The sequence of human serum albumin cDNA and its expression in E. coli

Serum albumin and cardiovascular disease: a Mendelian randomization study

BACKGROUND

An increasing body of evidence suggests that serum albumin levels play a role in cardiovascular diseases. However, the specific causal relationship between serum albumin levels and cardiovascular disease remains partially unknown.

METHODS

Mendelian randomization (MR) was employed in this study to examine potential causal relationships between instrumental variables and cardiovascular diseases. Specifically, we utilized genetic variants of serum albumin levels within the reference range as our instrumental variables. To acquire data on genetic associations with cardiovascular diseases, we sourced information from renowned genome-wide association studies such as UK BioBank, EMBL-EBI, and FinnGen. Notably, our study leveraged summary statistics from large cohorts that have been previously described.

RESULTS

We explored the association between serum albumin levels and various conditions, including heart failure (HF), venous thromboembolism (VTE), stroke, atrial fibrillation (AF), coronary artery disease (CAD), type 2 diabetes (T2DM), and pulmonary heart disease (PHD). Genetically predicted serum albumin levels were associated with PHD (odds ratio = 0.737, 95% CI = 0.622 - 0.874, P < 0.001), AF (odds ratio = 0.922, 95% CI = 0.870 - 0.977, P = 0.006), VTE (odds ratio = 0.993, 95% CI = 0.991 - 0.995, P < 0.001), and Stroke (odds ratio = 0.997, 95% CI = 0.995 - 0.999, P = 0.002). However, genetically predicted serum albumin level traits were not associated with HF, CAD and T2DM.

CONCLUSION

Our study demonstrates a significant association between serum albumin levels and cardiovascular disease, underscoring the crucial role of low serum albumin as a predictive factor in patients with cardiovascular disease.

Stable Mammalian Serum Albumins Designed for Bacterial Expression

Albumin is the most abundant protein in the blood serum of mammals and has essential carrier and physiological roles. Albumins are also used in a wide variety of molecular and cellular experiments and in the cultivated meat industry. Despite their importance, however, albumins are challenging for heterologous expression in microbial hosts, likely due to 17 conserved intramolecular disulfide bonds. Therefore, albumins used in research and biotechnological applications either derive from animal serum, despite severe ethical and reproducibility concerns, or from recombinant expression in yeast or rice. We use the PROSS algorithm to stabilize human and bovine serum albumins, finding that all are highly expressed in E. coli. Design accuracy is verified by crystallographic analysis of a human albumin variant with 16 mutations. This albumin variant exhibits ligand binding properties similar to those of the wild type. Remarkably, a design with 73 mutations relative to human albumin exhibits over 40 °C improved stability and is stable beyond the boiling point of water. Our results suggest that proteins with many disulfide bridges have the potential to exhibit extreme stability when subjected to design. The designed albumins may be used to make economical, reproducible, and animal-free reagents for molecular and cell biology. They also open the way to high-throughput screening to study and enhance albumin carrier properties.

Synthesis, Biological, Spectroscopic and Computational Investigations of Novel N-Acylhydrazone Derivatives of Pyrrolo[3,4-d]pyridazinone as Dual COX/LOX Inhibitors

Secure and efficient treatment of diverse pain and inflammatory disorders is continually challenging. Although NSAIDs and other painkillers are well-known and commonly available, they are sometimes insufficient and can cause dangerous adverse effects. As yet reported, derivatives of pyrrolo[3,4-d]pyridazinone are potent COX-2 inhibitors with a COX-2/COX-1 selectivity index better than meloxicam. Considering that N-acylhydrazone (NAH) moiety is a privileged structure occurring in many promising drug candidates, we decided to introduce this pharmacophore into new series of pyrrolo[3,4-d]pyridazinone derivatives. The current paper presents the synthesis and in vitro, spectroscopic, and in silico studies evaluating the biological and physicochemical properties of NAH derivatives of pyrrolo[3,4-d]pyridazinone. Novel compounds 5a-c-7a-c were received with high purity and good yields and did not show cytotoxicity in the MTT assay. Their COX-1, COX-2, and 15-LOX inhibitory activities were estimated using enzymatic tests and molecular docking studies. The title N-acylhydrazones appeared to be promising dual COX/LOX inhibitors. Moreover, spectroscopic and computational methods revealed that new compounds form stable complexes with the most abundant plasma proteins-AAG and HSA, but do not destabilize their secondary structure. Additionally, predicted pharmacokinetic and drug-likeness properties of investigated molecules suggest their potentially good membrane permeability and satisfactory bioavailability.

Low serum albumin: A neglected predictor in patients with cardiovascular disease

Albumin, the most abundant circulating protein in blood, is an essential protein which binds and transports various drugs and substances, maintains the oncotic pressure of blood and influences the physiological function of the circulatory system. Albumin also has anti-inflammatory, antioxidant, and antithrombotic properties. Evidence supports albumin's role as a strong predictor of cardiovascular (CV) risk in several patient groups. Its protective role extends to those with coronary artery disease, heart failure, hypertension, atrial fibrillation, peripheral artery disease or ischemic stroke, as well as those undergoing revascularization procedures or with aortic stenosis undergoing transcatheter aortic valve replacement, and patients with congenital heart disease and/or endocarditis. Hypoalbuminemia is a strong prognosticator of increased all-cause and CV mortality according to several cohort studies and meta-analyses in hospitalized and non-hospitalized patients with or without comorbidities. Normalization of albumin levels before discharge lowers mortality risk, compared with hypoalbuminemia before discharge. Modified forms of albumin, such as ischemia modified albumin, also has prognostic value in patients with coronary or peripheral artery disease. When albumin is combined with other risk factors, such as uric acid or C-reactive protein, the prognostic value is enhanced. Although albumin supplementation may be a plausible approach, its efficacy has not been established and in patients with hypoalbuminemia, priority is focused on diagnosing and managing the underlying condition. The CV effects of hypoalbuminemia and relevant issues are considered in this review. Large cohort studies and meta-analyses are tabulated and the physiologic effects of albumin and the deleterious effects of low albumin are pictorially illustrated.

A versatile insertion point on albumin to accommodate peptides and maintain their activities

Genetic fusion of human serum albumin to peptides is an important strategy to enhance the plasma half-life of the peptide. An inherent challenge of such method is the reduction of specific activity of the cargo peptides upon connecting at N- or C-termini of albumin. Here, we report a finding that residue 363-364 of albumin can be inserted with a peptide while maintaining the peptide activities. We insert a peptide inhibitor into this site, and at the N-terminus of albumin, for comparison. The chimeric protein displays potent inhibition (IC₅₀ value of 30 nM) to its target (uPAR), but not the N-terminally fused construct. We also study the chimera of HSA with a cyclic peptide inhibitor of murine urokinase-type plasminogen activator grafted at either the internal site or the N-terminus. The internally peptide-grafted protein possesses a much more potent inhibition compared to the N-terminally located fusion (IC₅₀ value of 32 nM vs 19 μM). We further demonstrate that such internal fusion does not affect albumin expression, secondary structure, and inherent drug binding activity. Thus, this work identifies a versatile insertion point inside albumin for maintaining fusion peptide activity, and opens a new avenue to expand the applications of albumin fusion technology.

The Expression of Recombinant Human Serum Albumin in the Mammary Gland of Transgenic Mice

Human serum albumin (HSA) is widely used in the clinic for the treatment of several diseases in large amount each year. With the increasing demands of HSA in clinic and limited blood resource, recombinant HSA (rHSA) is becoming an attractive and alternative source for HSA production. In this study, we aimed to express rHSA in the mammary glands of transgenic mice by using a tissue-specific promoter and other regulatory elements. An rHSA expression vector was constructed bearing the cDNA and first intron of HSA under the control of bovine αs1-casein promoter with a 2 × chicken β-globin insulator in the front. Transgenic mice were generated and reverse transcription polymerase chain reaction showed that rHSA was expressed only in the mammary gland, indicating the tissue specificity of the bovine αs1-casein promoter in directing transgene transcription in transgenic mice. Enzyme-linked immunosorbent assay test showed that rHSA was successfully secreted into the milk of transgenic mice with the highest level at 1.98 ± 0.12 g/L. Our results indicate the ability of the bovine αs1-casein promoter to induce successful expression of rHSA in the mammary gland of transgenic mice.

Medium optimization for high yield production of human serum albumin in Pichia pastoris and its efficient purification

OBJECTIVE

To improve the yield of recombinant human serum albumin (HSA) in Pichia pastoris by medium optimization and establish the related purification scheme.

RESULTS

A simplified version of the generally used buffered glycerol complex medium (BMGY), which contained yeast extract, glycerol and potassium salts, was found to be applicable. By decreasing the salt concentration of basal salt medium (BSM) to half of the original formula further, we achieved a high yield of 17.47 g/L HSA in the supernatant within a 192 h induction, which is the highest rHSA yield ever reported as far as we know. Accompanied with a three-step purification procedure which recovered two thirds of the desired protein at high purity, our work lays a solid foundation for large-scale industrial production of HSA.

CONCLUSION

Medium optimization plays a significant role in improving the yield of desired protein, lowering the production cost and helping to explore the producing strain's character.

Factor VIII: the protein, cloning its gene, synthetic factor and now - 35 years later - gene therapy; what happened in between?

The foundation of haemophilia A therapy in the last 35 years has been critically dependent on isolation of the Factor VIII (FVIII) protein and discovery of the cDNA sequence of the FVIII gene, published in 1984. Identification of the FVIII sequence resulted in a new era of recombinant concentrates and led to significant improvements in safety, set against the tragedy of widespread HIV and hepatitis infections in haemophilia patients from contaminated plasma-based products. We chronicle the scientific methods and race leading up to the publication of the FVIII DNA sequence and the legacy that follows through to revolutionary gene therapy treatment in clinical trials today.

Serum Albumin, Lipid and Drug Binding

Albumin is widely conserved from vertebrates to invertebrates, and nature of mammalian albumins permit them to bind various endogenous ligands and drugs in the blood. It is known that at least two major ligand binding sites are present on the albumin molecule, which are referred to as Site I and Site II. These binding sites are thought to be almost completely conserved among mammals, even though the degree of binding to these sites are different depending on the physical and chemical properties of drugs and differences in the microenvironment in the binding pockets. In addition, the binding sites for medium and long-chain fatty acids are also well conserved among mammals, and it is considered that there are at least seven binding sites, including Site I and Site II. These bindings properties of albumin in the blood are also widely known to be important for transporting drugs and fatty acids to various tissues. It can therefore be concluded that albumin is one of the most important serum proteins for various ligands, and information on human albumin can be very useful in predicting the ligand binding properties of the albumin of other vertebrates.

A Chalcone-Based Potential Therapeutic Small Molecule That Binds to Subdomain IIA in HSA Precisely Controls the Rotamerization of Trp-214

The principal intent of this work is to explore whether the site-specific binding of a newly synthesized quinoline-appended anthracenyl chalcone, (E)-3-(anthracen-10-yl)-1-(6,8-dibromo-2-methylquinolin-3-yl)prop-2-en-1-one (ADMQ), with an extracellular protein of the human circulatory system, human serum albumin (HSA), can control the rotamerization of its sole tryptophan residue, Trp-214. With this aim, we have systematically studied the binding affinity, interactions, and localization pattern of the title compound inside the specific binding domain of the transport protein and any conformation alteration caused therein. Multiple spectroscopic experiments substantiated by an in silico molecular modeling exercise provide evidence for the binding of the guest ADMQ in the hydrophobic domain of HSA, which is primarily constituted by residues Trp-214, Arg-218, Arg-222, Asp-451, and Tyr-452. Rotationally restricted ADMQ prefers to reside in Sudlow site I (subdomain IIA) of HSA in close proximity (2.45 nm) to the intrinsic fluorophore Trp-214 and is interestingly found to control its vital rotamerization process. The driving force for this rotational interconversion is predominantly found to be governed by the direct interaction of ADMQ with Trp-214. However, the role of induced conformational perturbation in the biomacromolecule itself upon ADMQ adoption cannot be ruled out completely, as indicated by circular dichroism, 3D fluorescence, root-mean-square deviation, root-mean-square fluctuation, and secondary structure element observations. The comprehensive spectroscopic study outlined herein provides important information on the biophysical interaction of a chalcone-based potential therapeutic candidate with a carrier protein, exemplifying its utility in having a regulatory effect on the microconformations of Trp-214.

Non-oncotic properties of albumin. A multidisciplinary vision about the implications for critically ill patients

INTRODUCTION

Effective resuscitation with human albumin solutions is achieved with less fluid than with crystalloid solutions. However, the role of albumin in today's critical care unit is also linked to its multiple pharmacological effects. Areas covered: The potential clinical benefits of albumin in select populations of critically ill patients like sepsis seem related to immunomodulatory and anti-inflammatory effects, antibiotic transportation and endothelial stabilization. Albumin transports many drugs used in critically ill patients. Such binding to albumin is frequently lessened in critically ill patients with hypoalbuminemia. These changes could result in sub-optimal treatment. Albumin has immunomodulatory capacity by binding several bacterial products. Albumin also influences vascular integrity, contributing to the maintenance of the normal capillary permeability. Moreover, the albumin molecule encompasses several antioxidant properties, thereby significantly reducing re-oxygenation injury, which is especially important in sepsis. In fact, most studies of albumin administration are a combination of a degree of resuscitation with a degree of maintenance or supplementation of albumin. Expert commentary: The potential clinical benefits of the use of albumin in selected critically ill patients such as sepsis seem related to its immunomodulatory and anti-inflammatory effects, antioxidant properties, antibiotic transportation and endothelial stabilization. Additional studies are warranted to further elucidate the underlying physiologic and molecular rationale.

Revisiting Escherichia coli as microbial factory for enhanced production of human serum albumin

BACKGROUND

Human serum albumin (HSA)-one of the most demanded therapeutic proteins with immense biotechnological applications-is a large multidomain protein containing 17 disulfide bonds. The current source of HSA is human blood plasma which is a limited and unsafe source. Thus, there exists an indispensable need to promote non-animal derived recombinant HSA (rHSA) production. Escherichia coli is one of the most convenient hosts which had contributed to the production of more than 30% of the FDA approved recombinant pharmaceuticals. It grows rapidly and reaches high cell density using inexpensive and simple subst-rates. E. coli derived recombinant products have more economic potential as fermentation processes are cheaper compared to the other expression hosts. The major bottleneck in exploiting E. coli as a host for a disulfide-rich multidomain protein is the formation of aggregates of overexpressed protein. The majority of the expressed HSA forms inclusion bodies (more than 90% of the total expressed rHSA) in the E. coli cytosol. Recovery of functional rHSA from inclusion bodies is not preferred because it is difficult to obtain a large multidomain disulfide bond rich protein like rHSA in its functional native form. Purification is tedious, time-consuming, laborious and expensive. Because of such limitations, the E. coli host system was neglected for rHSA production for the past few decades despite its numerous advantages.

RESULTS

In the present work, we have exploited the capabilities of E. coli as a host for the enhanced functional production of rHSA (~ 60% of the total expressed rHSA in the soluble fraction). Parameters like intracellular environment, temperature, induction type, duration of induction, cell lysis conditions etc. which play an important role in enhancing the level of production of the desired protein in its native form in vivo have been optimized. We have studied the effect of assistance of different types of exogenously employed chaperone systems on the functional expression of rHSA in the E. coli host system. Different aspects of cell growth parameters during the production of rHSA in presence and absence of molecular chaperones in E. coli have also been studied.

CONCLUSION

In the present case, we have filled in the gap in the literature by exploiting the E. coli host system, which is fast-growing and scalable at the low cost of fermentation, as a microbial factory for the enhancement of functional production of rHSA, a crucial protein for therapeutic and biotechnological applications.

Co-opting biology to deliver drugs

The goal of drug delivery is to improve the safety and therapeutic efficacy of drugs. This review focuses on delivery platforms that are either derived from endogenous pathways, long-circulating biomolecules and cells or that piggyback onto long-circulating biomolecules and cells. The first class of such platforms is protein-based delivery systems--albumin, transferrin, and fusion to the Fc domain of antibodies--that have a long-circulation half-life and are designed to transport different molecules. The second class is lipid-based delivery systems-lipoproteins and exosomes-that are naturally occurring circulating lipid particles. The third class is cell-based delivery systems--erythrocytes, macrophages, and platelets--that have evolved, for reasons central to their function, to exhibit a long life-time in the body. The last class is small molecule-based delivery systems that include folic acid. This article reviews the biology of these systems, their application in drug delivery, and the promises and limitations of these endogenous systems for drug delivery.

Quantitation of 4,4'-methylene diphenyl diisocyanate human serum albumin adducts

4,4′-Methylene diphenyl diisocyanate (herein 4,4′-MDI) is used in the production of polyurethane foams, elastomers, coatings, adhesives and the like for a wide range of commercial products. Occupational exposure to MDI levels above current airborne exposure limits can elicit immune mediated hypersensitivity reactions such as occupational asthma in sensitive individuals. To accurately determine exposure, there has been increasing interest in developing analytical methods to measure internal biomarkers of exposure to MDI. Previous investigators have reported methodologies for measuring MDI diamine metabolites and MDI-Lysine (4,4′-MDI-Lys) adducts. The purpose of this study was to develop and validate an ultra performance liquid chromatography isotope dilution tandem mass spectrometry (UPLC-ID/MS/MS) quantitation method via a signature peptide approach to enable biomonitoring of 4,4′-MDI adducted to human serum albumin (HSA) in plasma. A murine, anti-4,4′-MDI monoclonal IgM antibody was bound to magnetic beads and utilized for enrichment of the MDI adducted HSA. Following enrichment, trypsin digestion was performed to generate the expected 414 site (primary site of adduction) 4,4′-MDI-adducted HSA signature peptide that was quantified by UPLC-ID/MS/MS. An Agilent 6530 UPLC/quadrupole time of flight MS (QTOF) system was utilized for intact adducted protein analysis and an Agilent 6490 UPLC/MS/MS system operated in multiple reaction monitoring (MRM) mode was utilized for quantification of the adducted signature peptide biomarker both for in chemico and worker serum samples. Worker serum samples were initially screened utilizing the previously developed 4,4′-MDI-Lys amino acid method and results showed that 12 samples were identified as quantifiable for 4,4′-MDI-Lys adducts. The signature peptide adduct approach was applied to the 12 worker samples identified as quantifiable for 4,4′-MDI-Lys adducts. Results indicated no positive results were obtained above the quantification limit by the signature peptide approach. If the 414 site of lysine adduction accounted for 100% of the 4,4′-MDI adductions in the signature peptide adduct approach, the three highest quantifiable samples by the 4,4′-MDI-Lys method should have at least been detectable by the signature peptide method. Results show that although the 4,4′-MDI signature peptide approach is more selective, it is 18 times less sensitive than the 4,4′-MDI-Lys method, thus limiting the ability to detect adduct levels relative to the 4,4′-MDI-Lys amino acid method.

Improving pharmaceutical protein production in Oryza sativa

Application of plant expression systems in the production of recombinant proteins has several advantages, such as low maintenance cost, absence of human pathogens, and possession of complex post-translational glycosylation capabilities. Plants have been successfully used to produce recombinant cytokines, vaccines, antibodies, and other proteins, and rice (Oryza sativa) is a potential plant used as recombinant protein expression system. After successful transformation, transgenic rice cells can be either regenerated into whole plants or grown as cell cultures that can be upscaled into bioreactors. This review summarizes recent advances in the production of different recombinant protein produced in rice and describes their production methods as well as methods to improve protein yield and quality. Glycosylation and its impact in plant development and protein production are discussed, and several methods of improving yield and quality that have not been incorporated in rice expression systems are also proposed. Finally, different bioreactor options are explored and their advantages are analyzed.

Human serum albumin: from bench to bedside

Human serum albumin (HSA), the most abundant protein in plasma, is a monomeric multi-domain macromolecule, representing the main determinant of plasma oncotic pressure and the main modulator of fluid distribution between body compartments. HSA displays an extraordinary ligand binding capacity, providing a depot and carrier for many endogenous and exogenous compounds. Indeed, HSA represents the main carrier for fatty acids, affects pharmacokinetics of many drugs, provides the metabolic modification of some ligands, renders potential toxins harmless, accounts for most of the anti-oxidant capacity of human plasma, and displays (pseudo-)enzymatic properties. HSA is a valuable biomarker of many diseases, including cancer, rheumatoid arthritis, ischemia, post-menopausal obesity, severe acute graft-versus-host disease, and diseases that need monitoring of the glycemic control. Moreover, HSA is widely used clinically to treat several diseases, including hypovolemia, shock, burns, surgical blood loss, trauma, hemorrhage, cardiopulmonary bypass, acute respiratory distress syndrome, hemodialysis, acute liver failure, chronic liver disease, nutrition support, resuscitation, and hypoalbuminemia. Recently, biotechnological applications of HSA, including implantable biomaterials, surgical adhesives and sealants, biochromatography, ligand trapping, and fusion proteins, have been reported. Here, genetic, biochemical, biomedical, and biotechnological aspects of HSA are reviewed.

Improved expression and purification of recombinant human serum albumin from transgenic tobacco suspension culture

Most human serum albumin (HSA) for medical applications is derived from human plasma due to the lack of suitable heterologous expression systems for recombinant HSA (rHSA). To determine whether plant cell cultures could provide an alternative source, we employed the hyper-translatable cowpea mosaic virus protein expression system (CPMV-HT) to stably express rHSA in tobacco Bright Yellow-2 (BY-2) cells. rHSA was stably produced with yield up to 11.88μg/ml in the culture medium, accounting for 0.7% of total soluble protein, in a 25-ml flask. Cultivation of transgenic cells in modified Murashige and Skoog medium with a pH of 8.0 improved the yield of rHSA two-fold, which may be the result of reduced proteolytic activity in the modified medium. A simple purification scheme was developed to purify the rHSA from culture medium, resulting in a recovery of 48.41% of the secreted rHSA. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and N-terminal sequence analysis of the purified rHSA revealed that plant cell-derived rHSA is identical to that of the plasma-derived HSA. Our results show that the CPMV-HT system, which was originally developed as a transient expression system for use in whole plants, can also be used for high-level expression of rHSA, a protein highly susceptible to proteolysis, in transgenic tobacco cells.

Direct observation of covalent adducts with Cys34 of human serum albumin using mass spectrometry

The interactions of the unpaired thiol residue (Cys34) of human serum albumin (HSA) with low-molecular-weight thiols and an Au(I)-based antiarthritic drug have been examined using electrospray ionization mass spectrometry. Early measurements of the amount of HSA containing Cys34 as the free thiol suggested that up to 30% of circulating HSA bound cysteine as a mixed disulfide. It has also been suggested that reaction of HSA with cysteine, occurs only on handling and storage of plasma. In our experiments, there were three components of HSA in freshly collected plasma from normal volunteers, HSA, HSA+cysteine, and HSA+glucose in the ratio approximately 50:25:25. We addressed this controversy by using iodoacetamide to block the free thiol of HSA in fresh plasma, preventing its reaction with plasma cysteine. When iodoacetamide was injected into a vacutaner tube as blood was collected, the HSA was modified by iodoacetamide, with 20-30% present as the mixed disulfide with cysteine (HSA+cys). These data provide strong evidence that 20-30% of HSA in normal plasma contains one bound cysteine. Reaction of HSA with [Au(S(2)O(3))(2)](3-) resulted in formation of the adducts HSA+Au(S(2)O(3)) and HSA+Au. Reaction of HSA with iodoacetamide prior to treatment with [Au(S(2)O(3))(2)](3-) blocked the formation of gold adducts.

Presence of markers for liver progenitor cells in human-derived intrahepatic biliary epithelial cells

AIMS

Rodent intrahepatic bile duct may harbor bipotential liver progenitor cells. In this study, human-derived intrahepatic biliary epithelial cells (BECs) were investigated in terms of whether they have the character of liver progenitor cells.

METHODS

Ten liver tissue specimens were obtained after partial hepatectomy or liver explantation. Intrahepatic BECs were isolated by density-gradient centrifugation and immunomagnetic separation using anti-human epithelial antigen and cultured in medium containing epidermal growth factor and hepatocyte growth factor. The isolated and cultured cells were characterized by immunostaining and reverse transcription polymerase chain reaction with a variety of markers for fetal hepatocytes and liver progenitor cells.

RESULTS

These cells had proliferated for up to 18 weeks in vitro. They continuously expressed epithelial markers (cytokeratin (CK) 8 and CK 18) as well as biliary markers (CK 7 and CK 19). Remarkably, some isolated and cultured cells also expressed markers for fetal hepatocytes and liver progenitor cells, including albumin, alpha-fetoprotein, alpha1-antitrypsin, c-kit and chromogranin-A.

CONCLUSION

Some human-derived intrahepatic BECs coexpressed markers for liver progenitor cells. This finding further supports the hypothesis that the human biliary tree may also consist of liver progenitor cells.

The Human Cytochrome P450 1A1 mRNA Is Rapidly Degraded In HepG2 Cells

The cytochromes P450 are a superfamily of enzymes that can carry out a wide range of oxidative reactions. While the transcriptional control of the cytochrome P450 genes has been relatively well-studied, posttranscriptional regulatory mechanisms that contribute to the regulation of P450s are much less well understood. We followed the decay of CYP1A1, CYP1A2, and CYP1B1 mRNAs after induction by the AH receptor ligand 2,3,7,8,-tetrachlorodibenzo-p-dioxin. CYP1A2 and CYP1B1 mRNAs were long-lived in this cell line (to > 24 h). In contrast, the CYP1A1 mRNA decays remarkably quickly. To determine if this rapid decay was unique to CYP1A1, we assessed the decay of selected human P450 and liver-specific mRNAs in HepG2 cells as a comparison. We analyzed albumin, phosphofructokinase, and GAPDH mRNAs and found that they were long-lived, with half-lives >24 h. We show that CYP2E1 mRNA can be detected in HepG2 cells by RT-PCR and that this mRNA also has a basal half-life of >24 h. Thus the CYP1A1 mRNA with its half-life of 2.4 h was one of the shortest-lived mRNA studied and is the most unstable of the cytochrome P450 mRNAs we have tested. The rapid decay of CYP1A1 mRNA is associated with a rapid loss in poly(A) tail length, suggesting that deadenylation is the first step in the decay pathway. The short half-life appears to be conserved across species, which suggests that this characteristic of the CYP1A1 mRNA is important for its function.

Structural and functional studies of UDP-glucuronosyltransferases

UDP-Glucuronosyltransferases (UGTs) are glycoproteins localized in the endoplasmic reticulum (ER) which catalyze the conjugation of a broad variety of lipophilic aglycon substrates with glucuronic acid using UDP-glucuronic acid (UDP-GIcUA) as the sugar donor. Glucuronidation is a major factor in the elimination of lipophilic compounds from the body. In this review, current information on the substrate specificities of UGT1A and 2B family isoforms is discussed. Recent findings with regard to UGT structure and topology are presented, including a dynamic topological model of UGTs in the ER. Evidence from experiments on UGT interactions with inhibitors directed at specific amino acids, photoaffinity labeling, and analysis of amino acid alignments suggest that UDP-GIcUA interacts with residues in both the N- and C-terminal domains, whereas aglycon binding sites are localized in the N-terminal domain. The amino acids identified so far as crucial for substrate binding and catalysis are arginine, lysine, histidine, proline, and residues containing carboxylic acid. Site-directed mutagenesis experiments are critical for unambiguous identification of the active-site architecture.

Photoaffinity labeling probe for the substrate binding site of human phenol sulfotransferase (SULT1A1): 7-azido-4-methylcoumarin

A novel fluorescent photoactive probe 7-azido-4-methylcoumarin (AzMC) has been characterized for use in photoaffinity labeling of the substrate binding site of human phenol sulfotransferase (SULT1A1 or P-PST-1). For the photoaffinity labeling experiments, SULT1A1 cDNA was expressed in Escherichia coli as a fusion protein to maltose binding protein (MBP) and purified to apparent homogeneity over an amylose column. The maltose moiety was removed by Factor Xa cleavage. Both MBSULT1A1 and SULT1A1 were efficiently photolabeled with AzMC. This labeling was concentration dependent. In the absence of light, AzMC competitively inhibited the sulfation of 4MU catalyzed by SULT1A1 (Ki = 0.47 +/- 0.05 mM). Moreover, enzyme activity toward 2-naphthol was inactivated in a time- and concentration-dependent manner. SULT1A1 inactivation by AzMC was protected by substrate but was not protected by cosubstrate. These results indicate that photoaffinity labeling with AzMC is highly suitable for the identification of the substrate binding site of SULT1A1. Further studies are aimed at identifying which amino acids modified by AzMC are localized in the binding site.

Photoaffinity labeling of the aglycon binding site of the recombinant human liver UDP-glucuronosyltransferase UGT1A6 with 7-azido-4-methylcoumarin

7-Azido-4-methylcoumarin (AzMC) is a fluorescent photoactive compound structurally related to 4-methylumbelliferone (4-MU), a marker substrate of the human liver recombinant UDP-glucuronosyltransferase (UGT) 1A6. AzMC was synthesized and utilized to label the substrate binding site of UGT1A6. AzMC exhibits a fluorescence spectrum with maximum excitation and emission wavelengths of 380 and 442 nm, respectively. Upon irradiation, the probe irreversibly inhibited glucuronidation activity measured with para-nitrophenol (pNP) as substrate and interacted with UGT1A6 according to a saturable process indicative of reversible binding before covalent incorporation of the photoaffinity label. This inhibition was both time and concentration dependent and led to the calculation of an inhibition constant, k(2) = 0.113 mM min(-1), and dissociation constant, K(d) = 2.89 mM, for the reaction. Partial photoinactivation of UGT1A6 with AzMC revealed that the probe decreased the apparent V(max) of the pNP glucuronidation reaction, but not the K(m). Moreover, inhibition was partially prevented by 1-naphthol, a surrogate substrate for the enzyme, or by preincubation with an active-site directed inhibitor, 5'-O-[[(2-decanoylamino-3-phenyl-propyloxycarbonyl)amino]-su lfonyl]-2 ',3'-O-isopropylideneuridine. In contrast, UDP-glucuronic acid (UDP-GlcUA) did not have any protective effect against photoinactivation and AzMC did not affect the photoaffinity labeling of UGT1A6 by 5-[beta-(32)P]N(3)UDP-GlcUA, a photoaffinity analog of UDP-GlcUA. Additionally, in the absence of irradiation, AzMC was found to be a competitive inhibitor of 4MU glucuronidation. Collectively, these results strongly indicate that AzMC specifically binds to the UGT1A6 aglycon binding site. Amino acid alignment of phenol-binding proteins revealed a conserved motif, YXXXKXXPXP. It is possible that this motif is involved in phenol binding to UGT1A6 and other phenol-accepting proteins.

Use of the KlADH4 promoter for ethanol-dependent production of recombinant human serum albumin in Kluyveromyces lactis

KlADH4 is a gene of Kluyveromyces lactis encoding a mitochondrial alcohol dehydrogenase activity which is specifically induced by ethanol. The promoter of this gene was used for the expression of heterologous proteins in K. lactis, a very promising organism which can be used as an alternative host to Saccharomyces cerevisiae due to its good secretory properties. In this paper we report the ethanol-driven expression in K. lactis of the bacterial beta-glucuronidase and of the human serum albumin (HSA) genes under the control of the KlADH4 promoter. In particular, we studied the extracellular production of recombinant HSA (rHSA) with integrative and replicative vectors and obtained a significant increase in the amount of the protein with multicopy vectors, showing that no limitation of KlADH4 trans-acting factors occurred in the cells. By deletion analysis of the promoter, we identified an element (UASE) which is sufficient for the induction of KlADH4 by ethanol and, when inserted in the respective promoters, allows ethanol-dependent activation of other yeast genes, such as PGK and LAC4. We also analyzed the effect of medium composition on cell growth and protein secretion. A clear improvement in the production of the recombinant protein was achieved by shifting from batch cultures (0.3 g/liter) to fed-batch cultures (1 g/liter) with ethanol as the preferred carbon source.

Detection of hepatitis C virus in paraffin-embedded liver biopsies of patients negative for viral RNA in serum

The diagnosis of hepatitis C is based on serological testing for antibodies against various epitopes of the hepatitis C virus (HCV) and detection of HCV RNA in serum, because anti-HCV antibodies alone cannot discriminate patients who are infectious from those who have resolved the infection. If HCV RNA is not detected, which is the case in at least 20% of enzyme immunoassay (EIA)-positive patients, diagnosis remains unclear in a state of disease possibly well suited for therapeutic intervention. Therefore, we investigated if detection of HCV antigens or HCV RNA in routinely processed, formalin-fixed and paraffin-embedded (ffpe) liver biopsy specimens of patients positive for anti-HCV, but negative for HCV RNA in serum, could confirm diagnosis in this serological constellation. We detected HCV RNA by reverse-transcription polymerase chain reaction (RT-PCR) in 27 (61%) of 44 ffpe liver biopsies from EIA-positive, but HCV-RNA-seronegative, patients. Testing of 18 of these biopsies by a panel of polyclonal antibodies against structural and nonstructural HCV proteins revealed positive immunostaining in 6 cases (33%), which were also positive by RT-PCR. Most biopsies showed necroinflammation compatible with chronic hepatitis C, and the detection of tissue HCV RNA correlated significantly with a higher grade of inflammatory activity. Detectability of HCV RNA did not correlate with HCV subtype. In conclusion, the search for HCV RNA by RT-PCR within the liver biopsy specimen can establish rapid and unequivocal diagnosis of hepatitis C in at least 60% of anti-HCV antibody-positive patients who are seronegative for HCV RNA, and thus may help to avoid repeated testing and delayed therapy. Tissue RT-PCR may also be more efficient than serological testing for surveillance of interferon therapy response, because ongoing chronic active hepatitis C is clearly demonstrated in the absence of detectable serum HCV RNA.

Bacterial expression of human vitamin D-binding protein (Gc2) in functional form

In this report, we report the first expression of human vitamin D-binding protein (hDBP), a serum protein with several functions and a multidomained structure, in Escherichia coli. The recombinant protein (reDBP) was expressed as a fusion partner of glutathione S-transferase in order to facilitate proper folding of the reDBP; E. coli-expressed DBP was found to be fully functional with respect to vitamin D sterol binding, interaction with actin, and cross-reactivity with anti-DBP antibody. Furthermore, both natural DBP and reDBP were affinity-labeled with 25-hydroxyvitamin D3-3-bromo[1-14C]acetate in a similar fashion. Availability of an expression system for hDBP in functional form provides opportunity to develop mutants and truncated DBPs to study multiple ligand-binding properties of this protein in relationship with its structure.

Allergic cross-reactions between cat and pig serum albumin. Study at the protein and DNA levels

After observing a patient allergic to cat dander and pork but devoid of other allergies, we prospectively screened patients known to be allergic to cat for a second sensitization to pork. After collecting the sera of 10 young patients found to contain specific IgE to cat dander and pork, we undertook this study to detect the possible cross-reactive allergen, define its molecular characteristics, and evaluate its clinical relevance. Through immunoblotting techniques, cat and porcine serum albumin were found to be jointly recognized molecules. These findings were further analyzed by specific anti-albumin IgE titrations and cross-inhibition experiments. Cat serum albumin cDNA was obtained from cat liver, and the corresponding amino acid sequence was deduced and compared to the known porcine and human serum albumin sequences. Inhibition experiments showed that the spectrum of IgE reactivity to cat serum albumin completely contained IgE reactivity to porcine serum albumin, suggesting that sensitization to cat was the primary event. In two cohorts of cat-allergic persons, the frequency of sensitization to cat serum albumin was found to lie between 14% and 23%. Sensitization to porcine albumin was found to lie between 3% and 10%. About 1/3 of these persons are likely to experience allergic symptoms in relation to pork consumption. Sensitization to cat serum albumin should be considered a useful marker of possible cross-sensitization not only to porcine serum albumin but also to other mammalian serum albumins.

Biochemical characterization of alpha-fetoprotein and other serum proteins produced by a uterine endometrial adenocarcinoma

A high serum alpha-fetoprotein (AFP) level was found in a patient with endometrial adenocarcinoma of the uterus, which appeared to be hepatoid on histological examination. The AFP of this unusual patient was purified by immunoaffinity chromatography and characterized. The electrophoretic profiles on sodium dodecyl sulfate-polyacrylamide get electrophoresis both before and after glycopeptidase F treatment were indistinguishable from those of a hepatoma AFP. This indicates that the patient's AFP was also composed of a single polypeptide chain of Mr 67,000 and an N-linked sugar chain of Mr 3,000. Amino acid sequence analyses of this AFP, and of AFP from hepatoma and umbilical cord serum indicated that the N-terminal sequences were essentially the same. The sequence, Arg-Thr-Leu-His-Arg-Asn-Glu-Tyr-Gly-Ile, was slightly different from previous reports, but matched that deduced from the cDNA sequence. AFP isoforms due to microheterogeneity of the sugar chain were analyzed by lectin affinity electrophoresis using a series of lectins. The AFP isoform profiles were distinct from those of proteins derived from cord serum, hepatoma, yolk sac tumor and gastric cancer. The reverse-transcription of RNA from the tumor tissue followed by a polymerase chain reaction using primers with AFP-specific sequences gave a product of the size and nucleotide sequence expected for AFP. mRNAs possessing the requisite sequences for albumin and transferrin syntheses were also detected in the tumor. The expression of these hepatocyte-specific proteins supported the hepatoid nature of this tumor.

Sequence of the gene encoding cat (Felis domesticus) serum albumin

The complete nucleotide (nt) sequence of the gene encoding cat serum albumin has been determined. The nt and deduced amino-acid sequences were compared to those of other known mammalian serum albumins (SA).

Characterization of cell lines established from human hepatocellular carcinoma

We characterized 8 human hepatocellular-carcinoma cell lines established from the primary tumors of Korean patients. All lines showed substrate adherence and one line from anaplastic tumor also grew as floating aggregates. Most cultured cells maintained many morphological characteristics of the original tumors from which they were derived. Doubling times varied from 34 to 72 hr. All lines showed relatively high viability and were not contaminated with Mycoplasma or bacteria. All lines showed aneuploidy and were proven to be unique by DNA fingerprinting analysis. Hepatitis-B-virus (HBV) DNA was integrated in the genomes of all lines. Two of the cell lines (SNU-354, SNU-368) showed expression of HBV and HBVx (HBx) transcripts. SNU-354 strongly expressed albumin, and SNU-368 expressed transferrin and insulin-like growth factor II. No lines produced alpha-fetoprotein at the RNA and protein level. These cell lines represent useful tools for in vitro studies related to hepatocellular carcinoma.

Nucleotide substitution type dependence of generation time effect of molecular evolution

Using DNA sequence data of 18 genes from 14 mammals, we analyzed how the average molecular evolution rate per year per site (Vy) depends on the generation time (g). (I) Assuming the relation Vy varies; is directly proportional to g(-alpha), the index of generation time effect, (alpha) was estimated to be about 0.14 for amino acid replacement substitutions (A), and about 0.32 for synonymous substitutions (S). (II) Assuming the relation Vy = V(m)g g-1 + V(e)y, where V(m)g and V(e)y are constant independent of g, the fraction, r(e) = V(e)y/Vy, of the mutation rate independent part (V(e)y) in the total evolution rate (Vy) was estimated under the assumptions of the star phylogeny and the constancy of the mutation rate per generation. r(e) was smallest for mouse with the shortest generation time among our analyzed species, and it was estimated to be about 0.57 for A and 0.31 for S. Both results do not support the view that Vy is equal to the neutral mutation rate per site both for A and for S. They are in line with the thesis that, at least for A and probably even for S, the molecular evolution rate is influenced by some causes other than the mutation rate, such as changing environment.

Tryptic peptide mapping of sequence 299-585 of human serum albumin by high-performance liquid chromatography and fast atom bombardment mass spectrometry

The determination of the tryptic peptide mapping of sequence 299-585 (cyanogen bromide fragment A) of human serum albumin (HSA) by chemical and enzymatic cleavages and combined use of HPLC and FAB-MS is described. Reduction and carboxymethylation of A gave four subfragments which were separated by HPLC and digested with trypsin. Tryptic fragments were separated by HPLC and identified by FAB-MS. A total coverage of about 95% of the entire sequence was obtained. Tryptic fragments not identified include mostly single amino acids and very hydrophilic peptides which were absent in the chromatograms. The high reproducibility of the experiments and the satisfactory yield of the tryptic fragments identified demonstrate the great potential of the combined use of HPLC separation and FAB-MS analysis for the structural investigation of HSA.

Correction of the cystic fibrosis defect by gene complementation in human intrahepatic biliary epithelial cell lines

BACKGROUND/AIMS

Hepatobiliary disease is the second most common cause of mortality in patients with cystic fibrosis (CF). In the liver, only the intrahepatic biliary epithelial (IBE) cells express cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. The aim of this study was to determine whether human CF-derived IBE cells can be infected with adenovirus and the CF phenotype complemented.

METHODS

IBE cells were isolated from 2 patients with CF and immortalized using retrovirus transduction of SV40 large T antigen. Immortalized cells were infected with the adenovirus vector Ad2/CFTR2 and assayed 2-31 days postinfection for cyclic adenosine monophosphate (cAMP)-induced halide efflux. Halide efflux was measured in single cells using fluorescence microscopy and the fluorescent probe 6-methoxy-N-(3-sulfopropyl)-quinolinium.

RESULTS

CF-derived IBE cell lines express biliary specific markers and express no cAMP-inducible halide efflux. Following infection with the adenovirus vector Ad2/CFTR2, a cAMP-induced halide efflux was observed for 31 days, although the number of responsive cells decreased with time.

CONCLUSIONS

Human CF-IBE cells can be infected by adenovirus and the defective CFTR complemented. The loss of responsive cells with time could be due to loss of construct and/or a reduced growth of cells that are overexpressing CFTR. These CF-IBE cell lines offer an opportunity to determine the mechanisms responsible for hepatobiliary disease in the patients with CF.

Tryptic peptide mapping of sequence 1-298 of human serum albumin by high-performance liquid chromatography and fast-atom bombardment mass spectrometry

The determination of the tryptic peptide mapping of sequence 1-298 of human serum albumin (HSA) by chemical and enzymatic cleavage and combined use of high-performance liquid chromatography (HPLC) and fast-atom bombardment mass spectrometry (FAB-MS) is described. A total coverage of about 75% of the entire sequence was obtained. Unidentified fragments included some peptides which were not present in the chromatograms because of their extreme hydrophobic or hydrophilic character, as indicated by the calculated retention times. Due to the high reproducibility of the experiments and to the satisfactory yield of the tryptic fragments identified, the combined use of HPLC and FAB-MS appears to possess great potential for structural investigation of HSA.

A nucleotide insertion and frameshift cause analbuminemia in an Italian family

In analbuminemia, a very rare inherited syndrome, subjects produce little or no albumin (1/100th to 1/1000th normal), presumably because of a mutation in the albumin gene; yet, they have only moderate edema and few related symptoms owing to a compensatory increase in other plasma proteins. Because of the virtual absence of albumin the defect must be identified at the DNA level. In this study the mutation causing analbuminemia in an Italian family was investigated by analysis of DNA from a mother and her daughter. The mother was homozygous for the trait and had a serum albumin value of < 0.01 g/dl (about 1/500th normal); the daughter was heterozygous for the trait and had a nearly normal albumin value. Molecular cloning and sequence analysis of DNA from both mother and daughter showed that the mutation is caused by a nucleotide insertion in exon 8; this produces a frameshift leading to a premature stop, seven codons downstream. The methods of heteroduplex hybridization and single-strand conformation polymorphism were used to compare the DNA of the mother and daughter to the DNA of two unrelated analbuminemic individuals (one Italian and one American). This showed that all three analbuminemic individuals had different mutations; these also differed from the mutation in the only human case previously studied at the DNA level, which was a splicing defect affecting the ligation of the exon 6-exon 7 sequences. Thus, analbuminemia may result from a variety of mutations and is genetically heterogeneous.

Molecular characterization of dog albumin as a cross-reactive allergen

Indoor allergens comprise a group of allergenic proteins that are commonly derived from house dust mite and cat and dog dander. In addition to the two major dog allergens (molecular weights: 19 and 23 kd), dog albumin represents an important allergen for up to 35% of patients who are allergic to dogs. In IgE immunoblot inhibition studies and histamine release tests it has been demonstrated that patients who react to dog albumin exhibit IgE reactivity with purified albumins from cat, mouse, chicken, and rat. The proportion of dog-specific IgE directed against dog albumin was determined for patients allergic to dog albumin, and it ranges from 70% to 90%. By IgE immunoscreening of a lambda gt11 expression library from a dog salivary gland, we identified a number of reactive complementary DNA clones. All patients with IgE reactivity against natural dog albumin displayed IgE reactivity to the beta-galactosidase fusion protein encoded by clone 54c, which was therefore assumed to contain major IgE epitopes of dog albumin. The deduced amino acid sequence of clone 54c was compared with the Swiss-Prot library, and significant sequence homologies were found with albumins from different species (human: 82.6%, pig: 81.8%, cattle: 77.3%, sheep: 78.8%, mouse: 75.8%, and rat: 76.2%). Several other IgE-positive clones hybridized with oligonucleotides that were prepared according to this sequence. Partial complementary DNA coding for dog albumin fragments may be considered a useful tool for further characterization of major IgE epitopes of dog albumin.

Homeostatic regulation of hepatocyte nuclear transcription factor 1 expression in cultured hepatoma cells

Serum colloid osmotic pressure is believed to control the hepatic output of plasma proteins, including albumin. The present study was aimed at identifying the molecular basis for feedback control of albumin gene expression in highly differentiated hepatoma cells. The steady-state level of albumin mRNA and the activity of a 282-bp albumin promoter-chloramphenicol acetyltransferase reporter gene in cells incubated in the presence of increasing amounts of serum albumin or dextran were significantly and selectively decreased. When nuclear extracts from cells exposed to 5% (wt/vol) serum albumin were tested in a gel-retardation assay with six oligonucleotide probes containing DNA elements of the albumin promoter, only the element B-retarded band, which contains the nucleotide recognition sequence for hepatocyte nuclear transcription factor 1 alpha (HNF-1 alpha), was consistently decreased as compared to nuclear extract from cells not exposed to serum albumin. Moreover, the activity of a reporter gene with a basal TATA-promoter driven by multiple HNF-1 alpha recognition elements was selectively inhibited in cells incubated in the presence of 5% serum albumin. A reduction of HNF-1 alpha mRNA appears to be responsible for this response to a change in the level of macromolecules in the incubation medium. These results indicate that activity of a dominant liver transcription factor, HNF-1 alpha, controlling the transcription of several liver-specific genes, is modulated by a fluctuation in the level of oncotically active macromolecules.