Effect of naked eukaryotic expression plasmid encoding rat augmenter of liver regeneration on acute hepatic injury and hepatic failure in rats

Blocking the short isoform of augmenter of liver regeneration inhibits proliferation of human multiple myeloma U266 cells via the MAPK/STAT3/cell cycle signaling pathway

Multiple myeloma (MM) is the second most common haematological malignancy and remains an incurable disease, with most patients relapsing and requiring further treatment. Augmenter of liver regeneration (ALR) is a vital protein affecting fundamental processes such as energy transduction, cell survival and regeneration. Silencing ALR inhibits cell proliferation and triggers apoptosis in human MM U266 cells. However, little is known about the role of 15-kDa-ALR on MM. In the present study, the role of 15-kDa-ALR in human MM cells was investigated. Blocking extracellular 15-kDa-ALR with an anti-ALR monoclonal antibody (McAb) decreased the proliferation and viability of U266 cells. However, the results of flow cytometry revealed no changes in apoptosis, and the expression levels of Bax, Bcl-2, caspase-3 and cleaved caspase-3 were not affected. However, combined treatment with anti-ALR McAb and epirubicin increased the apoptosis of U266 cells. RNA sequencing results indicated that the ERK1/2, JNK-MAPK and STAT3 signaling pathways, as well as the cell cycle, were associated with the mechanism of action of the anti-ALR McAb, and PCR, western blotting and cell cycle analysis confirmed these results. The present findings suggested that blocking extracellular 15-kDa-ALR in U266 cells with an anti-ALR McAb decreased cell proliferation via the MAPK, STAT3 and cell cycle signaling pathways without increasing apoptosis. Thus, 15-kDa-ALR may be a new therapeutic target for myeloma.

Augmenter of liver regeneration: Essential for growth and beyond

Liver regeneration is a well-orchestrated process that is triggered by tissue loss due to trauma or surgical resection and by hepatocellular death induced by toxins or viral infections. Due to the central role of the liver for body homeostasis, intensive research was conducted to identify factors that might contribute to hepatic growth and regeneration. Using a model of partial hepatectomy several factors including cytokines and growth factors that regulate this process were discovered. Among them, a protein was identified to specifically support liver regeneration and therefore was named ALR (Augmenter of Liver Regeneration). ALR protein is encoded by GFER (growth factor erv1-like) gene and can be regulated by various stimuli. ALR is expressed in different tissues in three isoforms which are associated with multiple functions: The long forms of ALR were found in the inner-mitochondrial space (IMS) and the cytosol. Mitochondrial ALR (23 kDa) was shown to cooperate with Mia40 to insure adequate protein folding during import into IMS. On the other hand short form ALR, located mainly in the cytosol, was attributed with anti-apoptotic and anti-oxidative properties as well as its inflammation and metabolism modulating effects. Although a considerable amount of work has been devoted to summarizing the knowledge on ALR, an investigation of ALR expression in different organs (location, subcellular localization) as well as delineation between the isoforms and function of ALR is still missing. This review provides a comprehensive evaluation of ALR structure and expression of different ALR isoforms. Furthermore, we highlight the functional role of endogenously expressed and exogenously applied ALR, as well as an analysis of the clinical importance of ALR, with emphasis on liver disease and in vivo models, as well as the consequences of mutations in the GFER gene.

Human augmenter of liver regeneration: probing the catalytic mechanism of a flavin-dependent sulfhydryl oxidase

Augmenter of liver regeneration is a member of the ERV family of small flavin-dependent sulfhydryl oxidases that contain a redox-active CxxC disulfide bond in redox communication with the isoalloxazine ring of bound FAD. These enzymes catalyze the oxidation of thiol substrates with the reduction of molecular oxygen to hydrogen peroxide. This work studies the catalytic mechanism of the short, cytokine form of augmenter of liver regeneration (sfALR) using model thiol substrates of the enzyme. The redox potential of the proximal disulfide in sfALR was found to be approximately 57 mV more reducing than the flavin chromophore, in agreement with titration experiments. Rapid reaction studies show that dithiothreitol (DTT) generates a transient mixed disulfide intermediate with sfALR signaled by a weak charge-transfer interaction between the thiolate of C145 and the oxidized flavin. The subsequent transfer of reducing equivalents to the flavin ring is relatively slow, with a limiting apparent rate constant of 12.4 s(-1). However, reoxidation of the reduced flavin by molecular oxygen is even slower (2.3 s(-1) at air saturation) and thus largely limits turnover at 5 mM DTT. The nature of the charge-transfer complexes observed with DTT was explored using a range of simple monothiols to mimic the initial nucleophilic attack on the proximal disulfide. While β-mercaptoethanol is a very poor substrate of sfALR (∼0.3 min(-1) at 100 mM thiol), it rapidly generates a mixed disulfide intermediate allowing the thiolate of C145 to form a strong charge-transfer complex with the flavin. Unlike the other monothiols tested, glutathione is unable to form charge-transfer complexes and is an undetectable substrate of the oxidase. These data are rationalized on the basis of the stringent steric requirements for thiol-disulfide exchange reactions. The inability of the relatively bulky glutathione to attain the in-line geometry required for efficient disulfide exchange in sfALR may be physiologically important in preventing the oxidase from catalyzing the potentially harmful oxidation of intracellular glutathione.

Nrf2 activates augmenter of liver regeneration (ALR) via antioxidant response element and links oxidative stress to liver regeneration

Liver regeneration can be impaired by permanent oxidative stress and activation of nuclear factor erythroid 2-related factor 2 (Nrf2), known to regulate the cellular antioxidant response, and has been shown to improve the process of liver regeneration. A variety of factors regulate hepatic tissue regeneration, among them augmenter of liver regeneration (ALR), attained great attention as being survival factors for the liver with proproliferative and antiapoptotic properties. Here we determined the Nrf2/antioxidant response element (ARE) regulated expression of ALR and show ALR as a target gene of Nrf2 in vitro and in vivo. The ALR promoter comprises an ARE binding site and, therefore, ALR expression can be induced by ARE-activator tertiary butylhydroquinone (tBHQ) in hepatoma cells and primary human hepatocytes (PHH). Promoter activity and expression of ALR were enhanced after cotransfection of Nrf2 compared with control and dominant negative mutant of Nrf2. Performing partial hepatectomy in livers from Nrf2+/+ mice compared with Nrf2-/- knock-out (KO) mice, we found increased expression of ALR in addition to known antioxidant ARE-regulated genes. Furthermore, we observed increased ALR expression in hepatitis B virus (HBV) compared with hepatitis C virus (HCV) positive hepatoma cells and PHH. Recently, it was demonstrated that HBV infection activates Nrf2 and, now, we add results showing increased ALR expression in liver samples from patients infected with HBV. ALR is regulated by Nrf2, acts as a liver regeneration and antioxidative protein and, therefore, links oxidative stress to hepatic regeneration to ensure survival of damaged cells.

Augmenter of liver regeneration attenuates tubular cell apoptosis in acute kidney injury in rats: the possible mechanisms

Augmenter of liver regeneration (ALR), the expression of which increased in rat kidneys after renal ischemia/reperfusion (I/R) injury, enhances renal tubular cell regeneration in vivo and in vitro. We aimed to investigate the effects of ALR on apoptosis of renal tubular cells after renal I/R injury in vivo and consider the possible mechanisms. Rats that were subjected to bilateral renal ischemia for 60 min followed by reperfusion were administered with either vehicle or recombinant human ALR (rhALR). Renal dysfunction and histologic injury were assessed by the measurement of serum biochemical markers and histological grading. Apoptosis was assessed by terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick-end labeling (TUNEL). Caspase-3 activity was measured using a colorimetric protease assay. Expression of Bcl-2, Bax Fas, phosphorylated-Akt (p-Akt), and phosphorylated-p53 (p-p53) was determined by western blotting. Compared with vehicle-treated rats, renal dysfunction and histologic injury were significantly attenuated by administration of rhALR. The number of TUNEL-positive tubular cells and caspase-3 activity were decreased, Bcl-2 and p-Akt expression was up-regulated, and Bax and p-p53 expression was down-regulated by administration of rhALR. However, administration of rhALR had no effect on Fas protein expression. These results indicate that the protective effect of rhALR on renal I/R injury is associated with its anti-apoptotic action in renal tubular cells. RhALR inhibits apoptosis by increasing the ratio of Bcl-2 to Bax and by decreasing the activity of caspase-3. The activation of Akt and inactivation of p53 are involved in the rhALR anti-apoptosis process.

Augmenter of liver regeneration (ALR) protects human hepatocytes against apoptosis

Augmenter of liver regeneration (ALR) is known to support liver regeneration and to stimulate proliferation of hepatocytes. However, it is not known if ALR exerts anti-apoptotic effects in human hepatocytes and whether this protective effect is cell type specific. This is relevant, because compounds that protect the liver against apoptosis without undesired effects, such as protection of metastatic tumour cells, would be appreciated in several clinical settings. Primary human hepatocytes (phH) and organotypic cancer cell lines were exposed to different concentrations of apoptosis inducers (ethanol, TRAIL, anti-Apo, TGF-β, actinomycin D) and cultured with or without recombinant human ALR (rhALR). Apoptosis was evaluated by the release of cytochrome c from mitochondria and by FACS with propidium iodide (PI) staining. ALR significantly decreased apoptosis induced by ethanol, TRAIL, anti-Apo, TGF-β and actinomycin D. Further, the anti-apoptotic effect of ALR was observed in primary human hepatocytes and in HepG2 cells but not in bronchial (BC1), colonic (SW480), gastric (GC1) and pancreatic (L3.6PL) cell lines. Therefore, the hepatotrophic growth factor ALR acts in a liver specific manner with regards to both its mitogenic and its anti-apoptotic effect. Unlike the growth factors HGF and EGF, rhALR acts in a liver specific manner. Therefore, ALR is a promising candidate for further evaluation as a possible hepatoprotective factor in clinical settings.

Gene therapy for liver regeneration: experimental studies and prospects for clinical trials

The liver is an exceptional organ, not only because of its unique anatomical and physiological characteristics, but also because of its unlimited regenerative capacity. Unfolding of the molecular mechanisms that govern liver regeneration has allowed researchers to exploit them to augment liver regeneration. Dramatic progress in the field, however, was made by the introduction of the powerful tool of gene therapy. Transfer of genetic materials, such as hepatocyte growth factor, using both viral and non-viral vectors has proved to be successful in augmenting liver regeneration in various animal models. For future clinical studies, ongoing research aims at eliminating toxicity of viral vectors and increasing transduction efficiency of non-viral vectors, which are the main drawbacks of these systems. Another goal of current research is to develop gene therapy that targets specific liver cells using receptors that are unique to and highly expressed by different liver cell types. The outcome of such investigations will, undoubtedly, pave the way for future successful clinical trials.

Augmenter of liver regeneration protects kidneys from ischaemia/reperfusion injury in rats

BACKGROUND

Augmenter of liver regeneration (ALR), which was identified originally for its crucial role in promoting hepatocyte proliferation, is expressed in both the liver and kidney. Protective effects of ALR have been demonstrated in experimental models of acute liver failure. In the present study, we investigated the effect of ALR on renal ischaemia/reperfusion (I/R) injury and the possible mechanisms of its action.

METHODS

Male Sprague-Dawley rats were subjected to renal ischaemia for 60 min and then administered with either saline or recombinant human ALR (rhALR). A sham-operated group served as control. The expression of ALR in the sham-operated and acute kidney injury (AKI) groups was detected by immunohistochemistry and western blotting. Renal dysfunction and injury were assessed by measurement of serum biochemical markers and histological grading. Expression of proliferating cell nuclear antigen (PCNA) was determined by immunohistochemistry.

RESULTS

Renal ALR expression increased significantly in rats with ischaemic AKI compared with the sham-operated rats. Serum biochemical parameters showed that renal dysfunction was improved by administration of rhALR. Histological analysis revealed that treatment with rhALR also reduced the extent of kidney injury. Intraperitoneal injection of rhALR enhanced the proliferation of renal tubular cells. Conclusions. Administration of rhALR effectively reduces tubular injury and ameliorates the impairment of renal function. The protective effect of rhALR is associated with enhancement of renal tubular cell regeneration.

Augmenter of liver regeneration: substrate specificity of a flavin-dependent oxidoreductase from the mitochondrial intermembrane space

Augmenter of liver regeneration (ALR) is both a growth factor and a sulfhydryl oxidase that binds FAD in an unusual helix-rich domain containing a redox-active CxxC disulfide proximal to the flavin ring. In addition to the cytokine form of ALR (sfALR) that circulates in serum, a longer form, lfALR, is believed to participate in oxidative trapping of reduced proteins entering the mitochondrial intermembrane space (IMS). This longer form has an 80-residue N-terminal extension containing an additional, distal, CxxC motif. This work presents the first enzymological characterization of human lfALR. The N-terminal region conveys no catalytic advantage toward the oxidation of the model substrate dithiothreitol (DTT). In addition, a C71A or C74A mutation of the distal disulfide does not increase the turnover number toward DTT. Unlike Erv1p, the yeast homologue of lfALR, static spectrophotometric experiments with the human oxidase provide no evidence of communication between distal and proximal disulfides. An N-terminal His-tagged version of human Mia40, a resident oxidoreductase of the IMS and a putative physiological reductant of lfALR, was subcloned and expressed in Escherichia coli BL21 DE3 cells. Mia40, as isolated, shows a visible spectrum characteristic of an Fe-S center and contains 0.56 +/- 0.02 atom of iron per subunit. Treatment of Mia40 with guanidine hydrochloride and triscarboxyethylphosphine hydrochloride during purification removed this chromophore. The resulting protein, with a reduced CxC motif, was a good substrate of lfALR. However, neither sfALR nor lfALR mutants lacking the distal disulfide could oxidize reduced Mia40 efficiently. Thus, catalysis involves a flow of reducing equivalents from the reduced CxC motif of Mia40 to distal and then proximal CxxC motifs of lfALR to the flavin ring and, finally, to cytochrome c or molecular oxygen.

Genetic recombinant expression and characterization of human augmenter of liver regeneration

AIMS

To establish a highly effective prokaryotic recombinant expression system for human augmenter of liver regeneration (hALR) and to characterize the recombinant hALR both in vitro and in vivo.

METHODS

ALR cDNA was synthesized and inserted into expression vector pET28a+, the recombinant plasmid was transformed into BL21, and expression of hALR was induced by IPTG. Recombinant hALR (rhALR) was purified by sequential detergent wash, enterokinase (EK) digestion, gel-filtration, and chelating chromatography. The rhALR was identified by SDS-PAGE, immunoblotting, MALDI-TOF-MS, and N-terminal sequencer. Cell proliferative effect of rhALR on human hepatocytes was analyzed by MTT. The protective effect of rhALR on liver function was observed on CCl(4)-induced intoxicated mice.

RESULTS

Recombinant expression plasmid of ALR [pET28(a+)-hALR] was confirmed by restriction enzyme digestion and DNA sequencing. The expressed rhALR constituted 30% of total bacterial protein. Molecular weight was 15,029 for monomer and 30,136 for dimer by mass determination. N-terminal was M-R-T-Q-Q, exactly the same as anticipated for hALR. The purified protein migrating at about 15 KD showed excellent antigenicity in immunoblotting. The rhALR also showed a strong stimulative effect on hepatocyte proliferation. ALT and AST levels, liver histological structure, as well as the survival rate of CCl(4)-intoxicated mice were significantly improved when rALR was administrated at 40 microg/kg or 200 microg/kg.

CONCLUSIONS

The rhALR is successfully expressed highly effectively with anticipated MW, N-terminal, and antigenicity. It could play an important role in relieving acute hepatic injury and hepatic failure by promoting hepatic cell proliferation and improving liver function in CCl(4)-intoxicated mice.

Expression of augmenter of liver regeneration in rats with gentamicin-induced acute renal failure and its protective effect on kidney

Augmenter of liver regeneration (ALR) enhances the proliferation of hepatocytes and accelerates recovery from acute liver failure in animal models. ALR is expressed in both the liver and kidney; however, the specific location of ALR expression and its biological effects in the kidney remain unknown. We aimed to investigate the efficacy of ALR in rats with gentamicin (GM)-induced acute renal failure (ARF). Rats were randomized into the normal group, GM+saline group, GM+vehicle group, and GM+rrALR group. Blood urea nitrogen, serum creatinine, and urine beta-N-acetyl-D-glucosaminidase were measured, and histological analyses of the kidneys were performed. The expression of ALR protein was determined by immunohistochemistry and Western blotting. In vitro incorporation of tritiated thymidine was used to measure the proliferation of renal tubular epithelial cells. In normal rats, the expression of ALR protein was faint in the medulla and absent in the cortex. However, in ARF rats, ALR expression increased significantly in both the renal cortex and medulla. Histological analyses revealed that treatment with recombinant rat ALR (rrALR) reduced the extent of injury of tubular cells in the renal cortex. Serum/urine biochemical parameters also showed that renal dysfunction was improved by the administration of rrALR. Intraperitoneal injection of rrALR enhanced the proliferation of tubular cells in vivo. We also confirmed that rrALR could promote the proliferation of renal tubular cells in vitro. These results indicate that rrALR effectively accelerates kidney recovery after ARF induced by gentamicin, and that the protective effect is associated with enhanced proliferation of renal tubular cells.

Augmenter of liver regeneration promotes hepatocyte proliferation induced by Kupffer cells

AIM

To observe the effects of augmenter of liver regeneration (ALR) on Kupffer cells and to determine whether ALR promotes hepatocyte proliferation induced by Kupffer cells.

METHODS

Kupffer cells and hepatocytes were cultured in vitro and various concentrations of recombinant rat ALR (rrALR) were added. 3H-thymidine, BrdU and 3H-leucine incorporation was determined in cultured Kupffer cells and hepatocytes, in hepatocytes conditioned by Kupffer cells, and in associated medium. rrALR was labeled by iodination and used to determine its binding activity by Scatchard analysis in Kupffer cells and primarily cultured rat hepatocytes.

RESULTS

rrALR stimulated DNA replication in Kupffer cells and protein synthesis both in cells and in medium in a non-concentration-dependent manner. The effect was significant at the concentration of 1 microg/L ALR. However, rrALR had no effect on primarily cultured hepatocytes, when hepatocytes were cultured with the Kupffer cell medium conditioned by ALR, DNA replication and protein synthesis in hepatocytes increased significantly at the concentration of 1 microg/L ALR. When the ALR concentration was increased, its effect on hepatocyte proliferation decreased to the basal level. Scatchard analysis indicated the presence of a single class of high affinity receptors with a dissociation constant (Kd) of 0.883 nmol/L and a maximum binding capacity (Bmax) of 126.1 pmol/g protein in the rat Kupffer cells.

CONCLUSION

ALR can promote hepatocyte proliferation induced by Kupffer cells, which is associated with the concentration of ALR, suggesting that Kupffer cells play a dual role in liver regeneration.