Brd4 Is Involved in Multiple Processes of the Bovine Papillomavirus Type 1 Life Cycle

Ilves, Ivar; Mäemets, Kristina; Silla, Toomas; Janikson, Kadri; Ustav, Mart

doi:10.1128/jvi.80.7.3660-3665.2006

Cited by 79 publications

(106 citation statements)

References 25 publications

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“…39 Third, the E8 Ù E2C protein acts as a repressor of transcription and replication 18,39,40 whereas Brd4 has been reported to contribute also to the activation of transcription and replication by E2. 32,56,59 Therefore, it is likely that the E8 domain interacts with host cell proteins different from Brd4 that may enhance binding of E8 Ù E2C to chromatin and also contribute to transcriptional repression. Taken together it can be hypothesized that a common function of the different aminoterminal domains in E2 or E8 Ù E2C is to allow for an efficient recognition of chromatinized HPV promoter sequences to achieve repression of the promoter.…”

Section: E2c-ha Psg E8mentioning

confidence: 99%

The E8 repression domain can replace the E2 transactivation domain for growth inhibition of HeLa cells by papillomavirus E2 proteins

Stubenrauch

Straub

Fertey

et al. 2007

Intl Journal of Cancer

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Continuous expression of the human papillomavirus (HPV) oncoproteins E6 and E7 is required for the growth of cervical cancer cell lines. So far, only the overexpression of the wild type papillomavirus E2 protein has been shown to induce growth arrest in HPV18-positive HeLa cells by repressing E6/E7 transcription. Growth arrest by E2 requires the aminoterminal transcription activation domain in addition to the carboxyterminal DNA-binding domain. Several papillomaviruses such as the carcinogenic HPV31 express in addition to E2 an E8 Ù E2C fusion protein in which the E8 domain, which is required for repression of replication and transcription, replaces the E2 activation domain. Infections with certain human papillomaviruses (HPV), most notably types 16 and 18, are a necessary risk factor for the development of cervical cancer.1 While the HPV genome is present in an episomal state in low-grade lesions, the whole viral genome or fragments thereof are often integrated into the chromosomal DNA of the host cell in the majority of HPV-induced carcinomas.2 The HeLa cell line was derived from a cervical cancer and contains a partial HPV18 genome integrated into the host chromosomes. 4-7 The E6 and E7 proteins derived from carcinogenic HPVs interfere with cell cycle control proteins. E6 forms a ternary complex with the E3 ubiquitin ligase E6AP and p53, which results in the degradation of p53 and therefore in the reduction of mRNA levels of p53 target genes. 8,9 The E7 protein binds to Rb family members and disrupts Rb/E2F complexes, resulting in increased expression of E2F-regulated genes. 10,11 In addition, the E7 protein enhances degradation of Rb family members. 12,13 A peculiar feature of carcinogenic HPV types is that the E6 and E7 transcripts are generated by alternative splicing from a common precursor RNA.14 Transfection studies using reporter plasmids of the corresponding promoters of HPV16, 18 or 31 demonstrated that coexpression of viral E2 proteins resulted in repression of promoter activity, which is due to binding of E2 to proximal recognition sequences. [15][16][17][18][19] Similarly, repression of the endogenous HPV18 E6/E7 promoter in HeLa cells could be observed when E2 genes from bovine papillomavirus Type 1 (BPV1), HPV16 or 18 were introduced into HeLa cells. [20][21][22] Overexpression of E2 resulted in growth arrest or apoptosis of HPV-positive cervical cancer cells. [20][21][22] This was mainly due to the specific repression of the HPV promoter as the growth of HPV negative cells was not influenced by overexpression of E2. [20][21][22][23][24] In line with this, the reduction of E6/E7 mRNA levels resulted in an increase in E6 and E7 target protein levels such as p53, p21 and pRb. [20][21][22][23][24] E2 proteins bind as dimers to specific DNA sequences (E2 binding site, E2BS) to modulate transcription and viral DNA replication. The carboxyterminal domain which comprises 100 amino acids (aa) is sufficient for sequence-specific DNA recognition and dimerization 25 (Fig. 1). The E2 aminoterminal domain of...

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Section: E2c-ha Psg E8mentioning

confidence: 99%

The E8 repression domain can replace the E2 transactivation domain for growth inhibition of HeLa cells by papillomavirus E2 proteins

Stubenrauch

Straub

Fertey

et al. 2007

Intl Journal of Cancer

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“…Another possible role for TopBP1 in regulating E2 function is as a chromatin receptor during mitosis. Although Brd4 is the chromatin receptor for some E2 proteins (1,7,23), it does not seem to be for HPV16 E2. We propose that TopBP1 is an excellent candidate to act as a mitotic chromatin receptor for HPV16 E2, as TopBP1 is associated with mitotic bodies (9, 15), and we have indeed observed colocalization of TopBP1 and E2 at late stages of mitosis (Fig.…”

Section: Vol 81 2007mentioning

confidence: 99%

TopBP1 Regulates Human Papillomavirus Type 16 E2 Interaction with Chromatin

Donaldson

Boner

Morgan

2007

J Virol

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Human papillomavirus type 16 (HPV16) E2 regulates transcription from and replication of the viral genome, in association with viral and cellular factors. HPV16 E2 interacts functionally with TopBP1, a cellular protein essential for the initiation of cellular, and potentially viral, DNA replication. This report demonstrates that the absence of TopBP1 results in the redistribution of HPV16 E2 into an alternative cellular protein complex, resulting in enhanced affinity for chromatin. This redistribution does not significantly alter the ability of HPV16 E2 to either activate or repress transcription. We also show colocalization of both proteins on chromatin at late stages of mitosis, suggesting that TopBP1 could be the mitotic chromatin receptor for HPV16 E2. The possible significance of the results for the regulation of the viral life cycle is discussed.All human papillomaviruses (HPVs) encode an E2 protein which regulates the replication of and transcription from the viral genome (5). We have previously identified TopBP1 as a functional cellular interacting partner for HPV type 16 (HPV16) E2 (hereafter called E2) which increases its transcriptional and DNA replication activity (2, 3). TopBP1 is a BRCT repeat-containing protein that can regulate many aspects of nucleic acid metabolism, including transcription, replication, and DNA damage and repair processes (6,10,12,14,(19)(20)(21)(22). As both E2 and TopBP1 are chromatin-associated proteins, we investigated whether TopBP1 may be a chromatin receptor for E2 and a regulator of E2 function.TopBP1 is not essential for E2 transcriptional activity. 293T cells (chosen due to their high transfectability and ease of TopBP1 knockdown as demonstrated below) were cultured and used in transcription assays as previously described (18). TopBP1 was depleted or mock depleted using pSUPERTopBP1 or pSUPER plasmids (8). From the results shown in Fig. 1A, it is clear that removal of TopBP1 has little effect on the ability of E2 to activate transcription from the thymidine kinase promoter or to repress transcription from the HPV18 promoter. Thirty micrograms of protein from each lysate from the assays whose results are shown in Fig. 1A was Western blotted and probed, as described previously (3), for TopBP1 and E2 (Fig. 1B). Good depletion of TopBP1 can be observed in samples transfected with the pSUPER-TopBP1 plasmid as opposed to the control plasmid. In samples where TopBP1 is depleted, the levels of E2 are markedly elevated. Using the same protein preparation technique, we demonstrated that this increased level of E2 was not due to enhanced stability of the E2 protein (not shown). We therefore investigated the ability of TopBP1 to alter the subcellular localization, and therefore potentially the solubilization, of E2.Depletion of TopBP1 alters the subcellular localization of E2. 293T cells transiently transfected with E2 and TopBP1 depletion plasmids were subjected to cytoplasmic/nuclear fractionation as depicted in Fig. 1C (17). Figure 1D shows that depletion of TopBP1 results in E...

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“…This recruitment of pTEFb by Brd4 stimulates the transcription of primary responsive genes (19). Moreover, papillomavirus E2-mediated viral transcriptional activation and repression functions are dependent on Brd4 (22,35,41,42,45,52).…”

mentioning

confidence: 99%

The Brd4 Extraterminal Domain Confers Transcription Activation Independent of pTEFb by Recruiting Multiple Proteins, Including NSD3

Rahman

Sowa

Ottinger

et al. 2011

Molecular and Cellular Biology

481

490

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Bromodomain protein 4 (Brd4) plays critical roles in development, cancer progression, and virus-host pathogenesis. To gain mechanistic insight into the various biological functions of Brd4, we performed a proteomic analysis to identify and characterize Brd4-associated cellular proteins. We found that the extraterminal (ET) domain, whose function has to date not been determined, interacts with NSD3, JMJD6, CHD4, GLTSCR1, and ATAD5. These ET-domain interactions were also conserved for Brd2 and Brd3, the other human BET proteins tested. We demonstrated that GLTSCR1, NSD3, and JMJD6 impart a pTEFb-independent transcriptional activation function on Brd4. NSD3 as well as JMJD6 is recruited to regulated genes in a Brd4-dependent manner. Moreover, we found that depletion of Brd4 or NSD3 reduces H3K36 methylation, demonstrating that the Brd4/NSD3 complex regulates this specific histone modification. Our results indicate that the Brd4 ET domain through the recruitment of the specific effectors regulates transcriptional activity. In particular, we show that one of these effectors, NSD3, regulates transcription by modifying the chromatin microenvironment at Brd4 target genes. Our study thus identifies the ET domain as a second important transcriptional regulatory domain for Brd4 in addition to the carboxyl-terminal domain (CTD) that interacts with pTEFb.One mechanism underlying the regulation of gene expression is the targeting of multiprotein complexes to modified histones, which then alters the chromatin microenvironment to stimulate or inhibit gene expression. The bromodomains and extraterminal (BET) domain family of proteins are characterized by the presence of two conserved domains, the tandem, amino-terminal bromodomains (BDI and BDII), which bind acetylated chromatin, and an extraterminal (ET) domain, whose function is unknown. The BET family is conserved from yeast to mammals and includes Saccharomyces cerevisiae bromodomain factor 1 (bdf1) and bromodomain factor 2 (bdf2), Drosophila melanogaster female sterile homeotic [fs(1)h], and mammalian Brd2, Brd3, Brd4, and testes/oocyte-specific BrdT/ Brd6. In yeast, deletion of bdf1 leads to a reduced growth rate and deletion of both bdf1 and bdf2 is lethal (27). Mutations of fs(1)h cause segmental abnormalities, including missing organs and homeotic transformations in the progeny of mutant females in Drosophila (13). Knockout of Brd4 or Brd2 in mice results in early embryonic lethality (18,21).The BET proteins have been shown to be important players in human disease, including viral infections and cancer. Several different viruses target the individual BET proteins for a variety of purposes but often to regulate viral and cellular transcription (4,7,31,37,41,45,57,60). The papillomavirus E2 proteins bind to Brd4, and some utilize this interaction in tethering the viral genomes to mitotic chromosomes (1,3,57,59). The papillomavirus E2 transcriptional activation functions are also mediated through Brd4 (35,41,42). With regard to human cancer, the Brd4-NUT and Brd3-NUT fusio...

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Brd4 Is Involved in Multiple Processes of the Bovine Papillomavirus Type 1 Life Cycle

Cited by 79 publications

References 25 publications

The E8 repression domain can replace the E2 transactivation domain for growth inhibition of HeLa cells by papillomavirus E2 proteins

The E8 repression domain can replace the E2 transactivation domain for growth inhibition of HeLa cells by papillomavirus E2 proteins

TopBP1 Regulates Human Papillomavirus Type 16 E2 Interaction with Chromatin

The Brd4 Extraterminal Domain Confers Transcription Activation Independent of pTEFb by Recruiting Multiple Proteins, Including NSD3

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