The Effect of Steroid Hormones on Gene Transcription

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Nuclei isolated from excised soybean plumules that were treated with 2,4-dichlorophenoxyacetic acid (2,4-D) were active in transcription of four auxin-regulated genes or DNA sequences, which have been described previously (G. Hagen, A. Kleinschmidt, and T. Guilfoyle, Planta 162:147-153, 1984). The rates of transcription of the auxin-responsive sequences were 10-to 100-fold greater with nuclei isolated from auxin-treated plumules than with those from untreated plumules. The transcriptional response was also observed with hypocotyls of intact soybean seedlings and hypocotyl sections, as well as with green bean and mung bean plumules that were treated with 2,4-D. Other auxins, including 2,4,5-trichlorophenoxyacetic acid, a-naphthaleneacetic acid, and indole-3-acetic acid, also induced the transcriptional response. Increased transcription rates were observed within 5 min after application of auxins to excised plumules, and half-maximal to maximal transcription rates were achieved by 15 min after application of auxins. As little as 10-7 to 10-8 M 2,4-D induced a transcriptional response, but maximal transcription rates were achieved at 10-3 M 2,4-D. Brief treatment with the protein synthesis inhibitor cycloheximide did not inhibit the induction of transcription by auxins. These results clearly demonstrated that auxin-regulated gene expression is under rapid transcriptional control.Several experimental approaches have recently been used to demonstrate that applied auxins rapidly alter gene expression. Zurfluh and Guilfoyle (20) showed that 35S-labeled polypeptide patterns displayed on fluorograms of two-dimensional polyacrylamide gels were altered within 1 to 3 h after application of 2,4-dichlorophenoxyacetic acid (2,4-D) to soybean hypocotyl sections. By using in vitro translation of polyadenylated RNA purified from either untreated or auxin-treated stem or coleoptile sections and analysis of radioactive translation products on two-dimensional polyacrylamide gels, Zurfluh and Guilfoyle (21)(22)(23) and Theologis and Ray (15) have demonstrated that the amounts of specific translatable mRNAs are increased within 10 to 30 min after auxin application. Walker and Key (18) and Walker et al. (J. C. Walker, J. Legocka, L. Edelman, and J. L. Key, Plant Physiol., in press) have identified two cDNA clones to auxin-responsive mRNAs and have shown by RNA blot hybridization that the amounts of these mRNAs are increased in excised soybean hypocotyl sections after brief exposure to a variety of auxins. Walker et al. (in press) have also shown that application of fusicoccin and ethylene does not result in accumulation of auxin-specific mRNAs, and cytokinin does not block the accumulation of these mRNAs when applied along with auxins. We have selected and characterized four independent cDNA clones to auxin-regulated mRNAs from 2,4-D-treated soybean seedlings (6). With the four cDNA clone probes (pGH1, pGH2, pGH3, and pGH4), we have shown that specific mRNAs increase in amount (up to 50-fold) within 15 to 30 min after auxin applic...

Section: Resultscontrasting

confidence: 77%

Rapid induction of selective transcription by auxins.

Hagen¹,

Guilfoyle²

1985

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“…Glucocorticoid hormones act via specific intracellular receptor proteins to elicit a broad spectrum of characteristic responses in many types of target tissues and in in vitro cultured cell lines (1,3,19,44). After crossing the plasma membrane by diffusion, glucocorticoids bind to and potentiate a functional change in the receptor, which results in increased DNA-binding activity and selective recognition of transcriptional enhancer elements linked to promoters of steroid-regulated genes (7, 20, 30-32, 34, 44).…”

mentioning

confidence: 99%

“…As a result of this apparent sequence specificity, glucocorticoid-receptor complexes can directly modulate the rate of RNA synthesis. Alterations in transcriptional efficiency can directly account for gene expression changes of certain glucocorticoid responses (1,44), although in most cases the precise molecular processes under hormonal control have not been fully defined. Many responses may actually result from secondary or regulatory steroid effects in which functional gene products under direct transcriptional control selectively affect transcription, posttranscriptional expression, or posttranslational maturation and sorting of other biologically active gene products.…”

mentioning

confidence: 99%

Glucocorticoid-regulated compartmentalization of cell surface-associated glycoproteins in rat hepatoma cells: evidence for an independent response that requires receptor function and de novo RNA synthesis.

Haffar¹,

Vallerga²,

Marenda³

et al. 1987

The role of glucocorticoid hormones in the compartmentalization of cell surface-associated mouse mammary tumor virus (MMTV) glycoproteins was examined in M1.54, a cloned line of MMTV-infected rat hepatoma tissue culture cells. The expression of cellular [2-3HJmannose-labeled and cell surface '21I-labeled MMTV glycoproteins was examined throughout a time course of exposure to dexamethasone, a synthetic glucocorticoid. Posttranslational localization of cell surface MMTV glycoproteins required 6 h of exposure to hormone and occurred approximately 4 h after their initial production in an intracellular fraction. This regulated localization to the cell surface correlated with glucocorticoid receptor occupancy and was inhibited by exposure to RU 38486, a powerful antagonist of glucocorticoid-mediated responses. Cell surface immunoprecipitation demonstrated that actinomycin D, an inhibitor of de novo RNA synthesis, prevented regulated expression of cell surface viral glycoproteins, suggesting that newly synthesized cellular components mediate this process. The localization of cell surface MMTV glycoproteins appeared normal in a transcriptional variant (CR1) that produces basal levels of MMTV RNA and glycoprotein precursors in the presence of dexamethasone. Thus, regulated compartmentalization of viral glycoproteins is not an obligate consequence of a critical precursor concentration. Taken together, our results suggest that posttranslational trafficking of cell surface-destined MMTV glycoproteins resulted from an independent glucocorticoid hormone response that required receptor function and de novo RNA synthesis.

“…MMTV phosphoproteins are differentially matured in the presence or absence of glucocorticoid hormones (16), and their unambiguous detection in infected rat hepatoma cells has allowed experimental access to a novel steroid-dependent posttranslational regulatory circuit. Given current concepts on glucocorticoid hormone action, which suggest that binding of steroid-receptor complexes to high-affinity enhancer-like sites at and around a regulated gene results in transcriptional changes of that gene (1;Yamamoto,in press), a likely mechanism by which dexamethasone can posttranslationally affect protein expression is the stimulation in de novo synthesis of a crucial cellular factor with a maturation function. Our results suggest that the viral phosphorylated precursor polyprotein is a substrate target for such a hormone-regulated processing activity.…”

Section: Discussionmentioning

confidence: 99%

“…Genet., in press). These hormonal effects appear to be mediated by specific intracellular receptor proteins; the steroid-receptor interaction potentiates a functional change in the receptor that results in its increased DNA-binding activity and selective recognition of enhancer-like sites at or around genes under glucocorticoid control (1,7,10,18,26,(31)(32)(33)(34)(35)(36)(37)44,52; Yamamoto, in press). As a result of this apparent sequence specificity for glucocorticoid-receptor complexes, the rate of transcription of glucocorticoid-regulated genes is selectively modulated and accounts for gene expression changes of certain steroid responses (1; Yamamoto, in press).…”

mentioning

confidence: 99%

A distinct glucocorticoid hormone response regulates phosphoprotein maturation in rat hepatoma cells.

Karlsen¹,

Vallerga²,

Hone³

et al. 1986

Glucocorticoid hormone-dependent maturation of the mouse mammary tumor virus (MMTV) Glucocorticoid hormones elicit many types of responses in a variety of target tissues and in vitro-cultured cell lines (1, 4, 24; K. R. Yamamoto, Annu. Rev. Genet., in press). These hormonal effects appear to be mediated by specific intracellular receptor proteins; the steroid-receptor interaction potentiates a functional change in the receptor that results in its increased DNA-binding activity and selective recognition of enhancer-like sites at or around genes under glucocorticoid control (1,7,10,18,26,(31)(32)(33)(34)(35)(36)(37)44,52; Yamamoto, in press). As a result of this apparent sequence specificity for glucocorticoid-receptor complexes, the rate of transcription of glucocorticoid-regulated genes is selectively modulated and accounts for gene expression changes of certain steroid responses (1; Yamamoto, in press). However, the mechanisms of most glucocorticoid responses are unknown, and many responses may result from secondary or regulatory steroid effects in which functional gene products under direct transcriptional control affect the expression of other biologically active genes at posttranscriptional or posttranslational levels. For example, the accumulation of alpha,-acid glycoprotein mRNA appears to result from selective message stabilization after glucocorticoid treatment (50), while steroid-mediated changes in the levels or activities of specific processing enzymes have also been reported (12, 27, 45); mechanisms of these regulated processes are largely unknown. We have been using the expression and subsequent maturation of mouse mammary tumor virus (MMTV) precursor polyproteins in virally infected cell lines as versatile and sensitive probes to explore posttranslational regulatory circuits under steroid control (16,17 (17).To begin to assess the molecular details and cellular requirements of the steroid-regulated posttranslational path-574 on May 10, 2018 by guest