scholarly journals Regulation of Alternative Splicing of Liver Scavenger Receptor Class B Gene by Estrogen and the Involved Regulatory Splicing Factors

Endocrinology ◽  
2007 ◽  
Vol 148 (11) ◽  
pp. 5295-5304 ◽  
Author(s):  
Xiaohui Zhang ◽  
Andrea N. Moor ◽  
Kathleen A. Merkler ◽  
Qiyuan Liu ◽  
Mark P. McLean
Keyword(s):  
Alternative Splicing ◽  
Scavenger Receptor ◽  
Splicing Factor ◽  
Splicing Factors ◽  
Type I ◽  
Hepatic Expression ◽  
Hepatic Cells ◽  
Scavenger Receptor Class ◽  
Class B ◽  
Alternative Splicing Factor

The scavenger receptor class B isoforms (SR-B) type I and type II mediate the selective uptake of high-density lipoprotein cholesterol and promote reverse cholesterol transport, an important atherosclerosis protection mechanism, in the liver. Previously it was shown that the hepatic expression of SR-BI and SR-BII is regulated by estrogen. In the present study, we demonstrate that estrogen differentially regulates expression of the glycosylated and nonglycosylated forms of SR-BI and SR-BII in rat liver and hepatic cells. We report that estrogen mainly induces the down-regulation of glycosylated SR-BI and the up-regulation of nonglycosylated SR-BII. To study how estrogen regulates expression of the SR-B isoforms, we constructed a SR-B minigene containing minimal genomic sequences and were able to demonstrate that estrogen directly regulates the pre-mRNA alternative splicing of the exogenously expressed SR-B minigene in hepatic cells. Furthermore, we showed that the overexpression of splicing factors alternative splicing factor/splicing factor 2, Transformer (Tra)-2α, and Tra2β changes the splicing pattern of SR-B dramatically, whereas other splicing factors, such as heterogeneous nuclear ribonucleoprotein-G, SC-35, and arginine/serine-rich p40, had no effect. We also demonstrate that estrogen regulates Tra2β expression levels in liver cells. These studies suggest that estrogen may regulate SR-B isoform expression at both the RNA splicing and posttranslational modification levels and that, for alternative splicing regulation, estrogen may function by regulating the expression of the splicing factors alternative splicing factor/splicing factor 2, Tra2α, and especially Tra2β.

Hyperglycemia suppresses hepatic scavenger receptor class B type I expression

2008 ◽  
Vol 294 (1) ◽  
pp. E78-E87 ◽  
Author(s):  
Koji Murao ◽  
Xiao Yu ◽  
Hitomi Imachi ◽  
Wen M. Cao ◽  
Ke Chen ◽  
...  
Keyword(s):  
P38 Mapk ◽  
Promoter Activity ◽  
Scavenger Receptor ◽  
Inhibitory Effect ◽  
Dominant Negative ◽  
Type I ◽  
Hepatic Expression ◽  
Endogenous Expression ◽  
Scavenger Receptor Class ◽  
Class B

Hyperglycemia is a major risk factor for atherosclerotic disease. Hepatic scavenger receptor class B type I (SR-BI) binds HDL particles that mediate reverse cholesterol transport and thus lowers the risk of atherosclerosis. Here we examined glucose regulation of SR-BI gene expression in both HepG2 cells and whole animals. Results showed that hepatic SR-BI mRNA, protein, and uptake of cholesterol from HDL were halved following 48 h of exposure to 22.4 vs. 5.6 mM glucose. As in the case of the cell culture model, hepatic expression of SR-BI was lower in diabetic rats than in euglycemic rats. Transcriptional activity of the human SR-BI promoter paralleled endogenous expression of the gene, and this activity was dependent upon the dose of glucose. Next, we used inhibitors of select signal transduction pathways to demonstrate that glucose suppression of SR-BI was sensitive to the p38 MAPK inhibitor. Expression of a constitutively active p38 MAPK inhibited SR-BI promoter activity in the presence or absence of glucose. A dominant-negative p38 MAPK abolished the inhibitory effect of glucose on promoter activity. Deletional analysis located a 50-bp fragment of the promoter that mediated the effects of glucose. Within this DNA fragment there were several specificity protein-1 (Sp1) binding sites, and cellular knockdown of Sp1 abrogated its suppression by glucose. Together, these results indicate that the glucose suppression of SR-B1 expression is partially mediated by the activation of the p38 MAPK-Sp1 pathway and raise the possibility that the inhibition of hepatic SR-BI expression under high-glucose conditions provides a mechanism for accelerated atherosclerosis in diabetics.

scholarly journals Reduced Plasma High-Density Lipoprotein Cholesterol in Hyperthyroid Mice Coincides with Decreased Hepatic Adenosine 5′-Triphosphate-Binding Cassette Transporter 1 Expression

Endocrinology ◽  
2008 ◽  
Vol 149 (7) ◽  
pp. 3708-3712 ◽  
Author(s):  
Ivan Tancevski ◽  
Andreas Wehinger ◽  
Egon Demetz ◽  
Philipp Eller ◽  
Kristina Duwensee ◽  
...  
Keyword(s):  
Scavenger Receptor ◽  
Density Lipoprotein ◽  
Atp Binding ◽  
Type I ◽  
Hepatic Expression ◽  
Atp Binding Cassette Transporter ◽  
Scavenger Receptor Class ◽  
Class B ◽  
Plasma High Density ◽  
Atp Binding Cassette

The aim of the study was to investigate the influence of severe hyperthyroidism on plasma high-density lipoprotein cholesterol (HDL-C). Recently, it was shown in mice that increasing doses of T3 up-regulate hepatic expression of scavenger receptor class B, type I, resulting in increased clearance of plasma HDL-C. Here, we show that severe hyperthyroidism in mice did not affect hepatic expression of scavenger receptor class B, type I, but reduced hepatic expression of ATP-binding cassette transporter 1, accompanied by a 40% reduction of HDL-C. The sterol content of bile, liver, and feces was markedly increased, accompanied by up-regulation of hepatic cholesterol 7α-hydroxylase, and ATP-binding cassette transporter 5, which is known to promote biliary sterol secretion upon dimerization with ATP-binding cassette transporter 8. Both control and hyperthyroid mice exerted identical plasma clearance of iv injected [3H]HDL-C, supporting the view that severe hyperthyroidism does not affect HDL-C clearance but, rather, its formation via hepatic ATP-binding cassette transporter 1.

scholarly journals HDL modification by secretory phospholipase A2 promotes scavenger receptor class B type I interaction and accelerates HDL catabolism

2000 ◽  
Vol 41 (11) ◽  
pp. 1849-1857 ◽  
Author(s):  
Frederick C. de Beer ◽  
Patrice M. Connell ◽  
J. Yu ◽  
Maria C. de Beer ◽  
Nancy R. Webb ◽  
...  
Keyword(s):  
Phospholipase A2 ◽  
Scavenger Receptor ◽  
Type I ◽  
Secretory Phospholipase A2 ◽  
Secretory Phospholipase ◽  
Scavenger Receptor Class ◽  
Class B

MS81 LIVER-SPECIFIC LIPOPLEXES FOR THE KNOCKDOWN OF SCAVENGER RECEPTOR CLASS B TYPE I

2010 ◽  
Vol 11 (2) ◽  
pp. 126
Author(s):  
K. Duwensee ◽  
I. Tancevski ◽  
E. Demetz ◽  
P. Eller ◽  
C. Heim ◽  
...  
Keyword(s):  
Scavenger Receptor ◽  
Type I ◽  
Scavenger Receptor Class ◽  
Class B

scholarly journals Feedback Inhibition of Human Scavenger Receptor Class B Type I Gene Expression by Glucocorticoid in Adrenal and Ovarian Cells

Endocrinology ◽  
2010 ◽  
Vol 151 (7) ◽  
pp. 3214-3224 ◽  
Author(s):  
Sofia Mavridou ◽  
Maria Venihaki ◽  
Olga Rassouli ◽  
Christos Tsatsanis ◽  
Dimitris Kardassis
Keyword(s):  
Gene Expression ◽  
Gene Transcription ◽  
Feedback Inhibition ◽  
Steroid Hormone ◽  
Scavenger Receptor ◽  
Type I ◽  
Mrna Levels ◽  
Ovarian Cells ◽  
Scavenger Receptor Class ◽  
Class B

Scavenger receptor class B type I (SR-BI) facilitates the reverse transport of excess cholesterol from peripheral tissues to the liver via high-density lipoproteins. In steroidogenic tissues, SR-BI supplies cholesterol for steroid hormone production. We show here that the transcription of the human SR-BI gene is subject to feedback inhibition by glucocorticoid in adrenal and ovarian cells. SR-BI mRNA levels were increased in adrenals from corticosterone-insufficient Crh−/− mice, whereas corticosterone replacement by oral administration inhibited SR-BI gene expression in these mice. SR-BI mRNA levels were increased in adrenals from wild-type mice treated with metyrapone, a drug that blocks corticosterone synthesis. Experiments in adrenocortical H295R and ovarian SKOV-3 cells using cycloheximide and siRNA-mediated gene silencing revealed that glucocorticoid-mediated inhibition of SR-BI gene transcription requires de novo protein synthesis and the glucocorticoid receptor (GR). No direct binding of GR to the SR-BI promoter could be demonstrated in vitro and in vivo, suggesting an indirect mechanism of repression of SR-BI gene transcription by GR in adrenal cells. Deletion analysis established that the region of the human SR-BI promoter between nucleotides −201 and −62 is sufficient to mediate repression by glucocorticoid. This region contains putative binding sites for transcriptional repressors that could play a role in SR-BI gene regulation in response to glucocorticoid. In summary, this is the first report showing that glucocorticoid suppress SR-BI expression suggesting that steroidogenic tissues maintain steroid hormone homeostasis by prohibiting SR-BI-mediated high-density lipoprotein cholesterol uptake when the endogenous levels of glucocorticoid are elevated.

scholarly journals Inhibition of hepatic scavenger receptor-class B type I by RNA interference decreases atherosclerosis in rabbits

2012 ◽  
Vol 222 (2) ◽  
pp. 360-366 ◽  
Author(s):  
Egon Demetz ◽  
Ivan Tancevski ◽  
Kristina Duwensee ◽  
Ursula Stanzl ◽  
Eva Huber ◽  
...  
Keyword(s):  
Rna Interference ◽  
Scavenger Receptor ◽  
Type I ◽  
Scavenger Receptor Class ◽  
Class B
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