Transcriptional activation and stabilization of malic enzyme mRNA precursor by thyroid hormone

One of the responses to the administration of thyroid hormone is an increase in malic enzyme (EC 1.1.1.40) mRNA in rat liver. We have previously shown that 3,5,3'-triiodo-L-thyronine (T3) causes a 3-4-fold increase in the rate of transcription of the malic enzyme gene as determined by in vitro run-off assays with the cDNA probe following T3 treatment for 10 days (Dozin, B., Magnuson, M.A., and Nikodem, V. M. (1986) J. Biol. Chem. 261, 10290-10292). Since the level of cytoplasmic mRNA increases 10-15-fold, one or more additional mechanisms must be operative to produce the full effect. We have now analyzed the time course of the effect of T3 on the rate of transcription and the accumulation of malic enzyme RNA in the nucleus using malic enzyme cDNAs and intronic probes. There is an approximately 10-12-fold increase in the level of nuclear RNA accompanied by the same increase in cytoplasmic mRNA, showing a half-rise time of about 60 h. The 3-4-fold increase in the transcription rate occurred with a half-time of about 18 h. The relative values for either the increase in transcriptional activity or the increase in the level of malic enzyme RNA in the nucleus were identical irrespective of the probes used. As a control, we examined the effect of a high carbohydrate diet which is known to increase malic enzyme mRNA without affecting either transcriptional rate or nuclear RNA (Dozin, B., Rall, J. E., and Nikodem, V. M. (1986) Proc. Natl. Acad. Sci. U.S.A. 83, 4705-4709). As expected, no change in the level of malic enzyme RNA in the nucleus was found with the intronic probes. We conclude that T3 both activates transcription of the malic enzyme gene in rat liver and decreases the rate of degradation of pre-mRNA coding for malic enzyme.

Specific role of manganese and magnesium on RNA synthesis in rabbit bone marrow erythroid cell nuclei

Specific roles of manganese (Mn) and magnesium (Mg) on the activities of DNA-dependent RNA polymerases I and II isolated from rabbit bone marrow erythroid cell nuclei were investigated. Three main polymerases were separated from the cell nuclei. When RNA polymerase I and Mg were added to the RNA synthesis assay mixture containing erythroid cell DNA as template, RNA transcription activity was highest, but when Mg was replaced with Mn, denatured calf thymus DNA formed a better template than erythroid cell DNA. In contrast, nucleoplasmic DNA from erythroid cell and liver DNA were the best templates to stimulate RNA transcription when RNA polymerase II and Mn were added to the assay mixture. However, if Mn was replaced with Mg, RNA synthesis activity was drastically reduced when the template was nucleoplasmic DNA of erythroid cell. RNA polymerase I and Mg synthesized GC rich RNA, whereas RNA polymerase II and Mn synthesized AU rich RNA. Sedimentation analysis showed that the molecular weights of the RNA produced by polymerase I were larger when the enzyme was activated with Mg than with Mn, whereas those of the RNA produced by polymerase II were larger with Mn than with Mg. Furthermore, RNA produced by polymerase I and Mg using chromatin as a template hybridized better with nucleolar DNA than with nucleoplasmic DNA, whereas that produced by polymerase II and Mn hybridized better with nucleoplasmic DNA than with nucleolar DNA. These results suggest that RNA synthesis is dependent on the activity of specific RNA polymerases and the presence of specific divalent cations and templates, and that the cofactor and template for RNA polymerase I are, respectively, Mg and the nucleolar DNA of cell nuclei, whereas those for RNA polymerase II are Mn and nucleoplasmic DNA.

Influence of prostaglandins on unidirectional zinc fluxes across the small intestine of the rat

1. The regulatory role of prostaglandins (PGs) E2 and F2 alpha on the zinc transport rate across the jejunal segments of rats was examined by employing the Ussing chamber technique. The Zn flux rate from mucosa to serosa across jejunal segments (Jms) was 5.24 (SE 1.54) nmol/h per cm2 (n 48) and that from serosa to mucosa (Jsm) was 15.16 (SE 2.38) nmol/h per cm2 (n 48) when both sides of the segment were bathed with Ringer's bicarbonate solution containing 0.5 mM-zinc chloride and 3 mM-L-histidine. 2. When 5.0 or 50 microM of either PGE2 or PGF2 alpha were added to the serosal side of the tissue, Jsm generally decreased and Jms generally increased, compared with controls. On the other hand, when PGE2 or PGF2 alpha was added to the mucosal side of the tissue, Jms either did not change or increased while Jsm had a tendency to decrease. 3. The Zn uptake capacity of tissue increased significantly when PG was added to the serosal side of the tissue-bathing medium, but not when PG was added to the mucosal side. The uptake capacity of mucosal Zn by jejunal segments was approximately twice that of serosal Zn. 4. When PG was included in the tissue-bathing medium, the short-circuit current, potential difference and conductance between the mucosa- and serosa-bathing media generally decreased. 5. These results suggest that (a) PGs influence Zn flux rate not by chelating Zn and carrying it across the mucosal cell membrane but by interacting with the cytosolic components, (b) it is the serosal PGs which control the Zn flux rate and (c) PGs play a part in triggering a transduction mechanism in the intestinal Zn transport process.

Intestinal zinc transport: influence of streptozotocin-induced diabetes, insulin and arachidonic acid

The influence of arachidonic acid (AA) on the zinc flux rates of jejunal segments, isolated from streptozotocin-induced diabetic rats injected with saline or with insulin, was investigated using an Ussing chamber technique. Although the zinc flux rates from mucosa-to-serosa (Jms) of normal rats were inhibited by addition of 5 microM AA to the jejunal segment bathing medium (46.4 +/- 5.0 vs 32.6 +/- 4.3 nmol/hr/cm2), AA had no effect on the Jms of diabetic rats either with or without insulin treatment. Induction of diabetes also significantly reduced Jms (46.4 +/- 5.0 vs 22.1 +/- 4.9 nmol/hr/cm2), but 3 day insulin treatment (NPH 8 U/Kg/day subcutaneously) did not reverse this effect (29.2 +/- 5.1 nmol/hr/cm2). Addition of AA to the serosal side did not significantly alter the zinc flux rate from serosa-to-mucosa (Jsm) in either control, diabetic or diabetic rats treated with insulin. The net zinc absorption rate (Jnet) of jejunal segments was decreased in diabetic rats compared to controls (13.2 +/- 3.0 vs -0.7 +/- 2.1 nmol/hr/cm2), but normalization of blood glucose with 3 day insulin treatment did not increase Jnet. Addition of AA was associated with a tendency to increase zinc uptake capacity. This change reached statistical significance in insulin treated diabetic rats. Short-circuit current (Isc) for diabetic rats was increased compared to controls but addition of AA to the mucosal side bathing medium decreased Isc in all groups. The results indicate that the zinc flux rate in the small intestine of streptozotocin-induced diabetic rats is decreased, that zinc uptake capacity of the small intestine does not directly reflect the zinc flux rate across the small intestine, and that AA or one of its metabolites may play a significant role in the control of the zinc flux across the intestinal epithelium.

Characterization of the low mol. wt zinc-binding ligand from rat small intestine by comparison to the organic zinc-binding ligands

1. 65Zn complexes of picolinate (PA), citrate (CA), L-histidine (L-his), arachidonic acid (AA) or low mol. wt zinc-binding ligand from rat intestine (LMW-ZBL) gave 65Zn eluting peak fraction numbers of 53, 53, 56, 59 and 59 respectively, in a Sephadex G-75 column chromatography. 2. The 65Zn eluting peak fraction numbers with CA, L-his, PA, prostaglandin (PG)E2, AA, no ligand, arachidonate (AT) or LMW-ZBL were 49, 50, 54, 55, 58, 64, 75 and 76 respectively in a Sephadex G-25 column chromatography. 3. In a Sephadex G-15 column chromatography, the 65Zn eluting peak fraction numbers with CA, PGE2, AA, L-his, LMW-ZBL or PA were 49, 50, 51, 52, 52 and 55 respectively. 4. The LMW-ZBL in rat small intestine appears to be an AA-like substance.

The intestinal zinc transport in aged rats

To determine if there are any age-related alterations in the intestinal zinc absorption that may contribute to zinc deficiency, we studied the zinc transport across the jejunal segments of 3-, 12- and 24-month-old Fisher 344 male rats using the Ussing chamber technique. We also evaluated the effect of 5 microM arachidonic acid in tissue bathing media. The zinc transport from mucosa to serosa in 24-month-old rats (55.0 +/- 3.5 nmol/h/cm2) was significantly greater than the transport in 12-month-old (30.1 +/- 6.3 nmol/h/cm2) and 3-month-old rats (41.0 +/- 5.2 nmol/h/cm2). There was no age-dependent differences in the zinc transport from the serosa to the mucosa. The addition of 5 microM arachidonic acid to the serosal side only resulted in a significant decrease in zinc transport rate from serosa to mucosa. The magnitude of change in the 24-month-old rats (36.0 +/- 3.9 vs. 26.5 +/- 3.2 nmol/h/cm2) was similar to the change seen in 12-month-old rats (34.5 +/- 4.6 vs. 20.1 +/- 3.5 nmol/h/cm2) and 3-month-old rats (34.5 +/- 4.6 vs. 26.1 +/- 3.9 nmol/h/cm2). The results indicate that intestinal zinc transport is increased in the aged rats, and that arachidonic acid or one of its metabolites may be important regulators of net zinc absorption through their effect on intestinal zinc secretion rates.

Elevated serum chymotrypsin levels in a patient with junctional epidermolysis bullosa. Normalization after UVB therapy with good clinical response

A 36-year-old Hispanic woman, covered with blisters since birth, was found to have markedly elevated chymotrypsin levels in her serum. This proteolytic enzyme is thought to digest laminin, thus causing separation of the basement membrane at the level of the lamina lucida, corroborating findings on electron microscopy. On the basis that the sun-exposed areas of the skin were relatively less involved, she received a course of UVB therapy, with total clinical clearance of her lesions after 3 weeks. A repeat estimation of serum chymotrypsin at this time revealed normal levels of this enzyme. It is thought that the elevated chymotrypsin levels were either released from the Langerhans cells themselves or from lymphocytes or keratinocytes as a result of Langerhans cell activity, and that the suppression of Langerhans cell activity by UVB inhibited the release of this proteolytic enzyme, resulting in the suppression of blister formation in our patient.

Low-molecular-weight zinc-binding ligand: a regulatory modulator for intestinal zinc transport

1. In the last two decades, vast numbers of studies on the zinc nutriture of animals and man have been made. However, the biochemical and physiological events in controlling zinc nutrition are still poorly understood. This report concerns the progress made toward understanding the intestinal zinc absorption and secretion mechanisms. 2. Evidence is accumulating that zinc absorption is a facilitated diffusion while zinc secretion is an active transport. 3. It is known that a low molecular weight zinc-binding ligand (LMW-ZBL) is a key regulator of intestinal zinc absorption, possibly a carrier molecule across the intestinal mucosal cells. Some high molecular weight zinc-binding ligands also appear to be involved in regulating intestinal zinc transport. 4. The identity of the LMW-ZBL is a matter of controversy and its specific role in regulating intestinal zinc transport is not well defined. 5. According to the available literature, no systemic investigations have been made to elucidate the intestinal zinc transport mechanisms, and much more information is needed to fully understand them.

Levels and distribution of zinc, copper, magnesium, and calcium in rats fed different levels of dietary zinc

Effects of altered dietary zinc on levels of zinc, copper, magnesium, and calcium in organ and peripheral tissues were studied. When rats fed a zinc-deficient diet (1.3 μg Zn/g) for 28 d were compared with rats fed a control diet (37.5 μg Zn/g), levels of zinc were slightly lower in plasma, hair, and skin and 50% lower in femur and pancreas, whereas the levels of copper were higher in all tissue except plasma. Magnesium levels were higher than controls in the heart and lower in the spleen, whereas the calcium levels were lower in plasma, lung, spleen, kidney, and skin and strikingly higher in brain, hair, and femur. When rats fed a zinc-supplemented diet (1.0 mg Zn/g) were compared to the same conrols, levels of zinc in these were higher in all organs and peripheral tissues studied, except heart, lung, and liver; copper levels were higher in liver, kidney, and spleen; magnesium levels were significantly higher in the spleen, but were little affected in other tissues, although calcium levels were higher in pancreas, spleen, kidney, and skin and lower in plasma and hair. These data indicate that overall copper organ and peripheral tissue levels are affected inversely, and zinc and calcium levels directly, by zinc nutriture.

Differential effects of transforming growth factor-beta on proliferation of normal and malignant rat liver epithelial cells in culture

Transforming growth factors (TGF-betas) have been shown to cause both stimulatory and inhibitory effects on cellular growth in a variety of normal and neoplastic cells. The nature of the inhibitory effects of TGF-beta on proliferation of different cell types is at present unclear. We have used freshly isolated rat hepatocytes, a normal diploid rat liver epithelial cell line (NRLM), and a subline (AFB) derived from it which was transformed in vitro by aflatoxin B1 to study the nature of TGF-beta-induced growth inhibition and its alteration following chemically induced neoplastic transformation. TGF-beta had a vastly different effect on proliferation of normal rat liver epithelial cells (both freshly isolated and NRLM cells) compared to aflatoxin B1-transformed cells. TGF-beta at 20 pg/ml caused 83% inhibition of colony formation of NRLM, whereas the growth of AFB cells was unaffected by TGF-beta at concentrations as high as 10 ng/ml. A parallel dose-dependent inhibition of DNA synthesis by TGF-beta was observed in both primary hepatocytes and NRLM cells at concentrations between 10 pg and 10 ng/ml. No inhibition of DNA synthesis was observed in AFB cells. Furthermore, TGF-beta did neither induce anchorage-independent growth of NRLM cells nor affect the growth of AFB cells in soft agar. TGF-beta-induced inhibition of the NRLM cells was irreversible in nature, since treated cells were unable to proliferate and form colonies upon removal of TGF-beta from the medium. Also, NRLM cells showed, after 4 days in the presence of 20 pg of TGF-beta per ml morphological changes characterized by cytoplasmic hypertrophy and the formation of abundant liposomal derivatives, some of which resemble lipofuscin. The finding that TGF-beta caused a high degree of irreversible inhibition of NRLM cells emphasizes the need for caution in interpreting data from inhibition studies, since most assays presently used are designed for assessing growth stimulation in vitro and do not adequately distinguish between the possible cytotoxic and/or cytostatic action of growth inhibitors.

Relative zinc-binding activities of ligands in the cytosol of rat small intestine

Relative zinc-binding activities of high-molecular-weight zinc-binding ligand (HMW-ZBL), metallothionein (MT) and low-molecular-weight zinc-binding ligand (LMW-ZBL) in the cytosols of rat small intestines under various experimental conditions were examined. Zinc-binding activities of MT decreased and those of LMW-ZBL increased in the intestinal cytosols from most of the experimental rat groups after incubating at 37 degrees C for 2 hr. The relative zinc-binding activity of MT increased with increasing doses of injected zinc and decreased with orally-administered zinc. Isolated MT did not lose zinc-binding activity during incubation at 37 degrees C for 48 hr, but moved from the MT eluting peak to the LMW-ZBL eluting peak after 1 week.

Measurement of cell proliferation in microculture using Hoechst 33342 for the rapid semiautomated microfluorimetric determination of chromatin DNA

We report the development and characterization of a semiautomated method for measurement of cell proliferation in microculture using Hoechst 33342, a non-toxic specific vital stain for DNA. In this assay, fluorescence resulting from interaction of cell chromatin DNA with Hoechst 33342 dye was measured by an instrument that automatically reads the fluorescence of each well of a 96-well microtiter plate within 1 min. Each cell line examined was shown to require different Hoechst 33342 concentrations and time of incubation with the dye to attain optimum fluorescence in the assay. In all cell lines, cell chromatin-enhanced Hoechst 33342 fluorescence was shown to be a linear function of the number of cells or cell nuclei per well when optimum assay conditions were employed. Because of this linear relation, equivalent cell doubling times were calculated from growth curves based on changes in cell counts or changes in Hoechst/DNA fluorescence and the fluorimetric assay was shown to be useful for the direct assay of the influence of growth factors on cell proliferation. The fluorimetric assay also provided a means for normalizing the incorporation of tritiated thymidine ( [3H] TdR) into DNA; normalized values of DPM per fluorescence unit closely paralleled values of percent 3H-labelled nuclei when DNA synthesis was studied as a function of the concentration of rat serum in the medium. In summary, the chromatin-enhanced Hoechst 33342 fluorimetric assay provides a rapid, simple, and reproducible means for estimating cell proliferation by direct measurement of changes in cell fluorescence or by measurement of changes in the normalized incorporation of thymidine into DNA.

Relationship between zinc and prostaglandin metabolisms in plasma and small intestine of rats

The effect of zinc nutriture on levels of prostaglandin (PG) E2, F2 alpha and 6-keto-PGF1 alpha in the plasma and small intestine of rats, and that of PGE2 and PGF2 alpha on unidirectional uptake of 65Zn by everted gut sac of rats was determined. When zinc was given intraperitoneally, plasma PGE2 and intestinal PGF2 alpha levels increased, while the intestinal PGE2 and the plasma PGF2 alpha and 6-keto-PGF1 alpha levels decreased in accordance with the amount of zinc given. Oral administration of excess zinc increased intestinal PGE2, PGF2 alpha and 6-keto-PGF1 alpha levels and the plasma 6-keto-PGF1 alpha levels. The intestinal levels of PGE2 increased significantly only in rats on zinc excess diet, and of PGF2 alpha only in rats on a zinc deficient diet. The plasma PGE2 levels in rats on both zinc deficient and zinc excess diets increased but PGF2 alpha levels in zinc deficient rats were greatly reduced compared to controls. Unidirectional zinc uptake by everted gut sac of the rat is also enhanced by PG metabolites. These results are consistent with the view that PGs participate in regulating the zinc transport mechanism in small intestine.

ADP-ribosylation of metaphase and interphase nonhistones using [3H]adenosine as a radioactive label

ADP-ribosylation of HeLa nonhistone proteins was investigated by using [3H]adenosine as an in vivo radioactive label. The aim was to determine basic differences in the patterns of modification of interphase and metaphase nonhistones. Fluorography revealed a relatively small number of modified proteins for isolated metaphase chromosomes. In addition to the core histones, a protein of 116 kDa, which is identified as poly-(ADP-ribose) polymerase, was a primary acceptor of [3H]adenosine. Two-dimensional gels revealed a profound difference in the modification of metaphase and interphase nonhistones. For interphase nuclei, 3H label was distributed among a large number of nonhistone acceptors.

Effect of oral administration of arachidonic acid on prostaglandin and zinc metabolism in plasma and small intestine of the rat

The effect of different doses of arachidonic acid (AA) on the intestinal zinc transport rate and on the plasma and intestinal PGE2, PGF2 alpha and 6-keto-PGF1 alpha levels in rats were measured to determine whether the metabolism of AA is involved in the zinc transport mechanism. Twenty-four rats were divided into 4 groups of 6 rats. Each rat received either 1.0 ml of distilled water, 0.5 mg, 1.0 mg or 1.5 mg/ml of AA intraduodenally at 24 and 4 hours before sacrifice. One hour before sacrifice, each rat also received 10 micrograms of 65Zn intraduodenally. The zinc transport rate decreased in comparison to controls when 0.5 mg of AA was given to the rats, but increased when 1.0 mg or 1.5 mg of AA was given. The levels of PGE2, PGF2 alpha and 6-keto-PGF1 alpha (PGI2 metabolite) in the intestinal mucosa all decreased in proportion to the amount of AA given. However, in the plasma, only PGF2 alpha levels decreased while PGE2 and 6-keto-PGF1 alpha levels showed no change compared to controls. When rats were given 1.5 mg of AA without oral administration of 65Zn, plasma PGE2 levels increased while PGF2 alpha levels decreased. The results suggest that AA metabolism influences the zinc transport mechanism by modulating the relative levels of PGE2, PGF2 alpha and PGI2 in plasma and small intestine.

Variations in ADP-ribosylation of nuclear scaffold proteins during the HeLa cell cycle

Cell cycle variations in ADP-ribosylation of nuclear scaffold proteins were determined. Nuclei of synchronized cells were isolated and labeled with [32P]NAD before nuclear scaffolds were obtained by digestion of DNA with DNase I and extraction of proteins with 2M NaCl. Autoradiograms revealed the three groups of "lamins" and a species identified as poly (ADP-ribose) polymerase to be the primary ADP-ribosylated proteins. The patterns of modification of nuclear scaffold proteins displayed similar features through the cell cycle. Radioactivity in the lamins increased from 20% in early-S phase to 40% in G1 phase of the next cell cycle.

Decrease in ADP-ribosylation of HeLa non-histone proteins from interphase to metaphase

Variations for non-histones in the ADP-ribosylating activities of interphase and metaphase cells were investigated. 32P-Labeled nicotinamide adenine dinucleotide ([32P]NAD), the specific precursor for the modification, was used to radioactively label proteins. Permeabilized interphase and mitotic cells, as well as isolated nuclei and chromosomes, were incubated with the label. One-dimensional and two-dimensional gels of the proteins of total nuclei and chromatin labeled with [32P]NAD showed more than 100 modified species. Changing the labeling conditions resulted in generally similar patterns of modified proteins, though the overall levels of incorporation and the distributions of label among species were significantly affected. A less complex pattern was found for nuclear scaffolds. The major ADP-ribosylated proteins included the lamins and poly(ADP-ribose) polymerase. Inhibitors of ADP-ribosylation were effective in preventing the incorporation of label by most non-histones. Snake venom phosphodiesterase readily removed protein-bound 32P radioactivity. A fundamentally different distribution of label from that of interphase nuclei and chromatin was found for metaphase chromosome non-histones. Instead of 100 or more species, the only major acceptor of label was poly(ADP-ribose) polymerase. This profound change during mitosis may indicate a structural role for ADP-ribosylation of non-histone proteins.

Rapid determination of DNA synthesis in adherent cells grown in microtiter plates

A specific, rapid, and economical method for measuring the extent of DNA synthesis in adherent rat hepatoma H4-II-E cells grown in 96-well microtiter plates is described. The adherent cells were pulsed for 1 h with [methyl-3H]thymidine, released from the substratum by trypsinization, and collected on fiberglass filters with a MASH II cell harvester. The amount of radioactivity incorporated was directly proportional to the number of cells per well. Growth curves generated by measuring [methyl-3H]thymidine incorporation and counting the number of cells per well were identical. Experiments with inhibitors of DNA, protein, and RNA synthesis demonstrated that this method selectively measured DNA synthesis. In addition, [3H]thymidine uptake showed excellent correlation with autoradiographic assessment of DNA synthesis. This specific and sensitive method for determining DNA synthesis in microtiter cultures should facilitate studies of effects of various growth-controlling agents on epithelial, fibroblastic, and other cells which grow as adherent cells in culture.

Metabolism of zinc-binding ligands in rat small intestine

Studies were conducted to determine the effects of zinc deficiency and excess zinc intake on the relative(65)Zn-binding activities of metallothionein (MT) and low-molecular-weight zinc-binding ligand (LMW-ZBL) in vitro and in vivo. Zinc-binding ligands of small intestine from four groups, each of five rats (normal, zinc-deficient, excess zinc injected, and excess zinc given orally), were separated by column chromatography on Sephadex G-75. The ratio of(65)Zn binding activities of MT to LMW-ZBL (MT/LMW-ZBL) in zinc-deficient rats was decreased both in vitro and in vivo compared to the control. When excess zinc was administered orally,(65)Zn-binding activity of MT was low in vitro and substantially increased in vivo. However, when excess zinc was injected intraperitoneally,(65)Zn-binding activity of MT in vitro greatly increased, but(65)Zn-binding activities of both MT and LMW-ZBL were significantly reduced in vivo as compared to the control. Based onA 280 readings of isolated MT and densities of protein bands in disc gel electrophoresis, the(65)Zn-binding activity of MT in vitro appeared to be proportional to the MT content. Hence, these data indicate that oral administration of excess zinc decreases MT whereas intraperitoneal injection of excess zinc stimulates its synthesis. Zinc deficiency has little to no effect on the intestinal MT metabolism. These results suggest that MT may be important in zinc secretion but not involved in zinc absorption; while LMW-ZBL participates both in zinc absorption and secretion.

Effect of different levels of dietary zinc on longevity of BALB/c mice inoculated with plasmacytoma MOPC 104E

The effect of different levels of Zn intake on survival was studied in 6 groups of 4-week-old BALB/c mice inoculated with MOPC 104E tumor cells. The first 3 groups received either a Zn-deficient (0.5 microgram Zn/g), a Zn-supplemented (1 mg Zn/g), or a control diet (37.5 micrograms Zn/g) starting 11 days after tumor inoculation (T11). The remaining 3 groups received the same diets starting the day the tumor was implanted (T0). The mean survival of rats beginning the Zn-deficient diet at T11 was significantly increased compared with that of the control group. However, when the same diet was begun at T0, the mean survival of the Zn-deficient group was significantly reduced; for this group the results probably related to the combined adverse effects from prolonged Zn deficiency and to those effects of the tumor itself. Similarly, excess Zn intake significantly prolonged the mean survival when given at T11. However, excess Zn intake at T0 produced no significant effect on survival, probably because of the elevation of plasma Zn level following oral Zn intake that occurred before the establishment of the tumor or possibly because of the inability of the small intestine to absorb excess Zn at T11 when the tumor was fully developed.

A new low-molecular-weight calcium-binding ligand in rat small intestine

Three calcium-binding ligands in the cytosol of rat small intestine have been separated using Sephadex G-75 column chromatography. The estimated molecular weights of these ligands were 85,000, 10,000, and 800, respectively. The two high-molecular-weight ligands were found only in young rats, while the low-molecular-weight calcium-binding ligand was found in all age groups and appeared to be a calcium-bound prostaglandin metabolite. Oral administration of arachidonic acid increased and PGE2 decreased in vivo calcium absorption, while PGF2 administration showed no discernible effect on this parameter. These results suggest that the intestinal calcium transport mechanism may be modulated by prostaglandins and related metabolites.

ADP-ribosylation of nonhistone proteins during the HeLa cell cycle

ADP-ribosylation of nonhistone proteins during the HeLa cell cycle was investigated. Proteins were radiolabeled by incubating interphase nuclei and mitotic cells with the specific precursor, [32P]NAD. Autoradiograms of two-dimensional gels of total nuclear nonhistone proteins showed a large number of modified species (more than 140). A complex pattern was also found for interphase chromatin. Nuclear scaffolds showed a simpler pattern of four major groups of modified species, which appeared to be the lamins and poly(ADP-ribose) polymerase. The labeling pattern for nonhistones of metaphase chromosomes was fundamentally different than with interphase nuclei. Autoradiograms were dominated by the incorporation of label into poly(ADP-ribose) polymerase.

Phosphorylation of nonhistone proteins during the HeLa cell cycle. Relationship to DNA synthesis and mitotic chromosome condensation

Cell cycle variations in the phosphorylation of chromatin-associated nonhistones were determined. Cells were radiolabeled with [32P]orthophosphate and chromatin was obtained by mild digestion of nuclei with micrococcal nuclease. The experiments were performed in the presence of a substrate inhibitor of alkaline phosphatase, beta-glycerophosphate. The results show that, while similar molecular weight species of phosphorylated nonhistones are associated with interphase chromatin through the HeLa cell cycle, the incorporation (32P cpm/micrograms of protein) profiles of selected major phosphononhistones show substantial changes. The most prominent peaks of specific radioactivity occur in the DNA synthesis phase (S phase). The phosphorylation states of the proteins of isolated metaphase chromosomes were also determined. Nonhistone proteins of isolated metaphase chromosomes are strikingly dephosphorylated, especially in comparison to histone H1. The phosphorylation of the major phosphononhistone of chromatin, which has a molecular weight of 55,000, was further characterized by techniques that included one-dimensional peptide mapping in sodium dodecyl sulfate-polyacrylamide gels and nonequilibrium pH gradient slab gel electrophoresis. Phosphoproteins are also components of the nuclear scaffold, and cell cycle variations in these proteins were investigated. The primary phosphorylated species has a molecular weight of 119,000. As with chromatin-associated nonhistones, this nuclear scaffold protein shows substantial incorporation of 32P in S phase, and a high level of incorporation also occurs close to mitosis.

Relationship between the functional status of the reticuloendothelial system and the outcome of experimentally induced pancreatitis in young mice

Physiologically, the main function of alpha 2-macroglobulin is the binding of active endopeptidases rather than their inhibition. The interaction results in a conformational change in the alpha 2-macroglobulin that leads to its rapid elimination by the reticuloendothelial system. In this way, the reticuloendothelial system may help in the regulation of extracellular proteolytic activity resulting from the release of proteinases from injured pancreatic acinar cells in acute pancreatitis. To evaluate this concept, the effect of feeding a choline-deficient diet supplemented with 0.5% DL-ethionine was determined in 4 and 6-wk-old mice in which the reticuloendothelial system was normal, stimulated, or depressed. Stimulating the reticuloendothelial system in 4-wk-old mice significantly (a) decreased the mortality rate; (b) lessened the drop in the plasma content of both alpha 2-macroglobulin and alpha 1-antitrypsin; and (c) decreased the severity of pancreatitis noted microscopically. In contrast, reticuloendothelial suppression in this group of mice had no demonstrable effect. However, when similar studies were done in 6-wk-old mice, in which this diet induces a milder disease, reticuloendothelial suppression significantly increased the mortality rate as compared with normal mice, whereas reticuloendothelial stimulation significantly decreased it. The possible mechanism for the salutory effect of stimulating the reticuloendothelial system on the outcome of diet-induced pancreatitis in mice is discussed.

Effect of calcium and copper on zinc absorption in the rat

The effect of cupric and calcium ions on zinc absorption was examined in Sprague-Dawley rats. In in vivo studies test solutions containing 7.5 mM 65ZnCl2 alone or in combination with 500 mM of either CuSO4 or CaCl2 were administered intraduodenally to three groups of rats. 2 h later the animals were sacrificed and their organ 65Zn content was determined. The results of these studies revealed that excess cupric ions had no effect on the 65Zn content of rat internal organs, whereas excess calcium ions decreased organs 65Zn content to 40%. Similar results were obtained in in vitro studies using three sets of rat jejunal sacs each filled with one of the above test solutions and incubated in oxygenated Eagle's medium. To investigate the reason(s) for the observed decreased rate of zinc absorption in the presence of excess luminal calcium, we examined zinc transport in 6 sets of jejunal sacs using six test solutions, each containing 7.5 mM 65ZnCl2 with 0, 12.5, 25, 37.5, 50, or 62.5 mM CaCl2. These experiments showed that 65Zn transport from mucosa to serosa was decreased by 40% in the presence of 25.0 mM CaCl2 but lower calcium concentrations had no effect on zinc transport. Increasing the luminal calcium concentration from 25 to 62.5 mM did not cause a further significant decrease in the rate of zinc transport. These results strongly suggest that zinc absorption in the rat is mediated by a transcellular transport process different from that which mediates copper and calcium absorption. The fact that calcium has been shown to reduce passive cation movements via shunt pathways in the gallbladder mucosa suggests the possibility that calcium in high luminal concentration may depress zinc absorption by reducing the passive component of jejunal zinc absorption.

Hyper-alpha-2-macroglobulinemia in narcotic addicts

Significant increases of serum alpha-2-macroglobulin (alpha-2-M) were detected in narcotic addicts presenting at a methadone treatment center. The mean alpha-2-M level was 341 +/- 14 mg/dl compared with 231 +/- 8 mg/dl in normal persons (p less than 0.01). In a comparable group of alcoholics with laboratory evidence of hepatic dysfunction the mean alpha-2-M level was 208 +/- 10 mg/dl. Although the serum immunoglobulin M content was also substantially elevated in the narcotic-addict group, no correlation was obtained between the serum content of this protein and alpha-2-M. Similarly, no correlation between alpha-2-M level and serum zinc content was observed. When the values of the trypsin-binding activity of serum measured in 13 addicts, 15 alcoholics with laboratory evidence of hepatic dysfunction, and 16 normal subjects were plotted against the amount of alpha-2-M measured in the same subjects, a linear correlation was obtained between trypsin-binding activity and alpha-2-M. Thus, the significantly increased serum trypsin-binding activity observed in the addicts is that which might be expected if normal alpha-2-M is being accumulated in large amounts as a result of increased macroglobulin synthesis.

Alpha2-macroglobulin deficiency in a patient with Ehlers-Danlos syndrome

A new genetic defect, alpha2-macroglobulin deficiency, was found in a patient with Ehlers-Danlos syndrome (EDS). Other members of the family of five exhibiting this abnormality were the mother and one sister. All members, including the patient, had normal serum albumin and alpha1-antitrypsin levels. The deficiency, reported here for the first time, appears to be inherited by an autosomal co-dominant mode. Statistical evaluation of the dihybrid crosses for independent assortment between EDS and hypo-alpha2-macroglobulinemia showed a probability of 0.7 to 0.75. However, a possible link between EDS and hypo-alpha2-macroglobulinemia is suggested since the observed ratios of four siblings are exactly as expected, assuming that double gene defects are linked in the mother's genotype.

Role of prostaglandin E2 in zinc absorption in the rat

The supernatant of cytoplasmic extract of rat small intestine was mixed with 65Zn and subjected to Sephadex G-75 column chromatography. The activity of 65Zn was detected in four peaks with estimated 800, 10,000, 50,000-75,000 mol wt, and larger than 100,000 daltons. The zinc-binding ligand from the 800 mol wt peak was prostaglandin or prostaglandin-like as indicated by ultra-violet absorption spectrum, by absorption spectrum shift in alcoholic potassium hydroxide, by its effects on pulmonary vascular resistance, and by radioimmunoassay. Addition of prostaglandin E2 or prostaglandin extracted from rat small intestine with ethyl acetate into the lumen of intestinal sacs resulted in a two to threefold increase in the activity of 65Zn in the external medium after 15-20 min incubation. The absorption and tissue distribution of orally administered 65Zn were decreased by 60% in indomethacin-treated rats and increased 70% when ethyl acetate-extracted prostaglandin and radioactive zinc were given simultaneously. These data suggest that prostaglandin not only binds zinc, but also facilitates its transport across the intestinal mucosa.

Binding of zinc to alpha-2-macroglobulin and its role in enzyme binding activity

Physicochemical studies performed on alpha-2-macroglobulin were correlated with the biological activities of this protein. Equilibrium dialysis of the binding of 65Zn by alpha-2-macroglobulin at pH 7.9 showed heterogeneous binding which could be attributed to two classes of binding sites. The site of greatest affinity for zinc had an apparent stoichiometry (n1 in gatoms/mol of alpha-2-macroglobulin monomer) of 12 and an apparent association constant (K1) of 3.06.10(7). The second binding site had an n2 of 60 and K2 of 1.32.10(5). The trypsin binding activity of alpha-2-macroglobulin did not depend on the presence of zinc in this protein since all but traces of this metal could be removed by EDTA without loss of trypsin binding activity. Saturation of site 1 with zinc did not affect the trypsin binding activity of alpha-2-macroglobulin, but binding of the metal by site 2 progressively decreased the trypsin binding activity by causing an irreversable association of the alpha-2-macroglobulin molecules. Removal of excess zinc from alpha-2-macroglobulin did not restore its trypsin binding activity. Our results also indicate that the high zinc content of alpha-2-macroglobulin (320--770 microgram/g protein) reported in the literature is an artifact and that native alpha-2-macroglobulin contains approximately 150--180 microgram Zn/g protein.

A simple, highly sensitive colorimetric method for the determination of zinc in serum

A simple, reliable, highly sensitive method for the determination of zinc in biological fluids is described. Interfering trace metals are removed as insoluble iodides or hydroxides prior to complex formation of zinc with dithizone in a Tris-buffered trichloroacetate centrifugate. Absorbance of the chelate is read at 555 nm. The sensitivity of the new method is comparable to that of atomic absorption spectrophotometry, and the results of zinc determinations of 23 sera by the two procedures agree to within acceptable limits of experimental error.