The E1A 13S product of adenovirus 5 activates transcription of the cellular human HSP70 gene

Hsp70 Inhibits the Replication of Fowl Adenovirus Serotype 4 by Suppressing Viral Hexon with the Assistance of DnaJC7

Fowl adenovirus serotype 4 (FAdV-4) infection results in serious hepatitis-hydropericardium syndrome (HHS) in broilers, which has caused great economic losses to the poultry industry; however, the specific host responses to FAdV-4 remain unknown. In this study, we identified 141 high-confidence protein-protein interactions (PPIs) between the main viral proteins (Hexon, Fiber 1, Fiber 2, and Penton bases) and host proteins via a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay. We found that heat shock protein 70 (Hsp70), the protein with the highest score, and its cofactor DnaJ heat shock protein 40 family member C7 (DnaJC7) could negatively regulate the replication of FAdV-4. Furthermore, the nucleotide binding domain (NBD) of Hsp70 and the J domain of DnaJC7 were necessary for inhibiting FAdV-4 replication. We verified that DnaJC7 as a bridge could bind to Hsp70 and Hexon, assisting the indirect interaction between Hsp70 and Hexon. In addition, we found that FAdV-4 infection strongly induced the expression of autophagy proteins and cellular Hsp70 in a dose-dependent manner. Blockage of Hexon by Hsp70 overexpression was significantly reduced when the autophagy pathway was blocked by the specific inhibitor chloroquine (CQ). Our results showed that Hsp70 was co-opted by DnaJC7 to interact with viral Hexon and inhibited Hexon through the autophagy pathway, leading to a considerable restriction of FAdV-4 replication. IMPORTANCE FAdV-4, as the main cause of HHS, has quickly spread all over the world in recent years, seriously threatening the poultry industry. The aim of this study was to identify the important host proteins that have the potential to regulate the life cycle of FAdV-4. We found that Hsp70 and DnaJC7 played crucial roles in regulating the amount of viral Hexon and extracellular viral titers. Moreover, we demonstrated that Hsp70 interacted with viral Hexon with the assistance of DnaJC7, followed by suppressing Hexon protein through the autophagy pathway. These results provide new insight into the role of the molecular chaperone complex Hsp70-DnaJC7 in FAdV-4 infection and suggest a novel strategy for anti-FAdV-4 drug development by targeting the specific interactions among Hsp70, DnaJC7 and Hexon.

Assessing the oncolytic potential of rotavirus on mouse myeloma cell line Sp2/0-Ag14

INTRODUCTION

Cancer is the second leading cause of death in the United States, surpassed only by cardiovascular disease. However, cancer has now overtaken cardiovascular disease as the main cause of death in 12 countries in Western Europe. The burden of cancer is posing a major challenge to health care systems worldwide and demanding improvements in methods for cancer prevention, diagnosis, and treatment. Alternative and complementary strategies for orthodox surgery, radiotherapy, and chemotherapy need to be developed.

OBJECTIVE

To determine the oncolytic potential of tumor cell-adapted rotavirus in terms of their ability to infect and lysate murine myeloma Sp2/0-Ag14 cells.

MATERIALS AND METHODS

We inoculated rotaviruses Wt1-5, WWM, TRUYO, ECwt-O, and WTEW in Sp2/0-Ag14 cells and we examined their infectious effects by immunocytochemistry, immunofluorescence, flow cytometry, and DNA fragmentation assays.

RESULTS

Rotavirus infection involved the participation of some heat shock proteins, of protein disulfide isomerase (PDI), and integrin β3. We detected the accumulation of viral antigens within the virus-inoculated cells and in the culture medium in all the rotavirus isolates examined. The rotavirus-induced cell death mechanism in Sp2/0-Ag14 cells involved changes in cell membrane permeability, chromatin condensation, and DNA fragmentation, which were compatible with cytotoxicity and apoptosis.

CONCLUSIONS

The ability of the rotavirus isolates Wt1-5, WWM, TRUYO, ECwt-O, and WTEW to infect and cause cell death of Sp2/0-Ag14 cells through mechanisms that are compatible with virus-induced apoptosis makes them potential candidates as oncolytic agents.

Time-resolved proteomics of adenovirus infected cells

Viral infections cause large problems in the world and deeper understanding of the disease mechanisms is needed. Here we present an analytical strategy to investigate the host cell protein changes during human adenovirus type 2 (HAdV-C2 or Ad2) infection of lung fibroblasts by stable isotope labelling of amino acids in cell culture (SILAC) and nanoLC-MS/MS. This work focuses on early phase of infection (6 and 12 h post-infection (hpi)) but the data is combined with previously published late phase (24 and 36 hpi) proteomics data to produce a time series covering the complete infection. As many as 2169 proteins were quantitatively monitored from 6 to 36 hpi, while some proteins were time-specific. After applying different filter criteria, 2027 and 2150 proteins were quantified at 6 and 12 hpi and among them, 431 and 544 were significantly altered at the two time points. Pathway analysis showed that the De novo purine and pyrimidine biosynthesis, Glycolysis and Cytoskeletal regulation by Rho GTPase pathways were activated early during infection while inactivation of the Integrin signalling pathway started between 6 and 12 hpi. Moreover, upstream regulator analysis predicted MYC to be activated with time of infection and protein and RNA data for genes controlled by this transcription factor showed good correlation, which validated the use of protein data for this prediction. Among the identified phosphorylation sites, a group related to glycolysis and cytoskeletal reorganization were up-regulated during infection. The results show specific aspects on how the host cell proteins, the final products in the genetic information flow, are influenced by Ad2 infection, which would be overlooked if only knowledge derived from mRNA data is considered.

Promyelocytic leukemia protein isoform II inhibits infection by human adenovirus type 5 through effects on HSP70 and the interferon response

Promyelocytic leukemia (PML) proteins have been implicated in antiviral responses but PML and associated proteins are also suggested to support virus replication. One isoform, PML-II, is required for efficient transcription of interferon and interferon-responsive genes. We therefore investigated the PML-II contribution to human adenovirus 5 (Ad5) infection, using shRNA-mediated knockdown. HelaΔII cells showed a 2-3-fold elevation in Ad5 yield, reflecting an increase in late gene expression. This increase was found to be due in part to the reduced innate immune response consequent upon PML-II depletion. However, the effect was minor because the viral E4 Orf3 protein targets and inactivates this PML-II function. The major benefit to Ad5 in HelaΔII cells was exerted via an increase in HSP70; depletion of HSP70 completely reversed this replicative advantage. Increased Ad5 late gene expression was not due either to the previously described inhibition of inflammatory responses by HSP70 or to effects of HSP70 on major late promoter or L4 promoter activity, but might be linked to an observed increase in E1B 55K, as this protein is known to be required for efficient late gene expression. The induction of HSP70 by PML-II removal was specific for the HSPA1B gene among the HSP70 gene family and thus was not the consequence of a general stress response. Taken together, these data show that PML-II, through its various actions, has an overall negative effect on the Ad5 lifecycle.

Detection of mRNA in living cells by double-stranded locked nucleic acid probes

Double-stranded probes are homogeneous biosensors for rapid detection of specific nucleotide sequences. These double-stranded probes have been applied in various molecular sensing applications, such as real-time polymerase chain reaction and detection of bacterial 16S rRNA. In this study, we present the design and optimization of double-stranded probes for single-cell gene expression analysis in living cells. With alternating DNA/LNA monomers for optimizing the stability and specificity, we show that the probe is stable in living cells for over 72 hours post-transfection and is capable of detecting changes in gene expression induced by external stimuli. The probes can be delivered to a large number of cells simultaneously by cationic liposomal transfection or to individual cells selectively by photothermal delivery. We also demonstrate that the probe quantifies intracellular mRNA in living cells through the use of an equilibrium analysis. With its effectiveness and performance, the double-stranded probe represents a broadly applicable approach for large-scale single-cell gene expression analysis toward numerous biomedical applications, such as systems biology, cancer, and drug screening.

De novo derivation of proteomes from transcriptomes for transcript and protein identification

Identification of proteins by tandem mass spectrometry requires a reference protein database, but these are only available for model species. Here we demonstrate that, for a non-model species, the sequencing of expressed mRNA can generate a protein database for mass spectrometry-based identification. This combination of high-throughput sequencing and protein identification technologies allows detection of genes and proteins. We use human cells infected with human adenovirus as a complex and dynamic model to demonstrate the robustness of this approach. Our proteomics informed by transcriptomics (PIT) technique identifies >99% of over 3,700 distinct proteins identified using traditional analysis that relies on comprehensive human and adenovirus protein lists. We show that this approach can also be used to highlight genes and proteins undergoing dynamic changes in post-transcriptional protein stability.

Posttranslational regulation of the NKG2D ligand Mult1 in response to cell stress

NKG2D is a major stimulatory receptor expressed by natural killer (NK) cells and some T cells. The receptor recognizes major histocompatability complex class I–like cell surface ligands that are poorly expressed by normal tissues but are often induced in transformed and infected cells. The existence of several NKG2D ligands in each individual, some with strikingly divergent protein sequences, raises the possibility that different ligands are regulated by distinct disease-associated stresses. The transcripts for some ligands, including murine UL16-binding proteinlike transcript 1 (Mult1), are abundant in certain normal tissues where cell surface expression is absent, suggesting the existence of translational or posttranslational regulation. We report here that under normal conditions, Mult1 protein undergoes ubiquitination dependent on lysines in its cytoplasmic tail and lysosomal degradation. Mult1 degradation and ubiquitination is reduced in response to stress imparted by heat shock or ultraviolet irradiation, but not by other forms of genotoxicity, providing a novel mechanism for stress-mediated cellular control of NKG2D ligand expression.

Chaperones in cell cycle regulation and mitogenic signal transduction: a review

Chaperones/heat shock proteins (HSPs) of the HSP90 and HSP70 families show elevated levels in proliferating mammalian cells and a cell cycle-dependent expression. They transiently associate with key molecules of the cell cycle control system such as Cdk4, Wee-1, pRb, p53, p27/Kip1 and are involved in the nuclear localization of regulatory proteins. They also associate with viral oncoproteins such as SV40 super T, large T and small t antigen, polyoma large and middle S antigen and EpsteinBarr virus nuclear antigen. This association is based on a J-domain in the viral proteins and may assist their targeting to the pRb/E2F complex. Small HSPs and their state of phosphorylation and oligomerization also seem to be involved in proliferation and differentiation. Chaperones/HSPs thus play important roles within cell cycle processes. Their exact functioning, however, is still a matter of discussion. HSP90 in particular, but also HSP70 and other chaperones associate with proteins of the mitogen-activated signal cascade, particularly with the Src kinase, with tyrosine receptor kinases, with Raf and the MAP-kinase activating kinase (MEK). This apparently serves the folding and translocation of these proteins, but possibly also the formation of large immobilized complexes of signal transducing molecules (scaffolding function).

The induction levels of heat shock protein 70 differentiate the vulnerabilities to mutant huntingtin among neuronal subtypes

The reason why vulnerabilities to mutant polyglutamine (polyQ) proteins are different among neuronal subtypes is mostly unknown. In this study, we compared the gene expression profiles of three types of primary neurons expressing huntingtin (htt) or ataxin-1. We found that heat shock protein 70 (hsp70), a well known chaperone molecule protecting neurons in the polyQ pathology, was dramatically upregulated only by mutant htt and selectively in the granule cells of the cerebellum. Granule cells, which are insensitive to degeneration in the human Huntington's disease (HD) pathology, lost their resistance by suppressing hsp70 with siRNA, whereas cortical neurons, affected in human HD, gained resistance by overexpressing hsp70. This indicates that induction levels of hsp70 are a critical factor for determining vulnerabilities to mutant htt among neuronal subtypes. CAT (chloramphenicol acetyltransferase) assays showed that CBF (CCAAT box binding factor, CCAAT/enhancer binding protein zeta) activated, but p53 repressed transcription of the hsp70 gene in granule cells. Basal and mutant htt-induced expression levels of p53 were remarkably lower in granule cells than in cortical neurons, suggesting that different magnitudes of p53 are linked to distinct induction levels of hsp70. Surprisingly, however, heat shock factor 1 was not activated in granule cells by mutant htt. Collectively, different levels of hsp70 among neuronal subtypes might be involved in selective neuronal death in the HD pathology.

Cellular stress rather than stage of the cell cycle enhances the replication and plating efficiencies of herpes simplex virus type 1 ICP0- viruses

This lab reported previously that the plating efficiency of a herpes simplex virus type 1 ICP0-null mutant was enhanced upon release from an isoleucine block which synchronizes cells to G1 phase (W. Cai and P. A. Schaffer, J. Virol. 65:4078-4090, 1991). Peak plating efficiency occurred as cells cycled out of G1 and into S phase, suggesting that the enhanced plating efficiency was due to cellular activities present in late G1/early S phase. We have found, however, that the enhanced plating efficiency did not occur when cells were synchronized by alternative methods. We now report that the plating efficiency of ICP0- viruses is not enhanced at a particular stage of the cell cycle but rather is enhanced by specific cellular stresses. Both the plating and replication efficiencies of ICP0- viruses were enhanced as much as 25-fold to levels similar to that of wild-type virus when monolayers were heat shocked prior to infection. In addition to heat shock, UV-C irradiation but not cold shock of monolayers prior to infection resulted in enhanced plating efficiency. We further report that the effect of cellular stress is transient and that cell density rather than age of the monolayers is the primary determinant of ICP0- virus plating efficiency. As both cell stress and ICP0 are required for efficient reactivation from latency, the identification of cellular activities that complement ICP0- viruses may lead to the identification of cellular activities that are important for reactivation from neuronal latency.

Most F508del-CFTR is targeted to degradation at an early folding checkpoint and independently of calnexin

Biosynthesis and folding of multidomain transmembrane proteins is a complex process. Structural fidelity is monitored by endoplasmic reticulum (ER) quality control involving the molecular chaperone calnexin. Retained misfolded proteins undergo ER-associated degradation (ERAD) through the ubiquitin-proteasome pathway. Our data show that the major degradation pathway of the cystic fibrosis transmembrane conductance regulator (CFTR) with F508del (the most frequent mutation found in patients with the genetic disease cystic fibrosis) from the ER is independent of calnexin. Moreover, our results demonstrate that inhibition of mannose-processing enzymes, unlike most substrate glycoproteins, does not stabilize F508del-CFTR, although wild-type (wt) CFTR is drastically stabilized under the same conditions. Together, our data support a novel model by which wt and F508del-CFTR undergo ERAD from two distinct checkpoints, the mutant being disposed of independently of N-glycosidic residues and calnexin, probably by the Hsc70/Hsp70 machinery, and wt CFTR undergoing glycan-mediated ERAD.

AR1 is an integral part of the adenovirus type 2 E1A-CR3 transactivation domain

We have previously shown that the nonconserved carboxy-terminal exon of the adenovirus type 2 E1A-289R protein contains two interchangeable sequence elements, auxiliary region (AR) 1 and AR2, that are required for efficient CR3-mediated transcriptional activation of the viral E4 promoter (M. Bondesson, C. Svensson, S. Linder, and G. Akusjärvi, EMBO J. 11:3347-3354, 1992). Here we show that CR3-mediated transactivation of all adenovirus early promoters and the HSP70 promoter requires the AR1 element. We further show that AR2 can substitute for AR1 only when artificially juxtaposed to CR3. AR1 consists of six tandem glutamic acid-proline (EP) repeats and is positioned immediately downstream of CR3. Genetic dissection of AR1 showed that the number of EP repeats in AR1 is critical for CR3 function. Thus, reducing or increasing the number of EP repeats reduces the CR3 transactivation capacity. Furthermore, the introduction of amino acid substitutions into AR1 suggested that the net negative charge in AR1 is of critical importance for its function as an enhancer of CR3-mediated transcriptional activation. Using an in vitro binding approach, we showed that the AR1 element is not part of the CR3 promoter localization signal mediating contact with the Sp1, ATF-2, or c-Jun upstream-binding transcription factors. Previous studies have suggested that the 49-amino-acid sequence constituting CR3 represents the minimal domain required for E1A-induced activation of viral early promoters. Since AR1 was required for efficient CR3-mediated transcriptional activation of all tested promoters, we suggest that the carboxy-terminal boundary for the CR3 transactivation domain should be extended to include the AR1 element.

Inhibition of cellular proliferation by the Wilms tumor suppressor WT1 requires association with the inducible chaperone Hsp70

The Wilms tumor suppressor WT1 encodes a zinc finger transcription factor that is expressed in glomerular podocytes during a narrow window in kidney development. By immunoprecipitation and protein microsequencing analysis, we have identified a major cellular protein associated with endogenous WT1 to be the inducible chaperone Hsp70. WT1 and Hsp70 are physically associated in embryonic rat kidney cells, in primary Wilms tumor specimens and in cultured cells with inducible expression of WT1. Colocalization of WT1 and Hsp70 is evident within podocytes of the developing kidney, and Hsp70 is recruited to the characteristic subnuclear clusters that contain WT1. The amino-terminal transactivation domain of WT1 is required for binding to Hsp70, and expression of that domain itself is sufficient to induce expression of Hsp70 through the heat shock element (HSE). Substitution of a heterologous Hsp70-binding domain derived from human DNAJ is sufficient to restore the functional properties of a WT1 protein with an amino-terminal deletion, an effect that is abrogated by a point mutation in DNAJ that reduces binding to Hsp70. These observations indicate that Hsp70 is an important cofactor for the function of WT1, and suggest a potential role for this chaperone during kidney differentiation.

A novel G1-specific enhancer identified in the human heat shock protein 70 gene

Expression of the human heat shock protein 70 gene (hsp70) is induced by various kinds of stress and by oncogenes. In the absence of stress, hsp70 is mainly expressed in the G1and S phases of the cell cycle, but the elements contributing to cell cycle-dependent expression from the hsp70 promoter remain elusive. We have previously reported that two elements, named HSP-MYCA and HSP-MYCB, located approximately 200 bp upstream (-200) from the transcription start site (+1) of human hsp70, are important for initiation of DNA replication at the hsp70 locus. In this report we examine the effect of these two elements on transcriptional activity from the hsp70 promoter, especially in terms of cell cycle-dependent expression. Various segments of the hsp70 promoter region (up to -300) were linked to the luciferase gene and the constructs were transfected into mouse L cells to examine their transcriptional activity. A strong enhancer activity was defined in the HSP-MYCB element, but not in HSP-MYCA. Mutations introduced within HSP-MYCB abolished the transcriptional activation. In synchronized cells, pHB-Luc (a luciferase construct containing approximately 2.4 kb of the hsp70 promoter region) as well as endogenous hsp70 showed two peaks of expression; one in G1 and the other in the S phase. Site-directed mutagenesis of HSP-MYCB in pHB-Luc abolished the expression peak in G1, but not that in the S phase. To test promoter specificity, wild-type and mutant HSP-MYCB elements were then linked to the luciferase gene in combination with the hsp70 , the cyclin A or the PCNA promoter. Both in transient experiments and established cell lines, a strong peak of expression in mid-G1phase was observed with all the constructs containing wild-type HSP-MYCB, but not with the constructs containing the mutant sequence. These results suggest that the HSP-MYCB sequence is a G1-specific enhancer and is responsible for cell cycle-dependent expression of hsp70.

Heat shock and light activation of a Chlamydomonas HSP70 gene are mediated by independent regulatory pathways

Induction of HSP70 heat shock genes by light has been demonstrated in Chlamydomonas. Our aim was to establish whether this induction by light is mediated by the heat stress sensing pathway or by an independent signal chain. Inhibitors of cytoplasmic protein synthesis revealed an initial difference. Cycloheximide and other inhibitors of protein synthesis prevented HSP70A induction upon illumination but not during heat stress. Analysis of HSP70A induction in cells that had differentiated into gametes revealed a second difference. While heat shock resulted in elevated HSP70A mRNA levels, light was no longer able to serve as an inducer in gametes. To identify the regulatory sequences that mediate the response of the HSP70A gene to either heat stress or light we introduced a series of progressive 5' truncations into its promoter sequence. Analyses of the levels of mRNA transcribed from these deletion constructs showed that in most of them the responses to heat shock and light were similar, suggesting that light induction is mediated by a light-activated heat shock factor. However, we show that the HSP70A promoter also contains cis-acting sequences involved in light induction that do not participate in induction by heat stress. Together, these results provide evidence for a regulation of HSP70A gene expression by light through a heat shock-independent signal pathway.

Expression of stress proteins (HSP-70 and HSP-90) in the rabbit urinary bladder subjected to partial outlet obstruction

Partial obstruction of the rabbit bladder outlet induces a rapid hypertrophy characterized by increased bladder mass, increased smooth muscle content, and increased collagen deposition. In addition, partial outlet obstruction induces decreased contractile responses to both field stimulation and postsynaptic receptor stimulation. Although the morphological and contractile responses to partial outlet obstruction have been well characterized, there is little information on the cellular and molecular mechanisms of these changes. In a previous study, we demonstrated that one of the earliest genes to be expressed following partial outlet obstruction in rabbits was the gene expressing stress protein-70 (HSP-70). In order to further define the genetic and molecular basis of these responses, the expression of stress gene products HSP-70 and HSP-90 in rabbit urinary bladder subjected to partial outlet obstruction has been quantitatively evaluated by Western blot coupled with laser densitometry using anti-HSP-70 and -90 monoclonal antibodies. The data show that stress gene products HSP-70 and HSP-90 are constitutively expressed in control rabbit bladder tissue and transiently increased following partial outlet obstruction. Increased content of HSP-70 was detected at 6 hr after obstruction and reached a maximum (2.7-fold over the control level) at 24 hr. Increased HSP-90 was also detected at 6 hr but reached a maximum (4.5-fold over the control level) at 12 hr. By 7 day post-obstruction, the content of these two proteins returned to the control levels.(ABSTRACT TRUNCATED AT 250 WORDS)

Concomitant cellular expression of heat shock regulated genes of hepatitis B virus surface antigen and of human growth hormone by a NIH-3T3 cell line

A plasmid carrying a DNA fragment of hepatitis B virus, coding for the pre-S2 and the entire S region of the surface antigen (HBsAg), placed under the control of the promoter of the human 70 kDa heat shock protein gene (hsp70), was introduced into Line 6, a recombinant cell line that was selected from NIH-3T3 cells previously transfected with a similar construct coding for the human growth hormone cDNA gene (chGH) and with the plasmid pEJ carrying the Ha-rasEJ activated cellular oncogene. The resulting cell line, EMS8, expressed: (1) hsp70/HBsAg and hsp70/hGH hybrid genes, (2) the human Ha-rasEJ oncogene, and (3) the neomycin resistance gene, the two last plasmid markers being used for cell selection. EMS8 cells were able to carry out post-translational modifications of the middle M and the major S envelope proteins of HBV, such as assembly and glycosylation. Accordingly, the cells synthesized and secreted both free and glycosylated M and S viral proteins, and the human growth hormone protein. In addition concomitant expression of HBsAg and hGH proteins as well as their mRNA were detected in EMS8 cells at least up to 72 hr after heat induction instead of 24 hr in the case of hGH in Line 6 cells.

Comparison between E1A gene from oncogenic and non-oncogenic adenoviruses in cellular transformation (Ad E1A conserved region)

All adenoviruses transform primary BRK cells in vitro, but only cells transformed by oncogenic adenoviruses are tumorigenic for immunocompetent animals. The transforming E1 regions of human Ad 2 and Ad 12 also differ from each other in the frequency in which they can transform BRK cells. We have investigated these properties which can be assigned to the specific domain of the E1A region. For this purpose, chimeric E1A regions between Ad 2 and Ad 12 have been constructed. The efficiency of cell transformation appeared to be determined by the encoding region. The promoter sequences were not important for an efficient cellular transformation although the E1B region cis activated in E1A transcription in both cell transformation and transient expression. We show that sequences located in the E1B promoter were responsible for this effect. In the encoding region the CR 1 domain was essential for the cell transformation frequency.

The hsp70 gene CCAAT-binding factor mediates transcriptional activation by the adenovirus E1a protein

Expression of the human hsp70 gene is cell cycle regulated and is inducible by both serum and the adenovirus E1a protein (K. Milarski and R. Morimoto, Proc. Natl. Acad. Sci. USA 83:9517-9521, 1986; M. C. Simon, K. Kitchener, H.-T. Kao, E. Hickey, L. Weber, R. Voellmy, N. Heintz, and J. R. Nevins, Mol. Cell. Biol. 7:2884-2890, 1987; B. Wu, H. Hurst, N. Jones, and R. Morimoto, Mol. Cell. Biol. 6:2994-2999, 1986; B. Wu and R. Morimoto, Proc. Natl. Acad. Sci. USA 82:6070-6074, 1985). This regulated expression is predominantly controlled by the CCAAT element at position -70 relative to the transcriptional initiation site (G. Williams, T. McClanahan, and R. Morimoto, Mol. Cell. Biol. 9:2574-2587, 1989; B. Wu, H. Hurst, N. Jones, and R. Morimoto, Mol. Cell. Biol. 6:2994-2999, 1986). A corresponding CCAAT-binding factor (CBF) of 999 amino acids has recently been cloned and shown to stimulate transcription selectively from the hsp70 promoter in a CCAAT element-dependent manner (L. Lum, L. Sultzman, R. Kaufman, D. Linzer, and B. Wu, Mol. Cell. Biol. 10:6709-6717, 1990). We report here that the first 192 residues of CBF, when fused to the DNA-binding domain of the heterologous activator GAL-4, are necessary and sufficient to mediate E1a-dependent transcriptional activation. E1a and CBF exhibit complex formation in vitro, suggesting that an in vivo interaction between these proteins may be relevant to the well-characterized E1a-induced transcriptional activation of the hsp70 promoter.

The hsp70 gene CCAAT-binding factor mediates transcriptional activation by the adenovirus E1a protein

Expression of the human hsp70 gene is cell cycle regulated and is inducible by both serum and the adenovirus E1a protein (K. Milarski and R. Morimoto, Proc. Natl. Acad. Sci. USA 83:9517-9521, 1986; M. C. Simon, K. Kitchener, H.-T. Kao, E. Hickey, L. Weber, R. Voellmy, N. Heintz, and J. R. Nevins, Mol. Cell. Biol. 7:2884-2890, 1987; B. Wu, H. Hurst, N. Jones, and R. Morimoto, Mol. Cell. Biol. 6:2994-2999, 1986; B. Wu and R. Morimoto, Proc. Natl. Acad. Sci. USA 82:6070-6074, 1985). This regulated expression is predominantly controlled by the CCAAT element at position -70 relative to the transcriptional initiation site (G. Williams, T. McClanahan, and R. Morimoto, Mol. Cell. Biol. 9:2574-2587, 1989; B. Wu, H. Hurst, N. Jones, and R. Morimoto, Mol. Cell. Biol. 6:2994-2999, 1986). A corresponding CCAAT-binding factor (CBF) of 999 amino acids has recently been cloned and shown to stimulate transcription selectively from the hsp70 promoter in a CCAAT element-dependent manner (L. Lum, L. Sultzman, R. Kaufman, D. Linzer, and B. Wu, Mol. Cell. Biol. 10:6709-6717, 1990). We report here that the first 192 residues of CBF, when fused to the DNA-binding domain of the heterologous activator GAL-4, are necessary and sufficient to mediate E1a-dependent transcriptional activation. E1a and CBF exhibit complex formation in vitro, suggesting that an in vivo interaction between these proteins may be relevant to the well-characterized E1a-induced transcriptional activation of the hsp70 promoter.

Wild-type p53 can down-modulate the activity of various promoters

The wild-type (wt) p53 protein is the product of a tumor suppressor gene that is a frequent target for inactivation in many types of tumors. The nuclear localization of the protein, as well as additional features, suggest that it may be involved in the regulation of gene expression. To explore this possibility, the effects of overproduced wt p53 were investigated in a number of systems. Induction of growth arrest via the antiproliferative effect of wt p53 greatly impaired the ability of cells to exhibit an increase in c-fos mRNA upon serum stimulation. Experiments in which cells were cotransfected with p53 expression plasmids together with a reporter gene linked to various promoters revealed that wt p53 could effectively reduce transcription from a series of promoters derived from serum-inducible genes, but not from a major histocompatibility complex gene. The p53-mediated repression of c-fos gene expression occurred even in the presence of cycloheximide. Kinetic studies indicate that the effect of wt p53 is rapid, rather than representing a secondary consequence of growth arrest. These findings support a role for p53 in transcriptional regulation, perhaps by reducing the expression of genes that are needed for ongoing cell proliferation.

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.

Nuclear colocalization of cellular and viral myc proteins with HSP70 in myc-overexpressing cells

The c-myc oncogene and its viral counterpart v-myc encode phosphoproteins which have been located within cell nuclei, excluding nucleoli. We have expressed the c-myc gene under the simian virus 40 early promoter and studied the distribution of its protein product in transient expression assays in COS, HeLa, and 293 cells. We found three distinct patterns of c-myc immunofluorescence in the transfected cells: one-third of the c-myc-positive cells displayed a diffuse nuclear distribution, and in two-thirds of the cells the c-myc fluorescence was accumulated either in small amorphous or in large multilobed phase-dense nuclear structures. Unexpectedly, these structures also stained for the HSP70 heat shock protein in both heat-shocked and untreated cells. Our results indicate that both transient and stable overexpression of either the c-myc or v-myc protein induces translocation of the endogenous HSP70 protein from the cytoplasm to the nucleus, where it becomes sequestered in structures containing the myc protein. Interestingly, the closely related N-myc protein does not stimulate substantial nuclear expression of the HSP70 protein. Studies with chimeric myc proteins revealed that polypeptide sequences encoded by the second exon of c-myc are involved in colocalization with HSP70.

A cloned human CCAAT-box-binding factor stimulates transcription from the human hsp70 promoter

The basal promoter of the human hsp70 gene is predominantly controlled by a CCAAT element at position -70 relative to the transcriptional initiation site. We report the isolation of a novel cDNA clone encoding a 114-kDa polypeptide that binds to the CCAAT element of the hsp70 promoter. Expression of this CCAAT-binding factor (CBF) cDNA activated transcription from cotransfected hsp70 promoter-reporter gene constructs in a CCAAT-dependent manner. CCAAT-binding factor shows no homology to the previously identified human CCAAT transcription factor or rat CCAAT/enhancer-binding protein.

The degradation sequence of adenovirus E1A consists of the amino-terminal tetrapeptide Met-Arg-His-Ile

The adenovirus E1A gene product is a potent transcriptional activator and nuclear oncoprotein. Like other regulatory proteins, E1A has a short half-life, in the range of 30 to 120 min. This short half-life, which was measured in cells synthesizing E1A, is not observed in cells injected with E1A protein made in bacteria or in vitro. In these cases, E1A is essentially refractory to degradation. In an attempt to reconcile this apparent paradox, we suggested that E1A was marked for degradation during its synthesis. Furthermore, we showed that a domain in the amino terminus of E1A was required for rapid degradation in cells translating E1A mRNA (J. M. Slavicek, N. C. Jones, and J. D. Richter, EMBO J. 7:3171-3180, 1988). In this study, we have used Xenopus laevis oocytes injected with mRNAs encoding altered E1A proteins to show that the amino-terminal tetrapeptide Met-Arg-His-Ile is required for E1A degradation. Even conservative amino acid substitutions in this degradation sequence render it nonfunctional. This degradation sequence can function as a transferable signal, since it induces instability when fused to another normally stable protein. Furthermore, the degradation sequence requires a proximity of no more than six residues from the amino terminus for activity. These data suggest that a trans-acting factor recognizes the amino terminus of E1A during the translation of its message to mark the protein for subsequent destruction.

A cloned human CCAAT-box-binding factor stimulates transcription from the human hsp70 promoter

The basal promoter of the human hsp70 gene is predominantly controlled by a CCAAT element at position -70 relative to the transcriptional initiation site. We report the isolation of a novel cDNA clone encoding a 114-kDa polypeptide that binds to the CCAAT element of the hsp70 promoter. Expression of this CCAAT-binding factor (CBF) cDNA activated transcription from cotransfected hsp70 promoter-reporter gene constructs in a CCAAT-dependent manner. CCAAT-binding factor shows no homology to the previously identified human CCAAT transcription factor or rat CCAAT/enhancer-binding protein.

The degradation sequence of adenovirus E1A consists of the amino-terminal tetrapeptide Met-Arg-His-Ile

The adenovirus E1A gene product is a potent transcriptional activator and nuclear oncoprotein. Like other regulatory proteins, E1A has a short half-life, in the range of 30 to 120 min. This short half-life, which was measured in cells synthesizing E1A, is not observed in cells injected with E1A protein made in bacteria or in vitro. In these cases, E1A is essentially refractory to degradation. In an attempt to reconcile this apparent paradox, we suggested that E1A was marked for degradation during its synthesis. Furthermore, we showed that a domain in the amino terminus of E1A was required for rapid degradation in cells translating E1A mRNA (J. M. Slavicek, N. C. Jones, and J. D. Richter, EMBO J. 7:3171-3180, 1988). In this study, we have used Xenopus laevis oocytes injected with mRNAs encoding altered E1A proteins to show that the amino-terminal tetrapeptide Met-Arg-His-Ile is required for E1A degradation. Even conservative amino acid substitutions in this degradation sequence render it nonfunctional. This degradation sequence can function as a transferable signal, since it induces instability when fused to another normally stable protein. Furthermore, the degradation sequence requires a proximity of no more than six residues from the amino terminus for activity. These data suggest that a trans-acting factor recognizes the amino terminus of E1A during the translation of its message to mark the protein for subsequent destruction.

Maximal stress-induced transcription from the human HSP70 promoter requires interactions with the basal promoter elements independent of rotational alignment

Transcription of the human HSP70 gene is regulated by a complex array of cis-acting promoter elements that respond to conditions that include normal conditions of cell growth and induction following physiological stress. We have examined the requirements of the basal and inducible promoter elements by using promoter mutations and a transient transfection assay. Multiple forms of stress-induced transcription, including heat shock and incubation with heavy metals or amino acid analogs, are mediated by a single heat shock element (HSE) between -105 and -91 consisting of three contiguous 5-base-pair units, NGAAN, that are inverted relative to adjacent units. Maximal inducible expression requires a fully functional basal promoter. Spacing mutations which alter the relative helical orientation of adjacent genetic elements have only minimal effects on basal and stress-inducible expression and show no effects of periodicity. In addition, placement of the HSE adjacent to the basal promoter removes the requirements for a fully functional basal promoter for maximal stress-inducible expression. These results suggest that factors bound at the HSE and the basal promoter can function through multiple interactions.

Maximal stress-induced transcription from the human HSP70 promoter requires interactions with the basal promoter elements independent of rotational alignment

Transcription of the human HSP70 gene is regulated by a complex array of cis-acting promoter elements that respond to conditions that include normal conditions of cell growth and induction following physiological stress. We have examined the requirements of the basal and inducible promoter elements by using promoter mutations and a transient transfection assay. Multiple forms of stress-induced transcription, including heat shock and incubation with heavy metals or amino acid analogs, are mediated by a single heat shock element (HSE) between -105 and -91 consisting of three contiguous 5-base-pair units, NGAAN, that are inverted relative to adjacent units. Maximal inducible expression requires a fully functional basal promoter. Spacing mutations which alter the relative helical orientation of adjacent genetic elements have only minimal effects on basal and stress-inducible expression and show no effects of periodicity. In addition, placement of the HSE adjacent to the basal promoter removes the requirements for a fully functional basal promoter for maximal stress-inducible expression. These results suggest that factors bound at the HSE and the basal promoter can function through multiple interactions.

Activation in vitro of RNA polymerase II and III directed transcription by baculovirus produced E1A protein

The baculovirus expression system has been successfully used to overproduce a number of different protein products. In this report we describe the construction of a recombinant baculovirus containing the adenovirus E1A 13s cDNA sequence. Infection of insect cells with this virus results in the production of phosphorylated E1A protein. The phosphorylation pattern appears to be similar to the complex pattern associated with E1A protein synthesis in mammalian cells. Purified baculovirus generated E1A protein activated transcription of specific poIIII promoters both in microinjected Xenopus laevis oocytes and in HeLa cell in vitro transcription extracts. The protein also stimulates in vitro transcription of the poIIII transcribed VA1 gene.

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.

E1a transactivation of human HSP70 gene promoter substitution mutants is independent of the composition of upstream and TATA elements

We have analyzed 41 deletion, linker scan, and substitution mutants of the human HSP70 gene promoter for activation by the adenovirus E1a region. No natural element of the HSP70 gene promoter was required for activation. To investigate specific interactions between E1a and transcription factors, a set of 24 promoters containing all possible combinations of eight different upstream or TATA motifs was investigated for E1a stimulation. E1a transactivated the promoter regardless of the particular TATA motif present. Furthermore, there was no dramatic correlation between any upstream motif and activation by E1a. These data suggest that E1a does not stimulate transcription via an interaction with any specific transcription factor but instead suggest that E1a interacts via the general transcription machinery.

E1a transactivation of human HSP70 gene promoter substitution mutants is independent of the composition of upstream and TATA elements

We have analyzed 41 deletion, linker scan, and substitution mutants of the human HSP70 gene promoter for activation by the adenovirus E1a region. No natural element of the HSP70 gene promoter was required for activation. To investigate specific interactions between E1a and transcription factors, a set of 24 promoters containing all possible combinations of eight different upstream or TATA motifs was investigated for E1a stimulation. E1a transactivated the promoter regardless of the particular TATA motif present. Furthermore, there was no dramatic correlation between any upstream motif and activation by E1a. These data suggest that E1a does not stimulate transcription via an interaction with any specific transcription factor but instead suggest that E1a interacts via the general transcription machinery.

Prostaglandins with antiproliferative activity induce the synthesis of a heat shock protein in human cells

Prostaglandins (PGs) A1 and J2 were found to potently suppress the proliferation of human K562 erythroleukemia cells and to induce the synthesis of a 74-kDa protein (p74) that was identified as a heat shock protein related to the major 70-kDa heat shock protein group. p74 synthesis was stimulated at doses of PGA1 and PGJ2 that inhibited cell replication, and its accumulation ceased upon removal of the PG-induced proliferation block. PGs that did not affect K562 cell replication did not induce p74 synthesis. p74 was found to be localized mainly in the cytoplasm of PG-treated cells, but moderate amounts were found also in dense areas of the nucleus after PGJ2 treatment. p74 synthesis was not necessarily associated with cytotoxicity or with inhibition of cell protein synthesis. The results described support the hypothesis that synthesis of the 70-kDa heat shock proteins is associated with changes in cell proliferation. The observation that PGs can induce the synthesis of heat shock proteins expands our understanding of the mechanism of action of these compounds whose regulatory role is well known in many physiological phenomena, including the control of fever production.

Transcription factor Sp1 binds to and activates a human hsp70 gene promoter

I investigated the binding of purified transcription factor Sp1 from HeLa cells to the human hsp70 promoter by DNase I footprinting. Three binding sites were detected within the upstream promoter region, including one located 46 base pairs upstream of the transcription start, between the TATA box and the proximal CCAAT box element. In vitro transcription demonstrated that the proximal site is capable of responding to Sp1-dependent stimulation. These results suggest that Sp1 might contribute to constitutive expression in vivo and might also be involved in the various regulatory responses that affect this gene.

E1a transactivation of the human HSP70 promoter is mediated through the basal transcriptional complex

We have examined the promoter sequence requirements for E1a transactivation of the human HSP70 gene by using a transient cotransfection assay. A 5' deletion study has defined a basal transcription unit extending to -74 relative to the transcription initiation site which was fully E1a responsive. Further deletion, abolishing a CCAAT element at -67, drastically reduced basal and E1a-induced expression. A linker-scanner analysis has identified four functional elements within the basal transcription unit which may interact with CTF, SP1, TFIID, and an ATF/AP1-like factor. Sequences between -100 and -188 can partially compensate for mutations in these elements. No mutation specifically abolished E1a inducibility. Any reduction in absolute E1a-induced levels was accompanied by a corresponding reduction in absolute basal levels, thereby maintaining a constant relative fold induction. We conclude that E1a transactivation of the human HSP70 promoter does not require any single basal transcription element. We also examined an HSP70 promoter fragment, containing the CCAAT element at -67 and the purine-rich element at -54, out of its normal context by fusing it upstream of a transcriptionally inactive herpes simplex virus thymidine kinase deletion construct containing only the TATA box. The resulting chimeric promoter was fully E1a responsive. Mutagenesis of this promoter fusion demonstrated that the CCAAT element was essential for detectable basal and E1a-induced expression. Mutations in the purine-rich element resulted in an approximately 10-fold elevation in basal levels and rendered the promoter nonresponsive to E1a.

Association of a cellular heat shock protein with simian virus 40 large T antigen in transformed cells

The viral oncoprotein of simian virus 40, large T antigen (T-ag), is essential for viral replication and cellular transformation. To understand the mechanisms by which T-ag mediates its multifunctional properties, it is important to identify the cellular targets with which it interacts. A cellular protein of 73 kilodaltons (p73) which specifically associates with T-ag in simian virus 40-transformed BALB/c 3T3E cells has been identified. The binding of p73 to T-ag was demonstrated by coimmunoprecipitation analyses using polyclonal and monoclonal antibodies specific for T-ag. The interaction of p73 with T-ag was independent of T-ag complex formation with the cellular protein p53. Partial V8 protease cleavage maps for p73 and the cellular heat shock protein hsp70 were identical. Immunoblot analyses indicated that p73 complexed to T-ag was antigenically related to hsp70. T-ag deletion mutants were constructed that remove internal, amino-terminal, and carboxy-terminal sequences. These mutants mapped the p73 binding domain to the amino terminus of T-ag. The specific dissociation of p73 from the p73/T-ag complex was mediated by ATP; GTP, CTP, and UTP were also utilized as substrates. These characteristics suggest that p73 may be a member of the hsp70 family of heat shock proteins. The biologic significance of p73/T-ag complex formation has yet to be determined.

Transcription factor Sp1 binds to and activates a human hsp70 gene promoter

I investigated the binding of purified transcription factor Sp1 from HeLa cells to the human hsp70 promoter by DNase I footprinting. Three binding sites were detected within the upstream promoter region, including one located 46 base pairs upstream of the transcription start, between the TATA box and the proximal CCAAT box element. In vitro transcription demonstrated that the proximal site is capable of responding to Sp1-dependent stimulation. These results suggest that Sp1 might contribute to constitutive expression in vivo and might also be involved in the various regulatory responses that affect this gene.

In vivo photocrosslinking reveals that transcription factor binding to the mammalian ATF recognition sequence is required for E1A-induced transactivation in injected Xenopus laevis oocytes

The adenovirus E1A 13S mRNA product transactivates genes injected into Xenopus laevis oocytes that are normally E1A-inducible in mammalian cells. However, E1A-stimulated transcription, but not basal (uninduced) transcription, was inhibited if oocytes were incubated in the presence of protein synthesis inhibitors. This suggests that a cellular protein(s) is required for E1A-induced transactivation, but that it is dispensable for basal transcription. In order to identify such a protein from Xenopus oocytes that interacts with the adenovirus E3 promoter, gel shift assays, a new in vivo photocrosslinking assay, and immunoselection of biotinylated oligonucleotides were employed. A protein of molecular size 75 kd, which bound to the mammalian ATF recognition sequence in vivo, was found to be essential for E1A-induced transactivation. Although cycloheximide treatment of oocytes inhibited factor binding. E1A exerted no effect on factor binding. These data suggest that E1A modulates the activity of an oocyte transcription factor, either directly or indirectly, but not its ability to bind DNA.

E1a transactivation of the human HSP70 promoter is mediated through the basal transcriptional complex

We have examined the promoter sequence requirements for E1a transactivation of the human HSP70 gene by using a transient cotransfection assay. A 5' deletion study has defined a basal transcription unit extending to -74 relative to the transcription initiation site which was fully E1a responsive. Further deletion, abolishing a CCAAT element at -67, drastically reduced basal and E1a-induced expression. A linker-scanner analysis has identified four functional elements within the basal transcription unit which may interact with CTF, SP1, TFIID, and an ATF/AP1-like factor. Sequences between -100 and -188 can partially compensate for mutations in these elements. No mutation specifically abolished E1a inducibility. Any reduction in absolute E1a-induced levels was accompanied by a corresponding reduction in absolute basal levels, thereby maintaining a constant relative fold induction. We conclude that E1a transactivation of the human HSP70 promoter does not require any single basal transcription element. We also examined an HSP70 promoter fragment, containing the CCAAT element at -67 and the purine-rich element at -54, out of its normal context by fusing it upstream of a transcriptionally inactive herpes simplex virus thymidine kinase deletion construct containing only the TATA box. The resulting chimeric promoter was fully E1a responsive. Mutagenesis of this promoter fusion demonstrated that the CCAAT element was essential for detectable basal and E1a-induced expression. Mutations in the purine-rich element resulted in an approximately 10-fold elevation in basal levels and rendered the promoter nonresponsive to E1a.

Differential distribution of the adenovirus E1A proteins and colocalization of E1A with the 70-kilodalton cellular heat shock protein in infected cells

Five distinct localization patterns were observed for the adenovirus E1A proteins in the nuclei of infected HeLa cells: diffuse, reticular, nucleolar, punctate, and peripheral. The variable distribution of E1A was correlated with the time postinfection and the cell cycle stage of the host cell at the time of infection. All staining patterns, with the exception of peripheral E1A localization, were associated with the early phase of infection since only the diffuse, reticular, nucleolar, and punctate staining patterns were observed in the presence of hydroxyurea. Because the E1A proteins (12S and 13S) stimulate the expression of the cellular heat shock 70-kilodalton protein (hsp70), we examined the intracellular distribution of hsp70 in the adenovirus-infected cells. Whereas hsp70 was predominantly cytoplasmic in the cells before infection, after adenovirus infection most of the protein was now found within the nucleus. Specifically, hsp70 was found within the nucleoli as well as exhibiting reticular, diffuse, and punctate nuclear staining patterns, analogous to those observed for the E1A proteins. Double-label indirect immunofluorescence of E1A and hsp70 in infected cells demonstrated a colocalization of these proteins in the nucleus. Translocation of hsp70 to the nucleus was dependent upon both adenovirus infection and expression of the E1A proteins. The localization of hsp70 was unaltered by infection with an E1A 9S cDNA virus which does not synthesize a functional E1A gene product. Moreover, the discrete nuclear localization patterns of E1A and the colocalization of E1A with hsp70 were not observed in adenovirus-transformed 293 cells which constitutively express E1A and E1B. E1A displayed exclusively diffuse nuclear staining in 293 cells; however, localization of E1A into the discrete nuclear patterns occurred after adenovirus infection of 293 cells. Immunoprecipitation of labeled infected-cell extracts with a monoclonal antibody directed against the E1A proteins resulted in precipitation of small amounts of hsp70 along with E1A. These data indicate that the adenovirus E1A proteins colocalize with, and possibly form a physical complex with, cellular hsp70 in infected cells. The relevance of this association, with respect to the function of these proteins during infection and the association of other oncoproteins with hsp70, is discussed.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

Interactions between cell growth-regulating domains in the products of the adenovirus E1A oncogene

Among the various biological activities expressed by the products of the adenovirus E1A gene are the abilities to induce cellular DNA synthesis and proliferation in quiescent primary baby rat kidney cells. The functional sites for these activities lie principally within two regions of the E1A proteins: an N-terminal region and a small second region of approximately 20 amino acids further downstream. To study the biological functions of the first domain, we constructed an in-frame deletion of amino acid positions 23 through 107 of the E1A products. This deletion did not impede the ability of the E1A products to transactivate the adenovirus early region 3 promoter in a transient-expression assay in HeLa cells. The ability to induce DNA synthesis in quiescent baby rat kidney cells was, however, lost in the absence of these sequences. Deletion of the small second region induced a form of S phase in which DNA synthesis occurred in the apparent absence of controls required for the cessation of DNA synthesis and progression through the remainder of the cell cycle. These cells did not appear to accumulate in or before G2, and many appeared to have a DNA content greater than that in G2. The functions of both domains are required for production of transformed foci in a ras cooperation assay. Focus formation occurred, however, even when the two domains were introduced on two separate plasmids. This complementation effect appeared to require expression of both of the mutant proteins and did not appear to result merely from recombination at the DNA level.

Identification and sequence analysis of a new member of the mouse HSP70 gene family and characterization of its unique cellular and developmental pattern of expression in the male germ line

A unique member of the mouse HSP70 gene family has been isolated and characterized with respect to its DNA sequence organization and expression. The gene contains extensive similarity to a heat shock-inducible HSP70 gene within the coding region but diverges in both 3' and 5' nontranslated regions. The gene does not yield transcripts in response to heat shock in mouse L cells. Rather, the gene appears to be activated uniquely in the male germ line. Analysis of RNA from different developmental stages and from enriched populations of spermatogenic cells revealed that this gene is expressed during the prophase stage of meiosis. A transcript different in size from the major heat-inducible mouse transcripts is most abundant in meiotic prophase spermatocytes and decreases in abundance in postmeiotic stages of spermatogenesis. This pattern of expression is distinct from that observed for another member of this gene family, which was previously shown to be expressed abundantly in postmeiotic germ cells. These observations suggest that specific HSP70 gene family members play distinct roles in the differentiation of the germ cell lineage in mammals.

Mitogen and lymphokine stimulation of heat shock proteins in T lymphocytes

We have examined the effects of phytohemagglutinin (PHA) and the polypeptide growth factor interleukin 2 (IL-2) on the synthesis of the 70- and 90-kDa heat shock proteins (HSP70 and HSP90, respectively) in human T lymphocytes. Resting T cells (G0) stimulated with PHA responded with a generalized increase in protein synthesis that included HSP70. Gel blot analysis indicated that steady-state levels of HSP70 mRNA were not specifically modulated by PHA. Synthesis of HSP90 protein, however, peaked very rapidly following PHA stimulation and decreased sharply after 1 hr. When IL-2-dependent human T cells, synchronized by IL-2 deprivation, were treated with IL-2, synthesis of HSP70 mRNA was increased as much as 15-fold. HSP70 and HSP90 protein synthesis increased significantly upon IL-2 stimulation of human T lymphocytes. Two distinct members of the ancient family of heat shock genes, HSP70 and HSP90, are shown to be stimulated at the activation and progression stages of lymphocyte mitogenesis, which suggests that genetic mechanisms evolved from primitive stress/adaptation responses may be conserved in mammalian cellular activation.

Induced heat shock mRNAs escape the nucleocytoplasmic transport block in adenovirus-infected HeLa cells

Under conditions in which cytoplasmic accumulation of HeLa cell mRNAs has been blocked by adenovirus infection, hsp70 family mRNAs are transported from the nucleus to the cytoplasm at near normal efficiency subsequent to heat shock. Heat shock does not reverse the general virus-induced block to host cell mRNA transport. The heat shock mRNAs are translated within the cytoplasm of the infected cell but at substantially reduced efficiency compared with that of uninfected cells. Thus, the hsp70 family of mRNAs can escape the transport block but not the translational block instituted late after adenovirus infection. The beta-tubulin gene family is induced by the viral E1A gene after infection, and its mRNAs also accumulate in the cytoplasmic compartment. Given these two examples, it seems likely that the process of transcriptional induction allows the resulting mRNA to escape the viral block of transport.

Posttranscriptional regulation of hsp70 expression in human cells: effects of heat shock, inhibition of protein synthesis, and adenovirus infection on translation and mRNA stability

We have examined the posttranscriptional regulation of hsp70 gene expression in two human cell lines, HeLa and 293 cells, which constitutively express high levels of HSP70. HSP70 mRNA translates with high efficiency in both control and heat-shocked cells. Therefore, heat shock is not required for the efficient translation of HSP70 mRNA. Rather, the main effect of heat shock on translation is to suppress the translatability of non-heat shock mRNAs. Heat shock, however, has a marked effect on the stability of HSP70 mRNA; in non-heat-shocked cells the half-life of HSP70 mRNA is approximately 50 min, and its stability increases at least 10-fold upon heat shock. Moreover, HSP70 mRNA is more stable in cells treated with protein synthesis inhibitors, suggesting that a heat shock-sensitive labile protein regulates its turnover. An additional effect on posttranscriptional regulation of hsp70 expression can be found in adenovirus-infected cells, in which HSP70 mRNA levels decline precipititously late during infection although hsp70 transcription continues unabated.

Interactions between cell growth-regulating domains in the products of the adenovirus E1A oncogene

Among the various biological activities expressed by the products of the adenovirus E1A gene are the abilities to induce cellular DNA synthesis and proliferation in quiescent primary baby rat kidney cells. The functional sites for these activities lie principally within two regions of the E1A proteins: an N-terminal region and a small second region of approximately 20 amino acids further downstream. To study the biological functions of the first domain, we constructed an in-frame deletion of amino acid positions 23 through 107 of the E1A products. This deletion did not impede the ability of the E1A products to transactivate the adenovirus early region 3 promoter in a transient-expression assay in HeLa cells. The ability to induce DNA synthesis in quiescent baby rat kidney cells was, however, lost in the absence of these sequences. Deletion of the small second region induced a form of S phase in which DNA synthesis occurred in the apparent absence of controls required for the cessation of DNA synthesis and progression through the remainder of the cell cycle. These cells did not appear to accumulate in or before G2, and many appeared to have a DNA content greater than that in G2. The functions of both domains are required for production of transformed foci in a ras cooperation assay. Focus formation occurred, however, even when the two domains were introduced on two separate plasmids. This complementation effect appeared to require expression of both of the mutant proteins and did not appear to result merely from recombination at the DNA level.