Annexin expressions are temporally and spatially regulated during rat hepatocyte differentiation

Annexin A6 in the liver: From the endocytic compartment to cellular physiology

Annexin A6 (AnxA6) belongs to the conserved annexin family - a group of Ca²⁺-dependent membrane binding proteins. AnxA6 is the largest of all annexins and highly expressed in smooth muscle, hepatocytes, endothelial cells and cardiomyocytes. Upon activation, AnxA6 binds to negatively charged phospholipids in a wide range of intracellular localizations, in particular the plasma membrane, late endosomes/pre-lysosomes, but also synaptic vesicles and sarcolemma. In these cellular sites, AnxA6 is believed to contribute to the organization of membrane microdomains, such as cholesterol-rich lipid rafts and confer multiple regulatory functions, ranging from vesicle fusion, endocytosis and exocytosis to programmed cell death and muscle contraction. Growing evidence supports that Ca²⁺ and Ca²⁺-binding proteins control endocytosis and autophagy. Their regulatory role seems to operate at the level of the signalling pathways that initiate autophagy or at later stages, when autophagosomes fuse with endolysosomal compartments. The convergence of the autophagic and endocytic vesicles to lysosomes shares several features that depend on Ca²⁺ originating from lysosomes/late endosomes and seems to depend on proteins that are subsequently activated by this cation. However, the involvement of Ca²⁺ and its effector proteins in these autophagic and endocytic stages still remains poorly understood. Although AnxA6 makes up almost 0.25% of total protein in the liver, little is known about its function in hepatocytes. Within the endocytic route, we identified AnxA6 in endosomes and autophagosomes of hepatocytes. Hence, AnxA6 and possibly other annexins might represent new Ca²⁺ effectors that regulate converging steps of autophagy and endocytic trafficking in hepatocytes. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Annexin A6 protein is downregulated in human hepatocellular carcinoma

Annexin A6 (AnxA6) is a lipid-binding protein highly expressed in the liver, regulating cholesterol homeostasis and signaling pathways with a role in liver physiology. Here, we analyzed whether hepatic AnxA6 levels are affected by pathological conditions that are associated with liver dysfunction and liver injury. AnxA6 levels in the fatty liver of mice fed a high-fat diet, in ob/ob and db/db animals and in human fatty liver are comparable to controls. Similarly, AnxA6 levels appear unaffected in murine nonalcoholic steatohepatitis and human liver fibrosis. Accordingly, adiponectin, lysophosphatidylcholine, palmitate, and TGFbeta, all of which have a role in liver injury, do not affect AnxA6 expression in human hepatocytes. Likewise, adiponectin and IL8 do not alter AnxA6 levels in primary human hepatic stellate cells. However, in hepatic tumors of 18 patients, AnxA6 protein levels are substantially reduced compared to nontumorous tissues. AnxA6 mRNA is even increased in the tumors suggesting that posttranscriptional mechanisms are involved herein. Lipidomic analysis shows trends toward elevated cholesteryl ester and sphingomyelin in the tumor samples, yet the ratio of tumor to nontumorous AnxA6 does not correlate with these lipids. The current study shows that AnxA6 is specifically reduced in human hepatocellular carcinoma suggesting a role of this protein in hepatocarcinogenesis.

Comparative proteomics reveals novel components at the plasma membrane of differentiated HepaRG cells and different distribution in hepatocyte- and biliary-like cells

Hepatitis B virus (HBV) is a human pathogen causing severe liver disease and eventually death. Despite important progress in deciphering HBV internalization, the early virus-cell interactions leading to infection are not known. HepaRG is a human bipotent liver cell line bearing the unique ability to differentiate towards a mixture of hepatocyte- and biliary-like cells. In addition to expressing metabolic functions normally found in liver, differentiated HepaRG cells support HBV infection in vitro, thus resembling cultured primary hepatocytes more than other hepatoma cells. Therefore, extensive characterization of the plasma membrane proteome from HepaRG cells would allow the identification of new cellular factors potentially involved in infection. Here we analyzed the plasma membranes of non-differentiated and differentiated HepaRG cells using nanoliquid chromatography-tandem mass spectrometry to identify the differences between the proteomes and the changes that lead to differentiation of these cells. We followed up on differentially-regulated proteins in hepatocytes- and biliary-like cells, focusing on Cathepsins D and K, Cyclophilin A, Annexin 1/A1, PDI and PDI A4/ERp72. Major differences between the two proteomes were found, including differentially regulated proteins, protein-protein interactions and intracellular localizations following differentiation. The results advance our current understanding of HepaRG differentiation and the unique properties of these cells.

Label-free quantitative proteomics of CD133-positive liver cancer stem cells

BACKGROUND

CD133-positive liver cancer stem cells, which are characterized by their resistance to conventional chemotherapy and their tumor initiation ability at limited dilutions, have been recognized as a critical target in liver cancer therapeutics. In the current work, we developed a label-free quantitative method to investigate the proteome of CD133-positive liver cancer stem cells for the purpose of identifying unique biomarkers that can be utilized for targeting liver cancer stem cells. Label-free quantitation was performed in combination with ID-based Elution time Alignment by Linear regression Quantitation (IDEAL-Q) and MaxQuant.

RESULTS

Initially, IDEAL-Q analysis revealed that 151 proteins were differentially expressed in the CD133-positive hepatoma cells when compared with CD133-negative cells. We then analyzed these 151 differentially expressed proteins by MaxQuant software and identified 10 significantly up-regulated proteins. The results were further validated by RT-PCR, western blot, flow cytometry or immunofluorescent staining which revealed that prominin-1, annexin A1, annexin A3, transgelin, creatine kinase B, vimentin, and EpCAM were indeed highly expressed in the CD133-positive hepatoma cells.

CONCLUSIONS

These findings confirmed that mass spectrometry-based label-free quantitative proteomics can be used to gain insights into liver cancer stem cells.

Quantitative proteomic analysis of pregnancy-related proteins from peripheral blood mononuclear cells during pregnancy in pigs

Information obtained from peripheral blood could help us understand the underlying mechanisms in autoimmune diseases, cancer, pregnancy, and other conditions. In this paper, we present the protein map of porcine peripheral blood mononuclear cells (PBMC) to better understand the molecular expression changes that occur during pregnancy using proteomic analysis. We detected 94 differentially expressed proteins in pregnant vs. non-pregnant (NP) pigs, and a representative set of the proteins was subjected to LC-MS/MS analysis. Furthermore, the identified proteins were categorized according to their biological process and molecular function. By classifying the proteins according to their functions, a large number of differentially regulated proteins involved in anti-oxidant, detoxification and stress response pathways were found, including peroxiredoxin (PRX) 1, 2, and 6, glutathione-S-transferase (GST), annexin A2, and A6, and heat shock protein 27 (HSP 27) during pregnancy (pregnancy d of E40, embryonic day 40; E70, embryonic day 70; and E93, embryonic day 93) compared with non-pregnancy. In this study, a proteomic approach utilizing 2-DE and LC-MS/MS was applied to evaluate specific molecular expression changes during pregnancy compared with non-pregnancy. Together, these data offer new information about the proteome map and factors that are differentially regulated during maintenance of normal pregnancy.

Isolation and characterization of a novel population of progenitor cells from unmanipulated rat liver

Widespread use of liver transplantation in the treatment of hepatic diseases is restricted by the limited availability of donated organs. One potential solution to this problem would be isolation and propagation of liver progenitor cells or stem cells. Here, we report on the isolation of a novel progenitor cell population from unmanipulated (that is, no prior exposure to chemicals and no injury) adult rat liver. Rat liver cells were cultured following a protocol developed in our laboratory to generate a unique progenitor cell population called liver-derived progenitor cells (LDPCs). LDPCs were analyzed by fluorescence-activated cell sorting, real-time polymerase chain reaction (RT-PCR), immunostaining and microarray gene expression. LDPCs were also differentiated into hepatocytes and biliary epithelium in vitro and examined for mature hepatic markers and urea and albumin production. These analyses showed that, LDPCs expressed stem cell markers such as cluster domain (CD)45, CD34, c-kit, and Thy 1, similar to hematopoietic stem cells, as well as endodermal/hepatic markers such as hepatocyte nuclear factor (HNF)3beta, hematopoietically-expressed homeobox gene-1, c-met, and transthyretin. LDPCs were negative for OV-6, cytokeratins (CKs), albumin, and HNF1alpha. The microarray gene expression profile demonstrated that they showed some similarities to known liver progenitor/stem cells such as oval cells. In addition, LDPCs differentiated into functional hepatocytes in vitro as shown by albumin expression and urea production. In conclusion, LDPCs are a population of unique liver progenitors that can be generated from unmanipulated adult liver, which makes them potentially useful for clinical applications, especially for cell transplantation in the treatment of liver diseases.

Change in annexin A3 expression by regulatory factors of hepatocyte growth in primary cultured rat hepatocytes

We have recently reported that annexin (Anx) A3 expression is necessary for hepatocyte growth in cultured rat hepatocytes seeded at half the subconfluent density on collagen. In the present study, we investigated the effects of various regulatory factors of hepatocyte growth on AnxA3 expression. AnxA3 expression was significantly reduced in hepatocytes cultured under various growth inhibitory conditions such as presence of dexamethasone, culture at subconfluent cell density, and on EHS-Matrigel and lactose-carrying styrene polymer. On the other hand, hepatocyte growth factor and epidermal growth factor, stimulators of hepatocyte growth, significantly increased AnxA3 expression in hepatocytes cultured on EHS-Matrigel. These results show close correlation between known stimulatory or inhibitory actions of various factors to hepatocyte growth and increase or decrease in AnxA3 expression, and suggest the involvement of AnxA3 in their regulation of hepatocyte growth.

Antiviral effect of Phyllanthus nanus ethanolic extract against hepatitis B virus (HBV) by expression microarray analysis

Ethanolic extract of Phyllanthus nanus (P. nanus) treatment exhibited potent antiviral activity against Hepatitis B virus (HBV). The effects of these extracts on HBV in the HBV genome integrated cell lines--Alexander cells and HepG2 2.2.15 cells were examined. Experimental results showed that the ethanolic extract of P. nanus produced suppressive effect on HBsAg secretion and HBsAg mRNA expression. The extract also inhibited HBV replication as measured by HBV DNA level in vitro. In addition, using a duck HBV (DHBV) primary culture model, the P. nanus ethanolic extract suppressed viral replication of DHBV in DHBV infected primary duck hepatocytes. The gene expression pattern in Alexander cells that had been treated with the ethanolic extract of P. nanus was also revealed by microarray techniques. The microarray results indicated that there was up-regulation of expression of several genes, including annexin A7 (Axn7). The subcellular localization of Axn7 and anti-HBV effect of Axn7 over-expression in Alexander cells were also investigated. Results showed that expression of Axn7-GFP fusion protein are localized around the secretory vesicles and could cause a decrease in HBsAg secretion in Alexander cells. Axn7 protein might play an important role in the medicinal effect of the active principle(s) of P. nanus.

Differentiation of human colon adenocarcinoma cells alters the expression and intracellular localization of annexins A1, A2, and A5

Butyrate induces differentiation and alters cell proliferation in intestinal-epithelial cells by modulation of the expression of several genes. Annexins are a superfamily of ubiquitous proteins characterized by their calcium-dependent ability to bind to biological membranes; their involvement in several physiological processes, such as membrane trafficking, calcium signaling, cell motility, proliferation, and differentiation has been proposed. Thus, we have analyzed changes in annexin A1 (AnxA1), annexin A2 (AnxA2), and annexin A5 (AnxA5) levels and localization in human colon adenocarcinoma cells differentiated by butyrate treatment or by culture in glucose-free inosine-containing medium. The acquired differentiated phenotype increased dipeptidyl peptidase-IV (DPP-IV) expression and alkaline phosphatase (ALP) activity, two well known brush border markers. Butyrate induces cell differentiation and growth arrest in BCS-TC2, BCS-TC2.2, HT-29, and Caco-2 cells, increasing the levels of AnxA1 and AnxA5, whereas AnxA2 decreases except in Caco-2 cells. Inosine-differentiated cells present increased amounts of the three studied annexins, as occurs in spontaneously differentiated Caco-2 cells. AnxA2 down-regulation is not due to proteasome activation and seems to be related to the butyrate-induced cell proliferation arrest; AnxA1 and AnxA5 expression is growth-state independent. AnxA1 and AnxA5 are mainly found in the cytoplasm while AnxA2 is localized underneath the plasma membrane in cell-to-cell contacts. Butyrate induces changes in subcellular localization towards a vesicle-associated pattern. Human colon adenocarcinoma cell differentiation is associated with an up-regulation of AnxA1, AnxA2, and AnxA5 and with a subcellular relocation of these proteins. No correlation between annexin levels and tumorigenicity was found. Up-regulation of AnxA1 could contribute to the reported anti-inflammatory effects of butyrate in colon inflammatory diseases.

Mesothelial Differentiation as Reflected by Differential Gene Expression

Human mesothelial cells obtained from benign effusions retain their proliferative capacity and grow uniformly either with a fibroblastic or epithelioid morphology in vitro. These cultures therefore provide a model for the process of mesothelial differentiation in vivo. To study this differentiation, we isolated differentially expressed genes obtained by suppression subtractive hybridization. Of the nine genes found to be overexpressed in fibroblastic mesothelial cells, three are matrix-associated (integrin alpha5, collagen binding protein 2, human cartilage glycoprotein 39), whereas the others are associated with a proliferative cell type (14-3-3 epsilon, plexin B2, N33, and three genes encoding ribosomal elements). Seven of the eight genes upregulated in the epithelioid phenotype are related rather to specialized functions, such as metabolism (aldose reductase, lecithin:cholesterol acyltransferase, ATPase 6), cytoskeletal composition (cytokeratins 7 and 8), and regulation of differentiation (granulin, annexin II). Immunohistochemistry with available antibodies to six of the differentially expressed gene products confirmed the differences also in pleural tissues, where submesothelial cells displayed the fibroblastic markers, whereas surface cells displayed the epithelioid markers. In summary, this approach revealed a pattern of genes coordinately regulated during mesothelial differentiation and suggests that mesothelium may regenerate also by recruiting cells from the submesothelial layer. Some of the gene products may also be useful markers for differentiation and activation in serosal tissues.

Isolated Small Rat Hepatocytes Express both Annexin III and Terminal Differentiated Hepatocyte Markers, Tyrosine Aminotransferase and Tryptophan Oxygenase, at the mRNA Level

We recently showed that annexin III is expressed in isolated small rat hepatocytes but, not in parenchymal hepatocytes. In the present study, we used reverse transcription polymerase chain analysis to examine the annexin III mRNA level in isolated small rat hepatocytes and parenchymal hepatocytes. Annexin III mRNA was detected in isolated small hepatocytes, but not in isolated parenchymal hepatocytes, confirming the presence of annexin III expression in isolated small rat hepatocytes at the mRNA level and indicating that the absence of annexin III expression in isolated parenchymal hepatocytes is due to the absence of annexin III mRNA. Furthermore, we examined the mRNA level of tyrosine aminotransferase and tryptophan oxygenase, two terminally differentiated hepatocyte markers. mRNA for these markers was detected in both parenchymal hepatocytes and small hepatocytes.

Fusion of lamellar body with plasma membrane is driven by the dual action of annexin II tetramer and arachidonic acid

Annexin II has been implicated in membrane fusion during the exocytosis of lamellar bodies from alveolar epithelial type II cells. Most previous studies were based on the fusion assays by using model membranes. In the present study, we investigated annexin II-mediated membrane fusion by using isolated lamellar bodies and plasma membrane as determined by the relief of octadecyl rhodamine B (R18) self-quenching. Immunodepletion of annexin II from type II cell cytosol reduced its fusion activity. Purified annexin II tetramer (AIIt) induced the fusion of lamellar bodies with the plasma membrane in a dose-dependent manner. This fusion is Ca2+-dependent and is highly specific to AIIt because other annexins (I and II monomer, III, IV, V, and VI) were unable to induce the fusion. Modification of the different functional residues of AIIt by N-ethylmaleimide, nitric oxide, or peroxynitrite abolished AIIt-mediated fusion. Arachidonic acid enhanced AIIt-mediated fusion and reduced its Ca2+ requirement to an intracellularly achievable level. This effect is due to membrane-bound arachidonic acid, not free arachidonic acid. Other fatty acids including linolenic acid, palmitoleic acid, myristoleic acid, stearic acid, palmitic acid, and myristic acid had little effect. AIIt-mediated fusion was suppressed by the removal of arachidonic acid from lamellar body and plasma membrane using bovine serum albumin. The addition of arachidonic acid back to the arachidonic acid-depleted membranes restored its fusion activity. Our results suggest that the fusion between lamellar bodies with the plasma membrane is driven by the synergistic action of AIIt and arachidonic acid.

Specific expression of annexin III in rat-small-hepatocytes

Small hepatocytes are cells that express characteristic phenotypes such as a high growth potential and differentiation capacity. In order to identify rat-small-hepatocyte specific proteins, we separated the cellular proteins of isolated small and parenchymal hepatocytes by 2D polyacrylamide gel electrophoresis. Comparison of their profiles revealed a protein with a molecular mass of 37 kDa in the small hepatocytes that was not present in the parenchymal hepatocytes. Proteolytic peptide mass fingerprinting was used to identify the protein and it was found to be annexin III. The validity of the identification was confirmed by Western blot analysis with anti-annexin III antibody.

Stress fibres-a Ca2+ -independent store for annexins?

Annexins belong to a family of lipid-binding proteins that are implicated in membrane organization. Several members are capable of binding to actin and, in smooth muscle cells, annexin 6 is known to form a Ca(2+)-dependent, plasmalemmal complex with actin filaments. Annexins can also associate with F-actin containing stress fibres within cultured smooth muscle cells or fibroblasts in a Ca(2+)-independent manner. Depolymerization of stress-fibre systems with cytochalasin D leads to the translocation of actin-bound annexin 2 from the cytoplasm to the plasma membrane at high intracellular levels of Ca(2+). This type of Ca(2+)-dependent annexin mobility is observed only in cells of mesenchymal phenotype, which have a well-developed stress-fibre system; not in epithelial cells.