Effect of consuming fiber from corn bran, soy hulls, or apple powder on glucose tolerance and plasma lipids in type II diabetes

The effects of consuming corn bran, soy hulls, or apple powder on glucose and lipid metabolism were investigated in two studies of persons with type II diabetes. Fiber sources, completely or partially added to bread, were incorporated into subjects' self-selected diets. Low fiber white bread served as a control. In study A, 10 subjects consumed 26 g fiber source daily; in study B, eight subjects consumed 52 g fiber source. Biochemical tests, including a 2-h postprandial glucose test using a low fiber formula meal, were scheduled after 2 and 4 wk of each dietary treatment. Soy hull consumption slightly improved some measures of glucose tolerance, with results varying between the studies. Consumption of 52 g corn bran decreased very low-density lipoprotein cholesterol, triglycerides, and glycosylated Hb, but subject tolerance was poor with the particle size used. Consumption of 52 g apple powder increased low-density lipoprotein and total cholesterol levels.

The effect of interactions between dietary egg white protein and zinc on body weight, bone growth and tissue trace metals in the 30-day-old rat

Nine groups of 30-day-old rats were fed different diets, which contained 8, 15 or 20% egg white (equivalent to 6.0, 11.3 and 15.0% protein, respectively) each at 3 levels of zinc (6, 12 and 18 ppm zinc) for 30 days. The rats consuming the 6.0% protein, regardless of zinc intake, gained less weight than the groups fed 11.3 or 15.0% protein. Plasma zinc was not influenced by dietary egg white protein content, whereas, plasma zinc levels were lower in the rats fed 6 ppm dietary zinc compared to those fed 12 or 18 ppm zinc. Of the liver trace metals measured, only iron appeared to be influenced by an egg white protein-zinc interaction. Increasing dietary egg white protein led to increased concentrations of liver zinc and magnesium. Dietary zinc levels had no effect on the concentration of these metals in the liver. Liver calcium and copper concentrations were not significantly influenced by either dietary zinc or egg white protein. Femur weights and lengths were lower in the rats fed 6.0% than in those fed 11.3 or 15.0% protein diet but were unaffected by dietary zinc. Femur width was related to dietary protein and zinc. Dietary protein and zinc were interrelated in their affect on femur zinc levels. Femur zinc concentrations increased with increasing dietary zinc levels. Also femur zinc levels decreased with increasing dietary protein content. Other femur metal (copper, iron and calcium) concentrations were higher in rats fed the low level versus the higher levels of protein, but were not influenced by dietary zinc. These results show that dietary zinc and egg white protein are interrelated with regard to their effect on body and femur growth and tissue trace metal content.

Folate status of adult males living in a metabolic unit: possible relationships with iron nutriture

Folate and iron status was monitored at monthly intervals in 40 adult males who were living in a metabolic unit for 2 to 8 months and consuming diets containing 150 to 250 micrograms of folate per day. There were significant (p less than 0.02) declines in hematocrit, serum folate, and serum ferritin. Men who participated in studies for 6 months or more or those with initial serum folate levels more than 10.5 ng/ml and erythrocyte folate levels more than 481 ng/ml also exhibited a highly significant (p less than 0.001) decline in red blood cell folate. Men with erythrocyte folate below 480 ng/ml or serum folate below 10 ng/ml and who participated in the studies for less than 5 months showed little or no change in folate status. The findings may reflect adjustments in body folate to reflect dietary intakes. Also a folate intake of 200 +/- 68 micrograms/day appeared to be adequate for maintenance of folate stores in adult males. A correlation between iron stores and folate status was also observed. However, this relationship may be coincidental.

Proliferative variability of endothelial clones derived from adult bovine aorta: influence of fibroblast growth factor and smooth muscle cell extracellular matrix

Four endothelial cell clones derived from adult bovine aorta were examined with respect to their proliferative characteristics in vitro. Three of these clones, derived in the absence of fibroblast growth factor (FGF), displayed variable basal proliferative rates. One of these non-FGF derived clones grew at a maximal rate which could not be further enhanced with FGF. The other two clones grew at a suboptimal rate which was stimulated by low doses of FGF (10-50 ng/ml) and inhibited by higher doses (100-250 ng/ml). The fourth clone, derived in the presence of FGF, was stimulated by FGF in a dose-dependent manner (10-250 ng/ml) and was not growth inhibited at high FGF concentrations (250-1,000 ng/ml). Growth of all four clones on extracellular matrix (ECM) derived from bovine aortic smooth muscle (BASM) cells was optimal in the absence of FGF. ECM-coated dishes also significantly increased the sensitivity of all clones by at least fivefold to mitogenic stimulation by serum. The proliferative lifespans of the clones ranged between 60 and 120 generations with the most actively proliferating clones attaining the greatest lifespan. Continuous subculture of two of the endothelial clones in the presence of FGF or on ECM-coated dishes did not induce a dependence of the cells on either factor for subsequent growth in its absence. The results indicate that aortic endothelial cells display considerable clonal variability in ther basal proliferative rate and in their response to FGF. This clonal variability is not observed when the cells are maintained on ECM-coated dishes derived from vascular smooth muscle cells.

Effect of a moderate increase in dietary protein on the retention and excretion of Ca, Cu, Fe, Mg, P, and Zn by adult males

Mineral utilization was studied by metabolic balance techniques in 10 healthy male volunteers fed diets containing 65 and 94 g protein. Both diets contained approximately 650 mg calcium, 1 mg copper, 16 mg iron, 250 mg magnesium 1000 mg phosphorus, and 7 mg zinc. The diet consisted of conventional foods; the additional 29 g protein was egg white protein mixed into a beverage and fed twice per day. Plasma mineral levels were not affected by the increase in dietary protein. When the diet provided 94 g of protein, urinary calcium and zinc were slightly, but significantly, increased by an average of 35 mg (p less than 0.05) and 0.15 mg (p less than 0.001), respectively. Apparent mineral absorption and balance were unchanged by this modest increase in dietary protein.

Altered adhesiveness of tumor cell surface variants with reduced metastasizing capacity--reduced adhesiveness to vascular wall components in culture

Heterotypic adhesiveness of surface variant clones of B-16 melanoma cells exhibiting different metastasizing capacity was studied with respect to components of the vascular wall in culture including endothelial (E) and smooth muscle (SM) cells from adult bovine aorta, and the extracellular matrices laid down by them. The ricin-resistant cells (ricinR) and the wheat-germ agglutinin-resistant (WGAR) cells, both of which showed reduced hematogenous metastases in vivo, showed reduced adhesiveness specifically to endothelial cells and extracellular matrices. This reduced heterotypic adhesiveness is in contrast to the homotypic adhesive properties in which respect the ricinR cells had similar values to the parental cells, while the WGAR cells had much higher values than the latter. There appeared to be a positive correlation between metastasizing capacity and specific adhesiveness to E cells and the extracellular matrix surfaces.

Glucocorticoid influence on growth of vascular wall cells in culture

Primary mass cultures and cloned strains of bovine aortic endothelial and smooth muscle cells were investigated with respect to their growth responses to glucocorticoid hormones. The growth of primary endothelial cells was not influenced by glucocorticoid treatment in the absence of fibroblast growth factor (FGF) but was inhibited by about 30% in the presence of FGF; with cloned endothelial cells, glucocorticoids were also growth inhibitory only in the presence of FGF. In contrast, smooth muscle cell growth was inhibited 30%-70% by glucocorticoid treatment in both primary cultures and in the cloned strains in the absence of FGF, and this inhibition was totally abolished by the addition of FGF for both cultures. The corticosteroid influences on cell growth were glucocorticoid specific, concentration dependent, and were observed to be independent of the serum concentration. The results indicate that glucocorticoid hormones have direct and pronounced growth inhibiting effects on aortic smooth muscle cells but only minimal effects on endothelial cells when these components of the vascular wall are analyzed under identical conditions in vitro.

Synthesis of growth hormone, prolactin, and proopiomelanocortin by intact adult ovine pituitary tissue in vitro

Synthesis of GH, PRL, and proopiomelanocortin (POMC) by the adult ovine pituitary was examined by culturing intact tissue explants in vitro and analyzing newly synthesized proteins by two-dimensional gel electrophoresis. Spots on autoradiographs of two-dimensional gels were identified by comigration with known standards, by analysis of tryptic peptides, or both. GH and PRL are the predominant proteins synthesized in the adult ovine pituitary, but their syntheses could not be detected in the neurointermediate lobe of the pituitary, the cerebral cortex, hypothalamus, mammillary body, or placenta. As quantified by cell-free translation in rabbit reticulocyte lysate, 14% of female ovine pituitary mRNA encodes pre-GH and 30% encodes pre-PRL. As determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, ovine pre-GH and pre-PRL have molecular weights of 24,500 and 26,000, respectively, indicating they contain leader peptides of 26-30 amino acids, as found in bovine, rat, and human pre-GH and pre-PRL. POMC, the precursor to corticotropin, endorphin, and other peptides, was synthesized primarily in the neurointermediate lobe of the pituitary, but synthesis was also detected in the anterior lobe. POMC synthesis was not detected in the hypothalamus, cerebral cortex, mammillary body, or placenta.

Synthesis and glycosylation of proopiomelanocortin by a Cushing tumor

ACTH derives from a larger protein, proopiomelanocortin (POMC), which is also the precursor to lipotropin, endorphin, melanotropin, and other peptides. The sequence of steps by which POMC is processed to ACTH has been delineated in detail in cultured mouse tumor cells, but little is known about these steps in human pituitary adenomas. Synthesis and glycosylation of POMC were studied in a pituitary adenoma causing Cushing disease and in adjacent tissue by incubating intact tissue explants in medium containing [35S]methionine or [3H]glucosamine. Labeled tissue was analyzed by two-dimensional gel electrophoresis, and a spot cut from these gels was analyzed by paper electrophoresis of tryptic digests. The location of the spot and the patterns of its [35S]methionine-labeled tryptic fragments resembled those found previously in other ACTH-secreting tissues and hence this spot appears to be POMC. Both the tumor and the adjacent pituitary produced this POMC, although tumor production of POMC was greater. The electrophoretic patterns of the putative POMC tryptic peptides labeled with [35S]methionine from this tumor are similar to the patterns of POMC tryptic peptides from a Nelson tumor and an ectopic ACTH- producing tumor when analyzed by the same techniques. This suggests that the excess ACTH in all three diseases arises from the same precursor POMC molecule. Two-dimensional gel electrophoresis of [3H]glucosamine-labeled tumor suggests that the first proteolytic cleavage occurs between the alpha ACTH-(1-39) and beta-lipotropin sequences and that a subsequent cleavage occurs between the N-terminal region of POMC and ACTH. Paper electrophoresis of [3H]glucosamine-labeled tryptic glycopeptides reveals at least three radioactive peaks, suggesting that the two known glycosylation sites in human POMC may be variably glycosylated.

Differential radiation response of cultured endothelial cells and smooth myocytes

In vivo observations have suggested that endothelial cells are the most radiosensitive elements of the vascular wall. To test whether this represents an intrinsic differential sensitivity, the response of bovine aortic endothelial cells and smooth myocytes was investigated in confluent cell cultures exposed to single doses of gamma radiation (250, 500, 1,000 or 2,000 rad). Both cell types showed a dose-dependent decrease in attachment efficiency when dissociated and replated at six hours after radiation. However, the attachment efficiency in both cell types was similar when a 72-hour postirradiation incubation period was used prior to dissociation of the cells. Growth inhibition was significantly greater (7- to 10-fold) in endothelial cells than in myocytes when examined four days after attachment. Confluent endothelial monolayers showed a dose-dependent, progressive cell loss during the 72-hour postirradiation period (70% after 1,000 rad); the myocyte cultures showed no radiation effect on the cell numbers. In spite of the reduction in number, the endothelial cells maintained the continuity of their monolayer by compensation with an increase in mean cell size. Endothelial cells developed multiple structural lesions, including an increase in the number and size of residual and lysosomal bodies, electron-lucent cytoplasmic defects, interruptions in the plasma membrane and irregular aggregation of chromatin, causing electron-lucent nuclei. These changes increased in severity with time and dose and were most pronounced 24 to 72 hours after 1,000 rad. No significant ultrastructural alterations were detected in myocytes four days after 2,000 rad.

Differential regulation by glucocorticoids of proopiomelanocortin mRNA levels in the anterior and intermediate lobes of the rat pituitary

Glucocorticoids negatively regulate de novo synthesis of proopiomelanocortin (POMC) and the steady state POMC mRNA levels in the rat pituitary anterior lobe. The POMC system of the intermediate lobe is far less sensitive to alterations in circulating glucocorticoid levels. Possible mechanisms for this differential regulation of POMC gene expression in the two tissues are discussed.

Senescence of aortic endothelial cells in vitro: influence of culture conditions and preliminary characterization of the senescent phenotype

The replicative lifespan of a cloned strain of adult bovine aortic endothelial cells has been examined by serial passage in culture using conditions where the cells were either dependent on fibroblast growth factor (FGF) for rapid growth or relatively independent on FGF for growth. In FGF-dependent cultures a replicative lifespan of 130 generations was attained with a phase III period which spanned approximately 20 generations. Withdrawal of FGF at generation 55 and repeated passage of such cultures in the absence of the growth factor resulted in the loss of proliferative potential within 15 generations. The morphological changes occurring upon FGF withdrawal were different than those that occurred when cultures senesced in the presence of FGF, FGF withdrawn cells showed a homogeneous increase in cell size and after several passages overgrew one another at confluency. Endothelial cells which senesced in the presence of FGF showed a very heterogeneous distribution of enlarged cells, many of which were binucleated but continued to form a confluent monolayer at high cell densities. Under FGF-independent conditions (begun at generation 48) a replicative lifespan of 105 generations was attained in the presence of the growth factor. FGF withdrawal under these conditions only decreased the replicative lifespan to 95 generations. Under these conditions the morphological changes occurring during phase III were identical in the presence and absence of FGF. Examination of the sensitivity of endothelial cells to FGF as they entered phase III showed that their dose-response characteristics were not qualitatively altered after the onset of phase III, although the number of cells responding to FGF progressively dropped. Comparison of the patterns of proteins synthesized in phase II and phase III cultures showed that phase III cultures even when plated at sparse densities continued to synthesize proteins which were normally observed in phase II confluent cultures. The results indicate that onset of the phase III period in aortic endothelial cells cloned and maintained in the presence of fibroblast growth factor can be delayed to a greated extent if the cells are maintained under conditions where they are made dependent on FGF for rapid growth in culture.

Dietary fiber and personality factors as determinants of stool output

We examined effects of fiber on stool output, since this is one of the primary mediating variables for the hypothesized relationship between fiber and disease. Total neutral detergent fiber in the dietary fiber source was predictive of stool weight but not frequency. Substantial individual differences in stool output remained when dietary factors were controlled. Personality measures were used to predict stool weight and frequency independently of diet, and accounted for about as much variance in stool output as did dietary fiber. These results suggest that personality factors predispose some persons to low stool output. These individuals may benefit particularly from dietary fiber.

Plasma zinc in hypertension/toxemia and other reproductive variables in adolescent pregnancy

A study was conducted at Charity Hospital, New Orleans, among 272 adolescent pregnant women to ascertain the relationship of pregnancy outcome to plasma zinc level measured once at the time of enrollment. Regression analyses were performed on zinc status versus parameters concerning success of pregnancy corrected for gestational stage at specimen collection. Analysis of variance was performed on groups according to presence or absence of complications, with analyses of covariance used to analyze dichotomous groups. Low, though widely variable, plasma zinc levels were found (mean = 58 +/- 12.6 micrograms/dl). Zinc values differed significantly by gestational stage at collection, the regression coefficient indicating a decline of 0.07 micrograms/dl/day. Plasma zinc level correlated significantly with Hb, red blood cells, ferritin, and folic acid. As to course of pregnancy, women experiencing hypertension/toxemia were found to have significantly lower plasma zinc level. Among infants displaying congenital defects at birth those with undescended testes and metatarsus varus were delivered by mothers whose plasma zinc was well below the mean for the group. These findings indicate the need to investigate the influence of dietary patterns and zinc intake on maternal plasma zinc level and pregnancy outcome, further delineating the role of zinc in human reproduction, particularly hypertension of pregnancy.

Accuracy of predictions of long-term energy needs

Energy needs as estimated by various methods were compared restrospectively with actual energy needs of eleven subjects who participated in long-term metabolic studies. Eight methods were compared with actual energy needs. The most satisfactory were the Harris and Benedict formula, the Kleiber formula, and the Mayo Foundation Nomogram, with an additional percentage allowed for activity energy. Interviewing methods were the least satisfactory for estimating energy needs. None of the methods was satisfactory for long-term use with individuals, indicating the necessity of follow-up and adjustment when energy intake is externally controlled.

Utility of serum ferritin as a measure of iron deficiency in normal males undergoing repetitive phlebotomy

Hematologic indices and iron balance data were obtained on 22 normal male volunteers who were subjected to a mean +/- SD phlebotomy of 164 +/- 34 ml whole blood/mo while living in a controlled environment. Over an average stay of 5 mo, volunteers did not develop anemia, but did display a reduction in iron stores that was quantitated by measurement of serum ferritin and iron balance. The percent saturation of transferrin and the usual erythrocyte parameters did not reflect changes in iron status. Loss of iron, which was calculated from quantitative phlebotomy and iron balance data, showed that a decrease of 1 ng of serum ferritin represented a loss of 4.5 +/- 5.3 mg of iron in 10 men whose initial serum ferritins were greater than 25 ng/ml, and 25.3 +/- 58.8 mg of iron in 7 men whose initial serum ferritins were less than 25 ng/ml. The period required for 3 volunteers who consumed a self-selected mixed diet at home to replace their depleted iron stores to prephlebotomy levels was about 4.5 mo. The sensitivity of serum ferritin as an index of iron stores was affirmed. In addition it was found that normal men who were consuming a mixed diet containing about 15 mg of iron daily and losing blood at a rate of 164 +/- 34 ml/mo did not increase their iron absorption sufficiently to compensate for the iron loss.

Nuclear accumulation of epidermal growth factor in cultured rat pituitary cells

Epidermal growth factor (EGF) is a mitogen for epidermal cells in vivo and for a wide variety of cells in culture. Recently, we and others have reported that EGF can also regulate the cellular levels of various hormones and fibronectin at concentrations which only minimally influence cell division. In addition, EGF treatment of GH3 cells affects chromatin structure such that isolated nuclei from treated cells have an increased capacity to bind bacterial RNA polymerase in initiation site complexes. Thus, the data suggest that various nuclear functions are modulated by EGF in GH3 cells despite its failure to affect DNA synthesis or cell proliferation. Recently, Yanker and Shooter have reported on the nuclear accumulation of nerve growth factor (NGF) in PC12 cells in which NGF does not promote cell division but does influence RNA and protein synthesis while inducing overt differentiation (neurite outgrowth). The similarities between the two systems and the various theories regarding the mechanism by which mitogens exert their growth-promoting and other effects led us to investigate whether an interaction between EGF and the cell nucleus can be demonstrated after surface binding and internalization of EGF in GH3 cells. We report here that when its lysosomal degradation is inhibited by chloroquine, EGF accumulates in the nucleus.

Processing of the precursor to corticotropin and beta-lipotropin in humans

The biosynthesis of human corticotropin (ACTH) was studied in organ culture of pituitary adenomas and by translating mRNA from an ectopic ACTH-producing tumor in a cell-free system. Peptides similar to human ACTH, beta-lipotropin, and the amino-terminal glycopeptide are cleaved from a common precursor with an apparent molecular weight of 35,000 on sodium dodecyl sulfate/polyacrylamide gels. The precursors synthesized in pituitary and ectopic ACTH-producing tissues are indistinguishable. The cleavage sites of the peptide chain appear to be similar to those previously deduced for murine and bovine ACTH. Immunoprecipitation studies suggest that the primary structure of the precursor peptide is similar in all three species. However, glycosylation is different in the human and murine precursors: the precursor to human ACTH appears to be glycosylated only in the amino-terminal fragment, not in the ACTH or beta-lipotropin sequences. Studies with an autopsied normal human pituitary suggest that neither normal nor adenomatous pituitary tissue glycosylates the ACTH sequence.

Early events after infection of Escherichia coli by bacteriophage T5. III. Inhibition of uracil-DNA glycosylase activity

The activity of uracil-DNA glycosylase in Escherichia coli decreases dramatically to less than 10% of its original level after infection of the cells by phage T5. Phage-induced protein synthesis is required for this inhibition to occur, and the inhibition is induced by a mutant capable of injecting only the first 8% of its DNA. The inhibitor activity in extracts of infected cells is heat labile and nondialyzable, and will inhibit enzyme activity present in extracts of uninfected cells.

Epidermal growth factor and expression of specific genes: effects on cultured rat pituitary cells are dissociable from the mitogenic response

Cultured rat pituitary tumor cells, GH3/D6, which synthesize both growth hormone and prolactin, have cell-surface epidermal growth factor (EGF) receptor sites (34,000 per cell) that bind 125I-labeled EGF with a high affinity (Kd approximately 1 nM). Prolonged treatment of the cells with EGF did not stimulate cell division but did inhibit thyroid hormone-stimulated cell growth. In addition, EGF altered the morphology of the cells from a rounded to an elongated conformation. EGF also induced a perturbation of chromatin structure in GH3 cell nuclei that was detected by an increase (40%) in the number of rifampicin-resistant initiation sites for bacterial RNA polymerase. This was accompanied by an increased synthesis of prolactin and an inhibition of synthesis of growth hormone. In the presence of EGF, the synthesis of growth hormone was no longer inducible by thyroid hormone, but it remained responsive to glucocorticoids. The results demonstrate that EGF can elicit major effects on the cellular phenotype and expression of specific genes in the absence of a proliferative response. This suggests that EGF can also regulate differentiated cellular functions.

Loss of hybridizable ribosomal DNA from human post-mitotic tissues during aging: I. Age-dependent loss in human myocardium

DNA obtained from 29 male humans at autopsy was hybridized in liquid phase with tritium-labelled 18 and 28S ribosomal RNA (rRNA) in order to determine whether a change in the dosage in rDNA, which codes for rRNA, occurs during human aging. The individuals ranged in age from 3 months to 76 years. It was found that the amount of rDNA hybridizable per 260 nm absorption unit by DNA decreases by about 0.5% per year with a regression coefficient of about -0.83. These findings confirm earlier ones from this laboratory and indicate either a loss of these key genes during aging of humans or decreased hybridizability due to some other factor or factors. In any event, this degree of loss or inactivation of genes involving an all protein synthesis would seem to impair function of post-mitotic cells in response to maximal stress to about the same degree that function is lost in various human organ systems during aging, as defined by Shock and others.

Vascular endothelial cells maintained in the absence of fibroblast growth factor undergo structural and functional alterations that are incompatible with their in vivo differentiated properties

Vascular endothelial cells cultured in the presence of fibroblast growth factor (FGF) adopt at confluence a morphological appearance similar to that of the vascular endothelium in vivo. Similarly, their apical cell surface is, as in vivo, nonthrombogenic. In contrast, when the cultures are maintained in the absence of FGF, the cells undergo within two to three passages structural and functional alterations that are incompatible with their in vivo morphological appearance and physiological function. Cultures maintained in the absence of FGF no longer adopt, upon reaching confluence, the configuration of a monolayer composed of small closely apposed and nonoverlapping, cuboidal cells. Instead, confluent cultures deprived of FGF consist of large, overlapping cells which have lost the polarity of cell surface characteristic of the vascular endothelium. The apical cell surface becomes thrombogenic, as reflected by its ability to bind platelets, whereas fibronectin, which at confluence is normally associated only with the basal cell surface, can be found both on top of and underneath the cell layer. Among other changes, both sparse and confluent cultures maintained in the absence of FGF showed a greatly increased production of fibronectin. CSP-60, a cell surface protein whose appearance is correlative with the adoption of a cell monolayer configuration, can no longer be detected in cultures maintained in the absence of FGF. Overlapping endothelial cells maintained in the absence of FGF can also no longer function as a protective barrier against the uptake of ligands such as low density lipoprotein. Exposure of the culture to FGF induces a restoration of the normal endothelial characteristics concomitant with the adoption of a flattened cell monolayer morphology. These results demonstrate that, in addition to being a mitogen. FGF is involved in controlling the differentiation and phenotypic expression of the vascular endothelium. This is reflected by its effect on the morphological appearance, polarity of cell surfaces, platelet binding capacity, and barrier function of the vascular endothelium.

Regulation of activity of chromatin receptors for thyroid hormone: possible involvement of histone-like proteins

Thyroid hormone receptors lose their capability for high-affinity binding of the biologically active triiodothyronine after solubilization and separation from other chromatin proteins. The high-affinity triiodothyronine-binding capacity can be reconstituted by addition of a histone-containing extract of chromatin of purified core histones (H2A, H2B, H3, and H4); a number of other acidic or basic proteins tested were ineffective. The data support a model of the receptor in which a "core" receptor subunit that contains a thyroid hormone-binding site interacts with a regulatory subunit, which is possibly a histone or histone-like species. This interaction with the "core" subunit enables the resulting "holo" receptor to bind biologically active hormones. These data also suggest that histones or related proteins can modulate the activity of nonhistone chromosomal proteins that are involved in regulating the expression of specific genes.

Inhibition of low density lipoprotein uptake in confluent endothelial cell monolayers correlates with a restricted surface receptor redistribution

Binding of either low density lipoprotein (LDL) or Concanavalin A (ConA) to actively growing vascular endothelial cells is associated with a redistrubution of the appropriate cell surface receptor sites which form patches and caps. This receptor lateral mobility is greatly restricted when endothelial cells reach confluence and adopt the configuration of a cell monolayer composed of closely apposed and non-overlapping cells. In this case, although the cells still exhibit specific LDL binding to the appropriate cell surface receptor sites, neither the binding of LDL nor of ConA induces a receptor redistribution. The lack of LDL receptor redistribution correlates with a marked decrease in the rate of LDL internalization. In contrast, no such density-dependent changes are observed in cell types which grow on top of each other and form multiple cell layers at confluence. Thus, neither LDL nor ConA induced cap formation in either sparse or confluent smooth muscle cell cultures and the same rate of LDL internalization is observed at both cell densities. Similarly, adsorptive endocytosis of cationized LDL (which enters the cells independently of the LDL receptor sites) was not correlated with a detectable receptor redistribution, nor was it significantly affected by changes in cell density and spatial organization. The formation of a confluent cell monolayer resting on an underlying basement membrane might therefore provide, via a change in membrane dynamics, a mechanism whereby the endothelium of large blood vessels can function as a protective barrier against the high circulating levels of LDL in plasma.

Stimulation and inhibition of cellular functions by glucocorticoids. Correlations with rapid influences on chromatin structure

The effect of media conditions on the glucocorticoid response has been examined in three types of cultured cells. In rat pituitary tumor cells (GC cells) growth hormone production was stimulated by glucocorticoids provided fresh culture media was present (enriched media conditions). In contrast, dexamethasone either failed to induce or deinduce growth hormone synthesis if added to cultures which had not received fresh media for 3 days (depleted media condition). With human skin fibroblasts, cortisol stimulated [3H]thymidine incorporation in the enriched condition but inhibited this response in the depleted condition. In mouse lymphoma (S49) cells the enriched media conditions significantly delayed the killing response to glucocorticoids (20% killing after 24 h versus 90% killing after 24 h for the depleted condition). Thus, the magnitude and in some cases, the direction of the glucocorticoid response are sensitive to the conditions to which the cells are exposed. In all three cell types the steroid also rapidly (detectable by 15 min, maximal by 2 h) altered chromatin structure as detected by a change in the number of initiation sites for Escherichia coli RNA polymerase assayed under cell-free conditions. This early nuclear response could be in a positive or negative direction and was also affected by the culture conditions; enriched media favored a positive or less negative effect on the initiation sites by the steroid, while depleted media favored a steroid-induced inhibition of this chromatin function. In S49 and GC cells the kinetics and magnitude of the change in chromatin closely followed receptor . glucocorticoid complex binding to nuclei while removal of dexamethasone from the culture media resulted in a rapid (t 1/2 = approximately 20 min) disappearance of the effect which paralleled loss of bound hormone from the nucleus. The glucocorticoid effect on chromatin was not observed in two lines of glucocorticoid-resistant mutant S49 cells. One line (R-) lacks detectable glucocorticoid receptors; the other line (Nti) has receptors that bind the hormone normally, but the receptor . glucocorticoid complexes bind more avidly to the nucleus. These results suggest that the receptor is involved in both the stimulatory and the inhibitory effects on chromatin. The findings in the Nti cells and of a slight lag between nuclear binding of receptors and initiation site alteration implies that some receptor property, in addition to nuclear binding per se, is responsible for the influence on chromatin. These results are discussed in terms of a model in which steroid hormones initiate their actions by influencing a reaction that modifies chromatin structure. The direction and magnitude of the reaction, and its effect on the expression of specific genes, are dictated by the metabolic state and differentiation of the cell.

Appearance in confluent vascular endothelial cell monolayers of a specific cell surface protein (CSP-60) not detected in actively growing endothelial cells or in cell types growing in multiple layers

The formation of a highly organized vascular and corneal endothelial cell monolayer is associated with the appearance of a 60,000-dalton cell surface protein (CSP-60) (30,000 daltons after reduction with dithiothreitol) which is not detectable in rapidly growing endothelial cells and in subconfluent cultures that do not yet exhibit the strict morphology of a confluent monolayer. It is also absent from vascular smooth muscle cells and from endothelial cultures that are maintained in the absence of fibroblast growth factor and grow on top of each other at confluence. After disorganization of cells in a confluent endothelial monolayer by urea, EDTA, or trypsin, CPS-60 is no longer exposed on the cell surface, but it reappears as soon as the cells readopt their characteristic two-dimensional configuration. This reorganization can be achieved in the presence of cycloheximide and despite removal of fibronectin by urea, EDTA, or trypsin. Maximal amounts of fibronectin and no CSP-60 are detected in subconfluent, but not yet organized, endothelial cultures or in endothelial cells that no longer form a monolayer of nonoverlapping cells at confluence. Likewise, cultures of vascular smooth muscle cells contain fibronectin but no CSP-60. These results suggest that CSP-60, rather than fibronectin, could be involved in the adoption of a monolayer configuration by confluent endothelial cells.

Developmental restrictions on transcription: determinants of the developmental program and their role in aging

A developing plant system, the soybean hypocotyl has been used to investigate early transcription events which restrict auxin induced cellular proliferation to the appropriate developmental stage. Auxin treatment of 4-day old seedlings resulted in an early (6 hour) activation of chromatin-bound RNA polymerase activity wihich approached 200% of control values by 18 hours. This occurred without a detectable alteration in chromatin template capacity (assayed with exogenous RNA polymerase) and resulted in the synthesis of "induced RNA transcripts" as determined in vitro by nearest neighbor analysis. In contrast, auxin treatment of unresponsive 8-day old seedlings did not alter the chromatin-bound RNA polymerase activity. Hormonal activation did, however, result in the exposure of "induced template" regions in chromatin which could only be transcribed in vitro if exogenous RNA polymerase was included in the transcription reaction. Isoelectric focusing of the endogenous chromatin-bound and soluble RNA polymerase enzymes from successive developmental stages revealed that the chromatin-bound enzymes at the 2-day stage were first released from the chromatin complex and could be recovered in the soluble pool (4-day stage). This was followed by a gradual disappearance of these subspecies (6-day stage) until only a limited ensemble of RNA polymerase subspecies remained bound to chromatin and free in the soluble pool (8-day stage). Similar analyses of both the bound and free enzymes at the 4 and 8-day stages following auxin treatment revealed that the 4-day soluble enzymes could be induced to rebind to the chromatin complex in a defined sequence after hormone treatment while those of the 8-day hypocotyl were unable to do so. These developmental events indicate that the select loss of certain RNA polymerase subspecies serves to restrict the hormone responsivness of this tissue to the early developmental stages. Such restrictions could thus commit the constituent hypocotyl cells to their terminal post-mitotic phase of development.

Developmental restrictions on hormone modulated gene transcription. II. Hormone induced interactions of RNA polymerase with chromatin

Chromatin-bound and soluble RNA polymerase subspecies have been isolated and fractionated by isoelectric focusing at various times (0, 6, 12 and 18 h) following auxin treatment of 4 day (responsive) and 8 day (unresponsive) soybean hypocotyls. Young 4 day seedlings displayed two well defined phases of auxin induced gene transcription. Phase I (6 h) evidenced the selective dissociation of many RNA polymerase subspecies from the chromatin complex which was accompanied by the retention of three class II enzymes. Phase II occurred after 12 h of treatment when the dissociated enzymes including some species which were soluble in the 0 h controls became re-associated with chromatin. These induced RNA polymerases may be responsible for the synthesis of auxin induced RNAs. In contrast, the unresponsive 8 day hypocotyl did not display two phases of auxin induction. Phase one, the dissociation of the chromatin bound enzymes, occurred at 12 h (compared to 6 h for the 4 day seedling) and was not followed by the later translocation of any soluble enzymes towards the chromatin complex. The results support earlier findings suggesting that the developmental "phasing out" of RNA polymerase subspecies limits the hormone induced growth response of this tissue and thus is regarded as an off switch for the transcription of such hormone controlled gene sequences.

Developmental transitions between chromatin-bound and soluble RNA polymerase subspecies in the soybean hypocotyl

RNA polymerase enzymes isolated from soybean hypocotyl tissue during successive developmental stages (2-8 days old) have been fractionated by Sephadex column isoelectric focusing. Both the enzymes bound to chromatin and those enzymes free in the soluble phase were investigated during development with respect to their distribution within these two pools. All observed activites were classified according to their alpha-amanitin sensitivity and isoelectric points. Two Class I subspecies (Ia, Ib) and two Class III subspecies (IIIa, IIIb) were continually present bound to chromatin throughout the developmental sequences except the IIb form which was absent at the latest stage. However, a great multiplicity (9 total) of Class II activities (totally inhibited by alpha-amanitin) were observed to be bound to chromatin at the 2nd day stage. These forms were first released from the chromatin complex and recovered in a soluble pool (4th day stage). Subsequent hypocotyl development was accompanied by the gradual disappearance of these Class II subspecies from this pool (6th day) until only two soluble species and one chromatin-bound Class II activity remained (8th day). These observations indicate that the early development of this tissue is accompanied by a dramatic alteration in the conplexity of chromatin-bound RNA polymerase subspecies. Such events may in part determine the domain of RNA secies synthesized at successive developmental stages.