Reporter-linked monitoring of transgene expression in living cells using the ecdysone-inducible promoter system

Construction and characterization of a synthetic Baculovirus-inducible 39K promoter

Background

Silkworm genetic engineering is widely used in gene function, silk engineering and disease-resistant engineering in most of Asia. Some of the earliest promoter elements are used to control the development of silkworm transgenic expression and gene therapy. However, the low expression and specificity of natural promoters limit the applications of genetic engineering. To construct a highly efficient synthetic inducible promoter in the Bombyx mori (Lepidoptera), we analyzed the regulatory elements and functional regions of the B. mori nucleopolyhedrovirus 39 K promoter.

Results

Truncated mutation analysis of the 39 K promoter showed that the transcriptional regulatory region spanning positions - 573 to - 274 and + 1 to + 62 are essential for virus-inducible promoter activity. Further investigations using the electrophoretic mobility shift assay revealed that the baculovirus IE-1 protein binds to the 39 K promoter at the - 310 to - 355 region, and transcription activates the expression of 39 K promoter assay. Finally, we successfully constructed a synthetic inducible promoter that increased the virus-inducing activity of other promoters using the baculovirus-inducible transcriptional activation region that binds to specific core elements of 39 K (i.e., spanning the region - 310 to - 355).

Conclusions

In summary, we constructed a novel, synthetic, and highly efficient biological tool, namely, a virus-inducible 39 K promoter, which provides endless possibilities for future research on gene function, gene therapy, and pest control in genetic engineering.

Effect of ecdysone receptor gene switch ligands on endogenous gene expression in 293 cells

Regulated gene expression may substantially enhance gene therapy. Correlated with structural differences between insect ecdysteroids and mammalian steroids, the ecdysteroids appear to have a benign pharmacology without adversely interfering with mammalian signaling systems. Consequently, the ecdysone receptor-based gene switches are attractive for application in medicine. In the present study, the effect of inducers of ecdysone receptor switches on the expression of endogenous genes in HEK 293 cells was determined. Four ligand chemotypes, represented by a tetrahydroquinoline (RG-120499), one amidoketone (RG-121150), two ecdysteroids [20-hydroxyecdysone (20E) and ponasterone A (Pon A)], and four diacylhydrazines (RG-102240, RG-102277, RG-102398 and RG-100864), were tested in HEK 293 cells. The cells were exposed to ligands at concentrations of 1 microm (RG-120499) or 10 microm (all others) for 72 h and the total RNA was isolated and analyzed using microarrays. Microarray data showed that the tetrahydroquinoline ligand, RG-120499 caused cell death at concentrations > or = 10 microm. At 1 microm, this ligand caused changes in the expression of genes such as TNF, MAF, Rab and Reprimo. At 10 microm, the amidoketone, RG-121150, induced changes in the expression of genes such as v-jun, FBJ and EGR, but was otherwise noninterfering. Of the two steroids tested, 20E did not affect gene expression, but Pon A caused some changes in the expression of endogenous genes. At lower concentrations pharmacologically relevant for gene therapy, intrinsic gene expression effects of ecdysteroids and amidoketones may actually be insignificant. A fortiori, even at 10 microm, the four diacylhydrazine ligands did not cause significant changes in expression of endogenous genes in 293 cells and therefore should have minimum pleiotropic effects when used as ligands for the ecdysone receptor gene switch.

Membrane and raft association of reggie-1/flotillin-2: role of myristoylation, palmitoylation and oligomerization and induction of filopodia by overexpression

The reggie protein family consists of two proteins, reggie-1 and -2, also called flotillins, which are highly ubiquitous and evolutionarily conserved. Both reggies have been shown to be associated with membrane rafts and are involved in various cellular processes such as T-cell activation, phagocytosis and insulin signalling. However, the exact molecular function of these proteins remains to be determined. In addition, the mechanism of membrane association of reggie-1, which does not contain any transmembrane domain, is not known. In this study, we have produced a fusion protein of reggie-1 with enhanced green fluorescent protein and generated targeted substitutions for the inactivation of putative palmitoylation and myristoylation sites. We were able to show that reggie-1 is myristoylated and multiply palmitoylated and that lipid modifications are necessary for membrane association of reggie-1. Overexpression of reggie-1 resulted in the induction of numerous filopodia-like protrusions in various cell lines, suggesting a role for reggie-1 as a signalling protein in actin-dependent processes.

Superimposition evaluation of ecdysteroid agonist chemotypes through multidimensional QSAR

The EC50 values for a training set of 66 ecdysteroids and 97 diacylhydrazines were measured in the ecdysteroid-responsive Drosophila melanogaster BII cell line, a prototypical homologous inducible gene expression system. Each of eight superimposition hypotheses for the folded diacylhydrazine conformation was evaluated and ranked on the basis of CoMFA and 4D-QSAR Q2 values for the training set and R2 values for a 52-member test set comprising randomly-chosen diacylhydrazines and chronologically-chosen ecdysteroids for which data became available after model construction. Both 4D-QSAR and CoMFA rate a common superimposition as the preferred one. Two additional superimpositions, with somewhat weaker 4D-QSAR and CoMFA consensus, nonetheless share several important topological features. The resultant QSAR models address the question of relative binding orientation of the two ligand families and can be useful as a virtual screen for new chemotypes.

Practical uses for ecdysteroids in mammals including humans: an update

Ecdysteroids are widely used as inducers for gene-switch systems based on insect ecdysteroid receptors and genes of interest placed under the control of ecdysteroid-response elements. We review here these systems, which are currently mainly used in vitro with cultured cells in order to analyse the role of a wide array of genes, but which are expected to represent the basis for future gene therapy strategies. Such developments raise several questions, which are addressed in detail. First, the metabolic fate of ecdysteroids in mammals, including humans, is only poorly known, and the rapid catabolism of ecdysteroids may impede their use as in vivo inducers. A second set of questions arose in fact much earlier with the pioneering "heterophylic" studies of Burdette in the early sixties on the pharmacological effects of ecdysteroids on mammals. These and subsequent studies showed a wide range of effects, most of them being beneficial for the organism (e.g. hypoglycaemic, hypocholesterolaemic, anabolic). These effects are reviewed and critically analysed, and some hypotheses are proposed to explain the putative mechanisms involved. All of these pharmacological effects have led to the development of a wide array of ecdysteroid-containing preparations, which are primarily used for their anabolic and/or "adaptogenic" properties on humans (or horses or dogs). In the same way, increasing numbers of patents have been deposited concerning various beneficial effects of ecdysteroids in many medical or cosmetic domains, which make ecdysteroids very attractive candidates for several practical uses. It may be questioned whether all these pharmacological actions are compatible with the development of ecdysteroid-inducible gene switches for gene therapy, and also if ecdysteroids should be classified among doping substances.

Antioxidative and free radical scavenging effects of ecdysteroids from Serratula strangulata

The antioxidative and free radical scavenging effects of four ecdysteroids, 20-hydroxyecdysone (E1), 25-deoxy-11,20-dihydroxyecdysone (E2), 24-(2-hydroxyethyl)-20-hydroxyecdysone (E3), and 20-hydroxyecdysone-20,22-monoacetonide (E4), isolated from the Chinese herb Serratula strangulata have been investigated in vitro. These ecdysteroids could protect human erythrocytes against oxidative hemolysis induced by a water-soluble azo initiator 2,2'-azobis(2-amidinopropane hydrochloride) (AAPH). They could also inhibit the peroxidation of rat liver microsomes induced by hydroxyl radicals, as monitored by the formation of thiobarbituric acid reactive substances (TBARS), and prevent radical-induced decrease of membrane fluidity as determined by fluorescence polarization. They reacted with galvinoxyl radicals in homogeneous solution, and the pseudo-first-order rate constants were determined spectrophotometrically by following the disappearance of galvinoxyl radicals. Compounds E1 and (or) E3 were the most active in both antioxidative and radical-scavenging reactions.

Murine calmodulin binding protein 1 (Calmbp1): tissue-specific expression during development and in adult tissues

Expression of the 1.9 kb cDNA of murine Calmbp1 has been shown to interfere with the mitotic S-M checkpoint in yeast (J. Cell Sci. 111 (1998) 3609). The physiological function and expression pattern of Calmbp1 in mice, however, are unknown. We have investigated the expression of Calmbp1 in mid-gestation and late-gestation fetuses and in adult organs of the mouse. In Northern blot analyses, using a Calmbp1-specific probe, a single mRNA of more than 7.4 kb was found that showed a progressive decline in total RNA preparations of fetal heads during the period from day E12 to E16. In the adult, this Calmbp1 transcript was detectable by Northern blot analysis exclusively in testis, ovary and spleen of all organs examined. In situ hybridizations revealed that Calmbp1 is expressed (a) in the differentiating central and peripheral nervous system, (b) in the epithelial cells lining the crypts of the small intestine in late gestation and adult mice, (c) in the fetal, but not the adult liver, (d) in both the fetal and adult spleen, where the signal colocalized with hematopoetic cells in the red pulp, (e) in late gestation embryos in the thymus, S-shaped tubules in the kidney, epidermis, and (f) in leptotene, zygotene and pachytene spermatocytes of the adult testis and the follicle epithelium of the activated follicles in the adult ovary.

4D-QSAR analysis of a set of ecdysteroids and a comparison to CoMFA modeling

The ecdysteroid-responsive Drosophila melanogaster B(II) cell line is a prototypical homologous inducible gene expression system. A training set of 71 ecdysteroids, for which the -log(EC(50)) potencies in the ecdysteroid-responsive B(II) cell line were measured, was used to construct 4D-QSAR models. Four nearly equivalent optimum 4D-QSAR models, for two modestly different alignments, were identified (Q(2) = 0.76-0.80). These four models, together with two CoMFA models, were used in consensus modeling to arrive at a three-dimensional pharmacophore. The C-2 and C-22 hydroxyls are identified as hydrogen-bond acceptor sites which enhance activity. A hydrophobic site near C-12 is consistent with increasing activity. The side-chain substituents at C-17 are predicted to adopt semiextended "active" conformations which could fit into a cylinder-shaped binding pocket lined largely with nonpolar residues for enhanced activity. A test set of 20 ecdysteroids was used to evaluate the QSAR models. Two 4D-QSAR models for one alignment were identified to be superior to the others based on having the smallest average residuals of prediction for the prediction set (0.69 and 1.13 -log[EC(50)] units). The correlation coefficients of the optimum 4D-QSAR models (R(2) = 0.87 and 0.88) are nearly the same as those of the best CoMFA model (R(2) = 0.92) determined for the same training set. However, the cross-validation correlation coefficient of the CoMFA model is less significant (Q(2) = 0.59) than those of the 4D-QSAR models (Q(2) = 0.80 and 0.80).

Phytoecdysteroids: biological aspects

Phytoecdysteroids are a family of about 200 plant steroids related in structure to the invertebrate steroid hormone 20-hydroxyecdysone. Typically, they are C27, C28 or C29 compounds possessing a 14alpha-hydroxy-7-en-6-one chromophore and A/B-cis ring fusion (5beta-H). In the present review, the distribution, biosynthesis, biological significance and potential applications of phytoecdysteroids are summarised.