AEGiS-11IAC: HIV Tat represses HLA-G expression in human trophoblasts.

11th International AIDS Conference

Vancouver, British Columbia — July 7-12, 1996

HIV Tat represses HLA-G expression in human trophoblasts.

Int Conf AIDS 1996 Jul 7-12; 11:23 (abstract no. LB.A.6008)
Slabiak TM, Lim KH; UCSF, Department of OB/GYN & Reproductive Sciences, San Francisco, CA. Fax: (415) 753-3271. E-mail: GIRL_CLONE@UCSF.EDU.

OBJECTIVE: To determine the effect of HIV Tat protein on trophoblast HLA-G expression in vitro.

METHODS: Transient transfections were performed on JEG human choriocarcinoma cells which are known to express the HLA-G molecule. JEG cells are grown to 1x10(6) cells per 60 mm petri dish. We co-transfected 1,2, and 3 micrograms of the eukaryotic expression vector containing the two exon HIV-Tat insert along with 5 micrograms of a construct containing the -200 bp HLA-G promoter attached to a beta-galactosidase reporter gene. Transfected cells were harvested after 72 hrs to determine their quantitative beta-galactosidase activity by measuring the chemiluminescent reaction with a single photon monitor (Boehringer Mannheim; beta-Gal Reporter Gene Assay). To demonstrate that our plasmid produces the HIV-Tat protein, we co-transfected 5 micrograms of an HIV-1 LTR linked to a CAT reporter gene (pBennCAT) with 1,2, and 3 micrograms of pcTAT DNA. Chloramphenical actyltransferase (CAT) enzymatic assays were performed to quantitatively measure the actual amount of CAT protein synthesized (Boehringer Mannheim; CAT ELISA). Transfection efficiency was normalized by using beta-galactosidase gene driven by the CMV promoter.

RESULTS: The two exon HIV-Tat insert plasmid yielded up to a 18-fold high CAT activities over the non-Tat expressing plasmid during co-transfection with the HIV-1 LTR construct. Our construct containing the two exon HIV-Tat insert demonstrated a two to three fold decrease in HLA-G promoter expression during co-transfections. Our results are normalized to the parental vector that does not contain the HIV-Tat insert.

CONCLUSION: While the Tat protein is known to stimulate HIV transcription, many other aspects of Tat have been recognized, including the suppression of MHC class I transcription. A sub-population of trophoblasts that invade the maternal tissue during pregnancy express high levels of the HLA-G molecule. Our co-transfection experiments suggest that the HIV-Tat protein can suppress HLA-G expression in vitro. HIV-Tat suppression of HLA-G appears to be mediated through the proximal 200 bp promoter region. Suppression of HLA-G transcription in trophoblasts may disturb the placental immunology resulting in adverse effects on the outcome of pregnancy. Since maternal HIV-1 infection has been indicated as a cause of miscarriage, the study of HLA-G expression during HIV-1 infection can provide a useful model for understanding maternal-fetal immunology of HIV-1 related miscarriage.

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LBA6008