although CerKin is closest to the catalytic domain of a protein tyrosine kinase from Dictyostelium discoideum, EC-R does not appear to phosphorylate tyrosine residues in vitro. From our data we conclude that PhyCer carries an active PK domain capable of phosphorylating serine and threonine residues.

The secreted tumor-associated antigen 90K is a potent immune stimulator

Immunization of mice with conditioned media from human breast cancer cells yielded the monoclonal antibody SP-2, which recognized an antigen of approximately 90-95 kDa. This protein, designated 90K, was found to be present in the serum of healthy individuals and at elevated levels in the serum of subpopulations of patients with various types of cancer and AIDS. Here we report the primary structure of the SP-2 antigen and demonstrate its relationship to a family of proteins which carry a scavenger receptor cysteine-rich domain. Northern blot analysis of normal tissues, primary tumors, and tumor-derived cell lines indicates a broad expression spectrum of the 90K gene at widely varying levels. Functional characterization reveals stimulatory effects of 90K on host defense systems, such as natural killer cell and lymphokine-activated killer cell activity, and indicates that its immunostimulatory effects may be mediated through the induction of interleukin-2 and possibly other cytokines.

Phosphatidylinositol 3′-kinase associates with p145c-kit as part of a cell type characteristic multimeric signalling complex

p145c-kit is expressed in cell lineages of diverse origin and appears to regulate distinct cell type characteristic functions. Independent mutations at the murine Dominant White Spotting (W) locus result in the alteration of p145c-kit tyrosine kinase activity and signalling potential, which differentially affects melanocyte migration, germ cell regeneration and hematopoietic cell differentiation. Molecules that may be involved in mediation and definition of p145c-kit signalling pathways were investigated in cell lines of hematopoietic, melanogenic and central nervous system origin. High-affinity association of endogenous cellular proteins with activated p145c-kit was limited to a characteristic set of molecules that correlated with the presence of phosphatidylinositol (PtdIns) 3'-kinase activity. The observed association pattern of proteins was cell type characteristic, and all of the proteins were displaced from the receptor by competition with excess receptor binding subunit of PtdIns 3'-kinase. Our data indicate that PtdIns 3'-kinase associates with p145c-kit as part of a multimeric signalling complex, and suggest that the cell type characteristic composition of this complex influences the signalling potential of p145c-kit in the diverse cell types in which it is expressed and thereby defines its cell type-specific functions.

Modulation of p145c-kit function in cells of patients with acute myeloblastic leukemia

The function of the steel factor receptor, p145c-kit, in patient-derived acute myeloblastic leukemia (AML) cells was investigated. Steel factor stimulation of AML cells coexpressing p145c-kit and the progenitor cell antigen CD34 resulted in complete receptor down-regulation, a marked decrease of CD34 antigen expression, and the induction of the granulocyte lineage antigen CD15. These changes in surface marker expression paralleled morphological differentiation to granulated blasts and promyelocytes. Interestingly, the same phenotype was achieved by IL-3 stimulation of AML cells. p145c-kit extracellular domain-specific antibodies had either blocking or enhancing effects on ligand binding, receptor phosphorylation and down-regulation, and induction of cell proliferation. Correlations of these phenomena with distinct effects of antibody stimulation on cell substrate phosphorylation provide clues for the dissection of the p145c-kit signal and the analysis of its relevance for AML.

Plastic occlusion stress test as a model to investigate the effects of skin delipidization on the stratum corneum water holding capacity in vivo

The purpose of the study was to develop an in vivo model to study the effects of lipid removal on skin barrier. 16 subjects (age 41 +/- 8) were delipidized in vivo on the volar forearm using respectively ether/acetone (EA; 1:1) and chloroform/methanol (CM; 2:1). A third site served as control. Water holding capacity (WHC) was measured according to the plastic occlusion stress test (POST) procedure: the water desorption curve after removal of the occlusion was recorded in terms of skin surface water loss (SSWL) using an evaporimeter for 30 min. In the central part of the evaporation curve (bound water) the CM-treated site is significantly different from control and EA-treated sites (p < 0.01). The SSWL decay constants reflecting the desorption rate of water from SC are higher in the CM-treated site (p < 0.01). The data are consistent with the effect of CM delipidization (polar lipids) on bound water. No differences are recorded in the evaporation of free water. We conclude that polar lipids have a key role in modulating barrier function and WHC of the stratum corneum. The POST can represent a useful in vivo model to study the effects of lipid extraction on skin function.

Differential effects of W mutations on p145c-kit tyrosine kinase activity and substrate interaction

The c-kit gene, mapped to the dominant white spotting (W) locus of the mouse (Chabot, B., Stephenson, D. A., Chapman, V. M., Besmer, P., and Bernstein, A. (1988) Nature 335, 88-89; Geissler, E. N., Ryan, M. A., and Housman, D. E. (1988) Cell 55, 185-192), encodes a receptor tyrosine kinase, p145c-kit. Germline mutations at the W locus lead to loss of function alterations in p145c-kit, and result in mice with developmental defects of varying severity in the melanocytic, hematopoietic stem cell, and primordial germ cell lineages. To investigate in more detail the effect of W mutations on p145c-kit signaling, three mutations, W42, Wv, and W41, that confer severe, intermediate, and mild phenotypic characteristics, respectively, were introduced into the human p145c-kit tyrosine kinase domain. These mutations attenuated the intrinsic tyrosine kinase activity of the receptor to different degrees. In addition, they had differential effects on the interaction of the p145c-kit substrates, phospholipase C gamma, GTPase-activating protein, and the receptor-binding subunit of phosphatidylinositol 3'-kinase, p85. Notably, the Wv mutation, while retaining significant receptor tyrosine kinase activity, was unable to bind phospholipase C gamma and GTPase-activating protein, but could still associate with p85. These results suggest that the location of W mutations may be an important determinant of the specificity of substrate association and phosphorylation, and may explain, at least in part, the cell type-specific defects associated with certain W alleles.

Substrate phosphorylation specificity of the human c-kit receptor tyrosine kinase

The chimeric EK-receptor (EK-R), consisting of the epidermal growth factor receptor (EGF-R) extracellular binding domain and p145c-kit cytoplasmic signal-generating sequences, was fully functional in forming high and low affinity EGF binding sites and in ligand-regulated receptor and substrate phosphorylation activities. Relative to EGF-R, EK-R activation stimulated kit-characteristic phosphorylation of human 293 fibroblast substrate polypeptides. Transient coexpression of EK-R with candidate substrates resulted in ligand-induced phosphorylation of phospholipase C gamma and guanosine triphosphatase-activating polypeptide. The RAF-1 serine/threonine kinase was shown to be associated with activated EK-R, but no tyrosine phosphorylation could be detected. The faithfulness of EK-R substrate phosphorylation specificity was confirmed with stem cell factor-stimulated p145c-kit.

[Lung maturation during artificial placentation and mechanical lung distension]

An new method of lung maturation during artificial placentation was evaluated during a series of 15 animal experiments in premature lambs (gestational age 125-132 days). Perfusion circuit with interposition of a membrane lung was connected with the umbilical vessels. Extracorporeal CO2-removal (ECCO2-R) and apneic oxygenation were provided during lung distension. The ultramicroscopic pattern approved a maturation of the lung during the procedure showing development of lamellar bodies and surfactant secretion into the alveolar space. The biochemical analysis of the tracheal fluid showed a significant increase of both PC and PG concentrations (3.225 +/- 1.112 mg/100g to 24.228 +/- 3.36 mg/100 g respectively 0.249 +/- 0.11 mg/100 g of 0.622 +/- 0.09 mg/100 g. The biophysical function of the lung was also improved as was shown by a significant increase of the statistical compliance. We conclude that artificial placentation and lung distension might be a new mode of prophylaxis for respiratory distress syndrome in critically immature babies.

Crystal structure of a zwitterionic detergent: n-octyl-2-hydroxyethylsulfoxide

The crystal structure of n-octyl-2-hydroxyethylsulfoxide (1) (space group P2(1)/c, a = 16.516(7), b = 9.053(4), c = 8.222(4) A, beta = 97.58 degrees) was determined by X-ray diffraction methods to 0.94 A resolution and refined to R = 0.050 (Rw = 0.052). In the crystal lattice the molecules are not arranged tail-to-tail, as usually observed with amphiphilic compounds, but head-to-tail and aligned in the a-axis direction. They form layers in the b, c plane which are interdigitated such that adjacent molecules in one layer are in antiparallel orientation. The packing is stabilized by intermolecular hydrogen bonds O-H--O-S. No solvent molecules were detectable.

In-vivo NMR spectroscopy of the fetal lung in guinea-pigs

We have been successful in achieving phosphorus NMR in-vivo spectra of the fetal lung in an animal model. We used pregnant guinea-pigs with a gestational age of 45 to 65 days. The spectra were recorded on a Bruker tomograph (BMT 24/30) with a field strength of 2.35 T. The spectra showed a typical pattern. After recording the animals were sacrificed and the lungs were prepared for electron microscopic examinations. In the spectra peaks were found which appeared to be phosphorylcholine and phosphatidylcholine. For one peak it could be observed that the relative signal intensity increased with increasing gestational age as well as with increasing lung maturity. This could not be observed for other peaks. So the lecithin of the surfactant in the tissue of the fetal lung appears to be directly accessible through phosphorus in-vivo NMR spectroscopy. The peaks found appear already before the lamellar bodies are present in the pneumocytes type II.

Iris transillumination and variable expression in ectopia lentis et pupillae

Six children in three families showed variations of the rare genetic syndrome, ectopia lentis et pupillae. The siblings in two affected families demonstrated intermingling of simple lens ectopia with ectopia lentis et pupillae, suggesting that some types of simple ectopia lentis represent an incompletely expressed form of the full ectopia lentis et pupillae syndrome. Those patients with simple lens ectopia as well as those with ectopic lenses and pupils had striking transillumination of the iris periphery. Microphakia, cataract, and other anterior segment abnormalities were also observed.

[Different ultrastructure of the right and left myocardium after preservation for 24 hours (author's transl)]

After a 24 hrs' preservation of rat hearts, in 22% the viability test with allogenic perfusion showed a singular recovery of the right ventricle (57 of 257 experiments). The ultrastructural aspects correlate with the differences of the function. The micrographs of the right myocardium show--except a mild edema--ultrastructural integrity, but the micrographs of the left myocardium show marked alterations of the ultrastructure: edema, swollen mitochondria with destroyed cristal membranes, swelling of the sacrotubular system and alterations of myofibrils.