Estradiol negatively regulates HIV-LTR promoter activity in glial cells.
HIV-associated dementia results from neuronal loss and an alteration of neuronal function due to a loss of synapses. While HIV infection in astrocytes is limited, astrocytes exhibit a chronic nonproductive infection that can lead to the release of neurotoxic proteins. Additionally, infection can disrupt the normal neurotrophic role of astrocytes that results in neuronal death. Gonadal steroid hormones are known to act as trophic and protective factors in the brain under a variety of normal and pathological conditions. In the present study, to determine if estrogen plays a role in the ability of Tat to function as a transcriptional activator within astrocytes, we examined the effect of estrogen on regulation of viral transcription. We utilized an immortalized human astrocyte cell line (SVGA) stably transfected with a reporter plasmid containing the HIV-1IIIB LTR driving the chloramphenicol acetyltransferase (CAT) gene. The amount of transcriptional activity was measured by quantifying the amount of CAT produced. We determined that 17beta-estradiol treatment (1 nM) had no effect on basal LTR activity. Following transfection with a Tat-expressing plasmid, there was a 100-fold increase in CAT production. This induction was reduced by 40% in cells pretreated with 17beta-estradiol. 17beta- Estradiol only suppressed transcription stimulated by Tat. Furthermore, we determined that this effect was specific to 17beta-estradiol and estrogen receptor agonists. This activity was limited to astrocytes as no effect was observed in a monocytic cell line. Finally, the mechanism of action did not involve an alteration in levels of Cdk9 or Cyclin T1 proteins necessary for Tat activation of the HIV-1 LTR. This study demonstrates a novel activity of 17beta-estradiol in glial cells that could play a role in the maintenance of neuronal health during HIV infection of the central nervous system.
Wilson
Melinda E
ME
Department of Physiology, College of Medicine, University of Kentucky, Lexington, Kentucky 40536, USA. mewils2@uky.edu
Allred
Kimberly F
KF
Bisotti
Anthony J
AJ
Bruce-Keller
Annadora
A
Chuahan
Ashok
A
Nath
Avindra
A
D000704:Analysis of Variance; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects*; D015153:Blotting, Western; D002461:Cell Line, Transformed; D002472:Cell Transformation, Viral; D015500:Chloramphenicol O-Acetyltransferase / Q000032:analysis / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004958:Estradiol / Q000494:pharmacology*; D005455:Fluorescent Antibody Technique; D005456:Fluorescent Dyes; D015967:Gene Expression Regulation, Viral / Q000187:drug effects*; D017930:Genes, Reporter; D015497:HIV-1 / Q000235:genetics*; D006367:HeLa Cells; D006801:Humans; D010957:Plasmids / Q000235:genetics; D011401:Promoter Regions, Genetic; D020079:Terminal Repeat Sequences / Q000235:genetics*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D005456:Fluorescent Dyes; D004958:Estradiol; D015500:Chloramphenicol O-Acetyltransferase