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M I Surks

Publications and source records attributed to M I Surks.

At least 19 recordsLinked to original sources
PubMed1992

Heat stress of cultured GC cells enhances triiodothyronine-induced growth hormone production by action within the 5'-flanking region of the rat growth hormone gene.

We studied the effect of incubation at 41 C on a clone of GC cells that had previously been stably transfected with a gene construct, pGHXGPT, containing -1800 to +8 of the rat growth hormone promoter fused to the structural gene for E. Coli xanthine guanine phosphoribosyl-transferase. The effect of incubation of the clone containing pGHXGPT at 41 C was to enhance triiodothyronine induction of growth hormone secretion (2-fold, p < 0.01) and of xanthine quanine phosphoribosyl-transferase activity (3-fold, p < 0.01). We conclude that the increase in triiodothyronine-induced growth hormone production during heat stress occurs by stimulation of the growth hormone promoter.

Animals↗
PubMed1991

The effects of chronic exposure to supraphysiological concentrations of 3, 5, 3' triiodo-L-thyronine (T3) on cultured GC cells.

We have characterized the effects of supraphysiological concentrations of T3 on GC cells, a cultured cell line in which physiologic concentrations of T3 regulate cell growth, protein content, and growth hormone (GH) production. GC cells were exposed to 3 times (1.0 nM) and 80 times (25.0 nM) the physiologic concentration of T3 (0.3 nM) for either 4 d or for greater than 3 months. Both short and prolonged exposure to supranormal T3 concentrations supported maximal cell growth rate and induced significant increases in total protein (P less than 0.025) and GH production (P less than 0.01) per cell when compared to measurements in control GC cells. In addition, exposure to 1.0 nM and 25.0 nM T3 for greater than 3 months enhanced the toxicity of heat shock in a manner similar to previously described effects on GC cells due to T3 exposure of shorter duration. Thus, initial responses to raised T3 concentrations in cultured GC cells persisted without alteration when hormone exposure was prolonged for greater than 3 months.

Animals↗
PubMed1991

Zinc(II) inhibits the release of thyroid and glucocorticoid receptors from chromatin of cultured GC cells.

The effect of Zn(II) on the association of thyroid and glucocorticoid hormone receptors with chromatin was studied in chromatin from cultured GC cells. Chromatin was incubated at 0-4 degrees C in 20 mM Tris, pH 7.4. When buffers contained 0.15 M NaCl, the release of T3 receptors from chromatin was time-dependent; 50% of T3 receptors were released after 30 min incubation. Receptor release appeared relatively specific since less than 10% of chromatin protein and DNA, and less than 13% of chromatin zinc were released under these conditions. Addition of Zn(II) inhibited receptor release; one-half maximal inhibition occurred at 1 microM ZnCl2. Cd(II) and to a lesser extent Co(II) had similar but smaller effects. Addition of EDTA prevented this effect of Zn(II); EDTA alone enhanced receptor release. Zn(II) also inhibited the release of glucocorticoid receptors from chromatin in similar incubations. Our findings suggest that Zn(II) increases the association of hormone receptors with chromatin and, thereby, may influence receptor function.

Cations, Divalent↗
PubMed1991

Role of L-thyroxine in nuclear thyroid hormone receptor occupancy and growth hormone production in cultured GC cells.

The contribution of L-thyroxine (T4) to nuclear thyroid receptor occupancy was studied in GC cells incubated with concentrations of 3,5,3'-triiodo-L-thyronine (T3) and T4 that resulted in free iodothyronine levels similar to those in serum of euthyroid rats. T4 accounted for 5.4-10% of the occupied receptors: T3 derived from T4 [T3(T4)] and T3 added to medium accounted for the remainder of receptor occupancy. Incubation with increasing medium free T4 resulted in a progressive increase in the contribution of T4 and T3(T4) to receptor occupancy. In incubations with 3.6-fold increased medium free T4, T4 accounted for 20.4%, and T3(T4) for 40.3% of receptor occupancy. These occupancy data and the experimentally determined Ka of thyroid receptor for T3 and T4 allowed calculation of nuclear free iodothyronine concentrations. Nuclear free T3 was 3-6-fold greater than medium free T3 and nuclear [corrected] free T4 was 12-19-fold greater than medium free T4. When GC cells were incubated with decreased medium free T3 and physiological medium free T4, both nuclear receptor occupancy and growth hormone production decreased as well. However, a twofold increase in medium free T4, in the presence of decreased medium free T3, restored receptor occupancy and growth hormone production to or near control values. These findings establish a role for T4 in addition to T3(T4) in nuclear receptor occupancy and biological activity in rat anterior pituitary tissue both in physiologic conditions and when medium free T4 is raised. The findings may have relevance to the sick euthyroid thyroid syndrome in which free T4 may be increased in some patients who have decreased serum free T3.

Animals↗
PubMed1991

Heat stress and hydrocortisone are independent stimulators of triiodothyronine-induced growth hormone production in cultured rat somatotrophic tumour cells.

We have reported that, in cultured GC cells, the stress of incubation at 41 degrees C enhances thyroid hormone stimulation of growth hormone (GH) in a manner similar to the effects observed in a model of nonthyroidal disease in rats. Since glucocorticoids are potentially involved in stress responses both in vivo and in cell culture, we studied the role of glucocorticoid in the enhancement of (which are rat somatotrophic tumor cells) triiodothyronine (T3)-induced GH synthesis due to heat stress. Hydrocortisone addition increased T3-induced GH synthesis and GH mRNA content in cultured GC cells at both 37 degrees C and 41 degrees C. Depletion of glucocorticoid endogenous to serum supplement of the tissue culture medium did not prevent the enhancement of T3-induced GH synthesis that occurred during incubation at 41 degrees C. The levels and affinity of glucocorticoid cytosolic receptors were not enhanced during incubation at 41 degrees C. Lastly, no change in the sedimentation coefficient of the cytosolic glucocorticoid receptor or in its translocation into the nucleus occurred during incubation at 41 degrees C. Thus, the enhancement of T3-induced GH production in GC cells by heat stress appeared independent of the effect of glucocorticoids and not mediated through glucocorticoid receptors.

Animals↗
PubMed1991

Simultaneous use of standard and low-melting agarose for the separation and isolation of DNA by electrophoresis.

In this communication we describe the sequential use of standard and low-melting agarose in a single gel slab for the electrophoresis of DNA. This method has the advantages of high resolution and reproducibility characteristic of standard agarose and the ease of manipulation of DNA for direct cloning, sequential digestion and isolation, characteristic of low-melting agarose.

DNA↗
PubMed1990

American Thyroid Association guidelines for use of laboratory tests in thyroid disorders.

Selection of appropriate laboratory determinations will enable the clinician to diagnose thyroid dysfunction readily in the majority of patients. At the present time, estimation of free thyroxine and a "sensitive" thyrotropin assay are recommended as the principal laboratory tests for thyroid disease. A decrease in serum free thyroxine estimate and a raised level of serum thyrotropin confirm the diagnosis of hypothyroidism caused by thyroid gland failure. An increase in free thyroxine estimate combined with a serum sensitive thyrotropin level suppressed to less than 0.1 mU/L establishes the diagnosis of thyrotoxicosis. In sick patients, a normal or raised serum free thyroxine estimate together with a normal level of serum thyrotropin suggests that the patient has neither hypothyroidism nor thyrotoxicosis. Patients with severe illnesses, generally in the intensive care unit, and those treated with certain drugs, as well as individuals with unusual thyroid disorders, may present with confusing laboratory findings. An understanding of the regulation of the thyroid hormone system and/or judicious consultation with an endocrinologist should enable the clinician to diagnose thyroid disease, if present, in such patients.

Female↗
PubMed1990

Differential response to L-triiodothyronine of anterior pituitary growth hormone messenger ribonucleic acid (mRNA) and beta-thyrotropin mRNA in a hypothyroid Walker 256 carcinoma-bearing rat model of nonthyroidal disease.

To continue our studies on the influence of T3 on TSH regulation in the Walker 256 carcinoma-bearing rat model of nonthyroidal disease, we measured the effect of T3 on pituitary content of beta TSH mRNA and rat (r) TSH in hypothyroid control (C) and tumor-bearing (T) rats. The effect of T3 on TSH regulation was compared to effects on GH mRNA and rGH in the same animals. mRNA content was normalized to a pool of pituitaries from euthyroid rats (= 1.0). beta TSH mRNA increased 18-fold in both hypothyroid C and T rats and then decreased similarly with increasing T3 infusion to a value of 0.1. GH mRNA content decreased to 0.11 +/- 0.01 in hypothyroid C rats, but to only 0.38 +/- 0.02 in T rats (P less than 0.001). The pituitary contents of GH mRNA and rGH in hypothyroid T rats was significantly greater than those in C rats at all T3 infusion rates. These data together with our previous report of decreased nuclear T3 in T rats suggest that regulation of beta TSH mRNA by T3 is intact in T rats, but occurs at a lower concentration of nuclear T3. In contrast, the GH mRNA response is enhanced, displaying differential regulation of these two T3-responsive gene products in this model of nonthyroidal illness.

Animals↗
PubMed1990

L-triiodothyronine (T3) regulates cellular growth rate, growth hormone production, and levels of nuclear T3 receptors via distinct dose-response ranges in cultured GC cells.

Cultured rat somatotrophic cells have been useful models for the study of thyroid hormone action. A consensus of previous reports has indicated that approximately 0.2 nM T3 results in 50% occupancy of T3 nuclear receptors as well as half-maximal stimulation of several T3 responses. To characterize the nature of thyroid hormone responses in GC cells, we studied in detail the T3 dose relationships between nuclear receptor occupancy and three thyroid hormone responses (cell growth, GH production, and T3 nuclear receptor regulation). The dose response to T3 for each parameter was unique, and none was identical to the dose response for receptor occupancy. Respective T3 concentrations and percentage of T3 nuclear receptor occupancy resulting in 50% of the maximal response for GC cell growth were 0.05 +/- 0.02 nM and 15 +/- 3% (four experiments), 0.15 +/- 0.04 nM and 27 +/- 3% for GH production (three experiments), and 2.1 nM and 69% for down-regulation of T3 nuclear receptors (two experiments). We conclude that the dose response for occupancy of the T3 nuclear receptor covers a wide range of T3 concentrations. Within the wide dose-response range for nuclear occupancy a spectrum of biological responses are regulated by distinct thyroid hormone dose ranges. These data suggest that the impact of T3 nuclear receptor occupancy on T3 responses might be variable and that the mechanisms involved may be clarified through studies in GC cells.

Animals↗
PubMed1990

Increase in hepatic mitochondrial alpha-glycerophosphate dehydrogenase activity after surgical stress in hyperthyroid rats.

We have established a rat model to investigate the relationship among serum thyroid hormones, nuclear iodothyronine receptors, and biological responses in thyrotoxic and euthyroid rats after surgical stress. Euthyroid or hyperthyroid rats (1.0 microgram T3/ml drinking water for 14 days) were subjected to surgical stress (ether anesthesia, laparotomy plus 50 mg talc, ip). Groups of control or stressed rats were killed 1, 2, and 3 days after surgical stress for measurement of thyroid hormone-responsive hepatic enzymes, alpha-glycerophosphate dehydrogenase (alpha GPD) and cytosol malic enzyme, serum T3, T3 nuclear receptors, and GH mRNA. Thyrotoxic rats had a 3.8-fold increase in alpha GPD compared to euthyroid rats before surgical stress; alpha GPD increased further to 5.9-fold the euthyroid value 1 day after surgery (P less than 0.001) to 5.1-fold after 2 days (P less than 0.05) and was similar to control after 3 days. Malic enzyme activity increased 10.5-fold before surgical stress and decreased slightly after surgical stress perhaps due to multifactorial regulation of that enzyme. No increases in T3 nuclear receptor or GH mRNA occurred after surgery in hyperthyroid rats or in any of the above parameters after surgical stress in euthyroid rats. Our findings suggest that increased alpha GPD after surgical stress in thyrotoxic rats was not due to either increased serum total T3 or free T3 or to increased T3-nuclear receptor complexes. Increased alpha GPD, therefore, appeared to be a consequence of postreceptor amplification of this thyroidal response.

Animals↗
PubMed1990

Medium 3,5,3'-triiodo-L-thyronine (T3) and T3 generated from L-thyroxine are exchangeable in cultured GC cells.

Previous studies in rats have shown that the ratio anterior pituitary nuclear L-triiodothyronine (T3) derived from intracellular deiodination of L-thyroxine [T3(T4)]/plasma T3(T4) is much greater than for exchangeable T3 [T3(T3)]. We have addressed the hypothesis that T3(T4) is either selectively accumulated or selectively retained by nuclei in comparison to exchangeable T3 [T3(T3)] in cultured GC cells. GC cells readily generated T3 from T4. When mean medium T3(T4) was experimentally maintained at a low percentage (less than 16%) of total medium T3, to mimic in vivo conditions, nuclear T3(T4) was 2-fold greater than nuclear T3(T3) and the nuclear: medium ratio for T3(T4) was 11-13-fold greater than for T3(T3). The t1/2 of release of nuclear T3(T4) and T3(T3) were indistinguishable from one another and both sources of T3 distributed similarly between the nuclear and cytosol compartments. Thus, in agreement with previous in vivo studies, T3(T4) is derived from cellular T4 and is a significant source of nuclear T3 in GC cells. No evidence for a separate nonexchangeable T3(T4) pool was found as the almost identical cellular distribution and release rates of T3(T4) and T3(T3) from nuclei suggest that T3(T4) generated in these pituitary tumor cells is fully exchangeable. Our findings suggest that the high concentration of T3(T4) in the nuclear fraction is the result of a high intracellular production rate of T3 from T4 relative to the rate of release of T3 from the cell.

Animals↗
PubMed1989

Effect of zinc(II) and other divalent cations on binding of 3,5,3'-triiodo-L-thyronine to nuclear receptors from cultured GC cells.

The effect of Zn(II) in 3,5,3'-triiodo-L-thyronine (T3) binding to nuclear receptors was studied in dialyzed 0.4 M NaCl extracts of nuclei from cultured GC cells. Addition of ZnCl2 to nuclear extracts resulted in a time- and concentration-dependent dissociation of T3 from nuclear receptors. Half-maximal dissociation occurred at 6 microM ZnCl2. Addition of ZnCl2 also resulted in a concentration-dependent inhibition of binding of T3 to nuclear receptors. Half-maximal inhibition of binding occurred at 1-3 microM ZnCl2. Scatchard analysis indicated that Zn(II) addition decreased kA and did not alter receptor concentration. These effects of Zn(II) were prevented when ZnCl2 was added to nuclear extracts in the presence of 5 mM EDTA or 5 mM dithiothreitol. Moreover, Zn(II)-induced inhibition of T3 binding was reversed by the addition of 5 mM EDTA. The inhibitory effect of Zn(II) on T3 binding seemed specific for nuclear receptors; no effect of Zn(II) on the binding of T3 to proteins in rat serum or GC cell cytosol or to rabbit anti-T3 serum was observed. Cd(II) had a similar concentration-dependent inhibition of T3 binding to nuclear receptors which was reversible. Our findings suggest that Zn(II) may play a role in T3 binding to nuclear receptors as well as its putative role in the binding of receptor to DNA.

Animals↗
PubMed1989

3,5,3'-Triiodothyronine determines the viability of GC cells after heat shock.

The heat shock (HS) response is a characteristic disruption of protein synthesis which occurs in cells exposed to a variety of noxious stimuli. The effects of HS on thyroid hormone-responsive GC cells were studied in an attempt to devise an in vitro model for the adaptive changes in thyroid hormone action caused by nonthyroidal disease. HS enhanced GC cell synthesis of 70 K and 90 K proteins in a manner previously described as characteristic of the HS response in many tissues. A step-wise decrease in GC cell viability occurred when cells were exposed to 45 C for 10 to 35 min. HS (45 C, 20 min) resulted in a rapid decrease in binding of T3 to nuclear receptors. Two hours after HS, analysis of T3 binding to isolated nuclei showed a 50% fall in binding capacity (240 fmol/100 micrograms DNA) compared to non-HS control cells (540 fmol/100 micrograms DNA); no difference in dissociation constant (Kd) was observed. The effect of thyroid hormone on cell viability after HS was then determined. Thyroid hormone depletion (less than or equal to 0.02 nM T3) resulted in significantly (P less than 0.05) enhanced cell viability compared to cells cultured with physiological T3 (0.2 nM) after incubation at 45 C for intervals of 10-35 min. This inverse relationship between medium T3 content and cell tolerance of HS occurred over a wide range of T3 concentrations. Mean cell viability after exposure to 45 C for 20 min was 44 +/- 3% in T3-depleted cultures (less than or equal to 0.02 nM), 27 +/- 1% to 32 +/- 5% in cultures containing 0.07-0.5 nM T3, and 13 +/- 3% in cultures containing 5 nM T3. Our results thus characterize the response to HS in GC cells and the relationship of this response to medium T3. Similar to the effect of various nonthyroidal diseases on rat hepatocytes in vivo, HS resulted in a decrease in T3 nuclear receptors. Similar to the adverse effect of thyroid hormone on morbidity in animals with experimental diseases or injury, GC cell viability after HS was inversely related to medium T3 content. Thus the HS response in GC cells may be a valuable in vitro model relevant to the effect on thyroid hormone action caused by nonthyroidal disease.

Animals↗
PubMed1989

Heat shock of cultured GC cells enhances the level of triiodothyronine induced growth hormone (GH) and GH messenger ribonucleic acid.

We have previously proposed that the effects of heat shock on thyroid hormone-responsive rat pituitary tumor (GC) cells may be a model relevant to the in vivo effects of nonthyroidal disease on thyroid hormone action. To determine the effects of heat shock on thyroid hormone responses, GC cells (normally cultured at 37 C) were studied after incubation at 41 C. After 18 h at 41 C there was enhanced synthesis of proteins (mol wt, 70,000 and 90,000) considered to be universal markers of the cellular response to heat shock. Incubation at 41 C also resulted in a significant decrease in GC cell viability and (after 24 h) arrest of GC cell growth. However, the induction of GH synthesis by T3 was significantly enhanced in GC cells stressed by incubation at 41 C. The addition of 5 nM T3 to thyroid hormone-depeleted GC cells resulted in a significantly greater (P less than 0.001) accumulation of GH (2642 +/- 280 ng/18 h) during 41 C incubation than during 37 C incubation (1223 +/- 175 ng/18 h). The enhanced T3-induced production of GH was coincident with a proportional increase (P less than 0.05) in cellular GH mRNA determined by dot hybridization analysis. Thus, the stress of 41 C incubation elicits a heat shock response in GC cells characterized by decreased viability and growth arrest, but enhanced accumulation of GH mRNA in response to T3. Our recent report on the identical effects due to the stress of implantation of the Walker 256 carcinoma on T3-induced rat pituitary GH mRNA in vivo suggests that heat shock of cultured GC cells is a valid in vitro model of nonthyroidal disease.

Animals↗
PubMed1989

Development and characterization of a variant GC cell line with L-triiodothyronine-independent growth and growth hormone production.

To facilitate studies of cell growth regulation by T3, we developed a variant GC cell line (V-GC) characterized by normal growth in T3-depleted (-T3) medium. The doubling time (dt) of V-GC cells was 28.8 h (-T3) and 28.0 h (+0.2 nM T3), respectively, whereas the dt of the parent GC cells, 24.0 h (+0.2 nM T3), increased to more than 100 h (-T3). The dt of V-GC cell was unaffected even by maximal T3 (5 nM). Cell protein (micrograms) per microgram DNA increased in GC cells in a T3 concentration-dependent manner, whereas V-GC cell protein was unaffected by T3. GH production appeared partially independent of T3 in V-GC cells. GH production (nanograms per 10(6)/h) in V-GC cells maintained for 3 months in -T3 medium was 3.3- to 4.6-fold greater than that in GC cells after 4 days in -T3 medium (P less than 0.001). Addition of T3 resulted in similar maximal GH production in both cell lines. The binding capacity and Ka of nuclear T3 receptors were similar in GC and V-GC cultures, and receptor down-regulation in response to added T3 occurred similarly in both cultures. Lastly, studies employing conditioned medium indicated that T3-independent growth of V-GC cells did not result from production of an autocrine growth factor. Our findings raise the possibility that overexpression of a transacting cell-specific gene-regulating protein that variably affects thyroid hormone-dependent genes may account for the phenotype of the V-GC cultures.

Animals↗
PubMed1989

Decreased anterior pituitary T3 nuclear receptors in a Walker 256 carcinoma-bearing rat model of nonthyroidal disease.

Rats bearing the Walker 256 carcinoma have decreased pituitary nuclear T3 but normal pituitary TSH content and response to experimental hypothyroidism. To elucidate further the role of T3 receptor occupancy and biological response in the tumor-bearing rat model of nonthyroidal disease, we measured the concentration of T3 nuclear receptors, rTSH and rGH and beta-TSH mRNA and GH mRNA in the anterior pituitary of euthyroid rats bearing the Walker 256 carcinoma. The abundance of T3 nuclear receptors was decreased in tumor-bearing rats and was associated with a decrease in mRNA content for beta-TSH and GH. alpha-tubulin mRNA was decreased to a comparable degree. The pituitary content of rTSH and rGH was, however, the same as in control animals. Since tumor rats have normal regulation of TSH secretion by thyroid hormone, the present findings suggest that TSH secretion in T rats is maintained by a lower T3 nuclear receptor occupancy than in controls. The decrease in beta-TSH mRNA may precede a decrease in TSH synthesis and changes in pituitary TSH stores. Since the decrease in GH mRNA was comparable to the decrease in alpha-tubulin mRNA, it does not appear to be specifically related to decreased T3 nuclear receptor occupancy. We conclude that, in the tumor-bearing rat model of nonthyroidal disease, decreases in beta-TSH mRNA occur despite a decreased T3 receptor occupancy. Both thyroid-dependent and thyroid-independent factors may be involved in regulating beta-TSH mRNA.

Animals↗
PubMed1988

Cell cycle dependence of thyroid hormone nuclear receptors in cultured GC cells: relationship to nuclear matrix.

The DNA synthesis (S) phase of cultured GC cells, a clonal rat pituitary tumor cell line, is characterized by increases in nuclear receptors for T3 and glucocorticoid (G) hormones. However, this increased receptor abundance appears functionally dissociated from the GH gene since GH messenger RNA (mRNA) synthesis is decreased in S-phase cells. We have now examined a putative structural correlate of this dissociation by measuring the abundance of T3 and G receptors and the GH gene in the nuclear matrix (NM)/scaffold fraction. NM of control and S-phase cultures both contained 30-50% of G receptors. Thirty to 50% of T3 receptors were also localized to NM of asynchronous cultures, but T3 receptor abundance (femtomoles per 100 micrograms of protein) was significantly decreased in NM of S-phase cultures: Exp 1 (control, 140 +/- 6.2; S-phase, 56.5 +/- 0.8; Exp 2 (control, 170 +/- 12; S-phase, 105 +/- 2.4). Nuclear scaffolds were digested with restriction enzymes to solubilize DNA loop structures and probed with GH complementary DNA (cDNA) to examine the distribution of transcribed regions of the GH gene. EcoR1 digestion resulted in an 11 kilobase fragment including the reported regulatory sequences for T3 receptors. No specific differences in GH gene localization to nuclear scaffold were observed between asynchronous and S-phase cultures or in different hormonal states. Thus, GH gene localization to nuclear scaffolds was not correlated with changes in transcription induced by T3 and G hormones or position in the cell cycle. These studies suggest that decreased concentration of T3 receptors in the NM fraction of S-phase cultures may be a structural correlate for cell cycle regulation of T3 receptor function.

Animals↗