Abstract
Expression of the adenovirus E1A N-terminal transcription repression domain alone (E1A 1-80) represses transcription from specific promoters such as HER2 [1] and from reconstituted chromatin [2]. Significantly, E1A 1-80 can induce the death of human breast cancer cells over-expressing the HER2 oncogene [1] as well as other cancer cells. Here, we report that E1A 1-80 alone is sufficient to inhibit H3K18 acetylation in vivo and p300-mediated H3K18 acetylation in reconstituted chromatin. Of interest, hypoacetylation of H3K18 has been correlated with the survival of tumor cells and the poor prognosis of many cancers [3, 4]. E1A 1-80 enhances p300 autoacetylation and concurrently inhibits H3K18 acetylation in chromatin in a dose-dependent manner. Pre-acetylation of p300 by incubation with acetyl-CoA alone reduces p300's ability to acetylate H3K18 in chromatin. Additional acetylation of p300 in the presence of E1A 1-80 produces stronger inhibition of H3K18 acetylation. These findings indicate that autoacetylation of p300 greatly reduces its ability to acetylate H3K18. The results reported here combined with our previous findings suggest that E1A can repress transcription by multiple strategies, including altering the chromatin modifying activity of p300 and dissociating TFIID from the TATA box thus disrupting formation of the transcription pre-initiation complex [5, 6].
Highlights
The first gene expressed after adenovirus (Ad) infection is early gene 1A (E1A)
These studies suggested a two-step model of E1A repression [16, 18]: first, E1A gains access to repressible promoters by interaction of E1A repression sub-domain 1 and 2 with a promoter-bound cellular target such as p300; second, the E1A N-terminus subdomain 1 interacts with TFIID and disrupts the TFIID/TATA complex blocking pre-initiation complex (PIC) formation [6, 18]
Since chromatin is the natural template for transcriptional regulation, we have recently examined E1A-mediated transcriptional repression in reconstituted chromatin, and found that transcription from an E1Arepressible template in chromatin is effectively repressed by E1A 1-80 and E1A 243R [2]
Summary
The first gene expressed after adenovirus (Ad) infection is early gene 1A (E1A). Group C Ad E1A transcribes two highly related mRNAs which code for two regulatory proteins (E1A 243R and E1A 289R). An important function encoded in the E1A 243R protein N-terminus is transcriptional repression of cellular genes involved in cell proliferation and differentiation [14, 15]. Single amino acid substitution analysis showed that there are two E1A N-terminal repression sub-domains which interact with the cellular multifunctional histone acetyl transferase (HAT), p300, as well as the basal transcription machinery through TBP (TATA-binding protein). These studies suggested a two-step model of E1A repression [16, 18]: first, E1A gains access to repressible promoters by interaction of E1A repression sub-domain 1 (amino acids ~1-30) and 2 (amino acids ~48-60) with a promoter-bound cellular target such as p300; second, the E1A N-terminus subdomain 1 interacts with TFIID and disrupts the TFIID/TATA complex blocking pre-initiation complex (PIC) formation [6, 18]. We investigate the effect of the E1A N-terminal repression domain on p300 autoacetylation and on p300mediated H3K18 acetylation in the context of in vitro assembled chromatin
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