Advances in liver regeneration

Liver regeneration after partial hepatectomy is the only example of a regenerative process in mammals in which the organ/body weight ratio returns to 100% of the original when the process is complete. The adjustment of liver weight to the needs of the body suggests a complicated set of control points, a 'hepatostat'. There has been much progress in elucidation of mechanisms involved in initiation of liver regeneration. More recent studies have focused on termination pathways, because these may be the underlying controls of the hepatostat and their elimination may be relevant to hepatic neoplasia. When the standard regenerative process is thwarted due to failure of either hepatocytes or biliary epithelial cells to proliferate, each of the two epithelial compartments can function as a source of facultative stem cells for the other.

Synthesis of IL-6 by hepatocytes is a normal response to common hepatic stimuli

Exogenous interleukin 6 (IL-6), synthesized at the initiation of the acute phase response, is considered responsible for signaling hepatocytes to produce acute phase proteins. It is widely posited that IL-6 is either delivered to the liver in an endocrine fashion from immune cells at the site of injury, or alternatively, in a paracrine manner by hepatic immune cells within the liver. A recent publication showed there was a muted IL-6 response in lipopolysaccharide (LPS)-injured mice when nuclear NFκB was specifically inactivated in the hepatocytes. This indicates hepatocellular signaling is also involved in regulating the acute phase production of IL-6. Herein, we present extensive in vitro and in vivo evidence that normal hepatocytes are directly induced to synthesize IL-6 mRNAs and protein by challenge with LPS, a bacterial hepatotoxin, and by HGF, an important regulator of hepatic homeostasis. As the IL-6 receptor is found on the hepatocyte, these results reveal that induction of the acute phase response can be regulated in an autocrine as well as endocrine/paracrine fashion. Further, herein we provide data indicating that following partial hepatectomy (PHx), HGF differentially regulates IL-6 production in hepatocytes (induces) versus immune cells (suppresses), signifying disparate regulation of the cell sources involved in IL-6 production is a biologically relevant mechanism that has previously been overlooked. These findings have wide ranging ramifications regarding how we currently interpret a variety of in vivo and in vitro biological models involving elements of IL-6 signaling and the hepatic acute phase response.

Development of a chemically defined medium and discovery of new mitogenic growth factors for mouse hepatocytes: mitogenic effects of FGF1/2 and PDGF

Chemically defined serum-free media for rat hepatocytes have been useful in identifying EGFR ligands and HGF/MET signaling as direct mitogenic factors for rat hepatocytes. The absence of such media for mouse hepatocytes has prevented screening for discovery of such mitogens for mouse hepatocytes. We present results obtained by designing such a chemically defined medium for mouse hepatocytes and demonstrate that in addition to EGFR ligands and HGF, the growth factors FGF1 and FGF2 are also important mitogenic factors for mouse hepatocytes. Smaller mitogenic response was also noticed for PDGF AB. Mouse hepatocytes are more likely to enter into spontaneous proliferation in primary culture due to activation of cell cycle pathways resulting from collagenase perfusion. These results demonstrate unanticipated fundamental differences in growth biology of hepatocytes between the two rodent species.

The liver is a peculiar organ when it comes to stem cells

This Commentary highlights the article by Sekiya and Suzuki, detailing genetic lineage tracing to determine the origin of cells that form primitive ductules in a mouse model of chronic liver injury.

The degree of segmental aneuploidy measured by total copy number abnormalities predicts survival and recurrence in superficial gastroesophageal adenocarcinoma

Background

Prognostic biomarkers are needed for superficial gastroesophageal adenocarcinoma (EAC) to predict clinical outcomes and select therapy. Although recurrent mutations have been characterized in EAC, little is known about their clinical and prognostic significance. Aneuploidy is predictive of clinical outcome in many malignancies but has not been evaluated in superficial EAC.

Methods

We quantified copy number changes in 41 superficial EAC using Affymetrix SNP 6.0 arrays. We identified recurrent chromosomal gains and losses and calculated the total copy number abnormality (CNA) count for each tumor as a measure of aneuploidy. We correlated CNA count with overall survival and time to first recurrence in univariate and multivariate analyses.

Results

Recurrent segmental gains and losses involved multiple genes, including: HER2, EGFR, MET, CDK6, KRAS (recurrent gains); and FHIT, WWOX, CDKN2A/B, SMAD4, RUNX1 (recurrent losses). There was a 40-fold variation in CNA count across all cases. Tumors with the lowest and highest quartile CNA count had significantly better overall survival (p = 0.032) and time to first recurrence (p = 0.010) compared to those with intermediate CNA counts. These associations persisted when controlling for other prognostic variables.

Significance

SNP arrays facilitate the assessment of recurrent chromosomal gain and loss and allow high resolution, quantitative assessment of segmental aneuploidy (total CNA count). The non-monotonic association of segmental aneuploidy with survival has been described in other tumors. The degree of aneuploidy is a promising prognostic biomarker in a potentially curable form of EAC.

Principles of liver regeneration and growth homeostasis

Liver regeneration is perhaps the most studied example of compensatory growth aimed to replace loss of tissue in an organ. Hepatocytes, the main functional cells of the liver, manage to proliferate to restore mass and to simultaneously deliver all functions hepatic functions necessary to maintain body homeostasis. They are the first cells to respond to regenerative stimuli triggered by mitogenic growth factor receptors MET (the hepatocyte growth factor receptor] and epidermal growth factor receptor and complemented by auxiliary mitogenic signals induced by other cytokines. Termination of liver regeneration is a complex process affected by integrin mediated signaling and it restores the organ to its original mass as determined by the needs of the body (hepatostat function). When hepatocytes cannot proliferate, progenitor cells derived from the biliary epithelium transdifferentiate to restore the hepatocyte compartment. In a reverse situation, hepatocytes can also transdifferentiate to restore the biliary compartment. Several hormones and xenobiotics alter the hepatostat directly and induce an increase in liver to body weight ratio (augmentative hepatomegaly). The complex challenges of the liver toward body homeostasis are thus always preserved by complex but unfailing responses involving orchestrated signaling and affecting growth and differentiation of all hepatic cell types.

Whole-genome methylation sequencing reveals distinct impact of differential methylations on gene transcription in prostate cancer

DNA methylation is one of the most important epigenetic mechanisms in regulating gene expression. Genome hypermethylation has been proposed as a critical mechanism in human malignancies. However, whole-genome quantification of DNA methylation of human malignancies has rarely been investigated, and the significance of the genome distribution of CpG methylation is unclear. We performed whole-genome methylation sequencing to investigate the methylation profiles of 13 prostate samples: 5 prostate cancers, 4 matched benign prostate tissues adjacent to tumor, and 4 age-matched organ-donor prostate tissues. Alterations of methylation patterns occurred in prostate cancer and in benign prostate tissues adjacent to tumor, in comparison with age-matched organ-donor prostates. More than 95% alterations of genome methylation occurred in sequences outside CpG islands. Only a small fraction of the methylated CpG islands had any effect on RNA expression. Both intragene and promoter CpG island methylations negatively affected gene expression. However, suppressions of RNA expression did not correlate with levels of CpG island methylation, suggesting that CpG island methylation alone might not be sufficient to shut down gene expression. Motif analysis revealed a consensus sequence containing Sp1 binding motif significantly enriched in the effective CpG islands.

Role of PINCH and its partner tumor suppressor Rsu-1 in regulating liver size and tumorigenesis

Particularly interesting new cysteine-histidine-rich protein (PINCH) protein is part of the ternary complex known as the IPP (integrin linked kinase (ILK)-PINCH-Parvin-α) complex. PINCH itself binds to ILK and to another protein known as Rsu-1 (Ras suppressor 1). We generated PINCH 1 and PINCH 2 Double knockout mice (referred as PINCH DKO mice). PINCH2 elimination was systemic whereas PINCH1 elimination was targeted to hepatocytes. The genetically modified mice were born normal. The mice were sacrificed at different ages after birth. Soon after birth, they developed abnormal hepatic histology characterized by disorderly hepatic plates, increased proliferation of hepatocytes and biliary cells and increased deposition of extracellular matrix. After a sustained and prolonged proliferation of all epithelial components, proliferation subsided and final liver weight by the end of 30 weeks in livers with PINCH DKO deficient hepatocytes was 40% larger than the control mice. The livers of the PINCH DKO mice were also very stiff due to increased ECM deposition throughout the liver, with no observed nodularity. Mice developed liver cancer by one year. These mice regenerated normally when subjected to 70% partial hepatectomy and did not show any termination defect. Ras suppressor 1 (Rsu-1) protein, the binding partner of PINCH is frequently deleted in human liver cancers. Rsu-1 expression is dramatically decreased in PINCH DKO mouse livers. Increased expression of Rsu-1 suppressed cell proliferation and migration in HCC cell lines. These changes were brought about not by affecting activation of Ras (as its name suggests) but by suppression of Ras downstream signaling via RhoGTPase proteins. In conclusion, our studies suggest that removal of PINCH results in enlargement of liver and tumorigenesis. Decreased levels of Rsu-1, a partner for PINCH and a protein often deleted in human liver cancer, may play an important role in the development of the observed phenotype.

Gliotoxin-induced changes in rat liver regeneration after partial hepatectomy

BACKGROUND

Hepatic non-parenchymal cells (NPCs), encompassing hepatic stellate cells (HSCs), macrophages and endothelial cells, synthesize new hepatocyte growth factor (HGF) during liver regeneration (LR), and also play an important function in matrix production at the end of regeneration.

AIMS

The aim of this study was to determine whether ablating NPCs either during hepatocyte proliferation or during matrix resynthesis will have any effect on LR.

METHODS

Rats were injected with either gliotoxin (which induces NPC apoptosis) or vehicle control at various stages during partial hepatectomy (PH). NPCs and hepatocytes were also treated in vitro with gliotoxin.

RESULTS

Proliferating cells were abundant in control livers 24 h after PH, while in gliotoxin-treated rats, mitosis was absent, apoptotic NPCs were apparent and HGF was decreased. In vitro studies demonstrated a > 50% decrease in cell viability in NPC cultures, while hepatocyte viability and proliferation were unaffected. Chronic elimination of NPCs over a period of 5 days after PH led to increased desmin-positive HSCs and fewer alpha smooth muscle actin-expressing HSCs. Finally, there was continued proliferation of hepatocytes and decreased collagen I and TGF-β when HSCs, the matrix-producing NPCs, were ablated during later stages of LR.

CONCLUSIONS

Ablation of NPCs at early time points after PH interferes with liver regeneration, while their ablation at late stages causes impairment in the termination of LR, demonstrating a time-dependent regulatory role of NPCs in the regenerative process.

Regulation of liver growth by glypican 3, CD81, hedgehog, and Hhex

Previous studies from our laboratory have found glypican 3 (GPC3) as a negative regulator of growth. CD81 was found to be a binding partner for GPC3, and its expression and co-localization with GPC3 increased at the end of hepatocyte proliferation. However, the mechanisms through which these two molecules might regulate liver regeneration are not known. We tested the hypothesis that GPC3 down-regulates the hedgehog (HH) signaling pathway by competing with patched-1 for HH binding. We found decreased GPC3-Indian HH binding at peak proliferation in mice followed by increase in glioblastoma 1 protein (effector of HH signaling). We performed a yeast two-hybrid assay and identified hematopoietically expressed homeobox (Hhex, a known transcriptional repressor) as a binding partner for CD81. We tested the hypothesis that Hhex binding to CD81 keeps it outside the nucleus. However, when GPC3 binds to CD81, CD81-Hhex binding decreases, resulting in nuclear translocation of Hhex and transcriptional repression. In support of this, we found decreased GPC3-CD81 binding at hepatocyte proliferation peak, increased CD81-Hhex binding, and decreased nuclear Hhex. GPC3 transgenic mice were used as an additional tool to test our hypothesis. Overall, our data suggest that GPC3 down-regulates cell proliferation by binding to HH and down-regulating the HH signaling pathway and binding with CD81, thus making it unavailable to bind to Hhex and causing its nuclear translocation.

Genome-wide methylation analysis of prostate tissues reveals global methylation patterns of prostate cancer

Altered genome methylation is a hallmark of human malignancies. In this study, high-throughput analyses of concordant gene methylation and expression events were performed for 91 human prostate specimens, including prostate tumor (T), matched normal adjacent to tumor (AT), and organ donor (OD). Methylated DNA in genomic DNA was immunoprecipitated with anti-methylcytidine antibodies and detected by Affymetrix human whole genome SNP 6.0 chips. Among the methylated CpG islands, 11,481 islands were found located in the promoter and exon 1 regions of 9295 genes. Genes (7641) were methylated frequently across OD, AT, and T samples, whereas 239 genes were differentially methylated in only T and 785 genes in both AT and T but not OD. Genes with promoter methylation and concordantly suppressed expression were identified. Pathway analysis suggested that many of the methylated genes in T and AT are involved in cell growth and mitogenesis. Classification analysis of the differentially methylated genes in T or OD produced a specificity of 89.4% and a sensitivity of 85.7%. The T and AT groups, however, were only slightly separated by the prediction analysis, indicating a strong field effect. A gene methylation prediction model was shown to predict prostate cancer relapse with sensitivity of 80.0% and specificity of 85.0%. These results suggest methylation patterns useful in predicting clinical outcomes of prostate cancer.

Preexisting epithelial diversity in normal human livers: a tissue-tethered cytometric analysis in portal/periportal epithelial cells

Routine light microscopy identifies two distinct epithelial cell populations in normal human livers: hepatocytes and biliary epithelial cells (BECs). Considerable epithelial diversity, however, arises during disease states when a variety of hepatocyte-BEC hybrid cells appear. This has been attributed to activation and differentiation of putative hepatic progenitor cells (HPC) residing in the canals of Hering and/or metaplasia of preexisting mature epithelial cells. A novel analytic approach consisting of multiplex labeling, high-resolution whole-slide imaging (WSI), and automated image analysis was used to determine if more complex epithelial cell phenotypes preexist in normal adult human livers, which might provide an alternative explanation for disease-induced epithelial diversity. "Virtually digested" WSI enabled quantitative cytometric analyses of individual cells displayed in a variety of formats (e.g., scatterplots) while still tethered to the WSI and tissue structure. We employed biomarkers specifically associated with mature epithelial forms (HNF4α for hepatocytes, CK19 and HNF1β for BEC) and explored for the presence of cells with hybrid biomarker phenotypes. The results showed abundant hybrid cells in portal bile duct BEC, canals of Hering, and immediate periportal hepatocytes. These bipotential cells likely serve as a reservoir for the epithelial diversity of ductular reactions, appearance of hepatocytes in bile ducts, and the rapid and fluid transition of BEC to hepatocytes, and vice versa.

CONCLUSION

Novel imaging and computational tools enable increased information extraction from tissue samples and quantify the considerable preexistent hybrid epithelial diversity in normal human liver. This computationally enabled tissue analysis approach offers much broader potential beyond the results presented here.

Conditional genetic elimination of hepatocyte growth factor in mice compromises liver regeneration after partial hepatectomy

Hepatocyte growth factor (HGF) has been shown to be indispensable for liver regeneration because it serves as a main mitogenic stimulus driving hepatocytes toward proliferation. We hypothesized that ablating HGF in adult mice would have a negative effect on the ability of hepatocytes to regenerate. Deletion of the HGF gene was achieved by inducing systemic recombination in mice lacking exon 5 of HGF and carrying the Mx1-cre or Cre-ER(T) transgene. Analysis of liver genomic DNA from animals 10 days after treatment showed that a majority (70-80%) of alleles underwent cre-induced genetic recombination. Intriguingly, however, analysis by RT-PCR showed the continued presence of both unrecombined and recombined forms of HGF mRNA after treatment. Separation of liver cell populations into hepatocytes and non-parenchymal cells showed equal recombination of genomic HGF in both cell types. The presence of the unrecombined form of HGF mRNA persisted in the liver in significant amounts even after partial hepatectomy (PH), which correlated with insignificant changes in HGF protein and hepatocyte proliferation. The amount of HGF produced by stellate cells in culture was indirectly proportional to the concentration of HGF, suggesting that a decrease in HGF may induce de novo synthesis of HGF from cells with residual unrecombined alleles. Carbon tetrachloride (CCl4)-induced regeneration resulted in a substantial decrease in preexisting HGF mRNA and protein, and subsequent PH led to a delayed regenerative response. Thus, HGF mRNA persists in the liver even after genetic recombination affecting most cells; however, PH subsequent to CCl4 treatment is associated with a decrease in both HGF mRNA and protein and results in compromised liver regeneration, validating an important role of this mitogen in hepatic growth.

Interaction of MCM7 and RACK1 for activation of MCM7 and cell growth

MCM7 is one of the pivotal DNA replication licensing factors in controlling DNA synthesis and cell entry into S phase. Its expression and DNA copy number are some of the most predictive factors for the growth and behavior of human malignancies. In this study, we identified that MCM7 interacts with the receptor for activated protein kinase C 1 (RACK1), a protein kinase C (PKC) adaptor, in vivo and in vitro. The RACK1 binding motif in MCM7 is located at the amino acid 221-248. Knocking down RACK1 significantly reduced MCM7 chromatin association, DNA synthesis, and cell cycle entry into S phase. Activation of PKC by 12-O-tetradecanoylphorbol-13-acetate dramatically decreased MCM7 DNA replication licensing and induced cell growth arrest. Activation of PKC induced redistribution of RACK1 from nucleus to cytoplasm and decreased RACK1-chromatin association. The MCM7 mutant that does not bind RACK1 has no DNA replication licensing or oncogenic transformation activity. As a result, this study demonstrates a novel signaling mechanism that critically controls DNA synthesis and cell cycle progression.

Signals and cells involved in regulating liver regeneration

Liver regeneration is a complex phenomenon aimed at maintaining a constant liver mass in the event of injury resulting in loss of hepatic parenchyma. Partial hepatectomy is followed by a series of events involving multiple signaling pathways controlled by mitogenic growth factors (HGF, EGF) and their receptors (MET and EGFR). In addition multiple cytokines and other signaling molecules contribute to the orchestration of a signal which drives hepatocytes into DNA synthesis. The other cell types of the liver receive and transmit to hepatocytes complex signals so that, in the end of the regenerative process, complete hepatic tissue is assembled and regeneration is terminated at the proper time and at the right liver size. If hepatocytes fail to participate in this process, the biliary compartment is mobilized to generate populations of progenitor cells which transdifferentiate into hepatocytes and restore liver size.

Expression of hepatocyte epidermal growth factor receptor, FAS and glypican 3 in EpCAM-positive regenerative clusters of hepatocytes, cholangiocytes, and progenitor cells in human liver failure

Liver regeneration under normal circumstances proceeds through proliferation of all cellular elements of the liver. Studies with rodent models have shown that when proliferation of hepatocytes is inhibited, progenitor cells arising from the biliary compartment transdifferentiate into "oval/progenitor" cells, which proceed to differentiate into hepatocytes. Recent studies have shown that the same pathways may operate in human liver failure. The growth factor receptors (HGF [hepatocyte growth factor] receptor) and epidermal growth factor receptor are key mitogenic receptors for both hepatocytes and progenitor cells. Our current study used the biliary and progenitor marker EpCAM (epithelial cell adhesion molecule) to detect "regenerative clusters" of mixed cholangiocyte-hepatocyte differentiation. We determined that expression of metabolic equivalent and epidermal growth factor receptor occurs in biliary cells, progenitor cells, and hepatocytes, whereas activation of metabolic equivalent and epidermal growth factor receptor is limited to regenerative cluster hepatocytes. These histologic events are associated with expression of apoptosis-inducing FAS and mitoinhibitory protein glypican 3. Cell proliferation was overall suppressed in regenerative clusters. Transdifferentiation of biliary and progenitor cells appears to be regulated by a complex interaction of signals promoting and arresting growth.

Interaction of CSR1 with XIAP reverses inhibition of caspases and accelerates cell death

Cellular Stress Response 1 (CSR1) is a tumor suppressor gene that is located at 8p21, a region that is frequently deleted in prostate cancer as well as a variety of human malignancies. Previous studies have indicated that the expression of CSR1 induces cell death. In this study, we found that CSR1 interacts with X-linked Inhibitor of Apoptosis Protein (XIAP), using yeast two-hybrid screening analyses. XIAP overexpression has been found in many human cancers, and forced expression of XIAP blocks apoptosis. Both in vitro and in vivo analyses indicated that the C-terminus of CSR1 binds XIAP with high affinity. Through a series of in vitro recombinant protein-binding analyses, the XIAP-binding motif in CSR1 was determined to include amino acids 513 to 572. Targeted knock-down of XIAP enhanced CSR1-induced cell death, while overexpression of XIAP antagonized CSR1 activity. The binding of CSR1 with XIAP enhanced caspase-9 and caspase-3 protease activities, and CSR1-induced cell death was dramatically reduced on expression of a mutant CSR1 that does not bind XIAP. However, a XIAP mutant that does not interact with caspase-9 had no impact on CSR1-induced cell death. These results suggest that cell death is induced when CSR1 binds XIAP, preventing the interaction of XIAP with caspases. Thus, this study may have elucidated a novel mechanism by which tumor suppressors induce cell death.

Phenotypic fidelity (or not?) of epithelial cells in the liver

Recent evidence has contradicted the prevailing view that homeostasis and regeneration of the adult liver are mediated by self duplication of lineage-restricted hepatocytes and biliary epithelial cells. These new data suggest that liver progenitor cells do not function solely as a backup system in chronic liver injury; rather, they also produce hepatocytes after acute injury and are in fact the main source of new hepatocytes during normal hepatocyte turnover. In addition, other evidence suggests that hepatocytes are capable of lineage conversion, acting as precursors of biliary epithelial cells during biliary injury. To test these concepts, we generated a hepatocyte fate-tracing model based on timed and specific Cre recombinase expression and marker gene activation in all hepatocytes of adult Rosa26 reporter mice with an adenoassociated viral vector. We found that newly formed hepatocytes derived from preexisting hepatocytes in the normal liver and that liver progenitor cells contributed minimally to acute hepatocyte regeneration. Further, we found no evidence that biliary injury induced conversion of hepatocytes into biliary epithelial cells. These results therefore restore the previously prevailing paradigms of liver homeostasis and regeneration. In addition, our new vector system will be a valuable tool for timed, efficient, and specific loop out of floxed sequences in hepatocytes.

Growth factor pathways in development and progression of hepatocellular carcinoma

Hepatocellular carcinoma accounts for approximately 700,000 deaths per year. This tumor displays morphologic and phenotypic heterogeneity, and heterogeneity extends to the molecular level. Nevertheless, common pathways have been identified that are variably employed by these tumors. Such pathways often include aberrant signaling by growth factors, many of which are involved in liver development and regeneration. This review focuses on several such pathways and highlights patterns of structural expression of relevant molecules as well as effects of pathway stimulation or inhibition, both in vitro and in vivo. Specifically, the HGF/MET axis, epidermal growth factor receptors and associated ligands, insulin growth factor, vascular endothelial growth factor, fibroblast growth factor, platelet-derived growth factor and TGF-beta pathways are reviewed in the context of experimental models of HCC. Clinical-pathologic correlations are drawn for each of these, and current status of molecular targeted therapies is assessed. Review of available information indicates that redundancies and interactions among these signaling pathways must be taken into account if they are to be exploited to block and reverse HCC growth and spread.

Genome abnormalities precede prostate cancer and predict clinical relapse

The prediction of prostate cancer clinical outcome remains a major challenge after the diagnosis, even with improved early detection by prostate-specific antigen (PSA) monitoring. To evaluate whether copy number variation (CNV) of the genomes in prostate cancer tumor, in benign prostate tissues adjacent to the tumor (AT), and in the blood of patients with prostate cancer predicts biochemical (PSA) relapse and the kinetics of relapse, 241 samples (104 tumor, 49 matched AT, 85 matched blood, and 3 cell lines) were analyzed using Affymetrix SNP 6.0 chips. By using gene-specific CNV from tumor, the genome model correctly predicted 73% (receiver operating characteristic P = 0.003) cases for relapse and 75% (P < 0.001) cases for short PSA doubling time (PSADT, <4 months). The gene-specific CNV model from AT correctly predicted 67% (P = 0.041) cases for relapse and 77% (P = 0.015) cases for short PSADT. By using median-sized CNV from blood, the genome model correctly predicted 81% (P < 0.001) cases for relapse and 69% (P = 0.001) cases for short PSADT. By using median-sized CNV from tumor, the genome model correctly predicted 75% (P < 0.001) cases for relapse and 80% (P < 0.001) cases for short PSADT. For the first time, our analysis indicates that genomic abnormalities in either benign or malignant tissues are predictive of the clinical outcome of a malignancy.

p53-induced gene 3 mediates cell death induced by glutathione peroxidase 3

Expression of glutathione peroxidase 3 (GPx3) is down-regulated in a variety of human malignancies. Both methylation and deletion of GPx3 gene underlie the alterations of GPx3 expression in prostate cancer. A strong correlation between the down-regulation of GPx3 expression and progression of prostate cancer and the suppression of prostate cancer xenografts in SCID mice by forced expression of GPx3 suggests a tumor suppression role of GPx3 in prostate cancer. However, the mechanism of GPx3-mediated tumor suppression remains unclear. In this report, GPx3 was found to interact directly with p53-induced gene 3 (PIG3). Forced overexpression of GPx3 in prostate cancer cell lines DU145 and PC3 as well as immortalized prostate epithelial cells RWPE-1 increased apoptotic cell death. Expression of GPx3(x73c), a peroxidase-negative OPAL codon mutant, in DU145 and PC3 cells also increased cell death. The induced expression of GPx3 in DU145 and PC3 cells resulted in an increase in reactive oxygen species and caspase-3 activity. These activities were abrogated by either knocking down PIG3 or mutating the PIG3 binding motif in GPx3 or binding interference from a peptide corresponding to PIG3 binding motif in GPx3. In addition, UV-treated RWPE-1 cells underwent apoptotic death, which was partially prevented by knocking down GPx3 or PIG3, suggesting that GPx3-PIG3 signaling is critical for UV-induced apoptosis. Taken together, these results reveal a novel signaling pathway of GPx3-PIG3 in the regulation of cell death in prostate cancer.

Gene deletions and amplifications in human hepatocellular carcinomas: correlation with hepatocyte growth regulation

Tissues from 98 human hepatocellular carcinomas (HCCs) obtained from hepatic resections were subjected to somatic copy number variation (CNV) analysis. Most of these HCCs were discovered in livers resected for orthotopic transplantation, although in a few cases, the tumors themselves were the reason for the hepatectomies. Genomic analysis revealed deletions and amplifications in several genes, and clustering analysis based on CNV revealed five clusters. The LSP1 gene had the most cases with CNV (46 deletions and 5 amplifications). High frequencies of CNV were also seen in PTPRD (21/98), GNB1L (18/98), KIAA1217 (18/98), RP1-1777G6.2 (17/98), ETS1 (11/98), RSU1 (10/98), TBC1D22A (10/98), BAHCC1 (9/98), MAML2 (9/98), RAB1B (9/98), and YIF1A (9/98). The existing literature regarding hepatocytes or other cell types has connected many of these genes to regulation of cytoskeletal architecture, signaling cascades related to growth regulation, and transcription factors directly interacting with nuclear signaling complexes. Correlations with existing literature indicate that genomic lesions associated with HCC at the level of resolution of CNV occur on many genes associated directly or indirectly with signaling pathways operating in liver regeneration and hepatocyte growth regulation.

A mouse model of accelerated liver aging caused by a defect in DNA repair

The liver changes with age, leading to an impaired ability to respond to hepatic insults and increased incidence of liver disease in the elderly. Therefore, there is critical need for rapid model systems to study aging-related liver changes. One potential opportunity is murine models of human progerias or diseases of accelerated aging. Ercc1(-/Δ) mice model a rare human progeroid syndrome caused by inherited defects in DNA repair. To determine whether hepatic changes that occur with normal aging occur prematurely in Ercc1(-/Δ) mice, we systematically compared liver from 5-month-old progeroid Ercc1(-/Δ) mice to old (24-36-month-old) wild-type (WT) mice. Both displayed areas of necrosis, foci of hepatocellular degeneration, and acute inflammation. Loss of hepatic architecture, fibrosis, steatosis, pseudocapillarization, and anisokaryosis were more dramatic in Ercc1(-/Δ) mice than in old WT mice. Liver enzymes were significantly elevated in serum of Ercc1(-/Δ) mice and old WT mice, whereas albumin was reduced, demonstrating liver damage and dysfunction. The regenerative capacity of Ercc1(-/Δ) liver after partial hepatectomy was significantly reduced. There was evidence of increased oxidative damage in Ercc1(-/Δ) and old WT liver, including lipofuscin, lipid hydroperoxides and acrolein, as well as increased hepatocellular senescence. There was a highly significant correlation in genome-wide transcriptional changes between old WT and 16-week-old, but not 5-week-old, Ercc1(-/Δ) mice, emphasizing that the Ercc1(-/Δ) mice acquire an aging profile in early adulthood.

CONCLUSION

There are strong functional, regulatory, and histopathological parallels between accelerated aging driven by a DNA repair defect and normal aging. This supports a role for DNA damage in driving aging and validates a murine model for rapidly testing hypotheses about causes and treatment for aging-related hepatic changes.