Roles of iron in neoplasia

Research and clinical observations during the past six decades have shown that: 1. Iron promotes cancer cell growth; 2. Hosts attempt to withhold or withdraw iron from cancer cells; and 3. Iron is a factor in prevention and in therapy of neoplastic disease. Although normal and neoplastic cells have similar qualitative requirements for iron, the neoplastic cells have more flexibility in acquisition of the metal. Excessive iron levels in animals and humans are associated with enhanced neoplastic cell growth. In invaded hosts, cytokine-activated macrophages increase intracellular ferritin retention of the metal, scavenge iron in areas of tumor growth, and secrete reactive nitrogen intermediates to effect efflux of nonheme iron from tumor cells. Procedures associated with lowering host intake of excess iron can assist in prevention and in management of neoplastic disease. Chemical methods for prevention of iron assimilation by neoplastic cells are being developed in experimental and clinical protocols. The antineoplastic activity of a considerable variety of chemicals, as well as of radiation, is modulated by iron. The present article focuses on recent findings and suggests directions for further cancer-iron research.     

Physical analysis of murine albino deletions that disrupt liver-specific gene regulation or mesoderm development

Complementation analyses of radiation-induced deletion mutations involving the albino (c) locus in Chromosome (Chr) 7 of the mouse have identified several loci, in addition toc, that have important roles in development. The mesoderm-deficient (msd) and hepatocyte-specific developmental regulation-1 (hsdr-1) loci, which are proximal and tightly linked toc, are important in the formation of mesoderm and in the regulation of liver- and kidney-specific induction of various enzymes and proteins, respectively. Cloning deletion-breakpoint-fusion fragments caused by lethal albino deletions that genetically define the extents of themsd andhsdr-1 loci is one way of generating molecular probes for studying the gene(s) involved in these phenotypes. The distal breakpoints of five such deletions were positioned on a long-range (PFGE) map of 1.7 Mb of wild-type DNA surrounding thec, D7Was12, andEmv-23 loci. In addition, the distal breakpoints of two viable albino deletions, which remove part of the tyrosinase gene and extend distally, were localized in the vicinity of the lethal deletion breakpoints. Therefore, the viable deletions can be exploited to generate additional DNA probes that should facilitate the isolation of breakpoint clones from chromosomes carrying lethal deletions defininghsdr-1 andmsd.     

Effect of an extract of nereis virens on mammalian spermatozoa

Epididymal sperm of the mouse, rat, and guinea pig and ejaculated sperm of rabbits are cleaved at the head-tail junction by an extract of Nereis virens. Annelids are extracted with water and the extract is purified by ion exchange chromatography. Electron microscopy shows that the extract acts on the filaments connecting the capitulum of the tail with the basal plate lining the nuclear envelope. Following detachment, the basal plate remains with the head. The extract contains proteases as indicated by hydrolysis of tosyl arginine methyl ester (TAME), benzoyl arginine ethyl ester (BAEE), and Azocoll, a general protease substrate. The hydrolysis of TAME is inhibited by tosyl lysine chloromethyl ketone (TLCK), a trypsin inhibitor, but TLCK does not prevent head-tail separation by the Nereis extract. Similarly tosyl phenylalanine chloromethyl ketone (TPCK), a chymotrypsin inhibitor, and phosphoramidon and leucyltryptophan, both thermolysin and acrolysin inhibitors — singly or in combination — do not prevent hydrolysis of Azocoll. Head-tail separation activity of the extract was inhibited by dithiothreitol, which reduces disulfide bonds, and phenylmethyl sulfonyl fluoride, an inhibitor of serine proteases. These results indicate that the extract is a mixture of proteases, one being a serine protease similar to trypsin. Digestion of the connecting filaments with the pure proteases, trypsin and Staphylococcus aureus V8 protease, has yielded the following information on the proteins of the filaments. The accessibility of arginine and/or lysine peptide bonds to enzyme action is highest in rat sperm filaments, whereas those in the filaments of mouse, rabbit, and guinea pig sperm are less accessible than in the rat. Another possibility is that the total content of arginine and/or lysine varies between the species. The most dramatic difference is the enzymatic action on glutamyl peptide bonds of the filaments, the order being: mouse 〉 rat 〉 rabbit, with guinea pig sperm filaments completely resistant over the time course of the experiment.     

QUANTITATIVE DIFFERENCES BETWEEN BENTHIC ALGAL COMMUNITIES ALONG A DEPTH GRADIENT IN LAKE MICHIGAN1,2

This study analyzes the impact of conditions associated with depth upon benthic algal communities in Lake Michigan. Diatom abundance was greater at 9.1 and 14.6 m depths than 6.5, 22.6 and 27.4 m. Shallow (6.5 m), mid-depth (9.1 and 14.6 m) and deep (22.6 and 27.4 m) zones were distinguishable on the basis of community composition, structure and abundance. Dominance of benthic species, high diversity and low abundance in shallow communities probably resulted from substantial substrate disturbance by wave action in this productive zone. Dominance of benthic species, high diversity and high abundance characterized mid-depth communities where less wave disturbance enabled algal accumulation. Preponderance of living planktonic taxa, low diversity and low abundance delineated deep communities where planktonic algae accumulated and low light levels reduced growth of benthic species.     

Plant tumor reversal associated with the loss of foreign DNA

Summary Transformation of plant tissues into crown gall tumors has been associated with the transfer of a portion of a tumor-inducing plasmid (Ti-plasmid) into plant DNA. Various laboratories have regenerated normal-appearing plants from a number of crown gall tumors. This study investigates the fate of the foreign DNA in a series of tissues derived from various parts of a plant regenerated from the tumor BT-37 by Braun and his coworkers. It was found that all the foreign DNA sequences were lost from tissues that had lost all their tumorous traits; whereas the plasmid DNA sequences were still present in tissues that appeared normal but still exhibited tumorous traits when returned to tissue culture media. From these studies it would appear that the presence of the Ti-plasmid sequences in the plant DNA is required for the maintenance of the transformed state. Presented in the Symposium on Gene Transfer, Differentiation and Neoplasia in Plant and Animal Cells at the 30th Annual Meeting of the Tissue Culture Association, Seattle, Washington, June 10–14, 1979. This symposium was supported in part by Grant CA 26748 from the National Cancer Institute, DHEW, and Grant RD-67 from the American Cancer Society.     

Sensitive gas chromatographic assay for the quantitation of bretylium in plasma,urine and myocardial tissue

A sensitive analytical method has been developed for the quantitation of bretylium in plasma, urine and myocardial tissue. Bretylium and the internal standard, UM-360 (o-iodobenzyltrimethylammonium), are extracted and isolated as the iodide salts. Sodium benzenethiolate is added and the mixture heated to 100° for one hour. This results in the formation of 2-bromobenzyl phenyl thioether and 2-iodobenzyl phenyl thioether, which can be separated and quantitated by gas chromatography. Good reliability and reproducibility can be obtained using electron-capture detection with quantities of bretylium as small as 1 ng.     

Absence of a correlation between cyclic nucleotide fluctuations and cell cycle progression

The levels of cAMP and cGMP were determined throughout the mitotic cycle of two independent strains of the naturally synchronous slime mold, Physarum polycephalum. The normal range of values was approx. 0.5–2.5 pmoles cAMP/ mg protein and 0.01–0.08 pmoles cGMP/mg protein. In our standard laboratory strain, there was no systematic pattern to the variations in the values within the normal range and no unique time in the cycle when values significantly above normal were noted. In the other strain recently cultured from spherules, elevated levels of cGMP, but not cAMP, were observed in late G2 and in the S phase. The data suggest that elevated levels of these cyclic nucleotides are not required for normal progression of the Physarum mitotic cycle which is unperturbed by artificial synchronizing procedures.     

Transport of Ammonium and Methylammonium Ions by Azotobacter vinelandii

Ammonium and methylammonium are rapidly taken up by cultures of Azotobacter vinelandii respiring in the presence of succinate. The rate of methylamine uptake increased with external pH from 5.5 to 7.5 but increasing the pH further to 8.5 had little effect on activity, indicating that methylammonium cation rather than uncharged methylamine is the permeant species. The kinetics of methylammonium entry followed the Michaelis-Menten relationship, yielding a K_m of 25 μM and a V_max of 3.8 nmol/min per mg of cell protein. At saturating concentrations ammonium was taken up at rates 30-fold higher than those for methylammonium. Ammonium was a competitive inhibitor of methylammonium uptake and gave an inhibition constant of 1 μM. Ammonium derivatives were inhibitors of methylammonium entry in order of effectiveness: hydrazine > methylhydrazine > formamidine > guanidine > dimethylamine > ethylamine; amides and amino acids did not block uptake. Likewise, metal cations inhibited in the order Tl⁺ > Cs⁺ > Rb⁺, whereas Na⁺, K⁺, and Li⁺ produced no significant effect. Methylammonium uptake was blocked in cells exposed to an uncoupler, p-trifluorome-thoxycarbonyl cyanide-phenyl hydrazone or gramicidin D, but not with dicyclo-hexylcarbodiimide or arsenate. Valinomycin stimulated methylammonium entry into cells in a K⁺-free medium but prevented entry in the presence of 10 mM K⁺. Monensin and nigericin had little effect on transport. These results indicate that methylammonium and ammonium ions enter A. vinelandii electrogenically via a specific transporter.     

Unit Cell Hypothesis for Streptococcus faecalis

The mass doubling times of exponential-phase cultures of Streptococcus faecalis were varied from 30 to 110 min by omitting glutamine from a defined growth medium and providing different concentrations of glutamate (ranging from 300 to 14 μg/ml). After Formalin fixation, cells were dried by the critical point method, and carbon-platinum replicas were prepared. The surface area and volume of cell poles seen in these replicas were estimated by a computer-assisted, three-dimensional reconstruction technique. It was found that the amount of surface area and volume of poles seen in these replicas were independent of the growth rate of culture from which the samples were taken. These observations were consistent with the unit cell model hypothesis of Donachie and Begg, in which a small number of surface sites would produce a constant amount of new cell surface regardless of the mass doubling time of the culture. However, measurements of the thickness of the cell wall taken from thin sections of the same cells showed that the cell wall increased in thickness as a function of the increase in cellular peptidoglycan content which occurs when the growth rate of this organism is slowed down by a decrease in glutamate concentration. Thus, it would seem that although the size of polar shells made by S. faecalis is invariant with growth rate, the amount of wall precursors used to construct these shells is not.