Matrix conditions and KLF2-dependent induction of heme oxygenase-1 modulate inhibition of HCV replication by fluvastatin

Background & Aims

HMG-CoA-reductase-inhibitors (statins) have been shown to interfere with HCV replication in vitro. We investigated the mechanism, requirements and contribution of heme oxygenase-1(HO-1)-induction by statins to interference with HCV replication.

Methods

HO-1-induction by fluva-, simva-, rosuva-, atorva- or pravastatin was correlated to HCV replication, using non-infectious replicon systems as well as the infectious cell culture system. The mechanism of HO-1-induction by statins as well as its relevance for interference with HCV replication was investigated using transient or permanent knockdown cell lines. Polyacrylamide(PAA) gels of different density degrees or the Rho-kinase-inhibitor Hydroxyfasudil were used in order to mimic matrix conditions corresponding to normal versus fibrotic liver tissue.

Results

All statins used, except pravastatin, decreased HCV replication and induced HO-1 expression, as well as interferon response in vitro. HO-1-induction was mediated by reduction of Bach1 expression and induction of the Nuclear factor (erythroid-derived 2)-like 2 (NRF2) cofactor Krueppel-like factor 2 (KLF2). Knockdown of KLF2 or HO-1 abrogated effects of statins on HCV replication. HO-1-induction and anti-viral effects of statins were more pronounced under cell culture conditions mimicking advanced stages of liver disease.

Conclusions

Statin-mediated effects on HCV replication seem to require HO-1-induction, which is more pronounced in a microenvironment resembling fibrotic liver tissue. This implicates that certain statins might be especially useful to support HCV therapy of patients at advanced stages of liver disease.

Meiotic inheritance of functional Gal80S gene product in Saccharomyces cerevisiae

Transcription factors inherited during meiosis play a crucial role directing subsequent gene activity. Factors of maternal origin have been shown to influence the pattern of early zygotic transcription during Drosophila and Xenopus embryogenesis. Nevertheless, little is known regarding the meiotic inheritance of the vast majority of transcription factors. In the case of yeast meiosis, for example, it is not yet known whether any of the multitude of transcription factors expressed in the diploid are transmitted to haploid spores in functional form. Here we use a GAL1-STE4 reporter whose activity is detectable in single living cells to identify a transcription factor inherited during sporulation in Saccharomyces cerevisiae. We show that functional Gal80S repressor is meiotically inherited at levels reflecting its expression in the diploid parent.

Fixation of epigenetic states in a population

Multiple steady-state levels of autoregulatory transcription factors constitute alternative epigenetic states, and could help specify the heritable phenotype of an organism. In this work, the inheritance of autoregulatory transcription factors through sexual reproduction is modeled to determine the conditions under which different alternative epigenetic states become fixed in a population. The influence of transient environmental perturbations on the fixation of states is discussed in the context of speciation.

Model genetic circuits encoding autoregulatory transcription factors

Multiple steady-state levels of autoregulatory transcription factors are capable of specifying alternative heritable phenotypes of a cell or an organism. Switching among steady states can result in long-term phenotypic change. In this paper, six model genetic circuits are presented, each encoding a set of autoregulatory transcription factors. The steady-state rate equations for each genetic circuit are formulated and solved to determine conditions under which multiple steady states exist. Each steady state of the genetic circuit constitutes an alternative heritable phenotype resulting from a single genotype.

Specifying epigenetic states with autoregulatory transcription factors

Epigenetic information, not DNA sequence, distinguishes different cell types within a multicellular organism. The molecular nature of epigenetic information specifying differentiated cell types is unknown. However, it must be stable over time and mitotically heritable. In this paper, steady-state levels of autoregulatory transcription factors are explored as a potential form of epigenetic information. In particular, a model autoregulatory transcription factor having two alternative stable steady-state levels is presented. Each steady-state level specifies a phenotypically distinguishable epigenetic state, analogous to a differentiated cell type. These states are mitotically stable if the transcription factor is inherited during cell division.

Only two of the five zinc fingers of the eukaryotic transcriptional repressor PRDI-BF1 are required for sequence-specific DNA binding

The eukaryotic transcriptional repressor PRDI-BF1 contains five zinc fingers of the C2H2 type, and the protein binds specifically to PRDI, a 14-bp regulatory element of the beta interferon gene promoter. We have investigated the amino acid sequence requirements for specific binding to PRDI and found that the five zinc fingers and a short stretch of amino acids N terminal to the first finger are necessary and sufficient for PRDI-specific binding. The contribution of individual zinc fingers to DNA binding was investigated by inserting them in various combinations into another zinc finger-containing DNA-binding protein whose own fingers had been removed. We found that insertion of PRDI-BF1 zinc fingers 1 and 2 confer PRDI-binding activity on the recipient protein. In contrast, the insertion of PRDI-BF1 zinc fingers 2 through 5, the insertion of zinc finger 1 or 2 alone, and the insertion of zinc fingers 1 and 2 in reverse order did not confer PRDI-binding activity. We conclude that the first two PRDI-BF1 zinc fingers together are sufficient for the sequence-specific recognition of PRDI.

Selection of sequences recognized by a DNA binding protein using a preparative southwestern blot

We have tested the feasibility of using a preparative scale Southwestern blot to select DNA sequences specifically recognized by a DNA binding protein. We constructed a library of random 15-mer oligonucleotides and screened it using a preparative Southwestern blot with the transcriptional repressor, PRDI-BF1. Several sequences specifically recognized by PRDI-BF1 were isolated. All of these sequences are similar to PRDI, a regulatory element previously demonstrated to bind PRDI-BF1.

Identification and characterization of a novel repressor of beta-interferon gene expression

We have identified and characterized a novel repressor of human beta-interferon (beta-IFN) gene expression. This protein, designated PRDI-BF1, binds specifically to the PRDI element of the beta-IFN gene promoter and is distinct from previously reported proteins that bind to this sequence. PRDI-BF1 is an 88-kD protein containing five zinc-finger motifs. Cotransfection experiments in cultured mammalian cells revealed that PRDI-BF1 is a potent repressor of PRDI-dependent transcription. PRDI-BF1 blocks virus induction of the intact beta-IFN gene promoter and of synthetic promoters containing multiple PRDI sites. PRDI-BF1 can also block the SV40 enhancer when PRDI sites are located between the enhancer and the promoter. This repression is highly dependent on the location of the PRDI sites, however, indicating that PRDI-BF1 cannot act at a distance. On the basis of the properties of PRDI-BF1 and the observation that PRDI-BF1 mRNA accumulation is virus inducible, we propose that PRDI-BF1 may act as a postinduction repressor of the beta-IFN gene by displacing positive regulatory proteins from the PRDI site of the promoter.

Identification of an inducible factor that binds to a positive regulatory element of the human beta-interferon gene

Human beta-interferon gene expression is induced by virus or poly(I).poly(C). This induction is due at least in part to an increase in the rate of transcription and does not require protein synthesis. A 40-base-pair DNA sequence within the beta-interferon promoter, termed the interferon gene regulatory element (IRE), is an inducible enhancer in mouse fibroblasts, and both positive and negative regulatory DNA sequences have been identified within this element. In this paper we identify three factors that bind specifically to two positive regulatory domains within the IRE. Two of these factors are present in nuclear extracts prepared from uninduced and induced cells; one is present only in extracts from induced cells. The functional significance of these binding activities was demonstrated by showing that point mutations within the IRE that decrease human beta-interferon gene transcription in vivo prevent binding in vitro. We propose that induction of the beta-interferon gene involves the modification of a protein to a form that binds specifically to a positive regulatory sequence within the IRE.