TR4 orphan receptor crosstalks to chicken ovalbumin upstream protein-transcription factor and thyroid hormone receptor to induce the transcriptional activity of the human immunodeficiency virus type 1 long-terminal repeat.
Here we investigate the roles of human testicular orphan receptors, TR2 and TR4, on the gene regulation of the long-terminal repeat of the human immunodeficiency virus type 1 (HIV-LTR). In gel-retardation assays, a palindromic element at the 5'-end of HIV-LTR,5'-AGGGGTCAGATATCCACTGACCTTT-3',showed high affinity to TR2 and TR4 with an equilibrium dissociation constant (Kd) of 1.11 +/- 0.48 (n = 3) and 0.52 +/- 0.12 nM (n = 3), respectively. Interestingly, each half-site of the palindromic element is sufficient to compete with the binding of the labeled palindromic element to TR2 or TR4 with an equilibrium inhibition constant (ki) around 10 nM. However, the transiently expressed TR2 or TR4 in Chinese hamster ovary (CHO) cells or Japanese quail muscle myoblasts (QM7) cells showed no activity in regulating the transcriptional activity of the chloramphenicol acetyltransferase (CAT) reporter gene inserted downstream of the HIV-LTR promoter. Although both TR2 and TR4 showed no effect on CAT activity by itself, our data showed only the TR4 could crosstalk to the chicken ovalbumin upstream protein-transcription factor (COUP-TF1) and thyroid hormone receptor (TR alpha 1), and potentiated the transcriptional activity of HIV-LTR on the CAT reporter gene regulated by COUP-TF1 and TR alpha 1. These results indicate that TR4, but not TR2, may couple to other nuclear receptors in the upregulation of the HIV replication.
George Whipple Laboratory for Cancer Research, Department of Pathology, University of Rochester, NY 14642, USA.
S B
SB
Hwang
J P
JP
Burbach
C
C
Chang
D000818:Animals; D016466:CHO Cells; D051838:COUP Transcription Factor I; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D003370:Coturnix; D006224:Cricetinae; D004268:DNA-Binding Proteins / Q000502:physiology*; D015870:Gene Expression; D016325:HIV Long Terminal Repeat / Q000235:genetics*; D006801:Humans; D008297:Male; D009132:Muscles; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000502:physiology*; D057107:Nuclear Receptor Subfamily 2, Group C, Member 1; D010047:Ovalbumin; D011401:Promoter Regions, Genetic; D011987:Receptors, Steroid / Q000235:genetics / Q000502:physiology*; D011988:Receptors, Thyroid Hormone / Q000235:genetics / Q000502:physiology*; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic; D014162:Transfection
D051838:COUP Transcription Factor I; D004268:DNA-Binding Proteins; C539822:NR2C1 protein, human; C490515:NR2C2 protein, human; C497589:NR2F1 protein, human; D009419:Nerve Tissue Proteins; D057107:Nuclear Receptor Subfamily 2, Group C, Member 1; D011987:Receptors, Steroid; D011988:Receptors, Thyroid Hormone; D014157:Transcription Factors; D010047:Ovalbumin; D015500:Chloramphenicol O-Acetyltransferase