The receptor for urokinase-plasminogen activator

Many human cells and cell lines possess a specific receptor that binds urokinase plasminogen activator (uPA) with an affinity of about 10(-10) M. Bound enzyme is not internalized, is slowly dissociated, and retains its enzymatic activity. The amino acid sequence of uPA responsible for receptor binding is located within the first 35 aminoterminal residues, ie, in the growth factor domain. Binding, however, is not competed for by other proteins that contain the growth factor domain (including epidermal growth factor). Cells that produce uPA secrete the pro-uPA form, which subsequently binds to the receptor. A431 cells, in fact, have their receptors completely saturated with pro-uPA. It is proposed that uPA:uPA-receptor interaction plays a direct role in physiological and pathological processes that require cell migration.     

Isolation and characterization of a human interleukin 2 gene

An interleukin 2 (IL-2) gene was isolated from a Charon 4A human gene library. Electron microscopic examination of 15 heteroduplexes formed between the genomic DNAs and the IL-2 cDNAs demonstrated that the size of the IL-2 gene is about 5.1 +/- 0.5 kb and that there are at least two introns in this gene. Nucleotide sequence of the 5' flanking region of the IL-2 gene showed a homology with that of the corresponding region of the human immune interferon gene.     

Toxoplasma gondii: Microassay to differentiate toxoplasma inhibiting factor and interleukin 2

Using a sensitive, economical, and reproducible microassay, the relationship of toxoplasma inhibiting factor to interleukin 2 has been examined. The assay developed took advantage of the observation that (1) Toxoplasma gondii tachyzoites replicated efficiently in the murine monocytic cell line, RAW 264; (2) treatment of RAW 264 cells with toxoplasma inhibiting factor prevented intracellular replication of the parasite to an extent similar to that observed with identical treatment of freshly isolated murine peritoneal exudate cells; and (3) [³H]uracil incorporation was an efficacious means to quantify replication (or inhibition of replication) of tachyzoites within the cell line. Although toxoplasma inhibiting factor and interleukin 2 were both present in the same lectin -and antigen-stimulated splenocyte supernatant fluids, results from microassays strongly suggested that the molecules were two distinct entities.     

Host Response to Sarisodera hydrophila Wouts and Sher, 1971

The histopathology of two populations of Sarisodera hydrophila Wouts and Sher, 1971 was examined on Salix lasiolepis Benth. (willow), Populus fremontii Wats. (cottonwood), and Lyonothamnus floribundus Gray (ironwood) using light microscopy as well as scanning and transmission electron microscopy. Sarisodera hydrophila induces formation of a single uninucleate hypertrophied cell (giant cell) which varies only slightly among the three hosts. The giant cell is enclosed by the root stele and contacts phloem, vascular cambium, and xylem. The single hypertrophied nucleus of the giant cell is ameboid or lobulate in shape, generally with a single nucleolus. The cell is characterized by a wall which is separated into two distinct regions about 2 μm and 13 μm thick; the thicker region occurs adjacent to the nematode head. Cell wall ingrowths, such as those associated with host responses to certain other plant-parasitic nematodes, were not observed in giant cells induced by S. hydrophila. However, a high frequency of pit fields with plasmodesmata occurred in the thinner portion of the cell wall which is adjacent to vascular elements. Roots of the three hosts simultaneously infected with S. hydrophila and Meloidogyne sp. resulted in adjacent responses characteristic of each nematode, supporting the view that the specific type of host response is a function of the nematode rather than the host. The varying expressions of host responses among Heteroderoidea may be useful in testing congruency with existing interpretations of phylogeny.     

Lung alveolar cell cytosomes: A consideration of their significance

Summary An ultrastructural comparison of mammalian, reptilian, and amphibian lung alveolar cells, and avian lung atrial cells reveals that morphologically similar cytoplasmic bodies (cytosomes) occur in these cells. The cytosomes, which appear generally as osmiophilic, lamellae-containing, membrane-bound, round bodies 0.3 to 0.5 in diameter, are also similar to bodies occurring in epithelial cells of both physoclistous and physostomatous swimbladders of fishes. Because the function of both lung alveolar and swimbladder epithelial cells is gas-handling, the possibility is raised that the morphologically similar lamellae-containing bodies of these vertebrate cells are functionally identical. One function, suggested by other investigators, is that, in mammalian lungs, these bodies supply a surface-tension lowering material (surfactant). Because several assumptions concerning this proposed function remain unproved, an alternative proposal is speculatively explored. The suggestion is offered that cytosomes contain an antioxidant needed to protect alveolar and swimbladder cells against the toxic effects of the relatively high concentration of oxygen to which these cells are exposed.Supported by a research grant from the American Cancer Society, Oregon Division, Inc.     

Effect of retinoic acid on the proliferation and tumorigenicity of mouse mastocytoma cells

Retinoic acid (RA) inhibited the in vitro growth of the mouse mast cell tumor line P₈₁₅ in a dose- and time-dependent manner. The inhibition was accompanied by an increase in the amount of neutral intracellular mucopolysaccharides. Study of cell cycle kinetics showed that exposure to retinoic acid led to a slowing-down of the cell-cycle progression possibly related to a more differentiated cell population disclosed by microscopy with a lower proliferative capacity. In vivo, delays in both tumor appearance and mouse mortality were observed after injecting RA into mice bearing mastocytomas. These results suggest that RA could be of interest in the treatment of human malignant systemic mastocytosis with proliferation of immature mast cells.     

Heparin-binding growth factors and their receptors

Heparin-binding growth factors modulate diverse biological activities including cellular proliferation, cellular differentiation, morphogenesis, and angiogenesis. Biochemical characterization for two members of the heparin-binding growth factor family, acidic and basic fibroblast growth factors, is extensive, while characterization of the remaining five members is forthcoming. Cell surface receptors have been identified for acidic and basic fibroblast growth factors, but little is known concerning their sites of action in vivo or the mechanisms involved in transducing the energy of growth factor binding to a biological response. An understanding of the biological basis for the diversity of the heparin binding growth factor family and the in vivo actions of these factors will prove a major challenge to future research efforts.     

Plant cell biology 150 years after Matthias Schleiden

Summary Exactly 150 years after the publication of the so-called cell theory the role of the botanist Schleiden has been reconsidered. It is emphasized that the study of plant sexual reproduction systems has contributed considerably to the development of the general cell concept. Recent examples show that 150 years later plant cell biology is flourishing, not least because of the great impact of the increasing use of plant reproductive cells and organs.