The tomato dark green mutation is a novel allele of the tomato homolog of the DEETIOLATED1 gene.

A comprehensive, multi-generation, allele test, carried out in this study, suggests that the tomato mutations dark-green (dg) and high pigment 2(j) (hp-2(j)) are allelic. The hp-2(j) mutant is caused by a mutation in the tomato homolog of the DEETIOLATED1 (DET1) gene, involved in the signal transduction cascade of light perception and morphogenesis. This suggestion is in agreement with the exaggerated photomorphogenic de-etiolation response of homozygous dg mutants grown under modulated light conditions. Sequence analysis of the DET1 gene was carried out in dg mutants representing two different lines, and revealed a single A-to-T base transversion in the second exon of the DET1 gene in comparison with the normal wild-type sequence. This transversion results in a conserved Asparagine(34)-to-Isoleucine(34) amino-acid substitution, and eliminates a recognition site for the AclI restriction endonuclease, present in the wild-type and in the other currently known tomato mutants at the DET1 locus. This polymorphism was used to develop a PCR-based DNA marker, which enables an early genotypic selection for breeding lycopene-rich tomatoes. Using this marker and sequence analysis we demonstrate that an identical base transversion also exists in dg mutants of the cultivar Manapal, in which the natural dg mutation was originally discovered. A linkage analysis, carried out in a F(2) population, shows a very strong linkage association between the DET1 locus of dg mutant plants and the photomorphogenic response of the seedlings, measured as hypocotyl length (12 < LOD Score < 13, R(2) = 51.1%). The results presented in this study strongly support the hypothesis that the tomato dg mutation is a novel allele of the tomato homolog of the DET1 gene.

An immortalized rat liver stellate cell line (HSC-T6): a new cell model for the study of retinoid metabolism in vitro.

Hepatocytes and hepatic stellate cells play important roles in retinoid storage and metabolism. Hepatocytes process postprandial retinyl esters and are responsible for secretion of retinol bound to retinol-binding protein (RBP) to maintain plasma retinol levels. Stellate cells are the body's major cellular storage sites for retinoid. We have characterized and utilized an immortalized rat stellate cell line, HSC-T6 cells, to facilitate study of the cellular aspects of hepatic retinoid processing. For comparison, we also carried out parallel studies in Hepa-1 hepatocytes. Like activated primary stellate cells, HSC-T6 express myogenic and neural crest cytoskeletal filaments. HSC-T6 cells take up and esterify retinol in a time- and concentration-dependent manner. Supplementation of HSC-T6 culture medium with free fatty acids (up to 300 micrometer) does not affect retinol uptake but does enhance retinol esterification up to 10-fold. RT-PCR analysis indicates that HSC-T6 cells express all 6 retinoid nuclear receptors (RARalpha, -beta, -gamma, and RXRalpha, -beta, -gamma) and like primary stellate cells, HSC-T6 stellate cells express cellular retinol-binding protein, type I (CRBP) but fail to express either retinol-binding protein (RBP) or transthyretin (TTR). Addition of retinol (10(-8)-10(-5) m) or all-trans-retinoic acid (10(-10)-10(-6) m) rapidly up-regulates CRBP expression. Using RAR-specific agonists and antagonists and an RXR-specific agonist, we show that members of the RAR-receptor family modulate HSC-T6 CRBP expression.Thus, HSC-T6 cells display the same retinoid-related phenotype as primary stellate cells in culture and will be a useful tool for study of hepatic retinoid storage and metabolism.

Transcriptional activation of transforming growth factor beta1 and its receptors by the Kruppel-like factor Zf9/core promoter-binding protein and Sp1. Potential mechanisms for autocrine fibrogenesis in response to injury.

We have explored the regulation of transforming growth factor beta (TGF-beta) activity in tissue repair by examining the interactions of Zf9/core promoter-binding protein, a Kruppel-like zinc finger transcription factor induced early in hepatic stellate cell (HSC) activation, with promoters for TGF-beta1 and TGF-beta receptors, types I and II. Nuclear extracts from culture-activated HSCs bound avidly by electrophoretic mobility shift assay to two tandem GC boxes within the TGF-beta1 promoter but minimally to a single GC box; these results correlated with transactivation by Zf9 of TGF-beta1 promoter-reporters. Zf9 transactivated the full-length TGF-beta1 promoter in either primary HSCs, HSC-T6 cells (an SV40-immortalized rat HSC line), Hep G2 cells, or Drosophila Schneider (S2) cells. Recombinant Zf9-GST also bound to GC box sequences within the promoters for the types I and II TGF-beta receptors. Both type I and type II TGF-beta receptor promoters were also transactivated by Zf9 in mammalian cells but not in S2 cells. In contrast, Sp1 significantly transactivated both receptor promoters in S2 cells. These results suggest that (a) Zf9/core promoter-binding protein may enhance TGF-beta activity through transactivation of both the TGF-beta1 gene and its key signaling receptors, and (b) transactivating potential of Zf9 and Sp1 toward promoters for TGF-beta1 and its receptors are not identical and depend on the cellular context.

Zf9, a Kruppel-like transcription factor up-regulated in vivo during early hepatic fibrosis.

Wound repair in the liver induces altered gene expression in stellate cells (resident mesenchymal cells) in a process known as "activation." A zinc finger transcription factor cDNA, zf9, was cloned from rat stellate cells activated in vivo. Zf9 expression and biosynthesis are increased markedly in activated cells in vivo compared with cells from normal rats ("quiescent" cells). The factor is localized to the nucleus and the perinuclear zone in activated but not quiescent cells. Zf9 mRNA also is expressed widely in nonhepatic adult rat tissues and the fetal liver. The zf9 nucleotide sequence predicts a member of the Kruppel-like family with a unique N-terminal domain rich in serine-proline clusters and leucines. The human zf9 gene maps to chromosome 10P near the telomere. Zf9 binds specifically to a DNA oligonucleotide containing a GC box motif. The N-terminal domain of Zf9 (amino acids 1-201) is transactivating in the chimeric GAL4 hybrid system. In Drosophila schneider cells, full length Zf9 transactivates a reporter construct driven by the SV40 promoter/enhancer, which contains several GC boxes. A physiologic role for Zf9 is suggested by its transactivation of a collagen alpha1(I) promoter reporter. Transactivation of collagen alpha1(I) by Zf9 is context-dependent, occurring strongly in stellate cells, modestly in Hep G2 cells, and not at all in D. schneider cells. Our results suggest that Zf9 may be an important signal in hepatic stellate cell activation after liver injury.

Coordinated induction of VEGF receptors in mesenchymal cell types during rat hepatic wound healing.

Homology PCR has been used to identify receptor tyrosine kinases (RTKs) expressed during activation of rat hepatic stellate cells, the key fibrogenic mesenchymal element in the liver. Partial cDNAs encoding several RTKs were cloned from stellate cells activated in vivo, including those of Flt-1, Flk-1, c-met, PDGFR, and Tyro10/DDR2. RNAse protection from cells activated in vivo demonstrated biphasic induction of flt-1 and flk-1 mRNAs, receptors for vascular endothelial growth factor (VEGF). Culture-activation of stellate cells was associated with increased [125I]VEGF binding and Flt-1 and Flk-1 receptor protein. Induction of VEGF binding sites correlated with an 2.5-fold increase in DNA synthesis in response to VEGF, but only if cells were activated by growth on collagen 1, whereas cells maintained in a quiescent state on a basement membrane-like substratum (EHS matrix) were nonproliferative. In both stellate and endothelial cells VEGF-induced mitogenesis was augmented by co-incubation with basic fibroblast growth factor (bFGF), a cytokine with known synergy with VEGF. These findings suggest that the cellular targets of VEGF in liver may not be confined to sinusoidal endothelial cells, and that VEGF responses reflect combined effects on both hepatic stellate cells and sinusoidal endothelium.

Early genes induced in hepatic stellate cells during wound healing.

Activation of mesenchymal cells is a central event in the wound healing response of most tissues. In liver, the mesenchymal element responsible for organ fibrosis is the hepatic stellate cell (HSC) (formerly known as lipocyte or Ito cell). The phenotypic cascade of stellate cell activation in liver fibrosis has been well documented and involves both marked morphologic changes and upregulation of several functional components including extracellular matrix, cytokine receptors, contractile filaments and metalloproteinases. However, the genetic regulation of stellate cell activation is poorly understood. In an attempt to clone genes that are involved in the regulation of HSC activation we have combined cDNA library amplification by PCR with subtraction hybridization/differential screening, and have successfully identified genes induced in vivo during early stellate cell activation in a rat model of liver fibrosis. The subtracted cDNA library comprised less than 100 unique sequences. Of these, 13 clones with sizes ranging from 322 to 745 were sequenced and characterized. Gene induction in HSCs was monitored by RNAse protection assay during early liver injury induced by the hepatotoxin CCl4. The sequenced cDNAs corresponding to the known genes included type II transforming growth factor beta receptor, glutathione peroxidase I, transferrin and several clones encoding cellular retrotransposons, whose expression was not previously identified in non-parenchymal liver cells. In addition, one partial cDNA predicted a zinc-finger motif, suggesting a possible role of a novel transcriptional regulator. Our approach represents a valuable strategy for clarifying in vivo regulatory mechanisms of mesenchymal cell activation in wound healing.

Purification, partial characterization and plasmid-linkage of pediocin SJ-1, a bacteriocin produced by Pediococcus acidilactici.

Pediococcus acidilactici SJ-1, isolated from a naturally-fermented meat product, produced an antibacterial agent active against selected strains of Lactobacillus spp., Clostridium perfringens and Listeria monocytogenes. The agent was bactericidal against sensitive indicators, and sensitive to proteolytic enzymes; it was identified as a bacteriocin, and was designated as pediocin SJ-1. It was stable over a wide pH range (3-9), and apparently most stable in the lower part of that range. At pH 3.6, pediocin SJ-1 was stable at heat-processing temperatures within the range 65-121 degrees C; its activity decreased significantly, however, when it was heated at pH 7.0. The activity of pediocin SJ-1 on sensitive indicator cells was lost in the presence of alpha-amylase, suggesting that it contains a glyco moiety, necessary for its antibacterial action. Native pediocin SJ-1 exists in the form of monomers and aggregates (with molecular weights in the range 80-150 kDa). Pediocin SJ-1 was purified 262-fold by direct application of cell-free supernatant fluids to a cation-exchange chromatography column, and was resolved by SDS-PAGE as a single peptide band with a MW of ca 4 kDa. The original pediocin SJ-1-producing strain (bac+) harbours three plasmids of 4.6, 23.5, and 45.7 MDa. Production of pediocin SJ-1, but not immunity to SJ-1, is associated with the 4.6 MDa plasmid.

Human apolipoprotein E. Receptor binding activity of truncated variants with carboxyl-terminal deletions.

The amino-terminal thrombolytic fragment (residues 1-191) of human apolipoprotein (apo) E was previously shown to be fully active in binding to the low density lipoprotein receptor. In this study, truncated apoE variants with progressive deletions at the carboxyl terminus were produced in Escherichia coli by linker-insertion mutagenesis to define the minimum amino-terminal structure necessary for full receptor binding. These truncated forms of apoE, comprising residues 1-166, 1-170, 1-174, or 1-183, were combined with the phospholipid dimyristoylphosphatidylcholine and tested for their ability to bind to low density lipoprotein receptors on human fibroblasts. All of the truncated variants formed typical discoidal particles when combined with the phospholipid, and the particles could be isolated by density gradient ultracentrifugation. The 1-166 and 1-170 variants had very little receptor binding activity (1%), whereas the 1-183 variant had nearly full activity (85%). The 1-174 variant had 19% activity. We conclude that the 171-183 region of apoE is important for receptor binding, either by contributing one or more residues essential for receptor binding or, more likely, by stabilizing or aligning the region known to be crucial for receptor binding, in the vicinity of residues 140-160.

Site-specific mutagenesis of human apolipoprotein E. Receptor binding activity of variants with single amino acid substitutions.

Apolipoprotein (apo) E, an important protein involved in cholesterol transport in the plasma, binds with high specificity and high affinity to the apoB, E (low density lipoprotein) receptor. Several lines of evidence have indicated that key basic residues in the vicinity of residues 140-160 of apoE are important in mediating binding to the receptor. Furthermore, apoE variants exhibiting defective receptor binding are associated with the genetic lipid disorder type III hyperlipoproteinemia. To determine whether other basic amino acids in this region of apoE also affect receptor binding activity, site-specific mutagenesis of apoE in a bacterial expression system was undertaken. This system had been used successfully to produce apoE3 that was structurally and functionally equivalent to human plasma apoE3. Variants of apoE in which neutral amino acids were substituted for basic residues at positions 136, 140, 143, and 150 were produced. The variants all displayed defective binding; their activity ranged from 9 to 52% of normal (a range similar to that seen with naturally occurring variants of human apoE). In addition, to determine whether the conformation of this region is important for receptor binding, we designed variants in which proline was substituted for leucine 144 or alanine 152. Both variants were defective, exhibiting 13 and 27% of normal binding, respectively. In contrast, a double mutant in which arginine was substituted for serine 139 and alanine for leucine 149 displayed slightly enhanced receptor binding activity. These studies confirm that the middle of the apoE molecule is important in receptor binding and indicate that only certain amino acid substitutions in this region interfere with receptor binding activity.

Viral and non-viral induced fusion of pronase-digested human erythrocyte ghosts.

Human erythrocyte ghosts but was able to fuse only iso-human erythrocyte ghosts. Iso- and hypo-human erythrocyte ghosts were incubated with the proteolytic enzyme pronase under isotonic (iso-human erythrocyte ghosts) or hypotonic (hypo-human erythrocyte ghosts) conditions. Gel electrophoresis and electron microscope (freeze-etching) studies revealed that most of the erythrocyte membrane polypeptides were hydrolyzed by pronase under hypotonic conditions. Sendai virus readily agglutinated both pronase-digested iso-human erythrocyte ghosts and hypo-human erythrocyte ghosts were fused by the non-viral fusogenic agent glyceromonooleate. Freeze-etching studies revealed that during fusion the membranes of pronase-digested human erythrocyte ghosts are intermixed.

Involvement of spectrin in membrane fusion: induction of fusion in human erythrocyte ghosts by proteolytic enzymes and its inhibition by antispectrin antibody.

In contrast to intact human erythrocytes, human erythrocyte ghosts can be agglutinated but not fused by Sendai virus. Membrane fusion can, however, be induced in virus-agglutinated erythrocyte ghosts by addition of proteolytic enzymes such as trypsin, papain, or Pronase. When erythrocyte ghosts were reacted with antispectrin antiserum, the antiserum inhibited both the induction of fusion and the proteolysis of the membrane spectrin. The correlation between the membrane fusion process and the membrane cytoskeleton is discussed.