Modulation of interleukin 2 internalization and interleukin 2-dependent cell growth by antireceptor antibodies

The growth factor interleukin 2 (IL2) binds to and is internalized together with high-affinity surface receptors present on lymphoid cells. This endocytosis thus results in down-regulation of the receptors. However, it is not known if the internalization is relevant to the induction of cell growth. In the present study a rat monoclonal antibody to the P55 chain of the IL2 receptor was used to examine the role of receptor internalization in the IL2-dependent autocrine human tumor T cell line IARC 301. When given alone, this antibody did not inhibit IL2 binding, internalization, or IL2-dependent cell proliferation. However, crosslinking by anti-rat immunoglobulins, which did not affect binding of the growth factor, inhibited both IL2 internalization and cell proliferation. Besides offering a novel means for the specific inhibition of the uptake of IL2 bound to IL2 high-affinity receptors, the results are compatible with the association of this receptor-ligand uptake to the growth stimulation by IL2.     

Resistance to DNA denaturation in irradiated Chinese hamster V79 fibroblasts is linked to cell shape

Exponentially growing Chinese hamster V79-171b lung fibroblasts seeded at high density on plastic (approximately 7 x 10(3) cells/cm2) flatten, elongate, and produce significant amounts of extracellular fibronectin. When lysed in weak alkali/high salt, the rate of DNA denaturation following exposure to ionizing radiation is exponential. Conversely, cells plated at low density (approximately 7 x 10(2) cells/cm2) on plastic are more rounded 24 h later, produce little extracellular fibronectin, and display unusual DNA denaturation kinetics after X-irradiation. DNA in these cells resists denaturation, as though "constraints" to DNA unwinding have developed. Cell doubling time and distribution of cells in the growth cycle are identical for both high and low density cultures as is cell survival in response to radiation damage. The connection between DNA conformation and cell shape was examined further in low density cultures grown in conditioned medium. Under these conditions, cells at low density were able to elongate, and DNA denaturation of low density cultures was identical to that of high density cultures. Conversely, cytochalasin D, which interferes with actin polymerization causing cells to "round up" and release fibronectin, allowed development of constraints in high density cultures. These results suggest that DNA conformation is sensitive to changes in cell shape which result when cells are grown in different environments. However, these changes in DNA conformation detected by the DNA unwinding assay do not appear to play a direct role in radiation-induced cell killing.     

Spectroscopic evidence for the uneven distribution of adenine and uracil residues in ribosomal ribonucleic acid of Drosophila melanogaster and of Plasmodium knowlesi and its possible evolutionary significance.

RNA was isolated from subribosomal particles of the malaria parasite Plasmodium knowlesi. The nucleotide composition (mole fraction) of the principal species was obtained (S-rRNA, 0.295A, 0.36U, 0.25G, 0.105C: L-rRNA, 0.326A, 0.31U, 0.228G, 0.144C). Ribosomal RNA was also isolated from Drosophila melanogaster. Optical properties of these A + U-rich species were measured. In all four cases analysis of the hypochromic effect revealed that adenine and uracil residues tended to form clusters along the polynucleotide chain. A substantial fraction of residues was located in bihelical regions of approx. 50% G-C base pairs or in regions of approx. 30-35% G-C base pairs. The possible evolutionary significance of these results was considered on the basis of comparison with properties of rRNA from bacteria (Escherichia coli) and a mammal (rabbit reticulocyte).     

Biosafety considerations of RNAi-mediated virus resistance in fruit-tree cultivars and in rootstock

A major application of RNA interference (RNAi) is envisaged for the production of virus-resistant transgenic plants. For fruit trees, this remains the most, if not the only, viable option for the control of plant viral disease outbreaks in cultivated orchards, due to the difficulties associated with the use of traditional and conventional disease-control measures. The use of RNAi might provide an additional benefit for woody crops if silenced rootstock can efficiently transmit the silencing signal to non-transformed scions, as has already been demonstrated in herbaceous plants. This would provide a great opportunity to produce non-transgenic fruit from transgenic rootstock. In this review, we scrutinise some of the concerns that might arise with the use of RNAi for engineering virus-resistant plants, and we speculate that this virus resistance has fewer biosafety concerns. This is mainly because RNAi-eliciting constructs only express small RNA molecules rather than proteins, and because this technology can be applied using plant rootstock that can confer virus resistance to the scion, leaving the scion untransformed. We discuss the main biosafety concerns related to the release of new types of virus-resistant plants and the risk assessment approaches in the application of existing regulatory systems (in particular, those of the European Union, the USA, and Canada) for the evaluation and approval of RNAi-mediated virus-resistant plants, either as transgenic varieties or as plant virus resistance induced by transgenic rootstock.     

Microsatellite Analysis of Oil Palms and their Progenies Bred in Papua New Guinea

Our aim was to assess parental and population genetic variability in a partially nested set of breeding populations from the breeding program at Dami Research Station (West New Britain, PNG). Twenty microsatellite markers were tested for their ability to characterize genetic variation in oil palm populations bred at Dami Research Station. One hundred and twenty six individuals, including 100 F₁ tenera hybrids of Dami Deli crossed with either AVROS, Ghana or AVROS/Ghana breeding lines were analysed. Eighteen of these markers were polymorphic within and among populations, amplifying 103 alleles in oil palm. Three individuals of other palm species (Cocos nucifera and two Phoenix spp.) were included as outliers. With these markers we have the power to distinguish individual palms, hence we conclude that they will facilitate association of markers with important phenotypic traits to streamline future breeding and selection.     

Mechanism of Action of Secreted Newt Anterior Gradient Protein

Anterior gradient (AG) proteins have a thioredoxin fold and are targeted to the secretory pathway where they may act in the ER, as well as after secretion into the extracellular space. A newt member of the family (nAG) was previously identified as interacting with the GPI-anchored salamander-specific three-finger protein called Prod1. Expression of nAG has been implicated in the nerve dependence of limb regeneration in salamanders, and nAG acted as a growth factor for cultured newt limb blastemal (progenitor) cells, but the mechanism of action was not understood. Here we show that addition of a peptide antibody to Prod1 specifically inhibit the proliferation of blastema cells, suggesting that Prod1 acts as a cell surface receptor for secreted nAG, leading to S phase entry. Mutation of the single cysteine residue in the canonical active site of nAG to alanine or serine leads to protein degradation, but addition of residues at the C terminus stabilises the secreted protein. The mutation of the cysteine residue led to no detectable activity on S phase entry in cultured newt limb blastemal cells. In addition, our phylogenetic analyses have identified a new Caudata AG protein called AG4. A comparison of the AG proteins in a cell culture assay indicates that nAG secretion is significantly higher than AGR2 or AG4, suggesting that this property may vary in different members of the family.     

CD45 Isoform Profile Identifies Natural Killer (NK) Subsets with Differential Activity

The leucocyte-specific phosphatase CD45 is present in two main isoforms: the large CD45RA and the short CD45RO. We have recently shown that distinctive expression of these isoforms distinguishes natural killer (NK) populations. For example, co-expression of both isoforms identifies in vivo the anti tumor NK cells in hematological cancer patients. Here we show that low CD45 expression associates with less mature, CD56^bright, NK cells. Most NK cells in healthy human donors are CD45RA⁺CD45RO^-. The CD45RA^-RO⁺ phenotype, CD45RO cells, is extremely uncommon in B or NK cells, in contrast to T cells. However, healthy donors possess CD45RA^dimRO^- (CD45RA^dim cells), which show immature markers and are largely expanded in hematopoietic stem cell transplant patients. Blood borne cancer patients also have more CD45RA^dim cells that carry several features of immature NK cells. However, and in opposition to their association to NK cell progenitors, they do not proliferate and show low expression of the transferrin receptor protein 1/CD71, suggesting low metabolic activity. Moreover, CD45RA^dim cells properly respond to in vitro encounter with target cells by degranulating or gaining CD69 expression. In summary, they are quiescent NK cells, with low metabolic status that can, however, respond after encounter with target cells.