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C K Glass

Publications and source records attributed to C K Glass.

98 records · Page 6Linked to original sources
PubMed1988

Retinoic acid and thyroid hormone induce gene expression through a common responsive element.

Studies of steroid receptors have led to the identification of a superfamily of ligand-inducible regulatory proteins that includes receptors for thyroid hormones and retinoic acid. This family of receptors regulates gene expression through binding to short cis-acting sequences referred to as hormone-response elements. Identification of a functional retinoic acid responsive element is crucial to our understanding of the mechanisms by which retinoic acid receptors activate gene expression and regulate cell differentiation. One impediment to such a study is the absence of any identified gene whose transcription is directly dependent on the receptor-hormone complex. Because the DNA-binding domains of the retinoic acid and thyroid hormone receptors are highly related (62% identical in their amino acid sequences), we have investigated the possibility that the retinoic acid receptor could activate gene expression through a thyroid hormone response element. We now report that a human retinoic acid receptor expressed from cloned complementary DNA or the endogenous retinoic acid receptor present in F9 teratocarcinoma cells can activate gene expression from promoters fused to a natural or synthetic thyroid hormone response element. The product translated in vitro from the human retinoic acid receptor cDNA can bind to a thyroid hormone response element with high affinity. The unexpected implication of these findings is that retinoic acid and thyroid hormones, acting through their respective receptors, could control overlapping gene networks involved in the regulation of vertebrate morphogenesis and homeostasis.

Binding Sites↗
PubMed1988

The thyroid hormone receptor binds with opposite transcriptional effects to a common sequence motif in thyroid hormone and estrogen response elements.

We report that the thyroid hormone (T3) receptor binds to DNA recognition sequences that are variations of the palindromic motif 5'-TCAGGTCA.TGACCTGA-3', resulting in transcriptional activation in vivo. This sequence is identical to the vitellogenin A2 estrogen response element except for the absence of 3 bp at the center of dyad symmetry, which we have termed a "gap." The T3 receptor binds to estrogen response elements with high affinity in vitro, as well as to variations of the same sequence containing gaps of 1-6 bp. The T3 receptor not only fails to activate transcription from estrogen response elements in vivo, but inhibits estrogen-dependent transactivation. We propose that the T3 receptor binds to estrogen response elements in a transcriptionally inactive form and competes for estrogen receptor binding, resulting in a net decrease in gene expression. These data reveal that only a subset of T3 receptor DNA-binding elements function as T3 response elements.

Animals↗
PubMed1988

Identification of rat growth hormone genomic sequences targeting pituitary expression in transgenic mice.

Constructs containing different segments of the 5' flanking region of the rat growth hormone gene fused to the human growth hormone coding sequences were introduced into fertilized mouse oocytes. As few as 181 base pairs of the rat growth hormone promoter targeted reporter gene expression to the pituitary gland of the resulting transgenic mice. A construct containing only 45 base pairs of the promoter failed to target expression of the reporter to the pituitary, indicating that the pituitary expression is directed by information contained in the segment spanning positions -181 to -45. In the pituitary, immunohistochemistry showed transgene expression mainly in the growth hormone-producing cells (somatotrophs), in a subset of cells producing thyrotropin, and occasionally in prolactin-producing cells. These data establish that cis-active elements contained within the first 180 base pairs of the promoter are sufficient for transcriptional activation of the growth hormone gene in somatotrophs and suggest a functional relationship among growth hormone, prolactin, and thyrotropin gene activation.

Animals↗
PubMed1987

Synthetic high density lipoprotein particles. Application to studies of the apoprotein specificity for selective uptake of cholesterol esters.

Particles closely resembling rat high density lipoproteins (HDL) in terms of equilibrium density profile and particle size were prepared by sonication of apoA-I with a microemulsion made with egg lecithin and cholesterol oleate. These particles, like authentic HDL, allowed selective uptake of their cholesterol ester moieties by cultured cells without parallel uptake of the particle itself. That uptake was saturable and competed by HDL. In rats, the plasma decay kinetics and sites of uptake of a cholesteryl ether tracer were similar whether that tracer was incorporated into synthetic or authentic HDL. Synthetic particles containing other apoproteins were made by generally the same method, but using in place of apoA-I either a mixture of rat apoCs or apoE that was either competent or reductively methylated to prevent interaction with the B/E receptor. These particles, of lower density and larger Stokes radius than those made with apoA-I, also allowed selective uptake of cholesterol esters, albeit with a lower degree of selectivity than in the case of apoA-I. Thus a specific apoprotein component in the subject lipoprotein particle is not required for selective uptake. However, selective uptake was shown to be a function of particle density or size, and part of the difference in rates of selective uptake from the particles made with various apoproteins was explained by their differences in density or size.

Animals↗
PubMed1983

A radioiodinated, intracellularly trapped ligand for determining the sites of plasma protein degradation in vivo.

We recently developed a general method for determining tissue sites of degradation of plasma proteins in vivo that made use of covalently attached radioactive sucrose. On degradation of the protein, the sucrose remained trapped in the cells as a cumulative marker of protein degradation. The method described here depends on the same principles, but uses an adduct of cellobiose and tyramine that is radioiodinated to high specific radioactivity and then covalently attached to protein. Use of the radioiodinated ligand increases the sensitivity of the method at least 100-fold and allows simplified tissue analysis. Proteins derivatized with the radioiodinated ligand were recognized as underivatized proteins both in vitro and in vivo. On degradation of derivatized low-density lipoprotein, the rate of leakage from cultured fibroblasts was only 5% during 24 h. Similarly, on injection of labelled proteins into rats and rabbits, urinary excretion of the label was in all cases less than 10% of total labelled catabolic products recovered 24 h after injection. Examination of the tissue contents of label at two times after injection of labelled asialofetuin or apolipoprotein A1 in rats, and asialotransferrin in rabbits showed that the label did not detectably redistribute between tissues after initial uptake and catabolism; a significant leakage from liver was quantitatively accounted for by label appearing in gut contents and faeces. A simple double-label method was devised to provide a correction for intact protein in trapped plasma, the extravascular spaces, and within cells. By using this method it becomes unnecessary to fractionate tissue samples.

Animals↗
PubMed1983

Tissue sites of degradation of apoprotein A-I in the rat.

The tissue sites of degradation of apoprotein A-I were determined in the rat in vivo using a newly developed tracer of protein catabolism, an adduct of 125I-tyramine and cellobiose. This methodology takes advantage of the fact that when a protein labeled with 125I-tyramine-cellobiose is taken up and degraded, the radiolabeled ligand remains trapped intracellularly. Thus, radio-iodine accumulation in a tissue acts as a cumulative measure of protein degradation in that tissue. In the present studies, apoprotein AI (apo-A-I) was labeled with tyramine-cellobiose (TC). The TC-labeled apo-A-I was then reassociated with high density lipoprotein (HDL) in vivo by injection into donor animals. After 30 min, serum from donor animals was recovered and then injected into recipient rats. TC-labeled apo-A-I in the donor serum was shown to be exclusively associated with HDL. The fractional catabolic rate of 125I-TC-apo-A-I was not significantly different from that of conventionally labeled apo-A-I. The kidney was the major site of degradation, accounting for 39% of the total. The liver was responsible for 26% of apo-A-I catabolism, 96% of which occurred in hepatocytes. The kidney was also the most active organ of catabolism/g of wet weight. The tissues next most active/g of wet weight were ovary and adrenal, a finding that is compatible with a special role of HDL in the rat for delivery of cholesterol for steroidogenesis. Immunofluorescence studies of frozen sections of rat kidney demonstrated the presence of apo-A-I on the brush-border and in apical granules of proximal tubule epithelial cells. Preliminary studies using HDL labeled both with 125I-TC-apo-A-I and [3H]cholesteryl ethers again demonstrated high rates of renal uptake of apo-A-I but less than 1% of total ether uptake. It is postulated that the high activity of kidney was not due to uptake of intact HDL particles, but rather, due to glomerular filtration and tubular reabsorption of free apo-A-I.

Animals↗
PubMedDate not supplied

A c-erb-A binding site in rat growth hormone gene mediates trans-activation by thyroid hormone.

The substance 3,5,3-triiodothyronine (T3) stimulates growth hormone gene transcription in rat pituitary tumour cells. This stimulation is thought to be mediated by the binding of nuclear T3 receptors to regulatory elements 5' to the transcriptional start site. Understanding of the mechanism by which thyroid hormone activates gene transcription has been limited by failure to purify nuclear T3 receptors because of their low abundance, and by the absence of defined T3 receptor-DNA binding sites affecting T3 regulation. Recently, human and avian c-erb-A gene products have been shown to bind thyroid hormone with high affinity and to have a molecular weight and nuclear association characteristic of the thyroid hormone receptor. In the present report, we describe the development of an avidin-biotin complex DNA-binding assay which can detect specific, high-affinity binding of rat pituitary cell T3 receptors to the sequence 5'CAGGGACGTGACCGCA3', located 164 base pairs 5' to the transcriptional start site of the rat growth hormone gene. An oligonucleotide containing this sequence transferred T3 regulation to the herpes simplex virus thymidine kinase promoter in transfected rat pituitary GC2 cells, and specifically bound an in vitro translation product of the human placental c-erb-A gene. The data provide supporting evidence that the human c-erb-A gene product mediates the transcriptional effects of T3 and also that GC2 cell nuclear extracts contain additional factors that modify the binding of pituitary T3 receptors to the rat growth hormone gene T3 response element.

Animals↗