Search PubMed⌕ Search

Biomedical subjects

A B Roberts

Publications and source records attributed to A B Roberts.

At least 181 records · Page 10Linked to original sources
PubMed1991

Overexpression of transforming growth factor-beta in transgenic mice carrying the human T-cell lymphotropic virus type I tax gene.

Human T-cell lymphotropic virus type I (HTLV-I) has been associated with an adult form of T-cell leukemia as well as tropical spastic paraparesis, a neurodegenerative disease. Adult T-cell leukemia patients express high levels of the type 1 isoform of transforming growth factor-beta (TGF-beta 1), which is mediated by the effects of the HTLV-I Tax transactivator protein on the TGF-beta 1 promoter. To understand further the regulation of TGF-beta 1 expression by Tax, we examined its expression in transgenic mice carrying the HTLV-I tax gene. We show that tumors from these mice and other tissues, such as submaxillary glands and skeletal muscle, which express high levels of tax mRNA selectively express high levels of TGF-beta 1 mRNA and protein. Moreover, TGF-beta 1 significantly stimulated the incorporation of tritiated thymidine into one of three cell lines derived from neurofibromas of tax-transgenic mice, which suggests that the excessive production of TGF-beta 1 may play a role in tumorigenesis and that these mice may serve as a useful model for studying the biological effects of TGF-beta in vivo.

Animals↗
PubMed1991

Secretion and transcriptional regulation of transforming growth factor-beta 3 during myogenesis.

Transforming growth factor-beta 3 (TGF-beta 3) mRNA is differentially expressed in developing and mature mouse tissues, including high-level expression in developing and adult cardiac tissue. We show now that TGF-beta 3 mRNA is also expressed highly in skeletal muscle as well as in the mouse skeletal myoblast cell line C2C12. We also show that C2C12 cells secrete TGF-beta 3, and that this TGF-beta is able to inhibit C2C12 myoblast fusion after activation. In order to begin to understand how the TGF-beta 3 promoter is regulated in specific tissues during development, we therefore studied the regulation of TGF-beta 3 during myoblast fusion. After fusion of C2C12 cells into myotubes, TGF-beta 3 mRNA levels increased eightfold as a result of increased TGF-beta 3 transcription. TGF-beta 3 transcriptional regulation was studied in myoblasts and myotubes by transfection of chimeric TGF-beta 3/CAT promoter plasmids. Chloramphenicol acetyltransferase (CAT) activity was stimulated in myoblasts by several upstream regions between -301 and -47 of the TGF-beta 3 promoter and by the TGF-beta 3 5' untranslated region. CAT activity directed by the TGF-beta 3 promoter in myotubes was stimulated by a distinct upstream region located between -499 and -221. Therefore, the high level of TGF-beta 3 mRNA expression in muscle cells appears to be dependent on multiple regulatory events during different stages of myogenesis.

Animals↗
PubMed1991

Localization and actions of transforming growth factor-beta s in the embryonic nervous system.

We present evidence for unique localization and specific biological activities for transforming growth factor-beta s (TGF-beta s) 2 and 3, as compared to TGF-beta 1, in the nervous system of the 12-18 day mouse embryo. Each TGF-beta isoform was localized immunohistochemically by specific antibodies raised to peptides corresponding to unique sequences in the respective TGF-beta proteins. Staining for TGF-beta 1 was principally in the meninges, while TGF-beta s 2 and 3 co-localized in neuronal perikarya and axons, as well as in radial glial cells. In the central nervous system, staining was most prominent in zones where neuronal differentiation occurs and less intense in zones of active proliferation, while in the peripheral nervous system, many nerve fibers as well as their cell bodies were strongly immunoreactive for TGF-beta s 2 and 3. Functionally, we have also found that in the presence of an extract of chick eye tissue, TGF-beta s 2 and 3 inhibit survival of cultured embryonic chick ciliary ganglionic neurons in a dose-dependent fashion; TGF-beta 1 shows no inhibitory effects. Our data suggest that TGF-beta s 2 and 3 may play a role in regulation of neuronal migration and differentiation, as well as in glial cell proliferation and differentiation.

Animals↗
PubMed1991

Regulated expression and growth inhibitory effects of transforming growth factor-beta isoforms in mouse mammary gland development.

Transforming Growth Factor-beta 1 (TGF-beta 1) was previously shown to inhibit reversibly the growth of mouse mammary ducts when administered in vivo by miniature slow-release plastic implants. We now report a comparative analysis of three TGF-beta isoforms with respect to gene expression and localization of protein products within the mouse mammary gland. Our studies revealed overlapping expression patterns of TGF-beta 1, TGF-beta 2 and TGF-beta 3 within the epithelium of the actively-growing mammary end buds during branching morphogenesis, as well as within the epithelium of growth-quiescent ducts. However, TGF-beta 3 was the only isoform detected in myoepithelial progenitor cells (cap cells) of the growing end buds and myoepithelial cells of the mature ducts. During pregnancy, TGF-beta 2 and TGF-beta 3 transcripts increased to high levels, in contrast to TGF-beta 1 transcripts which were moderately abundant; TGF-beta 2 was significantly transcribed only during pregnancy. Molecular hybridization in situ revealed overlapping patterns of expression for the three TGF-beta isoforms during alveolar morphogenesis, but showed that, in contrast to the patterns of TGF-beta 1 and TGF-beta 2 expression, TGF-beta 3 is expressed more heavily in ducts than in alveoli during pregnancy. Developing alveolar tissue and its associated ducts displayed striking TGF-beta 3 immunoreactivity which was greatly reduced during lactation. All three isoforms showed dramatically reduced expression in lactating tissue. The biological effects of active, exogenous TGF-beta 2 and TGF-beta 3 were tested with slow-release plastic implants. These isoforms, like TGF-beta 1, inhibited mammary ductal elongation in situ by causing the disappearance of the proliferating stem cell layer (cap cells) and rapid involution of ductal end buds. None of the isoforms were active in inhibiting alveolar morphogenesis. We conclude that under the limited conditions of these tests, the three mammalian isoforms are functionally equivalent. However, striking differences in patterns of gene expression and in the distribution of immunoreactive peptides suggest that TGF-beta isoforms may have distinct roles in mammary growth regulation, morphogenesis and functional differentiation.

Animals↗
PubMed1991

Molecular cloning and structure of the human transforming growth factor-beta 2 gene promoter.

Genomic DNA extending over 10 kb 5' of the transforming growth factor-beta 2 (TGF-beta 2) coding region was isolated from a human lung fibroblast lambda phage library. A 5.6 kb Hind III fragment containing the 5'-untranslated region and flanking sequences was subcloned and sequenced. S1 nuclease protection analysis identified a transcriptional initiation site 1357 nucleotides 5' of the methionine initiation codon (ATG). A "TATA box" consensus sequence was identified 30 bp from this transcriptional start site; however, consensus "CAT box" sequences were not observed. Approximately 50 nucleotides of homopurine-pyrimidine [d(GA.CT)50] sequence were identified in the 5'-untranslated region, as well as two short open reading frames of 5 and 45 amino acids. Several AP-1, AP-2, CRE and SP1-like DNA consensus sequence elements were also identified surrounding the transcription initiation site. 5'-deletion mutants of the promoter region were fused to the chloramphenicol acetyl transferase (CAT) gene and promoter activity of the isolated genomic DNA was demonstrated in several cell lines. DNA constructs containing nucleotides between -508 to +63 demonstrated high levels of promoter activity. However, sequences between -778 and -508 nucleotides modulated this promoter activity in a manner which was dependent upon the cell line utilized, suggesting that regulation of TGF-beta 2 gene transcription may be dependent upon the cellular background. The TGF-beta 2 promoter is markedly different from the promoters that have been recently characterized for TGF-beta 1 and TGF-beta 3.

Amino Acid Sequence↗
PubMed1990

Structural and functional characterization of the transforming growth factor beta 3 promoter. A cAMP-responsive element regulates basal and induced transcription.

Transforming growth factor beta 3 (TGF-beta 3) has been cloned from humans, chickens, pigs, and mice. Although the specific in vivo roles of this form of TGF-beta are unknown, the pattern of embryonic and tissue-specific expression of TGF-beta 3 suggests that it is involved in embryogenesis and cell differentiation. We have cloned and sequenced the TGF-beta 3 5'-flanking region to study the transcriptional regulation of this gene. Characterization of the 5'-flanking region showed a 1104-base pair 5'-untranslated region, a TATA box 21 bp upstream from the transcription start site, and cAMP-responsive element (CRE) and AP-2 binding site consensus sequences starting at 12 and 24 bp, respectively, upstream from the TATA box. Promoter fragments were cloned into a chloramphenicol acetyltransferase reporter plasmid to study functional activity. Basal transcriptional activity of the promoter was regulated by multiple upstream elements including the CRE and the AP-2 site. The CRE was important for both basal and forskolin induction of promoter activity. The TGF-beta 3 promoter was found to be strikingly dissimilar to the TGF-beta 1 promoter. Since the TGF-beta s have activity in promoting or inhibiting proliferation and differentiation of multiple cell types, it seems likely that the differential and tissue-specific transcriptional regulation of these genes is of fundamental importance in the induction and maintenance of differentiated cell types in various tissues.

Animals↗
PubMed1990

Transactivation of the transforming growth factor beta 1 (TGF-beta 1) gene by human T lymphotropic virus type 1 tax: a potential mechanism for the increased production of TGF-beta 1 in adult T cell leukemia.

We examined the effect of the human T lymphotropic virus type 1 (HTLV-I) Tax gene product on the human transforming growth factor beta 1 (TGF-beta 1) promoter. Transfection of deleted constructs of the TGF-beta 1 promoter revealed regions homologous with AP-1 binding sites that were required for Tax-induced transactivation of the TGF-beta 1 promoter. In addition, we examined the expression and secretion of TGF-beta in fresh leukemic cells isolated from patients with adult T cell leukemia (ATL) and in HTLV-1-infected T cell lines. We report that fresh leukemic cells from ATL patients constitutively produce high levels of TGF-beta 1 mRNA and secrete TGF-beta 1 but not TGF-beta 2 into the culture medium. In addition, long-term ATL cell lines expressed significant amounts of TGF-beta 1 mRNA as well as detectable levels of TGF-beta 1 protein. These results suggest a role for Tax in the upregulation of TGF-beta 1 in HTLV-I-infected cells.

Cell Line↗
PubMed1990

Pregnancy in women with diabetes mellitus, twenty years experience: 1968-1987.

This paper reviews 1528 pregnancies in women with diabetes mellitus between 1968 and 1987 at National Women's Hospital; 571 had established diabetes and 957 had gestational diabetes. During this period the perinatal mortality rate for women with established diabetes fell from 15.2% to 2% and for those with gestational diabetes from 6.7% to 0.5%. This improvement was probably related to changes in management which included a team approach to perinatal care and a concentration on lowering blood glucose levels during pregnancy. The outstanding problem is the high incidence of congenital abnormalities in women with established diabetes. Two to three percent of these pregnancies ended in a perinatal death due to congenital anomaly. Improved prepregnancy and early pregnancy blood glucose control must be the aim to reduce the congenital abnormality rate.

Blood Glucose↗
PubMed1990

Transforming growth factor-beta: multifunctional regulator of differentiation and development.

Transforming growth factors-beta (TGF-beta) are 25 kilodalton (kDa) homodimeric peptides with multifunctional actions controlling the growth, differentiation and function of a broad range of target cells of both epithelial and mesenchymal derivation. They are expressed early in embryogenesis and their tissue-specific and developmentally dependent expression is strongly suggestive of an essential role in particular morphogenetic and histogenetic events. Five distinct TGF-beta s have been characterized so far, with 65-80% homology to each other. By using both molecular biological and immunohistochemical techniques, we are currently attempting to define specific sites of expression of the different TGF-beta s and to determine whether TGF-beta s 1-5 might have unique functions in development and in the mature organism. Comparative study of the promoter regions for the different TGF-beta s and for any particular TGF-beta in different species is also underway. Mechanistically, TGF-beta s act to control gene expression of their target cells, many of their actions converging on a complex, multifaceted scheme of control of matrix proteins and their interactions with cells; these effects on matrix are thought to mediate many of the effects of TGF-beta on development.

Amino Acid Sequence↗
PubMed1990

Identification of a novel transforming growth factor-beta (TGF-beta 5) mRNA in Xenopus laevis.

A novel transforming growth factor-beta (TGF-beta) mRNA of about 3.0 kilobases, which encodes a putative protein of 382 amino acids, has been identified in amphibians by cDNA cloning. This mRNA, which we designate as TGF-beta 5, is developmentally regulated and highly expressed beginning at early neurula (stage 14) and in many adult tissues in Xenopus laevis. Following the first methionine, the putative precursor protein has a hydrophobic region, approximately 22 amino acids long, which probably represents a signal sequence, similar to that found in TGF-beta s 1-3. The precursor also has potential sites for glycosylation, integrin binding (RGD), and a tetrabasic amino acid (RKKR) site for potential cleavage of the precursor peptide to a biologically active protein. The putative mature protein consists of 112 amino acids with 9 cysteines and has 76, 66, 69, and 72% identity to TGF-beta s 1-4, respectively.

Amino Acid Sequence↗
PubMed1990

Direct ultrasonographic measurement of fetal lung length in normal pregnancies and pregnancies complicated by prolonged rupture of membranes.

Fetal lung length was measured directly with ultrasonography in 20 patients with prolonged rupture of membranes, commencing before 25 weeks' gestation. Measurements were made weekly and compared with data collected from 310 normal pregnancies. Measurement of fetal lung length by ultrasonography was a good predictor of pulmonary hypoplasia, predicting greater than 90% of cases. There was a good correlation between lung size assessed by the last ultrasonographic examination and lung weight postmortem (r = 0.783, p less than 0.05). Lung length measurements were superior to fetal chest circumference measurements in the identification of pulmonary hypoplasia. There was a significant negative association between the amount of amniotic fluid and pulmonary hypoplasia (p less than 0.05). There were fetuses with pulmonary hypoplasia that had respiratory movements seen at the majority of ultrasonographic examinations.

Biometry↗
PubMed1990

Transforming growth factor-beta and the initiation of chondrogenesis and osteogenesis in the rat femur.

We have investigated the ability of exogenous transforming growth factor-beta (TGF-beta) to induce osteogenesis and chondrogenesis, critical events in both bone formation and fracture healing. Daily injections of TGF-beta 1 or 2 into the subperiosteal region of newborn rat femurs resulted in localized intramembranous bone formation and chondrogenesis. After cessation of the injections, endochondral ossification occurred, resulting in replacement of cartilage with bone. Gene expression of type II collagen and immunolocalization of types I and II collagen were detected within the TGF-beta-induced cartilage and bone. Moreover, injection of TGF-beta 2 stimulated synthesis of TGF-beta 1 in chondrocytes and osteoblasts within the newly induced bone and cartilage, suggesting positive autoregulation of TGF-beta. TGF-beta 2 was more active in vivo than TGF-beta 1, stimulating formation of a mass that was on the average 375% larger at a comparable dose (p less than 0.001). With either TGF-beta isoform, the dose of the growth factor determined which type of tissue formed, so that the ratio of cartilage formation to intramembranous bone formation decreased as the dose was lowered. For TGF-beta 1, reducing the daily dose from 200 to 20 ng decreased the cartilage/intramembranous bone formation ratio from 3.57 to zero (p less than 0.001). With TGF-beta 2, the same dose change decreased the ratio from 3.71 to 0.28 (p less than 0.001). These data demonstrate that mesenchymal precursor cells in the periosteum are stimulated by TGF-beta to proliferate and differentiate, as occurs in embryologic bone formation and early fracture healing.

Animals↗
PubMed1990

TGF-beta: problems and prospects.

TGF-beta research is proceeding at an exponential pace. Studies in this area have become increasingly relevant to many areas of cell regulation, continually providing new surprises and findings. One may confidently predict that TGF-beta will be one of the key molecules in future attempts to establish an integrated view of the processes whereby cells coordinate their own and mutual functions. We have seen only the beginning, and this minireview is only a glimpse.

Animals↗
PubMed1990

Regulation of collagenase gene expression by okadaic acid, an inhibitor of protein phosphatases.

Human collagenase gene expression is regulated transcriptionally and is inducible by various mitogens in many cell types. To investigate the molecular mechanisms of this response, we examined the effects on collagenase gene expression of okadaic acid, a non-12-O-tetradecanoyl-phorbol-13-acetate (TPA)-type tumor promoter, which induces apparent "activation" of protein kinases by inhibition of protein phosphatases. Steady state levels of collagenase mRNA were markedly increased by okadaic acid treatment. We show that the AP-1 consensus sequence in the collagenase promoter is required for the induction of collagenase gene expression by okadaic acid, even though sequences upstream of the AP-1 consensus site have an additive effect. We also examined the regulation by okadaic acid of expression of the components of the AP-1 complex, c-fos and c-jun. c-fos expression is dramatically stimulated by okadaic acid, whereas c-jun expression is stimulated to a lesser extent. Induction of c-fos gene mRNA occurs through a region known to contain multiple regulatory elements. These results suggest that phosphorylation regulates collagenase gene expression mediated by an AP-1 binding site.

DNA-Binding Proteins↗