Sp1 Family Proteins Recognize the U5 Repressive Element of the Long Terminal Repeat of Human T Cell Leukemia Virus Type I through Binding to the CACCC Core Motif

Abstract

We have identified several nuclear proteins binding to the U5 repressive element (U5RE) at the U5 region of the human T cell leukemia virus type I (HTLV-I) long terminal repeat (LTR). In gel mobility shift assays with the U5RE DNA probe, Jurkat T cell nuclear proteins generated five different complexes, named U5RE binding protein complexes (U5RP)-A1, -A2, -A3, -B, and -C. Only U5RP-C was affected by pretreatment with an excess of poly(dI-dC) and was immunodepressed by anti-Ku/p80 antibodies, suggesting that U5RP-C is a nonspecific complex involving Ku antigen. UV cross-linking showed at least six nuclear proteins involved in the other complexes, including U5RP-A1, -A2, -A3, and -B. The sequence of the binding core element of these specific complexes, determined by competition assays and gel mobility shift assays using a series of the U5RE mutants, is CACCC which is identical to that for the Sp1 transcription factor. LTR with a mutant U5RE, which has no ability to bind with the nuclear proteins, showed stronger promoter activity than LTR with the wild U5RE, suggesting that the specific interaction of these U5RE-binding proteins might result in the U5-mediated repression. U5RP-A1 was supershifted by anti-Sp1 antibodies and U5RP-A2 and -B were supershifted by anti-Sp3 antibodies, suggesting that Sp1 or Sp3 is involved in U5RP-A1 or U5RP-A2 and -B, respectively. Although the other nuclear proteins remain to be characterized, these findings suggest that U5RE-binding proteins in U5RP-A1, -A2, -A3, and -B are involved in HTLV-I gene repression.

Transcription Factor HUB1 Represses Sp1-Mediated Gene Expression through the CACCC Box of HTLV-I U5RE but not the GC Box

“…9) We have identified a 27-bp transcriptional repressive element in the U5 region of 5′-long terminal repeat (LTR) (U5RE) to which several nuclear proteins bind -a process involving Sp1 and Sp3. 10) We also found that HUB1, a Krüppel type zinc finger protein, binds to U5RE by recognizing the TCCACCCC sequence.…”

“…10) We verified the effects of Sp1 using Drosophila SL2 cells, which are known to be devoid of endogenous Sp1 activity.…”

“…We previously showed that the sequence recognized by both Sp1 and HUB1 includes a CACCC motif within the U5RE, 10,11) and that whereas Sp1 mainly functions as a transcriptional activator of many genes, HUB1 is a repressor.…”

Characterization of Emerging European-Like Porcine Reproductive and Respiratory Syndrome Virus Isolates in the United States

“…2). CACCC stretches have been shown to be important in binding to host cell transcription factors important in growth control, apoptosis, and angiogenesis (4,44) and are also utilized for double-stranded DNA virus and retroviral transcription (38,44,56). Strict maintenance of these CACCC domains was seen in all but a few known PRRSV leader sequences (Fig.…”

Characterization of the Human Transcobalamin II Promoter

“…These include the rat D 2 dopamine promoter (43), the rat ␣ 2 A adrenergic promoter (44), the long terminal receptor of the human T cell leukemia virus type I promoter (45), the rat fatty acid synthase promoter (46), and the rat smooth muscle myosin heavy chain promoter (47). The finding that the GC or GT box is involved in the negative regulation of gene expression implies that the GC or GT box may play a more complicated role in transcriptional regulation.…”