Sequence-specific activation of transcription by adenovirus EIa products is observed in HeLa cells but not in 293 cells

Adenovirus late-phase infection is controlled by a novel L4 promoter

During human adenovirus 5 infection, a temporal cascade of gene expression leads ultimately to the production of large amounts of the proteins needed to construct progeny virions. However, the mechanism for the activation of the major late gene that encodes these viral structural proteins has not been well understood. We show here that two key positive regulators of the major late gene, L4-22K and L4-33K, previously thought to be expressed under the control of the major late promoter itself, initially are expressed from a novel promoter that is embedded within the major late gene and dedicated to their expression. This L4 promoter is required for late gene expression and is activated by a combination of viral protein activators produced during the infection, including E1A, E4 Orf3, and the intermediate-phase protein IVa2, and also by viral genome replication. This new understanding redraws the long-established view of how adenoviral gene expression patterns are controlled and offers new ways to manipulate that gene expression cascade for adenovirus vector applications.

Induction of a cellular enzyme for energy metabolism by transforming domains of adenovirus E1a

Brain creatine kinase is a major enzyme of cellular energy metabolism. It is overexpressed in a wide range of tumor cell lines and is used as a tumor marker. We reported recently that the promoter of the human gene has a strong sequence similarity to the adenovirus E2E promoter. This similarity suggested that the brain creatine kinase gene may be regulated by the viral activator E1a. Experiments reported here showed that both enzyme activity and mRNA levels were induced by the oncogenic products of the E1a region of adenovirus type 5, but unlike the viral E2E promoter, which is induced predominantly by E1a domain 3, brain creatine kinase induction required domains 1 and 2. These domains are important for transformation and for the association of E1a with the retinoblastoma gene product and other cellular proteins. The induction by an oncogene of a cellular gene for energy metabolism may be of significance for the metabolic events that take place after oncogenic activation.

Induction of a cellular enzyme for energy metabolism by transforming domains of adenovirus E1a

Brain creatine kinase is a major enzyme of cellular energy metabolism. It is overexpressed in a wide range of tumor cell lines and is used as a tumor marker. We reported recently that the promoter of the human gene has a strong sequence similarity to the adenovirus E2E promoter. This similarity suggested that the brain creatine kinase gene may be regulated by the viral activator E1a. Experiments reported here showed that both enzyme activity and mRNA levels were induced by the oncogenic products of the E1a region of adenovirus type 5, but unlike the viral E2E promoter, which is induced predominantly by E1a domain 3, brain creatine kinase induction required domains 1 and 2. These domains are important for transformation and for the association of E1a with the retinoblastoma gene product and other cellular proteins. The induction by an oncogene of a cellular gene for energy metabolism may be of significance for the metabolic events that take place after oncogenic activation.

Nuclear factor EF-1A binds to the adenovirus E1A core enhancer element and to other transcriptional control regions

We have identified a cellular enhancer-binding protein, present in nuclear extracts prepared from human and rodent cells, that binds to the adenovirus E1A enhancer element I sequence. The factor has been termed EF-1A, for enhancer-binding factor to the E1A core motif. EF-1A was found to bind to two adjacent, related sequence motifs in the E1A enhancer region (termed sites A and B). The binding of EF-1A to these adjacent sites, or to synthetic dimerized sites of either motif, was cooperative. The cooperative binding of EF-1A to these sites was not subject to strict spacing constraints. EF-1A also bound to related sequences upstream of the E1A enhancer region and in the polyomavirus and adenovirus E4 enhancer regions. The EF-1A-binding region in the E1A enhancer stimulated expression of a linked gene in human 293 cells when multimerized. Based on the contact sites for EF-1A binding determined by chemical interference assays, this protein appears to be distinct from any previously characterized nuclear binding protein.

Nuclear factor EF-1A binds to the adenovirus E1A core enhancer element and to other transcriptional control regions

We have identified a cellular enhancer-binding protein, present in nuclear extracts prepared from human and rodent cells, that binds to the adenovirus E1A enhancer element I sequence. The factor has been termed EF-1A, for enhancer-binding factor to the E1A core motif. EF-1A was found to bind to two adjacent, related sequence motifs in the E1A enhancer region (termed sites A and B). The binding of EF-1A to these adjacent sites, or to synthetic dimerized sites of either motif, was cooperative. The cooperative binding of EF-1A to these sites was not subject to strict spacing constraints. EF-1A also bound to related sequences upstream of the E1A enhancer region and in the polyomavirus and adenovirus E4 enhancer regions. The EF-1A-binding region in the E1A enhancer stimulated expression of a linked gene in human 293 cells when multimerized. Based on the contact sites for EF-1A binding determined by chemical interference assays, this protein appears to be distinct from any previously characterized nuclear binding protein.

Replication-induced stimulation of the major late promoter of adenovirus is correlated to the binding of a factor to sequences in the first intron

The sequence requirements for transcriptional stimulation of the adenovirus major late promoter (MLP) by the products of the early transcription unit Ela and by the replication of viral DNA were analyzed by in vitro transcription. Sequences upstream of +33 are involved in the moderate Ela-responsiveness of the MLP, while sequences between +33 and +131 are required for its major replication-induced transcriptional activation. Dnase I footprinting experiments delineate a sequence component, extending from +76 to +120, which binds protein(s) only in extracts of cells where viral DNA replication occurred. Taken together, these results suggest that the replication-dependent stimulation of the MLP is mediated by the increased binding of this protein(s).

Multiple transcription factors interact with the adenovirus-2 EII-late promoter: evidence for a novel CCAAT recognition factor

Multiple cellular transcription factors have been shown to interact with the upstream region of the adenovirus-2 EIIa-late promoter. One of these factors recognises each of the three CCAAT motifs present in the EIIL promoter at positions -72, -135 and -229, as well as the CCAAT elements in the rat albumin and herpes virus thymidine kinase promoters. A mutation known to reduce thymidine kinase promoter activity in vivo and in vitro abolishes binding of the factor, termed CCAAT recognition factor (CRF), which appears to be distinct from previously identified CCAAT factors. In addition, another protein, termed upstream factor II (USFII), shares binding sites at position -110 in the EIIL promoter and in the c-fos enhancer adjacent to the serum regulatable element. The recognition site for USFII is also found in the c-fos promoter and in the adenovirus early region EIV and EIIa-early promoters. An Sp1 recognition site has also been identified at position -41, and the binding sites for Sp1, USFII and CRF are all required for efficient EIIa-late promoter function. Finally, an additional factor recognising the consensus GGGGGGNT has been detected.

Promoter trans-activation of protooncogenes c-fos and c-myc, but not c-Ha-ras, by products of adenovirus early region 1A

The E1A (early region 1A) oncogene products of adenovirus type 2 trans-activate the other early viral transcription units, as well as some cellular promoters. Using a short-term cotransfection assay in murine NIH 3T3 fibroblasts, we show that c-fos and c-myc promoter activities are stimulated by the E1A proteins, whereas c-Ha-ras transcription is not affected. The product of E1A 13S mRNA is responsible for the trans-activation, whereas the 12S mRNA product has no effect. Analysis of the c-fos promoter sequences required for the E1A stimulation shows that responsive sequences are located between positions -402 and -240 upstream of the transcription initiation site. This same region also contains the c-fos serum-responsive element. Furthermore, transcription of the endogenous c-fos gene in HeLa cells is increased after E1A transfection.

A cellular transcription factor E4F1 interacts with an E1a-inducible enhancer and mediates constitutive enhancer function in vitro

Efficient transcription of the adenovirus E1a-inducible E4 gene is mediated by an E1a-dependent enhancer in vivo. In vitro, the enhancer functions constitutively in the absence of E1a, conferring high levels of transcription on the E4 and heterologous promoters. Binding of a cellular transcription factor, E4F1, to two sites within the E4 enhancer and to one other functionally important site located directly upstream of the E4 TATA box is required for transcriptional activity. The relationship between the enhancer and the TATA box proximal site is further demonstrated by the fact that the E4 enhancer can be functionally substituted by two copies of the TATA box proximal site. These and other results suggest that the E4 promoter may be comprised solely of multiple E4F1 binding sites and a TATA box. In addition to the E4 promoter, E4F1 interacts with other adenovirus early promoters and thus may be involved in the co-ordinate expression of E1a-inducible early viral genes.

Adenovirus E1a proteins repress expression from polyomavirus early and late promoters

We have examined the effects of the E1a products of adenovirus types 5 and 12 on the expression of polyomavirus early and late promoters. In cotransfection experiments in HeLa cells, plasmids expressing the E1a region of adenovirus type 5 or 12 repressed both the early and late promoters of polyomavirus, and deletion analysis indicates that the polyomavirus enhancers were the target of the E1a repression. With mutants lacking enhancer sequences, the polyomavirus early promoter but not the late promoter was trans-activated by E1a. Chimeric mutant plasmids with deletions in the regulatory region that contained either the A enhancer or the B enhancer were repressed to the same extent, indicating that E1a can repress both elements. Polyomavirus variant plasmids with rearrangements in the regulatory region conferring activity in embryonal carcinoma stem cells were repressed by E1a as was the wild type, suggesting that the repressor function is quite general. We discuss a model in which the influence of E1a on the transcriptional activity of a gene is the sum of positive and negative effects on promoter and enhancer elements and discuss possible mechanisms of negative regulation of enhancer function.

Activation of the adenovirus and BK virus late promoters: effects of the BK virus enhancer and trans-acting viral early proteins

We have examined the activation of the adenovirus major late promoter (MLP) by the cis-acting enhancer element of the human polyomavirus BK and by the trans-acting simian virus 40 (SV40) T antigen and adenovirus E1A proteins. By using chloramphenicol acetyltransferase expression vectors, we found that the MLP (pLP-CAT) was trans-activated in human and monkey kidney cells expressing the SV40 T antigen. In addition, the MLP could be cis-activated by the BK virus enhancer in both human and monkey kidney cells; approximately 20 times more chloramphenicol acetyltransferase was produced from expression vectors containing a hybrid promoter (BL), in which the BK enhancer was upstream of the MLP, than from expression vectors containing the MLP alone. This same level of enhancement of the MLP by the BK enhancer was observed in cells expressing the T antigen of SV40. However, in the 293 cell line, greater enhancement of MLP activity (70-fold) was observed with the BK enhancer sequence. In contrast, MLP activity in the 293 cell line was unchanged by the SV40 enhancer. In cotransfection experiments, MLP activity, augmented by the BK enhancer, could be further stimulated with a plasmid coding for the E1A gene products. By creating deletion mutants, we determined that the high-level activation of the hybrid BL transcriptional unit by the E1A proteins requires both MLP sequences and an intact BK virus enhancer. On the other hand, activation of the BL transcriptional unit by the T antigen did not require an intact enhancer sequence. Our results suggest that the SV40 T antigen and E1A proteins trans-activate the BL promoter by different mechanisms. We also demonstrate in cotransfection experiments that the BK late promoter is activated 45-fold by the SV40 T antigen.

Activation of the adenovirus and BK virus late promoters: effects of the BK virus enhancer and trans-acting viral early proteins

We have examined the activation of the adenovirus major late promoter (MLP) by the cis-acting enhancer element of the human polyomavirus BK and by the trans-acting simian virus 40 (SV40) T antigen and adenovirus E1A proteins. By using chloramphenicol acetyltransferase expression vectors, we found that the MLP (pLP-CAT) was trans-activated in human and monkey kidney cells expressing the SV40 T antigen. In addition, the MLP could be cis-activated by the BK virus enhancer in both human and monkey kidney cells; approximately 20 times more chloramphenicol acetyltransferase was produced from expression vectors containing a hybrid promoter (BL), in which the BK enhancer was upstream of the MLP, than from expression vectors containing the MLP alone. This same level of enhancement of the MLP by the BK enhancer was observed in cells expressing the T antigen of SV40. However, in the 293 cell line, greater enhancement of MLP activity (70-fold) was observed with the BK enhancer sequence. In contrast, MLP activity in the 293 cell line was unchanged by the SV40 enhancer. In cotransfection experiments, MLP activity, augmented by the BK enhancer, could be further stimulated with a plasmid coding for the E1A gene products. By creating deletion mutants, we determined that the high-level activation of the hybrid BL transcriptional unit by the E1A proteins requires both MLP sequences and an intact BK virus enhancer. On the other hand, activation of the BL transcriptional unit by the T antigen did not require an intact enhancer sequence. Our results suggest that the SV40 T antigen and E1A proteins trans-activate the BL promoter by different mechanisms. We also demonstrate in cotransfection experiments that the BK late promoter is activated 45-fold by the SV40 T antigen.

Adenovirus E1a proteins repress expression from polyomavirus early and late promoters

We have examined the effects of the E1a products of adenovirus types 5 and 12 on the expression of polyomavirus early and late promoters. In cotransfection experiments in HeLa cells, plasmids expressing the E1a region of adenovirus type 5 or 12 repressed both the early and late promoters of polyomavirus, and deletion analysis indicates that the polyomavirus enhancers were the target of the E1a repression. With mutants lacking enhancer sequences, the polyomavirus early promoter but not the late promoter was trans-activated by E1a. Chimeric mutant plasmids with deletions in the regulatory region that contained either the A enhancer or the B enhancer were repressed to the same extent, indicating that E1a can repress both elements. Polyomavirus variant plasmids with rearrangements in the regulatory region conferring activity in embryonal carcinoma stem cells were repressed by E1a as was the wild type, suggesting that the repressor function is quite general. We discuss a model in which the influence of E1a on the transcriptional activity of a gene is the sum of positive and negative effects on promoter and enhancer elements and discuss possible mechanisms of negative regulation of enhancer function.