Search PubMed⌕ Search

Biomedical subjects

A B Roberts

Publications and source records attributed to A B Roberts.

At least 145 records · Page 8Linked to original sources
PubMed1992

Intrauterine fetal transfusion, 1963-90.

The first fetal transfusion was performed at the National Women's Hospital in Auckland in 1963. From that time until the end of 1990, a total of 1041 transfusions have been completed on 459 fetuses. The survival rate for affected pregnancies rose significantly from 39% in 1963-65 to 90% in 1986-90. The initial 409 patients had fetal transfusions performed via the intraperitoneal cavity with X-ray guidance. Since 1986, 50 pregnancies have been treated with intravascular transfusions under ultrasound guidance and 45 fetuses survived.

Journal Article↗
PubMed1992

Autocrine secretion--10 years later.

The concept of autocrine secretion, its subsequent modifications, its application for understanding pathogenesis of disease, and its potential for developing new approaches to prevention and treatment are reviewed. Peptide growth factors (cytokines) act as local autocrine and paracrine mediators of tissue homeostasis. Many diseases, including cancer, atherosclerosis, rheumatoid arthritis, and other fibrotic diseases characterized by chronic inflammation, are associated with aberrant expression and cellular coordination of the homeostatic action of these regulatory molecules. Modern biotechnology and pharmacology offer unique opportunities for the therapeutic prevention and treatment of these molecular and cellular lesions, using either cytokines or other agents that modify their synthesis and activity.

Amino Acid Sequence↗
PubMed1992

Chorionic villus sampling in Auckland 1989-90.

AIMS: to perform an audit of all 197 chorionic villus sampling procedures performed in Auckland in 1989-90. METHOD: an attempt to trace the outcome in all 197 cases and this was possible in 188 cases. RESULTS: 89% of chorionic villus samples were performed transvaginally and 11% transabdominally. The total fetal loss rate was 9.6% (18) with six spontaneous miscarriages before 20 weeks gestation (3.2%), one intermediate fetal death and one neonatal death. There were 10 elective terminations of pregnancy following abnormal results so the spontaneous loss rate was 4.3%. CONCLUSIONS: the loss rate was lower than that reported in the European and Canadian multicentre trials. The sampling success rate, however, was poor with 13.7% failed procedures. This improved in the second year of the service to 10%. There were no failure cultures or examples of mosaicism.

Abortion, Spontaneous↗
PubMed1992

Inhibition of protein phosphatases blocks myogenesis by first altering MyoD binding activity.

To examine the role of protein phosphatases in skeletal muscle differentiation, C2C12 myoblasts were treated with okadaic acid, a potent in vitro inhibitor of protein phosphatases 1 and 2A which regulate various cellular events in intact cells. We now show that okadaic acid treatment of the mouse myoblast C2C12 cell line reversibly altered the morphology of the cells and blocked differentiation. At a molecular level, it extinguished expression of the myogenic determination genes, MyoD1 and myogenin, but induced the expression of an inhibitor of differentiation, Id. Analysis of the MyoD1 promoter showed that inhibition of MyoD1 expression by okadaic acid occurs at the transcriptional level. These changes occur 10-20 h after okadaic acid treatment. However, within 1 h of treatment the ability of muscle extracts to support a specific MyoD-dependent gel mobility shift using a MyoD DNA binding site is lost. These data suggest that protein phosphatases play an important role during myogenic differentiation.

Animals↗
PubMed1992

Identification of a structural domain that distinguishes the actions of the type 1 and 2 isoforms of transforming growth factor beta on endothelial cells.

A chimeric transforming growth factor beta (TGF-beta) molecule has been synthesized to map the amino acids responsible for the substantially greater activity of TGF-beta 1 than TGF-beta 2 on growth and migration of endothelial cells. This chimera consists of a dimer of a monomeric unit composed of amino acids 1-39 of TGF-beta 2, 40-82 of TGF-beta 1, and 83-112 of TGF-beta 2. Structural identity of the purified recombinant protein has been confirmed by immunoblotting and NH2-terminal sequencing. The biological potency of the TGF-beta 2-1-2 chimera was equal to that of TGF-beta 1 in inhibition of growth of both fetal bovine heart endothelial cells and rat epididymal fat pad microvascular endothelial cells. Similarly, the TGF-beta 2-1-2 chimera was nearly equivalent to TGF-beta 1 and at least 10-fold more active than TGF-beta 2 in inhibiting migration of bovine aortic endothelial cells. These results identify the sequence between amino acids 40-82 as an important region within TGF-beta that functions to specify a TGF-beta 1- or TGF-beta 2-like activity.

Animals↗
PubMed1992

Post-transcriptional regulation of the human transforming growth factor-beta 1 gene.

Since many lines of evidence suggest that expression of the transforming growth factor-beta 1 (TGF-beta 1) gene may be regulated post-transcriptionally, we examined the effect of the 5'-untranslated region (UTR) of this gene on TGF-beta 1 expression. For this purpose, fragments of the 840-nucleotide highly GC-rich TGF-beta 1 5'-UTR were inserted into the 5'-UTR of the structural gene for human growth hormone driven by the simian virus 40 early promoter. A portion of the 5'-UTR of TGF-beta 1 mRNA spanning the sequences from +11 to +147 was shown to inhibit growth hormone expression by as much as 22-fold. This effect was cell-specific; growth hormone production was inhibited in PC-3 human prostate adenocarcinoma and A-549 human lung adenocarcinoma cells, while no effect was seen in rat pheochromocytoma PC12 cells, which show efficient translation of endogenous TGF-beta 1 mRNA. Computer analysis showed that this region of the 5'-UTR contained a stable secondary stem-loop structure spanning sequences +49 to +76. This stem-loop region alone is sufficient to inhibit expression of the growth hormone gene, suggesting that it plays an important role in post-transcriptional regulation of TGF-beta 1 gene expression.

Animals↗
PubMed1992

The interaction between retinoic acid and the transforming growth factors-beta in calf articular cartilage organ cultures.

In calf articular cartilage organ cultures, retinoic acid depressed proteoglycan anabolism to levels approximately 10% of control values and increased their catabolism approximately 14-fold at concentrations of 1 x 10(-8) and 1 x 10(-6) M, respectively, leading to a severe depletion of this component from the extracellular matrix (95% loss in 3 weeks). These effects were powerfully antagonized by maximal levels of transforming growth factors-beta (TGF-beta s) 1, 2, and 3, leading to preservation of matrix components. At a concentration of 1 x 10(-8) M retinoic acid, the TGF-beta s restored anabolism to control levels and lowered catabolic rates greater than 3-fold. While the TGF-beta s increased protein synthesis 2- to 3-fold over controls, retinoic acid alone did not change protein synthesis, as determined by incorporation of [3H]serine. Nevertheless, retinoic acid effectively antagonized the stimulation of protein synthesis by TGF-beta and restored control levels of synthesis at 1 x 10(-7) M. Analysis of proteins, labeled using [3H]serine and [35S]sulfate as precursors, by SDS-PAGE revealed that large molecular weight proteins (greater than 100 kDa) were not detectable in retinoic-acid-treated cultures, but treatment with the TGF-beta s restored these components in coincubation cultures, again supporting the antagonistic role of the polypeptide effectors on retinoid action. Treatment of the cultures with retinoic acid elevated levels of TGF-beta 2 synthesis, but not TGF-beta 1. While the role of the newly synthesized TGF-beta 2 in the set of events elicited by retinoic acid in articular cartilage is unclear, the results establish an intrinsic metabolic link between the isoprenoid and TGF-beta in articular cartilage. We propose that the retinoids and TGF-beta s are integral parts of a regulatory network that controls homeostasis, resorption, or growth, depending on their relative contributions.

Animals↗
PubMed1992

Inhibition of growth by transforming growth factor-beta following fusion of two nonresponsive human carcinoma cell lines. Implication of the type II receptor in growth inhibitory responses.

Loss of growth regulation by transforming growth factor-beta (TGF-beta) may be an important step in carcinogenesis. We have used a cell fusion system to show that inhibition of growth by TGF-beta can be restored to carcinoma cell lines that are unresponsive to the inhibitory effects of TGF-beta. In a previous study, the EJ bladder carcinoma line was fused to the SW480 colon adenocarcinoma line and found to produce nontumorigenic hybrid cells along with one hybrid cell clone of low tumorigenicity. Here we show that the capacity of the nontumorigenic hybrid cells to respond to either TGF-beta 1 or TGF-beta 2 has been restored, while the parental or tumorigenic hybrid cells show little or no inhibition of growth following TGF-beta treatment. Cross-linking analyses with labeled TGF-beta 1 demonstrated much higher levels of the type II (85 kDa) receptor in the hybrid cells compared with the parental tumor lines. Both the parental and tumorigenic hybrid cell lines were capable of responding to TGF-beta as evidenced by increased levels of mRNA for fibronectin, type IV collagenase, and plasminogen activator inhibitor after treatment with TGF-beta 1. These results suggest that the type II receptor is necessary for mediating the effects of TGF-beta on inhibition of growth but not on gene activation of the hybrid cells.

Blotting, Northern↗
PubMed1992

Suppressor T cells generated by oral tolerization to myelin basic protein suppress both in vitro and in vivo immune responses by the release of transforming growth factor beta after antigen-specific triggering.

Oral administration of myelin basic protein (MBP) is an effective way of suppressing experimental autoimmune encephalomyelitis (EAE). We have previously shown that such suppression is mediated by CD8+ T cells, which adoptively transfer protection and suppress immune responses in vitro. In the present study we have found that modulator cells from animals orally tolerized to MBP produce a suppressor factor upon stimulation with MBP in vitro that is specifically inhibited by anti-transforming growth factor beta (TGF-beta) neutralizing antibodies. No effect was observed with antibodies to gamma interferon, tumor necrosis factor alpha/beta, or indomethacin. In addition, the active form of the type 1 isoform of TGF-beta 1 (TGF-beta 1) can be directly demonstrated in the supernatants of cells from animals orally tolerized to MBP or ovalbumin after antigen stimulation in vitro. Antiserum specific for TGF-beta 1 administered in vivo abrogated the protective effect of oral tolerization to MBP in EAE. Furthermore, injection of anti-TGF-beta 1 serum to nontolerized EAE animals resulted in an increase in severity and duration of disease. These results suggest that immunomodulation of EAE induced by oral tolerization to MBP and natural recovery mechanisms use a common immunoregulatory pathway that is dependent on TGF-beta 1. Implications of such an association are of therapeutic relevance to human autoimmune diseases and may help to explain one of the mechanisms involved in the mediation of active suppression by T cells.

Administration, Oral↗
PubMed1992

Pattern of expression of transforming growth factor-beta 4 mRNA and protein in the developing chicken embryo.

Expression of TGF-beta 4 mRNA and protein was studied in the developing chicken embryo using specific cDNA probes and antibodies for chicken TGF-beta 4. Expression of TGF-beta 4 mRNA was detected by day 4 of incubation (Hamburger and Hamilton stage 22, E4) by RNA Northern blot analysis and increased with developmental age until day 12 of incubation (stage 38, E12) where it was detected in every embryonic tissue examined, with expression being highest in smooth muscle and lowest in the kidney. The steady-state level of expression of TGF-beta 4 mRNA remained relatively constant in most embryonic tissues through day 19 (stage 45, E19). In situ hybridization analysis detected TGF-beta 4 mRNA as early as the "definitive primitive streak" stage (stage 4); during neurulation (stage 10), TGF-beta 4 mRNA was detected in all three germ layers, including neuroectoderm. Following neurulation, TGF-beta 4 mRNA was detected in the neural tube, notochord, ectoderm, endoderm, sclerotome, and myotome, but not dermotome at stage 16. By day 6 of incubation (stage 29, E6), TGF-beta 4 mRNA was localized in several tissues including heart, lung, and gizzard. Immunohistochemical staining analysis also showed expression of TGF-beta 4 protein in all three germ layers as early as stage 4 in various cell types in qualitatively similar locations as TGF-beta 4 mRNA. These results suggest that TGF-beta 4 may play an important role in the development of many tissues in the chicken.

Animals↗
PubMed1992

Differential regulation of the expression of transforming growth factor-beta mRNAs by growth factors and retinoic acid in chicken embryo chondrocytes, myocytes, and fibroblasts.

Transforming growth factor-beta (TGF-beta) autoregulates its expression in several mammalian cell types. We now report that addition of TGF-beta s 1, 2, and 3 to primary chicken embryo cells differentially affects expression of the messenger RNAs for the different TGF-beta isoforms depending on the cell type. In cultured sternal chondrocytes, addition of TGF-beta s 1, 2, or 3 results in an increase in the steady-state levels of the messenger RNAs for TGF-beta s 2 and 3, but does not change expression of TGF-beta 4 mRNA. In contrast, in cultured cardiac myocytes, addition of TGF-beta s 1, 2, or 3 results in an increase in expression of TGF-beta s 3 and 4 mRNAs, but does not change expression of TGF-beta 2 mRNA. Moreover, expression of TGF-beta s 2, 3, and 4 mRNAs is not affected by addition of any of the TGF-beta s to fibroblasts. Addition of platelet-derived growth factor (PDGF), epidermal growth factor (EGF), or interleukin-1 (IL-1) to these chicken cells also has differential effects on expression of the different TGF-beta mRNAs depending on the cell type. Retinoic acid also has contrasting effects on chondrocytes and myocytes either increasing or decreasing, respectively, expression of TGF-beta s 2 and 3 mRNAs and TGF-beta 2 protein. Our results indicate a complex pattern of regulation of the different TGF-beta genes by themselves as well as by PDGF, EGF, IL-1, dexamethasone, TPA, and retinoic acid in chicken embryo cells.

Animals↗
PubMed1992

Differential expression of the TGF-beta isoforms in embryogenesis suggests specific roles in developing and adult tissues.

The TGF-beta's are multifunctional, pleiotropic molecules with major effects in control of cellular migration, cellular proliferation, and elaboration of extracellular matrix. Thus far, five distinct isoforms of TGF-beta have been described, each approximately 65-85% homologous and containing the characteristic 9 positionally conserved cysteine residues. Although the actions of the activated mature forms of the different isoforms on cells are qualitatively similar in most cases, there are a few examples of distinct activities. For example, TGF-beta's 1 and 3, but not TGF-beta 2, inhibit the growth of large vessel endothelial cells, and TGF-beta's 2 and 3, but not TGF-beta 1, inhibit the survival of cultured embryonic chick ciliary ganglionic neurons. In addition, selective targeting of the latent forms of the TGF-beta's is suggested by the observation that latent TGF-beta 2 is the prominent isoform found in body fluids such as amniotic fluid, breast milk, and the aqueous and vitreous humor of the eye; it is noteworthy in this regard that TGF-beta 2 is unique among various isoforms in that it lacks a RGD integrin-binding sequence in its precursor. The most dramatic differences in the TGF-beta isoforms are seen at the level of expression, where there is now a wealth of data demonstrating both spatially and temporally distinct expression of both the mRNAs and proteins in developing tissues, regenerating tissues, and in pathologic responses.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Regulation of mammary morphogenesis: evidence for extracellular matrix-mediated inhibition of ductal budding by transforming growth factor-beta 1.

Branching morphogenesis in the mammary gland involves focal regions of cell proliferation, the terminal and lateral ductal buds, that exist simultaneously with extensive regions of differentiated ducts in which budding and growth are actively suppressed. Exogenous transforming growth factor-beta 1 (TGF-beta 1) has previously been shown to locally inhibit the formation and growth of mammary ductal buds. Here we report that endogenous TGF-beta 1, produced by epithelial and stromal mammary cells, forms complexes with extracellular matrix (ECM) molecules surrounding those ductal structures in which budding is inhibited. The largest amounts of immunostainable TGF-beta 1 are found in mature periductal ECM, and the least in newly synthesized ECM. In all areas of active ductal growth, where DNA-synthetic buds were forming new ductal branches, we found a highly focal loss of TGF-beta 1 from the periductal ECM at the bud-forming region of the duct. When growth of the new buds terminated, the structures again became associated with TGF-beta-rich ECM. These findings indicate that ECM must reach a certain state of maturity before it becomes associated with TGF-beta 1 and that TGF-beta 1 can be depleted selectively from the periductal ECM at focal growth points. A different type of growth point, the alveolar (secretory) buds, was also investigated. These buds are known not to be inhibited by exogenous TGF-beta 1, and we found them not to be associated with changes in ECM-bound TGF-beta 1. Our results support the concept that the periductal ECM acts as a reservoir for TGF-beta 1 that functions to maintain an open pattern of mammary branching by inhibiting ductal, but not alveolar, bud formation.

Animals↗
PubMed1992

Identification of multiple active growth factors in basement membrane Matrigel suggests caution in interpretation of cellular activity related to extracellular matrix components.

We have recently demonstrated the formation of interconnecting canalicular cell processes in bone cells upon contact with basement membrane components. Here we have determined whether growth factors in the reconstituted basement membrane (Matrigel) were active in influencing the cellular network formation. Various growth factors including transforming growth factor beta (TGF-beta), epidermal growth factor (EGF), insulin-like growth factor 1, bovine fibroblast growth factor (bFGF), and platelet-derived growth factor (PDGF) were identified in Matrigel. Exogenous TGF-beta blocked the cellular network formation. Conversely, addition of TGF-beta 1 neutralizing antibodies to Matrigel stimulated the cellular network formation. bFGF, EGF, and PDGF all promoted cellular migration and organization on Matrigel. Addition of bFGF to MC3T3-E1 cells grown on Matrigel overcame the inhibitory effect of TGF-beta. Some TGF-beta remained bound to type IV collagen purified from the Engelbreth-Holm-Swarm tumor matrix. These data demonstrate that reconstituted basement membrane contains growth factors which influence cellular behavior, suggesting caution in the interpretation of experiments on cellular activity related to Matrigel, collagen type IV, and possibly other extracellular matrix components.

Animals↗
PubMed1992

Role of transforming growth factor-beta in maintenance of function of cultured neonatal cardiac myocytes. Autocrine action and reversal of damaging effects of interleukin-1.

The three isoforms of transforming growth factor-beta (TGF-beta) have previously been implicated in embryonic development of the heart as well as in repair of myocardial damage after ischemia/reperfusion injury. TGF-beta 1 has also been localized intracellularly to both mitochondria and contractile filaments of cardiac myocytes, although its role in these structures has not been defined. We now report that exogenous TGF-beta stabilizes the beating rate of neonatal rat cardiac myocytes cultured on fibroblast matrix, and sustains their spontaneous rhythmic beating in serum-free medium. Moreover, using blocking antibodies to TGF-beta, we show that endogenous TGF-beta secreted by these myocytes acts in an autocrine fashion to maintain their beating rate. In contrast, IL-1 beta, an inflammatory mediator secreted by immune cells during myocardial injury, inhibits the beating of cardiac myocytes, and TGF-beta can overcome this inhibition. The antagonistic effects of TGF-beta and IL-1 were not observed when the myocytes were cultured on gelatin, as compared to native fibroblast matrix. The data indicate that TGF-beta is an important regulator of contractile function of the heart and have significant implications for understanding cardiac physiology in health and disease.

Animals↗
PubMed1992

Role of nitric oxide in antagonistic effects of transforming growth factor-beta and interleukin-1 beta on the beating rate of cultured cardiac myocytes.

We have recently shown that transforming growth factor-beta (TGF beta) acts in an autocrine manner to maintain the beating rate of neonatal rat cardiac myocytes cultured in serum-free medium on cardiac fibroblast matrix. Interleukin-1 beta (IL-1 beta) suppresses the myocyte-beating rate, and TGF beta antagonizes this effect. We now show that TGF beta and IL-1 beta also have antagonistic effects on the secretion of nitric oxide (NO) by these myocytes, and that NO secretion, the activity of NO synthase (NOS), and expression of the inducible form of NOS correlate inversely with the effects of these two agents on the beating rate. Western blot analysis shows that treatment of myocytes with TGF beta antagonizes the induction of NOS after treatment with IL-1 beta. Release of NO, induced by IL-1 beta, is dependent upon the availability of the substrate, L-arginine, and is suppressed by a competitive inhibitor, NG-monomethyl-L-arginine. L-Arginine (> 0.25 mM) also suppresses, and NG-monomethyl-L-arginine (> 0.5 mM) enhances the myocyte-beating rate. Treatment with IL-1 beta, but not TGF beta, increases cellular cGMP, presumably by activation of guanylate cyclase by NO. Methylene blue, an inhibitor of guanylate cyclase, reverses the suppression of beating caused by IL-1 beta. Bacterial lipopolysaccharide, present in the serum-free medium, is a coinducer of NO secretion. The suppressive effects of NO on the beating rate can be overcome by altering either the set of cytokines employed to induce NO or the matrix on which the myocytes are cultured, demonstrating that additional parameters are also involved in regulation of the beating rate.

Amino Acid Oxidoreductases↗