A new regulatory element that augments the Tax-dependent enhancer of human T-cell leukemia virus type 1 and cloning of cDNAs encoding its binding proteins

Abstract

The Tax protein of human T-cell leukemia virus type 1 (HTLV-1) trans activates the 21-bp enhancer of HTLV-1. A sequence of more than two copies of the 21-bp enhancer is efficiently activated by Tax, but one copy is not activated extensively. Another sequence (TRE-2, positions-163 to-117) adjacent to the 21-bp enhancer in the long terminal repeat of HTLV-1 can enhance a single copy of the 21-bp enhancer activity in trans activation by Tax. This sequence contains motifs related to the Ets-and NF-KB-binding sequences, but mutations at these sites indicated that neither is responsive to cooperation with the 21-bp enhancer. A deletion mutation of TRE-2 identified 25 bases at positions-158 to-134 (TRE-2S) as an essential sequence, and TRE-2S was sufficient to give maximum cooperation with one copy of the 21-bp enhancer in trans activation by Tax protein. Using TRE-2S as a probe, we screened a cDNA library of HUT102 cells by the Southwestern (DNA-protein) procedure and isolated two cDNA clones, THP-1 and-2. These two clones encode TRE-2Sbinding proteins, and they differ by only an extra 17 amino acids in THP-2. Both THP proteins contain five zinc finger motifs which are strikingly similar to those of the GLI family, an amplified gene product in glyoma cells. The binding site of THP-1 and-2 was GAACCACCCA in TRE-2S, which is highly homologous to the GLI-binding site. These results suggest that binding of THP to TRE-2S may be involved in cooperation with one copy of the 21-bp enhancer in responding to Tax trans activation.

Interaction of Gli2 with CREB Protein on DNA Elements in the Long Terminal Repeat of Human T-Cell Leukemia Virus Type 1 Is Responsible for Transcriptional Activation by Tax Protein

“…The Gal4 fusion protein of Gli2 isoforms enhanced gene expression from a reporter carrying the Gal4binding site and the 21-bp sequence in the presence of Tax, but not in the absence of Tax. These previous observations suggest that binding of Gli2 to TRE2S is involved in Tax-mediated trans activation cooperating with 21-bp sequence (31), implying that another cellular signal may control HTLV-1 gene expression in addition to that through 21-bp sequence.…”

“…Hut102 cells, a T-cell line infected with HTLV-1, were maintained in RPMI 1640 with 10% fetal calf serum. A reporter plasmid, pTK-Luc, containing a basic promoter of thymidine kinase which is linked to the luciferase gene, and pUCdN55-CAT, carrying the promoter region of HTLV-1 LTR, from which enhancers were deleted, were previously described (31). Into these basic constructs, TRE2S, consisting of 25 bp (31) and the 21-bp sequence, was inserted, constructing pTRE2S-(n)-21bp-TK-Luc.…”

“…Gene expression of retroviruses is regulated by cis elements in the long terminal repeats (LTRs) at both termini of the proviral genome. HTLV-1, however, has a unique regulatory system to enhance its own gene expression: HTLV-1 transcription is trans activated by its own product, Tax (4,6,25,26), responding to three repeats of 21-bp sequence in the LTR (7,24), and TRE2S (18,30,31). Reconstitution experiments have revealed that at least two direct repeats of the 21-bp sequence alone are sufficient for efficient activation by Tax (7,20,24); however, one copy of the 21-bp sequence is activated only weakly.…”

“…On the other hand, another element termed TRE2S was proposed to contribute to trans activation induced by Tax (1). However, the TRE2S element requires the 21-bp sequence to respond to Tax protein (18,30,31); furthermore, TRE2S alone was totally inactive even in its multiple form (30,31). TRE2S, therefore, seems to have a unique property as an enhancer, although enhancers are generally active in a multiple form.…”

A Novel Zinc Finger Protein, Zic, Is Involved in Neurogenesis, Especially in the Cell Lineage of Cerebellar Granule Cells

“…Yoshida (Institute of Medical Science, University of Tokyo) . Their nucleotide sequences were based on the GLI-binding sites or the tax-responsive element of HTLV-I (Tanimura et al ., 1993) . The double-stranded oligonucleotide probes were prepared by annealing of the following two complementary oligonucleotides : where the underlining indicates the GLI-binding sites .…”