TATA-dependent and TATA-independent function of the basal and heat shock elements of a human hsp70 promoter

The carboxyl-terminal transactivation domain of heat shock factor 1 is negatively regulated and stress responsive

We have characterized a stress-responsive transcriptional activation domain of mouse heat shock factor 1 (HSF1) by using chimeric GAL4-HSF1 fusion proteins. Fusion of the GAL4 DNA-binding domain to residues 124 to 503 of HSF1 results in a chimeric factor that binds DNA yet lacks any transcriptional activity. Transactivation is acquired upon exposure to heat shock or by deletion of a negative regulatory domain including part of the DNA-binding-domain-proximal leucine zippers. Analysis of a collection of GAL4-HSF1 deletion mutants revealed the minimal region for the constitutive transcriptional activator to map within the extreme carboxyl-terminal 108 amino acids, corresponding to a region rich in acidic and hydrophobic residues. Loss of residues 395 to 425 or 451 to 503, which are located at either end of this activation domain, severely diminished activity, indicating that the entire domain is required for transactivation. The minimal activation domain of HSF1 also confers enhanced transcriptional response to heat shock or cadmium treatment. These results demonstrate that the transcriptional activation domain of HSF1 is negatively regulated and that the signal for stress induction is mediated by interactions between the amino-terminal negative regulator and the carboxyl-terminal transcriptional activation domain.

A heat shock-responsive domain of human HSF1 that regulates transcription activation domain function

Human heat shock factor 1 (HSF1) stimulates transcription from heat shock protein genes following stress. We have used chimeric proteins containing the GAL4 DNA binding domain to identify the transcriptional activation domains of HSF1 and a separate domain that is capable of regulating activation domain function. This regulatory domain conferred heat shock inducibility to chimeric proteins containing the activation domains. The regulatory domain is located between the transcriptional activation domains and the DNA binding domain of HSF1 and is conserved between mammalian and chicken HSF1 but is not found in HSF2 or HSF3. The regulatory domain was found to be functionally homologous between chicken and human HSF1. This domain does not affect DNA binding by the chimeric proteins and does not contain any of the sequences previously postulated to regulate DNA binding of HSF1. Thus, we suggest that activation of HSF1 by stress in humans is controlled by two regulatory mechanisms that separately confer heat shock-induced DNA binding and transcriptional stimulation.

TATA-dependent enhancer stimulation of promoter activity in mice is developmentally acquired

Herpes simplex virus (HSV) thymidine kinase (tk) promoter activity depends on four transcription factor binding sites, one of which is a TATA box sequence, and the presence of either a cis-acting enhancer sequence or a transactivator protein. Studies presented here show that this TATA box was required for promoter activity only after cells began to differentiate and then only when promoter activity was stimulated by either an enhancer or a transactivator. When the HSV tk promoter was utilized by mouse embryos from the one-cell to eight-cell stage of development or by undifferentiated mouse embryonic stem cells, disruption of the HSV tk TATA box by site-specific mutations did not reduce promoter activity. This was true even when HSV tk promoter activity was stimulated strongly by either the embryo-responsive polyomavirus F101 enhancer or its natural transactivator, the HSV ICP4 gene product. However, stimulated expression was dependent on a distal Sp1 DNA binding site. Similarly, disruption of the TATA box did not reduce tk promoter activity in primary mouse embryonic fibroblasts or in immortalized 3T3 mouse fibroblasts; in fact, promoter activity was increased up to 2.6-fold. However, in these differentiated cells, stimulation of the HSV tk promoter by either the F101 enhancer or ICP4 protein required the TATA box. HSV tk promoter activity also was dependent on its TATA box in the mouse oocyte, a terminally differentiated cell with an endogenous transactivating activity. These results reveal that the need for a TATA box is developmentally acquired and depends on at least two parameters: the differentiated state of the cell and stimulation of the promoter by either an enhancer or a transactivator.

TATA-dependent enhancer stimulation of promoter activity in mice is developmentally acquired

Herpes simplex virus (HSV) thymidine kinase (tk) promoter activity depends on four transcription factor binding sites, one of which is a TATA box sequence, and the presence of either a cis-acting enhancer sequence or a transactivator protein. Studies presented here show that this TATA box was required for promoter activity only after cells began to differentiate and then only when promoter activity was stimulated by either an enhancer or a transactivator. When the HSV tk promoter was utilized by mouse embryos from the one-cell to eight-cell stage of development or by undifferentiated mouse embryonic stem cells, disruption of the HSV tk TATA box by site-specific mutations did not reduce promoter activity. This was true even when HSV tk promoter activity was stimulated strongly by either the embryo-responsive polyomavirus F101 enhancer or its natural transactivator, the HSV ICP4 gene product. However, stimulated expression was dependent on a distal Sp1 DNA binding site. Similarly, disruption of the TATA box did not reduce tk promoter activity in primary mouse embryonic fibroblasts or in immortalized 3T3 mouse fibroblasts; in fact, promoter activity was increased up to 2.6-fold. However, in these differentiated cells, stimulation of the HSV tk promoter by either the F101 enhancer or ICP4 protein required the TATA box. HSV tk promoter activity also was dependent on its TATA box in the mouse oocyte, a terminally differentiated cell with an endogenous transactivating activity. These results reveal that the need for a TATA box is developmentally acquired and depends on at least two parameters: the differentiated state of the cell and stimulation of the promoter by either an enhancer or a transactivator.

Transcriptional repression by Drosophila and mammalian Polycomb group proteins in transfected mammalian cells

The Polycomb group (Pc-G) genes are essential for maintaining the proper spatially restricted expression pattern of the homeotic loci during Drosophila development. The Pc-G proteins appear to function at target loci to maintain a state of transcriptional repression. The murine oncogene bmi-1 has significant homology to the Pc-G gene Posterior sex combs (Psc) and a highly related gene, Suppressor two of zeste [Su(z)2]. We show here that the proteins encoded by bmi-1 and the Pc-G genes Polycomb (Pc) and Psc as well as Su(z)2 mediate repression in mammalian cells when targeted to a promoter by LexA in a cotransfection system. These fusion proteins repress activator function by as much as 30-fold, and the effect on different activation domains is distinct for each Pc-G protein. Repression is observed when the LexA fusion proteins are bound directly adjacent to activator binding sites and also when bound 1,700 bases from the promoter. These data demonstrate that the products of the Pc-G genes can significantly repress activator function on transiently introduced DNA. We suggest that this function contributes to the stable repression of targeted loci during development.

Transcriptional repression by Drosophila and mammalian Polycomb group proteins in transfected mammalian cells

The Polycomb group (Pc-G) genes are essential for maintaining the proper spatially restricted expression pattern of the homeotic loci during Drosophila development. The Pc-G proteins appear to function at target loci to maintain a state of transcriptional repression. The murine oncogene bmi-1 has significant homology to the Pc-G gene Posterior sex combs (Psc) and a highly related gene, Suppressor two of zeste [Su(z)2]. We show here that the proteins encoded by bmi-1 and the Pc-G genes Polycomb (Pc) and Psc as well as Su(z)2 mediate repression in mammalian cells when targeted to a promoter by LexA in a cotransfection system. These fusion proteins repress activator function by as much as 30-fold, and the effect on different activation domains is distinct for each Pc-G protein. Repression is observed when the LexA fusion proteins are bound directly adjacent to activator binding sites and also when bound 1,700 bases from the promoter. These data demonstrate that the products of the Pc-G genes can significantly repress activator function on transiently introduced DNA. We suggest that this function contributes to the stable repression of targeted loci during development.

Mouse heat shock transcription factors 1 and 2 prefer a trimeric binding site but interact differently with the HSP70 heat shock element

To understand the function of multiple heat shock transcription factors in higher eukaryotes, we have characterized the interaction of recombinant mouse heat shock transcription factors 1 and 2 (mHSF1 and mHSF2) with their binding site, the heat shock element (HSE). For our analysis, we utilized the human HSP70 HSE, which consists of three perfect 5'-nGAAn-3' sites (1, 3, and 4) and two imperfect sites (2 and 5) arranged as tandem inverted repeats. Recombinant mHSF1 and mHSF2, which exist as trimers in solution, both bound specifically to this HSE and stimulated transcription of a human HSP70-CAT construct in vitro. Footprinting analyses revealed differential binding of mHSF1 and mHSF2 to the HSP70 HSE. Specifically, mHSF1 bound all five pentameric sites, whereas mHSF2 failed to interact with the first site of the HSE but bound to sites 2 to 5. Missing-nucleoside analysis demonstrated that the third and fourth nGAAn sites were essential for mHSF1 and mHSF2 binding. The binding of the initial mHSF1 trimer to the HSE exhibited preference for sites 3, 4, and 5, and then binding of a second trimer occurred at sites 1 and 2. These results suggest that HSF may recognize its binding site through the dyad symmetry of sites 3 and 4 but requires an adjacent site for stable interaction. Our data demonstrate that mHSF1 and mHSF2 bind specifically to the HSE through major groove interactions. Methidiumpropyl-EDTA footprinting revealed structural differences in the first and third repeats of the HSE, suggesting that the DNA is distorted in this region. The possibility that the HSE region is naturally distorted may assist in understanding how a trimer of HSF can bind to what is essentially an inverted repeat binding site.

Mouse heat shock transcription factors 1 and 2 prefer a trimeric binding site but interact differently with the HSP70 heat shock element

To understand the function of multiple heat shock transcription factors in higher eukaryotes, we have characterized the interaction of recombinant mouse heat shock transcription factors 1 and 2 (mHSF1 and mHSF2) with their binding site, the heat shock element (HSE). For our analysis, we utilized the human HSP70 HSE, which consists of three perfect 5'-nGAAn-3' sites (1, 3, and 4) and two imperfect sites (2 and 5) arranged as tandem inverted repeats. Recombinant mHSF1 and mHSF2, which exist as trimers in solution, both bound specifically to this HSE and stimulated transcription of a human HSP70-CAT construct in vitro. Footprinting analyses revealed differential binding of mHSF1 and mHSF2 to the HSP70 HSE. Specifically, mHSF1 bound all five pentameric sites, whereas mHSF2 failed to interact with the first site of the HSE but bound to sites 2 to 5. Missing-nucleoside analysis demonstrated that the third and fourth nGAAn sites were essential for mHSF1 and mHSF2 binding. The binding of the initial mHSF1 trimer to the HSE exhibited preference for sites 3, 4, and 5, and then binding of a second trimer occurred at sites 1 and 2. These results suggest that HSF may recognize its binding site through the dyad symmetry of sites 3 and 4 but requires an adjacent site for stable interaction. Our data demonstrate that mHSF1 and mHSF2 bind specifically to the HSE through major groove interactions. Methidiumpropyl-EDTA footprinting revealed structural differences in the first and third repeats of the HSE, suggesting that the DNA is distorted in this region. The possibility that the HSE region is naturally distorted may assist in understanding how a trimer of HSF can bind to what is essentially an inverted repeat binding site.

Mammalian promoter element function in the fission yeast Schizosaccharomyces pombe

We have analyzed the function of several mammalian promoter elements in the fission yeast, Schizosaccharomyces pombe. Mutants of the human HSP70 promoter were introduced into S. pombe as single copy integrants at a specific location. Transcription initiation sites utilized in S. pombe with the HSP70 TATA element were similar to those used in mammalian cells. Of three mammalian TATA elements tested, only the HSP70 TATA element functioned in S. pombe. The adenovirus Ella TATA element had little or no activity in S. pombe, indicating that S. pombe is deficient in the factor(s) necessary for recognition of this element. Of upstream promoter elements tested, the CCAAT, Sp1 binding, ATF binding and heat shock elements were functional in S. pombe. Strains containing mutant promoters fused to the ble gene were used to demonstrate that phleomycin can be used as a graded selection in S. pombe. These data demonstrate that S. pombe should provide a useful system in which to characterize and isolate mammalian factors involved in initiation site determination and transcriptional regulation.

DNA-binding properties of the E1A-associated 300-kilodalton protein

One of the major E1A-associated cellular proteins is a 300-kDa product (p300) that binds to the N-terminal region of the E1A products. The p300 binding site is distinct from sequences involved in binding the retinoblastoma product and other E1A-associated cellular products such as p60-cyclin A and p107. p300 binding to E1A is linked genetically to the enhancer repression function of E1A and the other E1A-mediated gene-regulating functions as well as to the transforming functions of E1A. However, the biochemical properties of p300 have not yet been characterized. We report here that p300 has an intrinsic DNA-binding activity and shows a preferential affinity for specific DNA sequences. The sequences selectively bound by p300 are related to those of a series of enhancer elements that are recognized by NF-kappa B. The direct physical interaction of p300 with enhancer elements provides a biochemical basis for the genetic evidence linking the E1A-mediated enhancer repression function with the p300-binding activity of E1A.

DNA-binding properties of the E1A-associated 300-kilodalton protein

One of the major E1A-associated cellular proteins is a 300-kDa product (p300) that binds to the N-terminal region of the E1A products. The p300 binding site is distinct from sequences involved in binding the retinoblastoma product and other E1A-associated cellular products such as p60-cyclin A and p107. p300 binding to E1A is linked genetically to the enhancer repression function of E1A and the other E1A-mediated gene-regulating functions as well as to the transforming functions of E1A. However, the biochemical properties of p300 have not yet been characterized. We report here that p300 has an intrinsic DNA-binding activity and shows a preferential affinity for specific DNA sequences. The sequences selectively bound by p300 are related to those of a series of enhancer elements that are recognized by NF-kappa B. The direct physical interaction of p300 with enhancer elements provides a biochemical basis for the genetic evidence linking the E1A-mediated enhancer repression function with the p300-binding activity of E1A.

Transactivation of the grp78 promoter by malfolded proteins, glycosylation block, and calcium ionophore is mediated through a proximal region containing a CCAAT motif which interacts with CTF/NF-I

The 78-kDa glucose-regulated protein (GRP78) is a major endoplasmic reticulum (ER) protein that can form stable associations with a variety of proteins retained in the ER because of underglycosylation or other conformational changes. In this study, we provide evidence at the transcriptional level that a conformationally abnormal protein, an altered herpes simplex virus type 1 envelope protein that is retained in the ER of a mammalian cell line, transactivates the grp78 promoter. In contrast, the normal viral envelope glycoprotein does not elevate grp78 promoter activity. Using a series of 5' deletions, linker-scanning, and internal deletion mutations spanning a 100-bp region from -179 to -80, we correlate the cis-acting regulatory elements mediating the activation of grp78 by malfolded proteins, glycosylation block, and the calcium ionophore A23187. We show that they all act through the same control elements, suggesting that they share a common signal. We report here that the highly conserved grp element, while important for basal level and induced grp78 expression, is functionally redundant. The single most important element, by linker-scanning analysis, is a 10-bp region that contains a CCAAT motif. It alone is not sufficient for promoter activity, but a 40-bp region (-129 to -90) that contains this motif is essential for mediating basal level and stress inducibility of the grp78 promoter. We show that the transcription factor CTF/NF-I is able to transactivate the grp78 promoter through interaction with this CCAAT motif.

Transactivation of the grp78 promoter by malfolded proteins, glycosylation block, and calcium ionophore is mediated through a proximal region containing a CCAAT motif which interacts with CTF/NF-I

The 78-kDa glucose-regulated protein (GRP78) is a major endoplasmic reticulum (ER) protein that can form stable associations with a variety of proteins retained in the ER because of underglycosylation or other conformational changes. In this study, we provide evidence at the transcriptional level that a conformationally abnormal protein, an altered herpes simplex virus type 1 envelope protein that is retained in the ER of a mammalian cell line, transactivates the grp78 promoter. In contrast, the normal viral envelope glycoprotein does not elevate grp78 promoter activity. Using a series of 5' deletions, linker-scanning, and internal deletion mutations spanning a 100-bp region from -179 to -80, we correlate the cis-acting regulatory elements mediating the activation of grp78 by malfolded proteins, glycosylation block, and the calcium ionophore A23187. We show that they all act through the same control elements, suggesting that they share a common signal. We report here that the highly conserved grp element, while important for basal level and induced grp78 expression, is functionally redundant. The single most important element, by linker-scanning analysis, is a 10-bp region that contains a CCAAT motif. It alone is not sufficient for promoter activity, but a 40-bp region (-129 to -90) that contains this motif is essential for mediating basal level and stress inducibility of the grp78 promoter. We show that the transcription factor CTF/NF-I is able to transactivate the grp78 promoter through interaction with this CCAAT motif.

Isolation of a cDNA for HSF2: evidence for two heat shock factor genes in humans

The heat shock response is transcriptionally regulated by an evolutionarily conserved protein termed heat shock factor (HSF). We report the purification to homogeneity and the partial peptide sequence of HSF from HeLa cells. The peptide sequence was used to isolate a human cDNA with a predicted open reading frame that has homology to the DNA binding domains of both Saccharomyces cerevisiae and Drosophila HSFs. The cDNA directs the synthesis of a protein that binds to the heat shock element with specificity identical to HeLa HSF and stimulates transcription from a heat shock promoter. The expressed protein cross-reacts with anti-HSF antibodies. Surprisingly, however, this cDNA does not encode all of the peptides obtained from purified HeLa HSF. These peptides are encoded by a distinct human cDNA, HSF1, described by Rabindran et al. [Rabindran, S. K., Giorgi, G., Clos, J. & Wu, C. (1991) Proc. Natl. Acad. Sci. USA 88, 6906-6910.] It therefore appears that there is a human heat shock factor gene family and that at least two separate but related HSF proteins regulate the stress response in humans.

Modular recognition of 5-base-pair DNA sequence motifs by human heat shock transcription factor

We investigated the recognition of the conserved 5-bp repeated motif NGAAN, which occurs in heat shock gene promoters of Drosophila melanogaster and other eukaryotic organisms, by human heat shock transcription factor (HSF). Extended heat shock element mutants of the human HSP70 gene promoter, containing additional NGAAN blocks flanking the original element, showed significantly higher affinity than the wild-type promoter element for human HSF in vitro. Protein-DNA contact positions were identified by hydroxyl radical protection, diethyl pyrocarbonate interference, and DNase I footprinting. New contacts in the mutant HSE constructs corresponded to the locations of additional NGAAN motifs. The pattern of binding indicated the occurrence of multiple DNA binding modes for HSF with the various constructs and was consistent with an oligomeric, possibly trimeric, structure of the protein. In contrast to the improved binding, the extended heat shock element mutant constructs did not exhibit dramatically increased heat-inducible transcription in transient expression assays with HeLa cells.

Modular recognition of 5-base-pair DNA sequence motifs by human heat shock transcription factor

We investigated the recognition of the conserved 5-bp repeated motif NGAAN, which occurs in heat shock gene promoters of Drosophila melanogaster and other eukaryotic organisms, by human heat shock transcription factor (HSF). Extended heat shock element mutants of the human HSP70 gene promoter, containing additional NGAAN blocks flanking the original element, showed significantly higher affinity than the wild-type promoter element for human HSF in vitro. Protein-DNA contact positions were identified by hydroxyl radical protection, diethyl pyrocarbonate interference, and DNase I footprinting. New contacts in the mutant HSE constructs corresponded to the locations of additional NGAAN motifs. The pattern of binding indicated the occurrence of multiple DNA binding modes for HSF with the various constructs and was consistent with an oligomeric, possibly trimeric, structure of the protein. In contrast to the improved binding, the extended heat shock element mutant constructs did not exhibit dramatically increased heat-inducible transcription in transient expression assays with HeLa cells.