E-box-binding repressor is down-regulated in hepatic stellate cells during up-regulation of mannose 6-phosphate/insulin-like growth factor-II receptor expression in early hepatic fibrogenesis

Expression of insulin-like growth factor 2 receptor in corneal keratocytes during differentiation and in response to wound healing

PURPOSE

Insulin-like growth factor 2 receptor (IGF2R) associates with ligands that influence wound healing outcomes. However, the expression pattern of IGF2R and its role in the cornea is unknown.

METHODS

Human keratocytes were isolated from donor corneas. Fibroblasts (fibroblast growth factor 2 [FGF2]-treated) or myofibroblasts (TGF-β1-treated) were analyzed for IGF2R and α-smooth muscle actin (α-SMA) expression by Western blotting and immunolocalization. Mouse corneas were wounded in vivo and porcine corneas ex vivo. The IGF2R and α-SMA protein expression were visualized and quantified by immunohistochemistry. The IGF2R gene expression in human corneal fibroblasts was knocked-down with targeted lentiviral shRNA.

RESULTS

The IGF2R is expressed in epithelial and stromal cells of normal human, mouse, and porcine corneas. The IGF2R increases (11.2 ± 0.4-fold) in the epithelial and (11.7 ± 0.9-fold) stromal layers of in vivo wounded mouse corneas. Double-staining with α-SMA- and IGF2R-specific antibodies reveals that IGF2R protein expression is increased in stromal myofibroblasts in the wounded cornea relative to keratocytes in the normal cornea (11.2 ± 0.8-fold). Human primary stromal keratocytes incubated with FGF2 or TGF-β1 in vitro demonstrate increased expression (2.0 ± 0.4-fold) of IGF2R in myofibroblasts relative to fibroblasts. Conversion of IGF2R shRNA-lentiviral particle transduced corneal fibroblasts to myofibroblasts reveals a dependence on IGF2R expression, as only 40% ± 10% of cells transduced converted to myofibroblasts compared to 86% ± 3% in control cells.

CONCLUSIONS

The IGF2R protein expression is increased during corneal wound healing and IGF2R regulates human corneal fibroblast to myofibroblast differentiation.

Enhanced activity of lysosomal proteases in activated rat hepatic stellate cells is associated with a concomitant increase in the number of the mannose-6-phosphate/insulin-like growth factor II receptor

Activated hepatic stellate cells (HSCs) play a central role during hepatic tissue repair through their influence on extracellular matrix remodelling. We have determined whether the activity levels of cathepsin B and D are affected by in vitro activation of rat HSCs, and whether the enzymes were released from the cells. Furthermore, given the important role of the mannose-6-phosphate/insulin-like growth factor II receptor (M6P/IGF-IIR) in the intracellular transport of lysosomal enzymes, we have examined whether changes in the activity of these proteases were associated with parallel changes in the level of the M6P/IGF-IIR. The activity of cathepsin B and D increased ∼4 times between 2 and 8 days of HSC culture. This result was supported by analysing mRNA expression by RT-PCR. The cells released the enzymes into the culture medium, amounting to ∼10% of the cell-associated activity over 24 h. The release of enzymes was not affected by reducing medium pH from 7.4 to 6.2, indicating that the enzymes were transported to the medium independently of the M6P/IGF-II-R. The released cathepsin B was mostly in the inactive proenzyme form. HSC activation led to a particularly large increase in M6P/IGF-IIR expression. A large proportion of the receptors was located on the cell surface and was found to be very suitable for measuring endocytosis of (125) I-IGF-II. The results show that the endocytic activity increased in parallel with the increase in surface receptors and activity of lysosomal enzymes. Degradation of the ligand was reduced by inhibitors of lysosomal proteases and therefore took place in lysosomes.

Histone acetylation is essential for ANG-II-induced IGF-IIR gene expression in H9c2 cardiomyoblast cells and pathologically hypertensive rat heart

The IGF-II/mannose 6-phosphate receptor (IGF-IIR/Man-6-P) up-regulation correlates with heart disease progression and its signaling cascades directly trigger pathological cardiac hypertrophy, fibrosis, and cardiomyocytes apoptosis. IGF-IIR gene expression/ suppression is able to prevent myocardial remodeling. However, the regulating mechanisms for the IGF-IIR gene remain unclear. This study performed reverse transcriptase PCR (RT-PCR) and methylation-specific PCR (MS-PCR) to detect expression and DNA methylation of CpG islands within the IGF-IIR genomic DNA region. Our finding revealed that the IGF-IIR gene was up-regulated both in H9c2 cells treated with tumor necrosis factor-alpha (TNF-α), lipopolysaccharide (LPS), angiotensin II (ANGII) and inomycin, and age-dependently in spontaneously hypertensive rat (SHR) heart. For the DNA methylation study, although there were four CpG islands within IGF-IIR genomic regions, the DNA methylation distribution showed no change either in cells treated with ANGII or in the SHR heart. Using chemical inhibitors to individually block histone acetyltransferase (HAT) and histone deacetylase (HDAC) activity, we found that histone acetylation was essential for ANGII-induced IGF-IIR gene expression using RT-PCR and luciferase assay. The Chromatin immuno-precipitation assay indicated that acetyl-Histone H3 and acetyl-Histone H4 associated with the IGF-IIR promoter increased in the presence of ANGII, otherwise methyl-CpG binding domain protein 2 (MeCP2) is disassociated with this. Taken together, this study demonstrates that histone acetylation plays a critical role in IGF-IIR up-regulation during pathological cardiac diseases and might provide a targeting gene in transcriptional therapies for the failing heart.

Bioconjugation of oligonucleotides for treating liver fibrosis

Liver fibrosis results from chronic liver injury due to hepatitis B and C, excessive alcohol ingestion, and metal ion overload. Fibrosis culminates in cirrhosis and results in liver failure. Therefore, a potent antifibrotic therapy is urgently needed to reverse scarring and eliminate progression to cirrhosis. Although activated hepatic stellate cells (HSCs) remain the principle cell type responsible for liver fibrosis, perivascular fibroblasts of portal and central veins as well as periductular fibroblasts are other sources of fibrogenic cells. This review will critically discuss various treatment strategies for liver fibrosis, including prevention of liver injury, reduction of inflammation, inhibition of HSC activation, degradation of scar matrix, and inhibition of aberrant collagen synthesis. Oligonucleotides (ODNs) are short, single-stranded nucleic acids, which disrupt expression of target protein by binding to complementary mRNA or forming triplex with genomic DNA. Triplex forming oligonucleotides (TFOs) provide an attractive strategy for treating liver fibrosis. A series of TFOs have been developed for inhibiting the transcription of alpha1(I) collagen gene, which opens a new area for antifibrotic drugs. There will be in-depth discussion on the use of TFOs and how different bioconjugation strategies can be utilized for their site-specific delivery to HSCs or hepatocytes for enhanced antifibrotic activities. Various insights developed in individual strategy and the need for multipronged approaches will also be discussed.

Chemical modification of interleukin-10 with mannose 6-phosphate groups yields a liver-selective cytokine

Cytokines are considered a promising immunotherapy for chronic diseases, because of their potency and fundamental roles in pathological processes. However, their therapeutic use is limited because of their poor pharmacokinetics and pleiotropic effects in various organs. These problems may be overcome by cell-specific delivery of the cytokine. This approach involves chemical modification of the protein with homing devices that recognize receptors on target cells. The cytokine interleukin-10 (IL10) may be valuable as a therapeutic cytokine for patients with liver cirrhosis. However, its rapid renal elimination and general immunosuppressive activities limit therapeutic use. We therefore aim to target this cytokine in the liver, in particular to fibrogenic hepatic stellate cells (HSCs). We show that IL10 is successfully modified with mannose 6-phosphate (M6P), which is a homing device for the mannose 6-phosphate/insulin-like growth factor II (M6P/IGFII) receptor expressed on activated HSCs. Chemical modification did not diminish IL10 efficacy with regard to in vitro anti-inflammatory (lipopolysaccharide-stimulated tumor necrosis factor alpha release) and antifibrotic (collagen deposition and degradation) activities. Biodistribution studies with radiolabeled M6P-IL10 and IL10 in rats with liver fibrosis showed that modification with M6P groups induced a shift in the distribution from the kidneys (IL10) to the liver (M6P-IL10). Hepatocellular binding of M6P-IL10 occurred via M6P/IGFII receptors and scavenger receptors, indicating that not only HSCs but also Kupffer and endothelial cells are target cells. IL10 did not bind to these receptors. We conclude that we prepared an active and liver-specific form of the cytokine IL10 that can be evaluated for its efficacy to treat liver diseases.

Mannose-6-phosphate/insulin-Like growth factor-II receptors may represent a target for the selective delivery of mycophenolic acid to fibrogenic cells

PURPOSE

The insulin-like growth factor axis plays an important role in fibrogenesis. However, little is known about mannose-6-phosphate/Insulin-like growth factor-II receptor (M6P/IGF-IIR) expression during fibrosis. When expressed preferentially on fibrogenic cells, this receptor may be used to selectively deliver drugs to these cells.

METHODS

We investigated M6P/IGF-IIR expression in livers of bile duct-ligated (BDL) rats and in renal vascular walls of renin transgenic TGR(mRen2)27 rats. Both models are characterized by fibrogenic processes. Furthermore, we studied whether drug delivery via M6P/IGF-II-receptor-mediated uptake is possible in fibroblasts.

RESULTS

M6P/IGF-IIR mRNA expression was investigated 3, 7 and 10 days after BDL. At all time-points hepatic M6P/IGF-IIR expression was significantly increased compared to healthy controls. Moreover, immunohistochemical staining revealed that alpha-sma-positive cells were M6P/IGF-IIR-positive. In kidneys of TGR(mRen2)27 rats, the number of M6P/IGF-IIR-positive arteries per microscopic field was increased 5.5 fold over healthy controls. To examine whether M6P/IGF-IIRs could be used as a port of entry for drugs, we coupled mycophenolic acid (MPA) to mannose-6-phosphate-modified human serum albumin (M6PHSA). M6PHSA-MPA inhibited 3T3-fibroblast proliferation dose-dependently, which was reversed by co-incubation with excess M6PHSA, but not by HSA.

CONCLUSIONS

M6P/IGF-IIRs are expressed by fibrogenic cells and may be used for receptor-mediated intracellular delivery of the antifibrogenic drug MPA.

Pharmacokinetics of a hepatic stellate cell-targeted doxorubicin construct in bile duct-ligated rats

BACKGROUND/AIMS

Inhibition of hepatic stellate cell (HSC) proliferation is a relevant strategy to inhibit liver fibrosis. Coupling of antiproliferative drugs to the HSC-selective drug carrier mannose-6-phosphate-modified human serum albumin (M6PHSA) may lead to cell-selective inhibition of HSC proliferation. We coupled the antiproliferative drug doxorubicin (DOX) to this drug carrier and investigated the pharmacokinetics of this construct in a rat model of liver fibrosis, as well as in cultured HSC.

METHODS/RESULTS

M6PHSA-DOX was cleared from the plasma in a biphasic manner. Upon i.v. injection of 4 microg kg(-1) (tracer), 2 and 20 mg kg(-1), the clearance in the distribution phase of drug disposition (CL(d)) significantly decreased from 9.7+/-0.7 to 4.7+/-2.3 and 1.0+/-0.1 ml kg(-1)min(-1), respectively. This indicates that saturation of clearance mechanisms occurs in this phase of drug disposition, likely reflecting saturable receptor-mediated uptake in the target cells. Gamma-camera studies revealed that the majority of the conjugate accumulated in the liver within 5 min, and immunohistochemical double-staining of liver sections demonstrated co-localization of the construct with HSC-markers. Simulation of the release of DOX from the carrier, after cellular uptake by HSC, showed that a gradual release of the drug takes place over a 9h period. Studies in cultured HSC illustrated that after 24h incubation with the conjugate, DOX was associated with the cell nucleus.

CONCLUSIONS

The rapid distribution of M6PHSA-DOX from the blood to HSC, in combination with the expected gradual release of DOX within these cells, make this construct a promising tool for achieving sustained and selective inhibition of HSC proliferation.

Effects of anoxia on expression of transforming growth factor-β1 in rat liver

AIM: To investigate the effect of anoxia on the expression of transforming growth factor-β₁ (TGF-β₁) in the rat liver.

METHODS: A total of 20 Sprague Dawley rats were used in this study. Trachea obstructive method was employed to establish the animal model of mild, moderate, and severe anoxia. Liver samples were collected 15 and 60 min after obstruction for the examination of TGF-β₁ expression using immunohistochemical technique.

RESULTS: TGF-β₁ was not or lowly expressed in normal rats (3.6 ± 1.9 and 3.6 ± 1.9, respectively at 15 and 60 min). The level of hepatic TGF-β₁ expression was increased with prolonging of anoxia time and enhancement of anoxia degree. The expression of hepatic TGF-β₁ at 15 and 60 min was 8.5 ± 2.0 and 15.2 ± 3.1 under mild anoxia, 18.4 ± 3.5 and 63.7 ± 3.8 under moderate anoxia, and 68.9 ± 3.2 and 86.7 ± 3.6 under severe anoxia, respectively. There were significant differences between normal and anoxia rats (P < 0.05 or P < 0.01).

CONCLUSION: TGF-β₁ expression is increased under the condition of anoxia, which accelerates the formation of extracellular matrix, and further contributes to the repair and regeneration of liver cells.

Receptor-mediated hepatic uptake of M6P-BSA-conjugated triplex-forming oligonucleotides in rats

Excessive production of extracellular matrix, predominantly type I collagen, results in liver fibrosis. Earlier we synthesized mannose 6-phosphate-bovine serum albumin (M6P-BSA) and conjugated to the type I collagen specific triplex-forming oligonucleotide (TFO) for its enhanced delivery to hepatic stellate cells (HSCs), which is the principal liver fibrogenic cell. In this report, we demonstrate a time-dependent cellular uptake of M6P-BSA-33P-TFO by HSC-T6 cells. Both cellular uptake and nuclear deposition of M6P-BSA-33P-TFO were significantly higher than those of 33P-TFO, leading to enhanced inhibition of type I collagen transcription. Following systemic administration into rats, hepatic accumulation of M6P-BSA-33P-TFO increased from 55% to 68% with the number of M6P per BSA from 14 to 27. Unlike 33P-TFO, there was no significant decrease in the hepatic uptake of (M6P)20-BSA-33P-TFO in fibrotic rats. Prior administration of excess M6P-BSA decreased the hepatic uptake of (M6P)20-BSA-33P-TFO from 66% to 40% in normal rats, and from 60% to 15% in fibrotic rats, suggesting M6P/insulin-like growth factor II (M6P/IGF II) receptor-mediated endocytosis of M6P-BSA-33P-TFO by HSCs. Almost 82% of the total liver uptake in fibrotic rats was contributed by HSCs. In conclusion, by conjugation with M6P-BSA, the TFO could be potentially used for the treatment of liver fibrosis.

Studies on the targeted delivery of the antifibrogenic compound mycophenolic acid to the hepatic stellate cell

BACKGROUND/AIMS

Hepatic stellate cell (HSC) activation and proliferation are key events in the pathology of liver fibrosis. Inhibiting these parameters, therefore, is a relevant option to treat liver fibrosis pharmacologically. The immunosuppressive drug mycophenolic acid (MPA) has been shown to inhibit proliferation and activation of various types of fibroblasts. In an effort to circumvent the immunosuppression and at the same time enhance this antifibrotic effect, we coupled MPA to the HSC-selective drug carrier mannose-6-phosphate modified human serum albumin and evaluated this conjugate for its specificity and antifibrotic activity.

METHODS/RESULTS

We found that MPA inhibited proliferation of HSC in vitro. The drug coupled to the drug carrier bound specifically to HSC and reduced HSC proliferation in vitro. In vivo studies demonstrated that our conjugate accumulated selectively in the liver with significant uptake in HSC apart from Kupffer and endothelial cells, whereas primary and secondary lymphoid tissues were avoided. Treatment of bile duct-ligated rats with this conjugate reduced hepatic inflammation and hepatic alpha-beta-Crystallin mRNA expression, a marker for HSC activation.

CONCLUSIONS

This study shows that targeted delivery of MPA to HSC results in a decrease in HSC activation, making it the first drug that is successfully delivered to this cell type.

Targeted delivery of a triplex-forming oligonucleotide to hepatic stellate cells

Liver fibrosis is characterized by abnormal accumulation of extracellular matrix (ECM), namely, fibrillar collagens in the hepatic stellate cells (HSCs). Earlier, we developed an antigene approach, using a type alpha1(I) collagen gene promoter specific triplex-forming oligonucleotide (TFO) to inhibit collagen gene expression. In this paper, to enhance overall delivery of TFOs to the liver and more specifically to HSCs, we synthesized mannose 6-phosphate-bovine serum albumin (M6P-BSA) by phosphorylating p-nitrophenyl-alpha-d-mannopyranoside, reducing its nitro group, and reacting it with thiophosgene to produce p-isothiocyanatophenyl-6-phospho-alpha-d-mannopyranoside (itcM6P) for conjugation with BSA. (33)P-TFO was conjugated with M6P-BSA via a disulfide bond, and the stability of the (M6P)(20)-BSA-TFO conjugate was determined. Following tail vein injection into rats, (M6P)(20)-BSA-(33)P-TFO rapidly cleared from the circulation and accumulated mainly in the liver. Almost 66% of the injected (M6P)(20)-BSA-(33)P-TFO accumulated in the liver at 30 min postinjection, which was significantly higher than that deposited after injection of (33)P-TFO. A large proportion of the injected (M6P)(20)-BSA-(33)P-TFO was taken up by the HSCs as evidenced by determination of radioactivity in the digested liver cells upon liver perfusion and separation on a Nycodenz gradient. Therefore, this TFO conjugate may be used for the treatment of liver fibrosis.

Hepatotoxicity and mechanism of action of haloalkanes: carbon tetrachloride as a toxicological model

The use of many halogenated alkanes such as carbon tetrachloride (CCl4), chloroform (CHCl3) or iodoform (CHI3), has been banned or severely restricted because of their distinct toxicity. Yet CCl4 continues to provide an important service today as a model substance to elucidate the mechanisms of action of hepatotoxic effects such as fatty degeneration, fibrosis, hepatocellular death, and carcinogenicity. In a matter of dose,exposure time, presence of potentiating agents, or age of the affected organism, regeneration can take place and lead to full recovery from liver damage. CCl4 is activated by cytochrome (CYP)2E1, CYP2B1 or CYP2B2, and possibly CYP3A, to form the trichloromethyl radical, CCl3*. This radical can bind to cellular molecules (nucleic acid, protein, lipid), impairing crucial cellular processes such as lipid metabolism, with the potential outcome of fatty degeneration (steatosis). Adduct formation between CCl3* and DNA is thought to function as initiator of hepatic cancer. This radical can also react with oxygen to form the trichloromethylperoxy radical CCl3OO*, a highly reactive species. CCl3OO* initiates the chain reaction of lipid peroxidation, which attacks and destroys polyunsaturated fatty acids, in particular those associated with phospholipids. This affects the permeabilities of mitochondrial, endoplasmic reticulum, and plasma membranes, resulting in the loss of cellular calcium sequestration and homeostasis, which can contribute heavily to subsequent cell damage. Among the degradation products of fatty acids are reactive aldehydes, especially 4-hydroxynonenal, which bind easily to functional groups of proteins and inhibit important enzyme activities. CCl4 intoxication also leads to hypomethylation of cellular components; in the case of RNA the outcome is thought to be inhibition of protein synthesis, in the case of phospholipids it plays a role in the inhibition of lipoprotein secretion. None of these processes per se is considered the ultimate cause of CCl4-induced cell death; it is by cooperation that they achieve a fatal outcome, provided the toxicant acts in a high single dose, or over longer periods of time at low doses. At the molecular level CCl4 activates tumor necrosis factor (TNF)alpha, nitric oxide (NO), and transforming growth factors (TGF)-alpha and -beta in the cell, processes that appear to direct the cell primarily toward (self-)destruction or fibrosis. TNFalpha pushes toward apoptosis, whereas the TGFs appear to direct toward fibrosis. Interleukin (IL)-6, although induced by TNFalpha, has a clearly antiapoptotic effect, and IL-10 also counteracts TNFalpha action. Thus, both interleukins have the potential to initiate recovery of the CCl4-damaged hepatocyte. Several of the above-mentioned toxication processes can be specifically interrupted with the use of antioxidants and mitogens, respectively, by restoring cellular methylation, or by preserving calcium sequestration. Chemicals that induce cytochromes that metabolize CCl4, or delay tissue regeneration when co-administered with CCl4 will potentiate its toxicity thoroughly, while appropriate CYP450 inhibitors will alleviate much of the toxicity. Oxygen partial pressure can also direct the course of CCl4 hepatotoxicity. Pressures between 5 and 35 mmHg favor lipid peroxidation, whereas absence of oxygen, as well as a partial pressure above 100 mmHg, both prevent lipid peroxidation entirely. Consequently, the location of CCl4-induced damage mirrors the oxygen gradient across the liver lobule. Mixed halogenated methanes and ethanes, found as so-called disinfection byproducts at low concentration in drinking water, elicit symptoms of toxicity very similar to carbon tetrachloride, including carcinogenicity.

Expression and regulation of the insulin-like growth factor axis components in rat liver myofibroblasts

Apart from hepatic stellate cells (HSC), liver myofibroblasts (MF) represent a second mesenchymal cell population involved in hepatic fibrogenesis. The IGF system including the insulin-like growth factors I and II (IGF-I, -II), their receptors (IGF-I receptor, IGF-IR; IGF-II/mannose 6-phosphate receptor, IGF-II/M6-PR), and six high affinity IGF binding proteins (IGFBPs) participate in the regulation of growth and differentiation of cells of the fibroblast lineage, possibly contributing to the fibrogenic process. The aim of this work was to study the expression and regulation of the IGF axis components in rat liver MF.

METHODS

Cultures of MF from passages 1 to 4 (P1-4) were studied. IGFBP secretion was analyzed by [(125)I]-IGF-I ligand and immunoblotting. IGF-I, IGF-IR, IGF-II/M6-PR, and IGFBP messenger RNA (mRNA) expression was assessed by Northern blot hybridization. DNA synthesis was evaluated by 5-bromo-2'-deoxyuridine (BrdU) incorporation assay.

RESULTS

MF from P1 to 4 constitutively expressed mRNA transcripts specific for IGF-I, IGF-IR, and IGF-II/M6-PR. In MF, biosynthesis of IGFBP-3 and -2 was observed that was stimulated by IGF-I, insulin, and transforming growth factor beta (TGF-beta), whereas platelet-derived growth factor (PDGF-BB) revealed inhibitory effects. IGF-I and to a lesser extent insulin increased DNA synthesis of MF. Simultaneous addition of recombinant human IGFBP-2 or -3 with IGF-I diminished the mitogenic effect of IGF-I on MF whereas preincubation of MF with IGFBP-2 or -3 further potentiated the IGF-I stimulated DNA synthesis. In conclusion, the present study demonstrates that the IGF axis may play a role in the regulation of MF proliferation in vitro which might be relevant in vivo for the process of fibrogenesis during acute and chronic liver injury.

The IGF2 receptor is a USF2-specific target in nontumorigenic mammary epithelial cells but not in breast cancer cells

The antiproliferative activities of the USF proteins and the frequent loss of USF function in cancer cells suggest a role for these ubiquitous transcription factors in tumor suppression. However, the cellular targets that mediate the effects of USF on cellular proliferation and transformation remain uncharacterized. IGF2R, with multiple functions in both normal growth and cancer, was investigated here as a possible USF target in both nontumorigenic and tumorigenic breast cell lines. The 5'-flanking sequences of the human IGF2R gene contain multiple, highly conserved E boxes almost identical to the consensus USF DNA-binding sequence. These E boxes were found to be essential for IGF2R promoter activity in the nontumorigenic mammary epithelial cell line MCF-10A. USF1 and USF2 bound the IGF2R promoter in vitro, and both USF1 and USF2, but not c-Myc, were present within the IGF2R promoter-associated chromatin in vivo. Overexpressed USF2, but not USF1, transactivated the IGF2R promoter, and IGF2R mRNA was markedly decreased by expression of a USF-specific dominant negative mutant, identifying IGF2R as a USF2 target. IGF2R promoter-driven expression was USF-independent in both MCF-7 and MDA-MB-231 breast cancer cell lines, suggesting that a defect in USF function may contribute to down-regulation of IGF2R expression in cancer cells.

Characteristics of the hepatic stellate cell-selective carrier mannose 6-phosphate modified albumin (M6P(28)-HSA)

BACKGROUND/AIMS

Drug targeting to hepatic stellate cells (HSC) may improve the pharmacological effects of antifibrotic drugs. Recently, albumin substituted with 28 mannose 6-phosphate moieties (M6P(28)-HSA) was found to distribute selectively to HSC in fibrotic rat livers. To assess whether this albumin can be used as a carrier for intracellular drug delivery, we explored the cellular handling of M6P(28)-HSA in HSC.

METHODS/RESULTS

Application of competitive substrates for the M6P/IGFII receptor or other receptors showed that the binding of M6P-HSA to the M6P/IGFII receptor is specific. Binding was strong to activated HSC, but not to quiescent HSC. Furthermore, M6P(28)-HSA was extensively internalized by these cells. Using monensin, a specific inhibitor of the lysosomal pathway, proof was obtained that M6P-HSA is endocytosed via this route. The experiments performed with tissue slices, prepared from rat and human livers, revealed a specific binding and uptake of M6P(28)-HSA in both normal and cirrhotic livers. In livers from cirrhotic patients, HSC contributed predominantly to the uptake of this neoglycoprotein.

CONCLUSIONS

Based on our in vivo data demonstrating the HSC-selectivity and on our in vitro data demonstrating binding and rapid internalization in activated HSC, we conclude that M6P(28)-HSA is applicable as a stellate cell-selective carrier for antifibrotic drugs that act intracellularly. This may have implications for the design of new strategies for the treatment of liver fibrosis.

JunD regulates transcription of the tissue inhibitor of metalloproteinases-1 and interleukin-6 genes in activated hepatic stellate cells

Activation of hepatic stellate cells (HSCs) to a myofibroblast-like phenotype is the pivotal event in hepatic wound healing and fibrosis. Rat HSCs activated in vitro express JunD, Fra2, and FosB as the predominant AP-1 DNA-binding proteins, and all three associate with an AP-1 sequence that is essential for activity of the tissue inhibitor of metalloproteinases-1 (TIMP-1) promoter. In this study, we used expression vectors for wild-type, dominant-negative, and forced homodimeric (Jun/eb1 chimeric factors) forms of JunD and other Fos and Jun proteins to determine the requirement for JunD in the transcriptional regulation of the TIMP-1 and interleukin-6 (IL-6) genes. JunD activity was required for TIMP-1 gene promoter activity, whereas overexpression of Fra2 or FosB caused a repression of promoter activity. The ability of homodimeric JunD/eb1 to elevate TIMP-1 promoter activity supports a role for JunD homodimers as the major AP-1-dependent transactivators of the TIMP-1 gene. IL-6 promoter activity was induced upon activation of HSCs and also required JunD activity; however, expression of JunD/eb1 homodimers resulted in transcriptional repression. Mutagenesis of the IL-6 promoter showed that an AP-1 DNA-binding site previously reported to be an activator of transcription in fibroblasts functions as a suppressor of promoter activity in HSCs. We conclude that JunD activates IL-6 gene transcription as a heterodimer and operates at an alternative DNA-binding site in the promoter. The relevance of these findings to events occurring in the injured liver was addressed by showing that AP-1 DNA-binding complexes are induced during HSC activation and contain JunD as the predominant Jun family protein. JunD is therefore an important transcriptional regulator of genes responsive to Jun homo- and heterodimers in activated HSCs.

Platelet-derived growth factor is a principal inductive factormodulating mannose 6-phosphate/insulin-like growth factor-II receptorgene expression via a distal E-box in activated hepatic stellate cells

Hepatic stellate cells (HSCs) become activated during the earlystages of hepatic injury associated with fibrogenesis. The mannose 6-phosphate/insulin-like growth factor-II receptor (M6P/IGFIIR) plays animportant role in early fibrogenesis by participating in the activationof latent transforming growth factor-beta, a potent inducer of thematrix proteins in activated stellate cells that produce the hepaticnodule. Platelet-derived growth factor (PDGF), a potent HSC mitogen, isreleased early in hepatic injury and activates several signallingpathways in HSCs. In this study we examined the role of PDGF-BB in HSCregulation of M6P/IGFIIR gene expression. Several promoter elementswere found and characterized that modulate M6P/IGFIIR expression inactivated stellate cells. The presence of a distal CACGTG E-box at-2695 was required for M6P/IGFIIR expression in transfectedstellate cells. When the distal E-box was removed there was no significant M6P/IGFIIR promoter activity. The distal E-box-binding protein responded specifically to PDGF-BB with increased binding. This coincided with PDGF-BB up-regulation of M6P/IGFIIR mRNA transcript levels. Downstream elements include two proximal (-2 to-48) CACGTG E-boxes that bind a different protein to the distal(-2695) E-box. The proximal E-boxes respond moderately to PDGF-BB. The promoter segment encompassing -144 to +109 is able to respond dramatically to serum but is refractory to PDGF-BB. However, a constitutively bound protein binding to the -611/-716 fragment appears to be a repressor that suppresses inductive changes in protein binding occurring downstream of -611. These results indicate that the M6P/IGFIIR promoter responds primarily and specifically to PDGF-BB through a distal E-box element and possibly through two proximal E-box elements.

Role of the Ets-1 transcription factor during activation of rat hepatic stellate cells in culture

During liver tissue repair, hepatic stellate cells (HSCs), a pericyte-like nonparenchymal liver cell population, transform from a quiescent status (resting HSCs) into myofibroblast like cells (activated HSCs); the latter is the principal matrix-synthesizing cell of the liver. Although several factors have been shown to be involved in this important process, the molecular mechanisms regulating HSC activation are still under investigation. To identify key regulatory proteins involved in the HSC activation process, we used different mRNA display technologies, with cDNAs prepared from HSCs at different stages of in vitro activation. With the latter technique, the transcription factor Ets-1 was detected through its down-regulation during activation. As confirmed by Northern blot and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, mRNAs coding for Ets-1 were present in the highest amounts in freshly isolated HSCs and in HSCs 2 days after plating (classified as resting HSCs/early activated HSCs) and were diminished in HSCs 7 days after plating (activated cells). Ets-1 protein was present in HSC-lysates, as assessed by Western blot, and bound to an oligonucleotide containing the Ets-1 consensus cis-acting motif, as demonstrated by electrophoretic mobility shift assay. Ets-1 binding activity peaked in nuclear extracts prepared from resting/early activated cells and was diminished in extracts derived from fully activated cells. In contrast, binding activity of the transcription factors TFIID, AP-1, and SP-1 was highest in activated HSCs and only barely detectable in resting/early activated HSCs. By Northern blot and RT-PCR analysis, Ets-1-specific transcripts were present in parenchymal and other nonparenchymal liver cells too, illustrating that hepatic Ets-1 expression is not specific or restricted to HSCs. However, the unique pattern of Ets-1 binding activity present in resting versus activated HSCs and its known implications for cellular differentiation and tissue remodeling suggest that Ets-1 could be of crucial importance for HSC activation and hepatic tissue repair.

UV irradiation activates JNK and increases alphaI(I) collagen gene expression in rat hepatic stellate cells

Hepatic stellate cells (HSCs) become activated into myofibroblast-like cells during the early stages of hepatic injury associated with fibrogenesis. The subsequent dysregulation of alphaI(I) collagen gene expression is a central pathogenetic step during the development of cirrhosis. Our recent study in rat HSCs (Davis, B. H., Chen, A., and Beno, D. (1996) J. Biol. Chem. 271, 11039-11042) found that ERK1,2 activation might be required for maximal alphaI(I) collagen gene expression. However, the role of the parallel JNK cascade in regulating alphaI(I) collagen gene expression was unknown. In this study, we initially found that UV irradiation of HSCs activated JNK but not ERK1,2. Furthermore, UV irradiation increased endogenous alpha I(I) collagen mRNA abundance and stimulated alpha I(I) collagen gene transcription in HSCs. The effect of the activation of JNK and Jun on alpha I(I) collagen gene expression was further evaluated via transfection of chloramphenicol acetyltransferase reporter plasmids with various sizes of truncated 5' upstream promoter sequence (UPS) of the alphaI(I) collagen gene. This revealed that dominant negative transcription factor JUN suppressed alpha I(I) collagen gene transcription in HSCs maintained in media with 20% serum and constitutively activated JUN increased alphaI(I) collagen gene transcription in HSCs cultured in media with 0.4% serum. UV activated JNK utilized a distal GC box in the 5'-UPS of the collagen gene to regulate gene transcription. This observation was confirmed by site-directed mutagenesis. In co-transfection experiments, the col-chloramphenicol acetyltransferase reporter with a mutagenized GC box was not suppressed by dn-JUN and was not stimulated by activated JUN or by UV irradiation. Southwestern blotting analyses and gel shift assays with basic transcription element-binding protein antiserum suggested that the GC box was bound by basic transcription element-binding protein, a recently described DNA-binding protein. In conclusion, the current study combined with our previous report suggests that ERK1,2 and JNK cascades regulate alphaI(I) collagen expression in HSCs through different regions of the 5'-UPS of the gene. The distal GC box in the 5'-UPS of the alphaI(I) collagen gene may play a central role in receiving extracellular signals through the JNK pathway.