Biosynthesis of abnormally glycosylated alpha 1-antitrypsin by a human hepatoma cell line

Modeling and integration of N-glycan biomarkers in a comprehensive biomarker data model

Molecular biomarkers measure discrete components of biological processes that can contribute to disorders when impaired. Great interest exists in discovering early cancer biomarkers to improve outcomes. Biomarkers represented in a standardized data model, integrated with multi-omics data, may improve understanding and use of novel biomarkers such as glycans and glycoconjugates. Among altered components in tumorigenesis, N-glycans exhibit substantial biomarker potential, when analyzed with their protein carriers. However, such data are distributed across publications and databases of diverse formats, which hampers their use in research and clinical application. Mass spectrometry measures of fifty N-glycans, on seven serum proteins in liver disease, were integrated (as a panel) into a cancer biomarker data model, providing a unique identifier, standard nomenclature, links to glycan resources, and accession and ontology annotations to standard protein, gene, disease, and biomarker information. Data provenance was documented with a standardized FDA-supported BioCompute Object. Using the biomarker data model allows capture of granular information, such as glycans with different levels of abundance in cirrhosis, hepatocellular carcinoma, and transplant groups. Such representation in a standardized data model harmonizes glycomics data in a unified framework, making glycan-protein biomarker data exploration more available to investigators and to other data resources. The biomarker data model we describe can be used by researchers to describe their novel glycan and glycoconjugate biomarkers, can integrate N-glycan biomarker data with multi-source biomedical data, and can foster discovery and insight within a unified data framework for glycan biomarker representation thereby making the data FAIR (Findable, Accessible, Interoperable, Reusable) (https://www.go-fair.org/fair-principles/).

Oncostatin M and TNF-α Induce Alpha-1 Antitrypsin Production in Undifferentiated Adipose Stromal Cells

Alpha-1 antitrypsin (A1AT), a circulating acute-phase reactant antiprotease, is produced and secreted by cells of endodermal epithelial origin, primarily hepatocytes, and by immune cells. Deficiency of A1AT is associated with increased risk of excessive lung inflammation and injury, especially following chronic cigarette smoke (CS) exposure. Exogenous administration of mesenchymal progenitor cells, including adipose tissue-derived stromal/stem cells (ASC), alleviates CS-induced lung injury through paracrine effectors such as growth factors. It is unknown, however, if mesodermal ASC can secrete functional A1AT and if CS exposure affects their A1AT production. Human ASC collected via liposuction from nonsmoking or smoking donors were stimulated by inflammatory cytokines tumor necrosis alpha (TNFα), oncostatin M (OSM), and/or dexamethasone (DEX) or were exposed to sublethal concentrations of ambient air control or CS extract (0.5%-2%). We detected minimal expression and secretion of A1AT by cultured ASC during unstimulated conditions, which significantly increased following stimulation with TNFα or OSM. Furthermore, TNFα and OSM synergistically enhanced A1AT expression and secretion, which were further increased by DEX. The A1AT transcript variant produced by stimulated ASC resembled that produced by bronchial epithelial cells rather than the variant produced by monocytes/macrophages. While the cigarette smoking status of the ASC donor had no measurable effect on the ability of ASC to induce A1AT expression, active exposure to CS extract markedly reduced A1AT expression and secretion by cultured ASC, as well as human tracheobronchial epithelial cells. ASC-secreted A1AT covalently complexed with neutrophil elastase in control ASC, but not in cells transfected with A1AT siRNA. Undifferentiated ASC may require priming to secrete functional A1AT, a potent antiprotease that may be relevant to stem cell therapeutic effects.

Alpha-1-antitrypsin in pathogenesis of hepatocellular carcinoma

CONTEXT

Alpha-1-antitrypsin (A1AT) is the most abundant liver-derived, highly polymorphic, glycoprotein in plasma. Hereditary deficiency of alpha-1-antitrypsin in plasma (A1ATD) is a consequence of accumulation of polymers of A1AT mutants in endoplasmic reticulum of hepatocytes and other A1AT-producing cells. One of the clinical manifestations of A1ATD is liver disease in childhood and cirrhosis and/or hepatocellular carcinoma (HCC) in adulthood. Epidemiology and pathophysiology of liver failure in early childhood caused by A1ATD are well known, but the association with hepatocellular carcinoma is not clarified. The aim of this article is to review different aspects of association between A1AT variants and hepatocellular carcinoma, with emphasis on the epidemiology and molecular pathogenesis. The significance of A1AT as a biomarker in the diagnosis of HCC is also discussed.

EVIDENCE ACQUISITIONS

Search for relevant articles were performed through Pub Med, HighWire, and Science Direct using the keywords "alpha-1-antitrypsin", "liver diseases", "hepatocellular carcinoma", "SERPINA1". Articles published until 2011 were reviewed.

RESULTS

Epidemiology studies revealed that severe A1ATD is a significant risk factor for cirrhosis and HCC unrelated to the presence of HBV or HCV infections. However, predisposition to HCC in moderate A1ATD is rare, and probably happens in combination with HBV and/or HCV infections or other unknown risk factors. It is assumed that accumulation of polymers of A1ATD variants in endoplasmic reticulum of hepatocytes leads to damage of hepatocytes by gain-of-function mechanism. Also, increased level of A1AT was recognized as diagnostic and prognostic marker of HCC.

CONCLUSIONS

Clarification of a carcinogenic role for A1ATD and identification of proinflammatory or some still unknown factors that lead to increased susceptibility to HCC associated with A1ATD may contribute to a better understanding of hepatic carcinogenesis and to the development of new drugs.

Proteomic analysis of alpha-1-antitrypsin in immunoglobulin A nephropathy

Immunoglobulin A nephropathy (IgAN) is recognized as the most common form of primary glomerulonephritis worldwide. It is characterized by mesangial cell proliferation with mesangial IgA deposition in the glomeruli, and is usually associated with secondary tubulointerstitial injury. Although significant progress has been made in the clarification of the pathogenesis of IgAN, the exact pathogenetic mechanism remains unclear. To find out the candidate proteins that play an important role in IgAN, renal cortex tissues and urine from IgAN patients were studied. The 2-DE was performed on renal tissues of IgAN and normal controls. A series of spots identified as alpha-1-antitrypsin (AAT) by mass spectrometry, were found to be significantly increased in patients with IgAN. Up-regulation of AAT variants was validated in renal cortex tissues of IgAN using Western blot and 2-DE immunoblot. Lower isoforms (˜48 kDa) and fragments (˜33 kDa), suspected as cleavage forms by proteinase attack, were especially increased in IgAN compared to normal controls. In addition, AAT proteins modified by tyrosine nitration (approximately 57 and 48 kDa), which reflects excessive oxidative stress, were increased in IgAN tissue. Additionally in the urine of IgAN, increase of AAT variants and fragments was detected by 2-DE immunoblot as well as Western blot. Immunohistochemical staining of IgAN kidney tissue revealed that the increase of AAT appeared to be derived from hypertrophic proximal tubules. The AAT staining in the glomerulus was not clear in IgAN. In addition, immunodepletion-zymography showed a positive correlation between AAT and 80-110-kDa proteinases in IgAN tissue. Further studies regarding the functional roles of AAT and the proteinases will allow better understanding of the pathogenesis of IgAN.

A study of glycoproteins in human serum and plasma reference standards (HUPO) using multilectin affinity chromatography coupled with RPLC-MS/MS

The glycoproteome is a major subproteome present in human plasma. In this study, we isolated and characterized approximately 150 glycoproteins from the human plasma and serum samples provided by HUPO using a multilectin affinity column. The corresponding tryptic digest was separated by RP-HPLC coupled to an IT mass spectrometer (3-D LCQ). Also in this study, a new system, namely an Ettan MDLC system coupled to a linear ITLTQ, was compared with the previous LCQ platform and gave a greater number of protein identifications, as well as better quality. When we compared the composition of the glycoproteomes for the plasma and serum samples there was a close correlation between the samples, except for the absence of fibrinogen from the identified-protein list in the latter sample, which was presumably as a result of the clotting process. In addition, the analysis of the samples from three ethnic specimens, Caucasian American, Asian American, and African American, were very similar but showed a higher angiotensinogen plasma level and a lower histidine-rich glycoprotein level in Caucasian American samples, and a lower vitronectin level in African American blood samples.

Oncostatin M is a potent stimulator of alpha1-antitrypsin secretion in lung epithelial cells: modulation by transforming growth factor-beta and interferon-gamma

alpha1-Antitrypsin (alpha1-AT) plays a key role in lung homeostasis. Although the hepatocyte is considered as the primary source of alpha1-AT, we have previously demonstrated that rat alveolar epithelial type II cells as well as the human A549 cell line synthesize alpha1-AT, suggesting its local production within the lung. In the present study, we showed that oncostatin M, as opposed to interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha), or IL-6, is a potent stimulator of alpha1-AT synthesis in the human A549 cell line. The oncostatin M-induced alpha1-AT secretion is modulated by interferon-gamma (IFN-gamma) and transforming growth factor-beta (TGF-beta) at both the protein and mRNA levels. IFN-gamma decreases oncostatin M-induced alpha1-AT secretion. By contrast, TGF-beta in combination with oncostatin M induces a dramatic and synergistic upregulation that is not observed in the HepG2 hepatocyte cell line. Our results suggest that during an inflammatory process, alveolar epithelial cells may contribute to the antiprotease defense within the lung.

Glycosylation of alpha-1-proteinase inhibitor and haptoglobin in ovarian cancer: evidence for two different mechanisms

The change in glycosylation of the two acute-phase proteins, alpha-1-proteinase inhibitor (API) and haptoglobin (Hp), in progressive ovarian cancer is different. This has been shown by monosaccharide analysis and lectin-binding studies of proteins purified from serum. In the glycan chains of API, there is decreased branching (more biantennary chains), less branches ending in alpha 2-3 sialic acid, more branches ending in alpha 2-6 sialic acid and more fucose, probably linked alpha 1-6 to the core region. On the other hand, Hp shows increased branching (more triantennary chains), more branches ending in alpha 2-3 sialic acid, less branches ending in alpha 2-6 sialic acid, and more fucose, probably in the alpha 1-3 linkage at the end of the chains. This is surprising because API and Hp are thought to be glycosylated by a common pathway in the liver. We have also shown that the fucose-specific lectin, lotus tetragonolobus, extracts abnormal forms of both Hp and API in ovarian cancer, but the expression of this Hp is related to tumour burden and the expression of this API is related to lack of response to therapy. It is suggested that this difference in the behaviour of API and Hp in ovarian cancer may be associated with the different changes in their glycosylation. Of the many mechanisms that could explain these findings, a likely one is that a pathological process is removing API with triantennary chains from the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential secretion of alpha 1-acid glycoprotein occurs in the Golgi complex of isolated rat hepatocytes. Evidence of partial retention in the Golgi

Using weakly basic amines, we investigated the step at which the secretion kinetics of concanavalin-A-retained and nonretained alpha 1-acid glycoprotein glycoforms diverge in isolated rat hepatocytes. Both chloroquine and primaquine, whose action on protein secretion is targeted to terminal domains of the Golgi apparatus, cancelled the kinetic difference without influencing carbohydrate chain sialylation. To test for a possible interaction of alpha 1-acid glycoprotein with Golgi membranes, we also permeabilized control and primaquine-treated hepatocytes, as well as purified Golgi preparations, with saponin. In each case, we found that alpha 1-acid glycoprotein was associated with Golgi membranes, the association being more marked in primaquine-treated cells than in control cells. Membrane-bound alpha 1-acid glycoprotein appeared to be preferentially retained on concanavalin A. Such retention could account for the divergent secretion kinetics of alpha 1-acid glycoprotein glycoforms.

Properties of alpha 1-antitrypsin secreted by human adenocarcinoma cell lines

alpha 1-Antitrypsin; (alpha 1-AT) produced by various human carcinoma (non-hepatoma) cell lines were analyzed. Five out of eight cell lines secreted detectable amounts of alpha 1-AT into the conditioned media. All were adenocarcinoma cell lines. The tumor cell-derived alpha 1-ATs had higher molecular weights (MW) than the normal plasma form. Most of this difference was an overall reflection of altered N-glycosylation. As judged by binding of lectins, the glycosylation had shifted towards higher levels of triantennary oligosaccharides and higher levels of fucosylation. The conditioned media also contained lower MW alpha 1-AT species, possibly, proteolytically cleaved forms.

Changes of immunoreactivity in alpha 1-antitrypsin in patients with autoimmune diseases

Recent studies from this laboratory have shown that a monoclonal antibody prepared against a specific epitope on alpha 1-antitrypsin is a valuable diagnostic marker for autoimmune conditions. In the present study we have further characterized this monoclonal antibody and reassessed its diagnostic value in screening samples from patients with various autoimmune conditions. alpha 1-Antitrypsin was micropurified from patients with selected autoimmune conditions and from normal donors. The purified alpha 1-antitrypsin isolated from patients with autoimmune conditions and normal donors was deglycosylated using both a mixture of exoglycosidases and endoglycosidase F. The immunoreactivity of the native and deglycosylated alpha 1-antitrypsin was examined using both a monoclonal antibody and a polyclonal antibody in enzyme linked immunosorbent assay (ELISA) and radioimmunoassay (RIA), respectively. It was noted that alpha 1-antitrypsin isolated from patients with autoimmune diseases generated a displacement curve dissimilar to alpha 1-antitrypsin purified from normal donors or alpha 1-antitrypsin from patients with autoimmune diseases subjected to deglycosylation when these samples were examined by ELISA using the monoclonal antibody. However, when the polyclonal antibody was used for these studies, no difference was found between the native and deglycosylated alpha 1-antitrypsin suggesting that the monoclonal antibody recognized an epitope not detectable by the polyclonal antibody.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro complex formation between cholesterol and alpha 1-proteinase inhibitor

The in vitro interaction between human alpha 1-proteinase inhibitor (alpha 1-PI) and cholesterol was studied with electrophoretic and gel chromatographic methods. The addition of cholesterol (from 1 to 20 mol/mol alpha 1-PI) at 37 degrees C resulted in retarded electrophoretic mobility of alpha 1-PI towards the anode, diminished immunoreactivity and antiproteinase activity. At a molar ratio of 2:1 (cholesterol/alpha 1-PI), antitryptic activity was reduced by 15% but antielastase activity by 50%. At this ratio the gel filtration alpha 1-PI peak appeared at 67 kDa, as compared to 52 kDa for native alpha 1-PI. No size difference was noted on SDS-PAGE. These results suggest the occurrence of noncovalent complex formation between cholesterol and alpha 1-PI in vitro.

Serum alpha-1-proteinase inhibitor with abnormal properties in ovarian cancer

It was previously reported that sera from ovarian cancer patients contained abnormal forms of alpha-1-proteinase inhibitor (API) that predicted unresponsiveness to chemotherapy. These molecules were detected by extracting the sera with the fucose-specific lectin, lotus tetragonolobus, and analysing the extracts by electrophoresis. In a new study of ovarian cancer, we report that API cannot be extracted by lotus from fresh sera, unless the specimens are subjected to repeated cycles of freezing and thawing. Furthermore, increases in lotus-extractable API in the pretreated sera are also associated with a poor response to chemotherapy. This would suggest that lotus is extracting the same molecules in both studies. It seems likely that the discrepancy between the two studies is due to the length of time the specimens were stored prior to analysis. We present evidence suggesting that the API extracted by lotus is present in serum as soluble complexes, the detailed composition of which is unclear. The change in the properties of API in cancer may be very important with respect to tumour spread.

Prognostic significance of alpha-1-antitrypsin in early stage of colorectal carcinomas

We have previously shown that human colorectal carcinoma cell lines, RCM-1 and CoCM-1, synthesize alpha-1-antitrypsin (alpha 1-AT) in culture. We have studied immunohistochemically the incidence of alpha 1-AT on histologic sections from paraffin-embedded tissues of surgically resected colorectal carcinomas and their metastatic foci, polypectomized adenomas, and normal mucosae. alpha 1-AT was detected in 89 (61%) of 145 carcinomas (including 14 carcinomas in adenoma), and 12 (39%) of 31 adenomas. But only 2 (4%) of 55 normal colorectal mucosae were positive for alpha 1-AT. In metastatic tumor cells of colorectal carcinomas in lymph nodes and other organs, alpha 1-AT positivity was 60% and 82%, respectively. The incidence of alpha 1-AT was markedly higher in advanced adenocarcinomas than in early ones and more frequent in adenocarcinomas of right side (including transverse colon) than those of left side and rectum, regardless of their histological malignancy grades. In mucinous carcinomas the frequency was greater (8 of 9 cases) than in conventional adenocarcinomas. Clinical follow-up of the patients with colorectal carcinomas suggested that alpha 1-AT positivity in Dukes' stage A/B tends to correlate with unfavorable prognosis irrespective of the grade of histologic differentiation of carcinoma, but there is no significant relation in Dukes' stage C/D. Our findings suggest that alpha 1-AT in colorectal carcinoma is related to the invasive and metastatic capacity. It may thus serve as a biologic marker for prognosis of colorectal carcinomas at relatively early stages (Dukes' stage A/B).

Affinity electrophoresis for studies of mechanisms regulating glycosylation of plasma proteins

A model system for studies of mechanisms governing the alterations of glycosylation of plasma glycoproteins was developed. The system employs two human hepatoma cell lines, Hep 3B and Hep G2, as target cells and agarose affinity electrophoresis with lectins for studies of microheterogeneity of alpha 1-protease inhibitor (PI), a model glycoprotein synthesized by hepatocytes. As an example for the application of the system, the effect of cytokines on major microheterogeneity of plasma proteins is demonstrated. The results indicate that interleukin 6, transforming growth factor beta 1 and, to some extent, tumor necrosis factor alpha are directly involved in regulating the pattern of glycosylation of plasma proteins in vitro, but the major effect is obtained by using combinations of interleukin 6, transforming growth factor beta 1, tumor necrosis factor alpha and interleukin 1. In addition, the results underline the dissociation between alteration of gene expression and the changes in the pattern of plasma protein glycosylation.

Interferon beta 2/B-cell stimulating factor 2/interleukin 6 affects glycosylation of acute phase proteins in human hepatoma cell lines

Undefined monocyte-derived cytokines have previously been shown to affect glycan processing in glycoproteins secreted by human hepatoma cell lines. Hep 3B cells, when incubated with the cytokine interferon beta 2/B-cell stimulating factor 2/interleukin 6, secreted forms of alpha 1-protease inhibitor, ceruloplasmin, and alpha-fetoprotein with increased reactivity with concanavalin A (Con A) while incubation of Hep G2 cells with this cytokine led to secretion of forms of these proteins with decreased reactivity with Con A, reflecting changes in their oligosaccharide chains. The difference in response of these two transformed cell lines to this cytokine undoubtedly reflects differences in their intracellular glycan processing mechanisms. Changes in glycosylation patterns were dissociated from changes in rate of synthesis: this cytokine caused increased synthesis of alpha 1-protease inhibitor and ceruloplasmin, and decreased synthesis of alpha-fetoprotein in both cell lines.

New human colorectal carcinoma cell lines that secrete proteinase inhibitors in vitro

Two new human cell lines, RCM-1 and CoCM-1, have been established from primary colorectal adenocarcinomas. Both cell lines were unique in that the cultures secreted trypsin inhibitors in vitro. The activities of these inhibitors were accumulated in serum-free media of both cell lines over a period of several days. Two inhibitors (PI-1 and PI-2) were isolated from serum-free conditioned medium in which RCM-1 was grown by anion-exchange and gel filtration high-performance liquid chromatography. PI-1 inhibited trypsin and chymotrypsin strongly, and pancreatic elastase weakly. Its molecular weight was about 57 kilodaltons (Kd) as determined by gel filtration chromatography. It cross-reacted with the antiserum elicited against human alpha 1-antitrypsin in double immunodiffusion. PI-1 corresponding to alpha 1-antitrypsin was also demonstrated immunohistochemically in both cell lines. PI-2 inhibited trypsin strongly, and chymotrypsin, kallikrein and plasmin weakly. It had higher molecular weight (200-300 Kd) than that of PI-1, and did not cross-react with antisera against human alpha 1-antitrypsin, alpha 2-macroglobulin, alpha 1-antichymotrypsin, alpha 2-plasmin inhibitor, inter-alpha-trypsin inhibitor and urinary trypsin inhibitor. RCM-1 and CoCM-1 are the first colorectal adenocarcinoma cell lines that secrete functionally active trypsin inhibitors, including alpha 1-antitrypsin in vitro, and are useful for the study of tumor-cell derived proteinase inhibitors.

Fucosylated forms of alpha-1-antitrypsin that predict unresponsiveness to chemotherapy in ovarian cancer

We have discovered modified fucosylation of alpha 1-antitrypsin (F-AT) in the sera of ovarian cancer patients. This was detected by SDS/electrophoresis and silver-staining after extracting the sera with the fucose-binding lectin, Lotus tetragonolobus, and was identified as alpha 1-antitrypsin by Western blotting. Initially, high F-AT levels appeared to be related to the recurrence of cancer, but later measurements showed that elevated levels were also present in patients who did not respond to therapy. Using an arbitrary grading system, the level of F-AT was assessed in pairs of sera from 29 ovarian cancer patients undergoing therapy; one specimen collected just after the start of therapy and the other on a later occasion. In 75% of the 15 non-responders, F-AT was higher when measured on a second occasion; whereas in 86% of the 14 responders the second measurement was either unchanged or lower, being frequently undetectable. F-AT levels were also low or undetectable in sera from healthy women. Eight responders were monitored for F-AT throughout cyclophosphamide chemotherapy. Despite a high tumour burden at the start of therapy, all patients had relatively low levels of F-AT and this was maintained throughout remission; the levels only becoming elevated with the recurrence of tumour growth. Increased F-AT expression did not appear to be particularly associated with the presence of liver metastases and frequently predated any clinical signs of a recurrence. The interesting characteristics of these molecules could make them useful in the management of ovarian cancer.

Tumour markers in diagnosis and management

The 20-year period since the discovery of AFP by Abelev has seen the introduction of a wide range of new tumour markers and it is now clear that PLC is biologically heterogeneous. Hepatoblastomas, fibrolamellar carcinomas, hepatocellular carcinomas and cholangiocarcinomas may secrete a variety of distinctive markers which are predominantly glycoproteins, and may resemble those found in placenta or fetal liver. Diagnostically, AFP remains the best marker for HCC, both in sensitivity and specificity; it is known to consist of isoforms. In patients with elevated serum AFP and filling defects on liver scan, Con A reactive AFP may differentiate PLC from hepatic metastases, whilst fucosylated AFP may distinguish PLC from benign disorders when AFP is non-diagnostically elevated. With this recognition of tumour heterogeneity the value of a multiple-marker approach has become apparent. The measurement of vitamin B12 binding protein and neurotensin should lead to the detection of most patients with the fibrolamellar variant of HCC and many of these should be resectable. In patients with normal serum AFP levels, HCC-associated GGTP is of major value whilst in low-incidence areas for HCC, patients should also be screened for H-ALP; using a multiple marker approach in high-risk groups, 90% of clinically diagnosed hepatocellular carcinomas are serologically positive. The Chinese and Alaskan studies, in which small, potentially resectable tumours were detected, suggest that it is now possible to achieve 5-year survival figures of up to 60% in HCC patients detected by screening. The value of such a strategy in low-incidence countries is currently under study. In patient monitoring, as in diagnosis, AFP remains the outstanding marker. In AFP-negative patients, other markers including vitamin B12-binding protein, neurotensin, HCC-specific isoenzymes, des-gamma-carboxy-prothrombin and alpha-fucosidase, are of undoubted diagnostic value, but their value as indicants of disease progression remains to be established. In monitoring the response of hepatic metastases, CEA remains the least unsatisfactory marker but should always be used in conjunction with serial ultrasound scans. Tumour markers now play an important role in the diagnosis and monitoring of PLC but a role is also emerging in tumour imaging and drug targeting. The next 20 years should see the introduction of tumour markers of high sensitivity and specificity which make a fundamental contribution not only to detection and monitoring, but also to the effective treatment of liver cancer.

Retroviral mediated transfer and expression of human alpha 1-antitrypsin in cultured cells

Genetic deficiency of alpha 1-antitrypsin in man is a predisposing factor to emphysema and a disorder potentially correctable by somatic gene therapy. A full-length human alpha 1-antitrypsin cDNA was cloned into a retroviral vector and introduced into cells which package the recombinant gene in a retroviral capsule. Cells infected with the recombinant retrovirus express human alpha 1-antitrypsin mRNA and protein. The recombinant protein is glycosylated, secreted and exhibits anti-protease activity against human neutrophil elastase.

Hepatic alpha 1-antitrypsin mRNA content in cirrhosis with normal and abnormal protease inhibitor phenotypes

We quantitated alpha 1-antitrypsin mRNA in normal, alpha 1-antitrypsin-deficient cirrhotic and biliary cirrhotic livers using two-dimensional electrophoretograms of [35S]methionine-labeled translational products of total hepatic RNA and RNA/DNA hybridization. alpha 1-Antitrypsin precursor product was identified by immunoprecipitation. The relative abundance of alpha 1-antitrypsin product from normal (0.989 +/- 0.197), cirrhotic (0.956 +/- 0.062) and alpha 1-antitrypsin deficient (0.818 +/- 0.12) livers was not significantly different. Although (RNA/DNA) was decreased in the PiZZ cirrhotic livers compared to normal (0.56 +/- 0.045 vs. 0.95 +/- 0.225), it equaled that found in the PiM cirrhotic livers (0.56 +/- 0.055). The concentration of alpha 1-antitrypsin mRNA [relative abundance X (RNA/DNA)], while decreased in PiZZ compared to normal liver, is thus no different in PiZZ cirrhotics than in PiM cirrhotics. We confirmed this observation by quantitation of the alpha 1-antitrypsin mRNA using an alpha 1-antitrypsin genomic probe. By RNA/DNA hybridization, alpha 1-antitrypsin mRNA was equal in PiM cirrhotic and PiZZ cirrhotic (38.48 +/- 4.5 vs. 31.93 +/- 2.1), but significantly decreased from noncirrhotic PiM liver (58.36 +/- 12.7). We conclude that alpha 1-antitrypsin mRNA is decreased in cirrhosis of any etiology, and this decrease appears to represent a general response of the liver to injury. Since the decreased alpha 1-antitrypsin mRNA in PiM cirrhotics is associated with normal serum alpha 1-antitrypsin levels, it is unlikely that the decreased alpha 1-antitrypsin mRNA in PiZZ cirrhotics accounts for their decreased serum levels.

Long-term biosynthesis of complement component C3 and alpha-1 acid glycoprotein by adult rat hepatocytes in a co-culture system with an epithelial liver cell-type

We used a system of co-culture of adult rat hepatocytes with another epithelial cell type from rat liver to study the synthesis of two acute-phase reactants, alpha-1 acid glycoprotein (alpha 1AGP) and the third component of complement (C3), and we have obtained long-term secretion of these two proteins. After a period of adaptation corresponding to the first 2-4 days of the co-culture, hepatocytes secreted C3 and alpha 1AGP for at least 2 weeks at a mean level higher than that observed in the first days of a pure culture of hepatocytes. When pulse-chase analysis was performed on day 6 of co-culture, kinetics of synthesis of alpha 1AGP and C3 were the same as those observed on day 1 of a conventional culture of pure hepatocytes. Furthermore, intracellular and extracellular alpha 1AGP had Mr values respectively of 39,000 and of 42,000-52,000, identical with those observed in pure cultures of hepatocytes. Similarly, the molecular size and subunit structures of C3 were the same in co-culture and in cultures, indicating an identical processing of this protein. C3 produced in co-culture was also haemolytically active. Therefore, the system of adult hepatocytes co-cultured with this liver epithelial cell provides a physiological system in vitro which permits long-term synthesis of the two acute-phase reactants C3 and alpha 1AGP. This model opens the possibility to study the modulation of the synthesis of these two proteins during a long period by inflammatory agents or by hormones.

Biosynthesis of abnormally glycosylated hepatoma secretory proteins in cell cultures

We studied, by electrophoretic techniques, the physiochemical properties of 4 glycoproteins, alpha 1-antitrypsin, alpha 1-antichymotrypsin, alpha 1-acid glycoprotein and transferrin synthesized by three different human hepatoma cell lines. A common feature was the export of glycoproteins with retarded electrophoretic mobility, indicating incomplete sialylation, and a predominance of atypical, highly branched carbohydrate chains. The abnormal glycosylation pattern may be specific for malignant transformation of hepatocytes and possibly related to the intracellular accumulation of some of these proteins in malignant cells.

Expression of the alpha 1-proteinase inhibitor gene in human monocytes and macrophages

Expression of the alpha 1-proteinase inhibitor (alpha 1PI) gene was studied in human mononuclear cells. Using RNA blot and dot hybridization, alpha 1PI mRNA was detected in human peripheral blood monocytes, bronchoalveolar and breast milk macrophages, but not in B or T lymphocytes. Using incorporation of a radiolabeled amino acid precursor, synthesis and secretion of alpha 1PI were demonstrated in human monocytes and macrophages, but not in lymphocytes. In addition, alpha 1PI was secreted in functionally active form as shown by complexing with serine proteases. Biosynthesis of alpha 1PI by mononuclear phagocytes was greatest during the first 24 hr in culture and progressively decreased over the next 10 days. The reduction in alpha 1PI biosynthesis in vitro involved a mechanism acting at the pretranslational level as alpha 1PI mRNA content also progressively declined over 10 days in culture. The ease of sampling human monocytes and macrophages now permits examination of the biochemical defect in homozygous PiZ and PiS alpha 1PI deficiencies and study of the functional significance of locally produced alpha 1PI in normal tissues and sites of injury or inflammation.