Cellular factors binding to a novel cis-acting element mediate steroid hormone responsiveness of mouse mammary tumor virus promoter

Mechanisms of transcriptional regulation by WT1 (Wilms' tumour 1)

The WT1 (Wilms' tumour 1) gene encodes a zinc finger transcription factor and RNA-binding protein that direct the development of several organs and tissues. WT1 manifests both tumour suppressor and oncogenic activities, but the reasons behind these opposing functions are still not clear. As a transcriptional regulator, WT1 can either activate or repress numerous target genes resulting in disparate biological effects such as growth, differentiation and apoptosis. The complex nature of WT1 is exemplified by a plethora of isoforms, post-translational modifications and multiple binding partners. How WT1 achieves specificity to regulate a large number of target genes involved in diverse physiological processes is the focus of the present review. We discuss the wealth of the growing molecular information that defines our current understanding of the versatility and utility of WT1 as a master regulator of organ development, a tumour suppressor and an oncogene.

Organizing principles of mammalian nonsense-mediated mRNA decay

Cells use messenger RNAs (mRNAs) to ensure the accurate dissemination of genetic information encoded by DNA. Given that mRNAs largely direct the synthesis of a critical effector of cellular phenotype, i.e., proteins, tight regulation of both the quality and quantity of mRNA is a prerequisite for effective cellular homeostasis. Here, we review nonsense-mediated mRNA decay (NMD), which is the best-characterized posttranscriptional quality control mechanism that cells have evolved in their cytoplasm to ensure transcriptome fidelity. We use protein quality control as a conceptual framework to organize what is known about NMD, highlighting overarching similarities between these two polymer quality control pathways, where the protein quality control and NMD pathways intersect, and how protein quality control can suggest new avenues for research into mRNA quality control.

The requirement of Ras and Rap1 for the activation of ERKs by cAMP, PACAP, and KCl in cerebellar granule cells

In cerebellar granule cells, the mitogen-activated protein kinase (MAPK) or extracellular signal-regulated kinase (ERK) cascade mediates multiple functions, including proliferation, differentiation, and survival. In these cells, ERKs are activated by diverse stimuli, including cyclic adenosine monophosphate (cAMP), pituitary adenylate cyclase activating protein (PACAP), depolarization induced by elevated extracellular potassium (KCl), and the neurotrophin brain-derived neurotrophic factor. Extensive studies in neuronal cell lines have implicated the small G proteins Ras and Rap1 in the activation of ERKs by cAMP, PACAP, and KCl. However, the requirement of Ras and Rap1 in these pathways in cerebellar granule cells has not been addressed. In this study, we utilize multiple biochemical assays to determine the mechanisms of action and requirement of Ras and Rap1 in cultured cerebellar granule cells. We show that both Ras and Rap1 can be activated by cAMP or PACAP via protein kinase (PKA)-dependent mechanisms. KCl activation of Ras also required PKA. Using both adenoviral and transgenic approaches, we show that Ras plays a major role in ERK activation by cAMP, PACAP, and KCl, while Rap1 also mediates activation of a selective membrane-associated pool of ERKs. Furthermore, Rap1, but not Ras, activation by PKA appears to require the action of Src family kinases.

Structures, mechanism, regulation and evolution of class III nucleotidyl cyclases

Cyclic 3',5'-guanylyl and adenylyl nucleotides function as second messengers in eukaryotic signal transduction pathways and as sensory transducers in prokaryotes. The nucleotidyl cyclases (NCs) that catalyze the synthesis of these molecules comprise several evolutionarily distinct groups, of which class III is the largest. The domain structures of prokaryotic and eukaryotic class III NCs are diverse, including a variety of regulatory and transmembrane modules. Yet all members of this family contain one or two catalytic domains, characterized by an evolutionarily ancient topological motif (betaalphaalphabetabetaalphabeta) that is preserved in several other enzymes that catalyze the nucleophilic attack of a 3'-hydroxyl upon a 5' nucleotide phosphate. Two dyad-related catalytic domains compose one catalytic unit, with the catalytic sites formed at the domain interface. The catalytic domains of mononucleotidyl cyclases (MNCs) and diguanylate cyclases (DGCs) are called cyclase homology domains (CHDs) and GGDEF domains, respectively. Prokaryotic NCs usually contain only one catalytic domain and are catalytically active as intermolecular homodimers. The different modes of dimerization in class III NCs probably evolved concurrently with their mode of binding substrate. The catalytic mechanism of GGDEF domain homodimers is not completely understood, but they are expected to have a single active site with each subunit contributing equivalent determinants to bind one GTP molecule or half a c-diGMP molecule. CHD dimers have two potential dyad-related active sites, with both CHDs contributing determinants to each site. Homodimeric class III MNCs have two equivalent catalytic sites, although such enzymes may show half-of-sites reactivity. Eukaryotic class III MNCs often contain two divergent CHDs, with only one catalytically competent site. All CHDs appear to use a common catalytic mechanism, which requires the participation of two magnesium or manganese ions for binding polyphosphate groups and nucleophile activation. In contrast, mechanisms for purine recognition and specificity are more diverse. Class III NCs are subject to regulation by small molecule effectors, endogenous domains, or exogenous protein partners. Many of these regulators act by altering the interface of the catalytic domains and therefore the integrity of the catalytic site(s). This review focuses on both conserved and divergent mechanisms of class III NC function and regulation.

Regulation of thioredoxin gene expression by vitamin A in human airway epithelial cells

Human thioredoxin (Trx) is a 12-kD protein known to be involved in various reduction/oxidation reactions essential for cell growth and cellular injury repair. We previously demonstrated, based on nuclear run-on assay, that retinoic acid (RA) stimulated Trx gene expression in airway epithelial cells at the transcriptional level. Nucleotide sequencing of the 5'-flanking region of the human Trx gene revealed the presence of a TATA box at -28 and four RA response element (RARE)-like half sites at -426, -453, -507, and -626 nt. Transient transfection assays with a Trx promoter-reporter gene, chloramphenicol acetyltransferase (CAT), demonstrated a dose-dependent involvement of these four RARE-like half sites in RA-enhanced promoter activity. When the DNA fragment that flanks these four RARE-like half sites from -357 to -671 nt was introduced into a heterologous promoter of the tk-CAT2 vector, both basal and RA-stimulated CAT activities were observed. A site-directed mutagenesis approach demonstrated an essential role for RARE-I and RARE-II at -426 and -453 nt, respectively, and an auxiliary role for RARE-III at -507 nt in both basal and RA-stimulated CAT activities. Both in vivo and in vitro genomic footprinting experiments further demonstrated specific protein-DNA interactions in these "putative" RARE-I/II/III half sites. Gel electrophoretic mobility shift assays demonstrated specific interactions of these RARE-like half sites with the nuclear extracts obtained from RA-treated cultures. The anti-RAR-alpha antibody super-shift experiment further confirmed the interactions of RARE-I/II sites with RAR-alpha nuclear receptor. These results suggest a classic RARE/RAR interaction involved in RA-stimulated Trx gene expression in human airway epithelium.

Transfection of keratinocytes abrogates detectable DNA-binding activity of CCAAT displacement protein

Transfection of keratinocytes with plasmid DNA leads to the loss of detectable DNA-binding activity of CCAAT displacement protein but not of Yin Yang 1, as monitored by electrophoretic mobility shift assay. This phenomenon was found to be attributable to the presence of plasmid DNA in the nuclear extracts prepared from transfected cells. Treatment of these nuclear extracts with DNase I restored the ability to monitor DNA-binding activity of CDP. This report documents a new pitfall associated with transfection.

Development of high-density DNA microarray membrane for profiling smoke- and hydrogen peroxide-induced genes in a human bronchial epithelial cell line

Development of the high-density DNA microarray technique permits the analysis of thousands of genes simultaneously for their differential expression patterns in various biological processes. Through clustering analysis and pattern recognition, the significance of differentially expressed genes can be recognized and correlated with biological events that may take place inside the cell and tissue. With this notion in mind, high-density DNA microarray nylon membrane with colorimetry detection was used to profile the expression of smoke- and hydrogen peroxide-inducible genes in a human bronchial epithelial cell line, HBE1. On the basis of the time course of expression, at least three phases of change in gene expression could be recognized. The first phase is an immediate event in response to oxidant injury. This phase includes induction of the bcl-2 and mdm-2 genes, which are involved in the regulation of apoptosis, and the mitogen-activated protein (MAP) kinase phosphatase 1 (MKP-1) gene, that functions as a regulator of various mitogen-activated protein kinase activities. The second phase, usually 5 h later, includes the induction of various stress proteins and ubiquitin, which are important in providing the chaperone mechanism and the turnover of damaged macromolecules. The third phase, which is 5-10 h later, includes the induction of genes that are apparently involved in reducing oxidative stress by metabolizing reactive oxygen species. In this phase, enzymes associated with tissue and cell remodeling are also elevated. These results demonstrate a complex gene expression array by bronchial epithelial cells in response to the insult of oxidants that are relevant to environmental pollutants.

In silico cloning of mouse Muc5b gene and upregulation of its expression in mouse asthma model

Using a BLAST-searching approach, we identified a mouse expressed sequence tag (EST) clone (AA038672) showing great similarity to the 3' end of the human MUC5B gene. The clone was named "3pmmuc5b-1" after complete nucleotide sequencing (Genbank Accession, AF369933). A subsequent search of the mouse genome database with the 3pmmuc5b-1 sequence identified two overlapping genomic clones (AC020817 and AC020794) that contained the sequence of both 3pmmuc5b-1 and the mouse Muc5ac gene. Like their human homologs, the genomic order of the mouse Muc genes is 5'-Muc5ac-Muc5b-3'. These results suggest that the newly identified EST clone, 3pmmuc5b-1, is part of the 3' portion of the mouse Muc5b gene. In situ hybridization demonstrated that this putative mouse Muc5b message was expressed in a restricted manner in the sublingual gland region of the tongue and the submucosal gland region of the mouse trachea in a normal animal. However, the gene expression was greatly enhanced in airway surface epithelium and the submucosal gland region in ovalbumin-induced asthmatic mice. These results were consistent with previous studies of human airway tissues. We therefore conclude that this newly cloned mouse Muc5b gene could be used as a marker for studying aberrant mucin gene expression in mouse models of various airway diseases.

Genes essential for early events in gonadal development

The acquisition of a sexually dimorphic phenotype is a critical event in mammalian development. The basic underlying principle of sexual development is that genetic sex--determined at fertilization by the presence or absence of the Y chromosome--directs the embryonic gonads to differentiate into either testes or ovaries. Thereafter, hormones produced by the testes direct the developmental program that leads to male sexual differentiation. In the absence of testicular hormones, the female pathway of sexual differentiation occurs. Recent studies have defined key roles in gonadal development for two transcription factors: Wilms' tumor suppressor 1 (WT1) and steroidogenic factor 1 (SF-1). After presenting a brief overview of gonadal development and sexual differentiation, this chapter reviews the studies that led to the isolation and characterization of WT1 and SF-1, and then discusses how interactions between these two genes may mediate their key roles in a common developmental pathway.

Induction of cell cornification and enhanced squamous-cell marker SPRR1 gene expression by phorbol ester are regulated by different signaling pathways in human conducting airway epithelial cells

Phorbol ester is a strong inducer for both cell cornification and squamous-cell marker SPRR1 gene expression in conducting airway epithelial cells. However, the signaling pathways involved in the regulation of both events have not been completely elucidated. The current study focuses on the common and divergent pathways involved in the induction of these two activities by phorbol-13-myristate-12-acetate (PMA). Using a protein kinase (PK) C inhibitor, bisindolylmaleimide I, PMA-induced cell cornification and SPRR1 gene expression were abolished. Further, a PKC activator, indolactam V, induced cell cornification in the absence of PMA treatment. These results suggest a PKC-dependent signaling pathway for both gene induction and enhanced cell cornification by PMA. However, a mitogen-activated protein kinase-specific inhibitor, PD98059, could only block the gene induction event but failed to prevent cell cornification induced by PMA. These results suggest that diverse signaling pathways after PKC activation by PMA are involved in the regulation of these two events.

Expression and regulation of a molecular marker, SPR1, in multistep bronchial carcinogenesis

A small proline-rich protein, SPR1, is overexpressed in squamous metaplasia of bronchial epithelium. We studied the expression and regulation of SPR1 in a series of human bronchial epithelial cell lines representing a model of multistep bronchial carcinogenesis. These cell lines included a primary culture of tracheobronchial epithelial cells (HTBE), a papilloma virus-transformed tracheobronchial epithelial cell line (HBE1), a cell line selected from HBE1 by a tobacco carcinogen and a phorbol ester (HBE1-C), a simian virus-transformed bronchial epithelial cell line (BEAS-2B), and a lung carcinoma cell line (H460). Different tumorigenic potentials of these cell lines were indicated by graded levels of telomerase activity. Concomitant with squamous transformation, there was an increase in SPR1 expression in HTBE, HBE1, and HBE1-C that was reversible by vitamin A. With progression of tumorigenicity, there was a marked reduction in SPR1 expression in BEAS-2B and a total loss of expression in H460. In these latter cell lines representing advanced malignant transformation, there was a loss of up- and downregulation, respectively, by the phorbol ester and vitamin A. Transfection study with chimeric constructs of the SPR1 promoter and a reporter gene showed that the dysregulation of SPR1 expression in malignant transformation was a result of perturbation of the basal and enhancer elements of the first 162 nucleotides in the 5'-flanking promoter region of the SPR1 gene. These findings suggest an association of transcriptional dysregulation of the SPR1 gene with multistep bronchial carcinogenesis.

Sites on the cytoplasmic region of phospholamban involved in interaction with the calcium-activated ATPase of the sarcoplasmic reticulum

Proton NMR studies have shown that when a peptide corresponding to the N-terminal region of phospholamban, PLB(1-20), interacts with the Ca2+ATPase of the sarcoplasmic reticulum, SERCA1a, docking involves the whole length of the peptide. Phosphorylation of Ser16 reduced the affinity of the peptide for the pump by predominantly affecting the interaction with the C-terminal residues of PLB(1-20). In the phosphorylated peptide weakened interaction occurs with residues at the N-terminus of PLB(1-20). PLB(1-20) is shown to interact with a peptide corresponding to residues 378-405 located in the cytoplasmic region of SERCA2a and related isoforms. This interaction involves the C-terminal regions of both peptides and corresponds to that affected by phosphorylation. The data provide direct structural evidence for complex formation involving residues 1-20 of PLB. They also suggest that phospholamban residues 1-20 straddle separate segments of the cytoplasmic domain of SERCA with the N-terminus of PLB associated with a region other than that corresponding to SERCA2a(378-405).

Advances in the molecular basis of renal neoplasia

The past 2 years have provided exciting progress in elucidating the molecular basis of renal cancer. Work on the von Hippel-Lindau tumor suppressor, pVHL, in clear-cell renal cancer is already suggesting new potential therapies, and should have important implications in the pathogenesis of renal cystic disease and tumor angiogenesis. In addition, study of the Wilms' tumor suppressor, WT1, is revealing much about the pathogenesis of Wilms' tumor, urogenital development, and glomerular podocyte biology. c-met, the gene encoding the hepatocyte growth factor receptor, has recently been identified as a causative gene for hereditary papillary renal cancer. This review will highlight these and other new molecular advances in the renal cancer field.

The interactions of adenylate cyclases with P-site inhibitors

Recent kinetic, binding and crystallographic studies using P-site inhibitors of mammalian adenylate bases provide new insights into the catalytic mechanism of these highly regulated enzymes. Here, Carmen Dessauer and colleagues discuss the conformational states of adenylate cyclase, the structural determinants of inhibitor binding and the potential uses of these inhibitors as pharmacological agents.

WT1--more than a transcription factor?

The Wilms tumor-suppressor gene WT1 was originally identified through its involvement in the development of a pediatric kidney tumor. Recent genetic data show that mutations in the WT1 gene cause a variety of other diseases, and new biochemical evidence suggests that the WT1 protein is not only a transcription factor but might also act at the post-transcriptional level.

Direct spectroscopic detection of molecular dynamics and interactions of the calcium pump and phospholamban

In order to test molecular models of cardiac calcium transport regulation, we have used spectroscopy to probe the structures, dynamics, and interactions of the Ca pump (Ca-ATPase) and phospholamban (PLB) in cardiac sarcoplasmic reticulum (SR) and in reconstituted membranes. Electron paramagnetic resonance (EPR) and phosphorescence of probes bound to the Ca pump show that the activity of the pump is quite sensitive to its oligomeric interactions. In cardiac SR, PLB aggregates and inhibits the pump, and both effects are reversed by PLB phosphorylation. Previous analyses of PLB's oligomeric state were only in detergent solutions, so we used EPR and fluorescence to determine the oligomeric structure of PLB in its native state in lipid bilayers. Wild-type PLB is primarily oligomeric in the membrane, while the mutant L37A-PLB is monomeric. For both proteins, phosphorylation shifts the dynamic monomer-oligomer equilibrium toward oligomers, and induces a similar structural change, as indicated by tyrosine fluorescence; yet L37A-PLB is more effective than wild-type PLB in inhibiting and aggregating the pump. Fluorescence energy transfer shows that the Ca pump increases the fraction of monomeric PLB, indicating that the pump preferentially binds monomeric PLB. These results support a reciprocal aggregation model for Ca pump regulation, in which the Ca pump is aggregated and inhibited by association with PLB monomers, and phosphorylation of PLB reverses these effects while decreasing the concentration of PLB monomers. To investigate the structure of the PLB pentamer in more detail, we measured the reactivities of cysteine residues in the transmembrane domain of PLB, and recorded EPR spectra of spin labels attached to these sites. These results support an atomic structural model, based on molecular dynamics simulations and mutagenesis studies, in which the PLB pentamer is stabilized by a leucine-isoleucine zipper within the transmembrane domain.

High-level coexpression of the canine cardiac calcium pump and phospholamban in Sf21 insect cells

Phospholamban is a pentameric transmembrane phosphoprotein that regulates the activity of the Ca(2+)-transporting ATPase (SERCA2a) in cardiac sarcoplasmic reticulum. To better understand the structure and function of phospholamban and its mode of regulation of the ATPase, phospholamban and SERCA2a were coexpressed at high levels in Sf21 insect cells using the baculovirus expression system. SERCA2a was expressed as a functionally active Ca2+ pump, accounting for > or = 20% of the total protein in Sf21 cell microsomes. Wild-type phospholamban, as well as phospholamban with different point mutations in the transmembrane region, inhibited both Ca2+ transport and ATP hydrolysis by the recombinant Ca2+ pump. The inhibition of SERCA2a activity was reversed by an anti-phospholamban monoclonal antibody. The phospholamban molecules studied decreased the apparent Ca2+ affinity of the Ca2+ pump, but had no effect on enzyme velocity measured at saturating Ca2+ concentration. Monomeric phospholamban produced by mutations in the leucine/isoleucine zipper domain decreased the apparent Ca2+ affinity the most, giving stronger inhibition of the Ca2+ pump than even wild-type phospholamban. Thus, the baculovirus cell expression system is ideally suited for examining functional interactions between phospholamban and SERCA2a. The results obtained suggest that the phospholamban monomer may be the active species inhibiting the Ca2+ pump in the cardiac sarcoplasmic reticulum membrane.

Co-reconstitution and co-crystallization of phospholamban and Ca(2+)-ATPase

Significant advances have recently been made in understanding the regulation of Ca(2+)-ATPase by phospholamban and in modeling their structures. However, these insights would be furthered by determining the 3-D structure of both proteins within the membrane, thus revealing the structural basis for their interaction. To this end, we have developed methods for reconstituting purified Ca(2+)-ATPase with recombinant phospholamban. After reconstitution at high lipid-to-protein ratios, we have verified their functional association by measuring calcium transport and ATPase activity. Furthermore, we have grown co-crystals after reconstitution at low lipid-to-protein ratios. The structure of Ca(2+)-ATPase has recently been solved by cryoelectron microscopy at 8-A resolution, thus revealing transmembrane alpha-helices. Using a variety of constraints, we have associated these helices with the predicted transmembrane sequences to produce a detailed model for the packing of transmembrane helices. Structure determination of the co-crystals is currently underway, which we hope will eventually reveal the interaction of phospholamban with Ca(2+)-ATPase at a similar level of detail.

The position and length of the steroid-dependent hypersensitive region in the mouse mammary tumor virus long terminal repeat are invariant despite multiple nucleosome B frames

Stimulation of the mouse mammary tumor virus with steroids results in the generation of a DNase I-hypersensitive region (HSR) spanning the hormone responsive element (HRE) in the long terminal repeat. Restriction enzymes were used to characterize the accessibility of various sites within the HSR of mouse mammary tumor virus long terminal repeat-reporter constructions in four different cell lines. The glucocorticoid-dependent HSR was found to span minimally 187 bases, a stretch of DNA longer than that associated with histones in the core particle. Although the 5'-most receptor binding site within the HRE is downstream of -190, hypersensitive sites were found further upstream to at least -295. The relationship in the accessibility between pairs of sites in the vicinity of the HSR was further examined in one cell line by a two-enzyme restriction access assay. In the uninduced state, the accessibilities at these sites were found to be independent of each other. In contrast, when stimulated with hormone, the accessibilities at these sites were observed to become linked. That is, once a distinct promoter was activated, all of the sites within the HSR of that molecule became accessible. The HSR formed along an invariant stretch of DNA sequence despite the multiplicity of nucleosome frames in the nucleosome B region, where the HRE is located. The results indicate that the macroscopic length of the HSR does not arise from core length-remodeling events in molecules containing Nuc-B in alternative positions.

Structural organization of cornified cell envelopes and alterations in inherited skin disorders

The cornified cell envelope is a highly insoluble and extremely tough structure formed beneath the cell membrane during terminal differentiation of keratinocytes. Its main function is to provide human skin with a protective barrier against the environment. Sequential cross-linking of several integral components catalyzed by transglutaminases leads to a gradual increase in the thickness of the envelope and underscores its rigidity. Key structural players in this cross-linking process include involucrin, loricrin, SPRRs, elafin, cystatin A, S100 family proteins, and some desmosomal proteins. The recent identification of genetic skin diseases with mutations in the genes encoding some of these proteins, including transglutaminase 1 and loricrin, has disclosed that abnormal cornified cell envelope synthesis is significantly involved in the pathophysiology of certain inherited keratodermas and reflects perturbations in the complex, yet highly orderly process of cornified cell envelope formation in normal skin biology.

Purification of the cardiac sarcoplasmic reticulum membrane protein phospholamban from recombinant Escherichia coli

Phospholamban (PLN) was expressed in Escherichia coli as a protein fusion with glutathione S-transferase (GST). GST-PLN was mostly present in the insoluble protein fraction and accounted for approximately 50% of total insoluble protein. Attempts to suppress inclusion body formation or to use GST as an affinity-purification tag failed. A successful purification method is based on preparative SDS/PAGE and electrodialysis. From 1 g cells we typically purified 13.5 mg fusion protein with a PLN content of 2.8 mg. We genetically inserted an enterokinase (EK) protease site just in front of the PLN sequence and demonstrated the proteolytical liberation of PLN from the carrier protein. The approach described represents a substantial advancement in PLN expression and purification.

Exploring the role of homeobox and zinc finger proteins in pancreatic cell proliferation, differentiation, and apoptosis

Transcription factors are DNA binding proteins that regulate gene expression in response to a large variety of extracellular stimuli, and thereby act as key molecular switches for controlling cell differentiation, proliferation, and apoptosis. During the last decade, a myriad of these proteins have been identified and classified into different structural families, including homeobox, zinc finger, leucine zipper, and helix-loop-helix transcription factors. Members of the homeobox and zinc finger superfamilies are among the best-characterized transcription factors known to act as potent regulators of normal development in organisms ranging from insects to humans. In addition, mutations or aberrant expression in genes encoding these proteins can result in neoplastic transformation in several different cell types, further supporting their role as "guardians" of normal cell growth and differentiation. Therefore, the purpose of this article is to review this field of research with a particular emphasis on the role of homeobox- and zinc finger-containing transcription factors in pancreatic cell growth, cell differentiation, and apoptosis. The potential participation of these proteins in neoplastic transformation is also discussed.

Progress in transcriptionally targeted and regulatable vectors for genetic therapy

Safety is an important consideration in the development of genetic therapy protocols; for example, proteins that are therapeutic in the context of one tissue may be harmful in another. This is particularly relevant to suicide gene strategies for cancer, which require in vivo delivery of DNA and which, in general, demand that the therapeutic product be limited as far as possible to malignant cells. This has led to a requirement for "transcriptionally targeted" vectors that can restrict the expression of the therapeutic sequence to appropriate cells. Furthermore, there may be a therapeutic window for certain proteins such that levels of expression below and above certain thresholds may be ineffective or toxic, respectively. Therefore, it would also be desirable to create vectors that allow exogenous control of expression, so that levels of the therapeutic protein can be raised or lowered according to therapeutic need. In the context of transcriptional targeting, one may sometimes use cis-acting sequences to limit transgene expression to the target cell type. In genetic therapy for cancer, for example, it may be possible to identify and use transcriptional control elements that drive expression of proteins unique to, or over-expressed in, malignant cells. These controls would greatly reduce collateral expression of the transgene, and hence reduce toxicity to healthy cells. With regard to exogenous control of expression subsequent to transduction, several synthetic gene regulation systems have now been produced. In these systems, an inducer or repressor acts on a synthetic transcription factor that recognizes motifs unique to the promoter of the transgene; this allows regulated expression of the therapeutic protein without nonspecific effects on cellular promoters. It is likely that a vector will soon be produced in which tissue-restricted expression of the synthetic transcription factor is combined with regulatable transgene expression thereby allowing precise control of therapeutic protein production in specific tissues via administration of an inducing or repressing agent.

Up-regulation of hormone response of human papillomavirus type 16 expression and increased DNA-protein binding by consensus mutations of viral glucocorticoid response elements

Human papillomaviruses (HPVs) and steroid hormones are linked to the development of cervical cancer. Studies from our laboratory and others showed that the steroid glucocorticoid and progesterone hormones activated the expression of HPV type 16. This activation was attributed to the specific interaction of the glucocorticoid receptor (GR) with the three glucocorticoid response elements (GREs) in the HPV16 regulatory region. In the present study, we first examined the glucocorticoid response mediated through the GREs, using GRE consensus (GREc) mutations and expression assays from a heterologous basal promoter. Both single and triple HPV16 GREc constructs increased expression in the presence of the dexamethasone glucocorticoid in HeLa cervical carcinoma cells and primary baby rat kidney epithelial cells, in comparison with the triple wild-type GREs. Further, the hormone increased significantly the expression of the viral E6-E7 oncogene mRNA from intact HPV in primary human ectocervical cells in in situ hybridization assays. Three in vitro assays of DNA-protein interaction with oligonucleotides and HeLa cell extracts showed a higher binding of protein to two of the HPV16 GREcs than to the wild-type GREs. This applied especially to the GRE containing an overlapping NF1 half site, that also had a greater differential induction by dexamethasone of expression in vivo. The NF1 site was mutated in the GREc that also was bound by unique, lower-mobility complexes in electrophoretic mobility shift assays. UV-crosslinking assays confirmed the increased binding and showed binding by a 96-kDa protein, probably the GR. Our results show an important role of glucocorticoids in HPV16 expression. The direct action through the HPV16 GREs is suggested to be mediated by the hormone-activated GR in association with other factors.

Adenylate cyclases: critical foci in neuronal signaling

Current findings show that adenylate cyclases comprise a heterogeneous multigene family, members of which are variously regulated by the alpha and beta gamma subunits of G proteins, by Ca2+ and by protein kinases. In the CNS, individual isoforms of adenylate cyclase are expressed discretely in select regions of the brain. At the subcellular level, adenylate cyclases can be concentrated into dendritic spines, thereby increasing their susceptibility to multiple regulatory influences. Altogether, such findings greatly expand knowledge of the potential role of this archetypical signaling system in the modulation of neuronal function.