Primary structure and cellular distribution of two fatty acid-binding proteins in adult rat kidneys

Native Mass Spectrometry Imaging and In Situ Top-Down Identification of Intact Proteins Directly from Tissue

Mass spectrometry imaging (MSI) provides information on the spatial distribution of molecules within a biological substrate without the requirement for labeling. Its broad specificity, i.e., the capability to spatially profile any analyte ion detected, constitutes a major advantage over other imaging techniques. A separate branch of mass spectrometry, native mass spectrometry, provides information relating to protein structure through retention of solution-phase interactions in the gas phase. Integration of MSI and native mass spectrometry ("native MSI") affords opportunities for simultaneous acquisition of spatial and structural information on proteins directly from their physiological environment. Here, we demonstrate significant improvements in native MSI and associated protein identification of intact proteins and protein assemblies in thin sections of rat kidney by use of liquid extraction surface analysis on a state-of-the-art Orbitrap mass spectrometer optimized for intact protein analysis. Proteins of up to 47 kDa, including a trimeric protein complex, were imaged and identified.

A Permeability-Limited Physiologically Based Pharmacokinetic (PBPK) Model for Perfluorooctanoic acid (PFOA) in Male Rats

Physiologically based pharmacokinetic (PBPK) modeling is a powerful in silico tool that can be used to simulate the toxicokinetics and tissue distribution of xenobiotic substances, such as perfluorooctanoic acid (PFOA), in organisms. However, most existing PBPK models have been based on the flow-limited assumption and largely rely on in vivo data for parametrization. In this study, we propose a permeability-limited PBPK model to estimate the toxicokinetics and tissue distribution of PFOA in male rats. Our model considers the cellular uptake and efflux of PFOA via both passive diffusion and transport facilitated by various membrane transporters, association with serum albumin in circulatory and extracellular spaces, and association with intracellular proteins in liver and kidney. Model performance is assessed using seven experimental data sets extracted from three different studies. Comparing model predictions with these experimental data, our model successfully predicts the toxicokinetics and tissue distribution of PFOA in rats following exposure via both IV and oral routes. More importantly, rather than requiring in vivo data fitting, all PFOA-related parameters were obtained from in vitro assays. Our model thus provides an effective framework to test in vitro-in vivo extrapolation and holds great promise for predicting toxicokinetics of per- and polyfluorinated alkyl substances in humans.

The major urinary protein system in the rat

The genomes of rats and mice both contain a cluster of multiple genes that encode small (18–20 kDa) eight-stranded β-barrel lipocalins that are expressed in multiple secretory tissues, some of which enter urine via hepatic biosynthesis. These proteins have been given different names, but are mostly generically referred to as MUPs (major urinary proteins). The mouse MUP cluster is increasingly well understood, and, in particular, a number of roles for MUPs in chemical communication between conspecifics have been established. By contrast, the literature on the rat orthologues is much less well developed and is fragmented. In the present review, we summarize current knowledge on the MUPs from the Norway (or brown) rat, Rattus norvegicus.

Major urinary protein 5, a scent communication protein, is regulated by dietary restriction and subsequent re-feeding in mice

Major urinary proteins (Mups) are important for rodent scent communication and sexual behaviour. Recent evidence suggests that Mup1 may be regulated by fasting and re-feeding (RF). However, other Mup isoforms are poorly investigated, and data on the impact of long-term dietary restriction (DR) and ad libitum RF on Mup expression are missing. We investigated the effects of long-term 25 per cent DR and subsequent RF on Mup expression in male C57BL6 mice. DR significantly decreased Mup gene expression, hepatic and urinary protein levels compared with ad libitum (AL) fed control mice, with the greatest downregulation found for Mup5 expression. The decline in Mup expression was inverted by six months of RF. Because of inhibitory glucocorticoid response elements in the genomic sequence of the Mup5 gene, the observed inverse correlation of nuclear glucocorticoid receptor levels with Mup expression in response to DR and subsequent RF is a possible regulatory mechanism. Additionally, gene-expression-inhibiting histone deacetylation (H3K9) occurred in the region of the Mup5 gene in response to DR. We assume that Mup may act as a molecular switch linking nutritional status to sexual behaviour of mice, and thereby regulating male fertility and reproduction in response to food supply.

Down-regulation of alpha-2u globulin in renal mitochondria of STZ-induced diabetic rats observed by a proteomic method

AIM

To identify the changes of mitochondrial protein expression in diabetic renal parenchyma and to characterize their molecular functions and biological processes in diabetes.

METHODS

Mitochondrial proteins extracted from renal parenchyma mitochondria of streptozotocin-induced diabetic rats and normal rats were separated by two-dimensional polyacrylamide gel electrophoresis and identified by matrix-assisted laser desorption/ionization tandem time-of-flight mass spectrometry.

RESULTS

Eleven proteins from 533 visualized protein spots displayed significant different expressions in mitochondria of diabetic kidneys compared with those in normal ones. Among these altered proteins, two proteins with the most obvious changes in protein expression were identified as alpha-2u globulin (mature protein, named A2) and its proteolytically modified form (named A2-fragment) respectively. These proteins were found in mitochondria of male rat renal parenchyma and were proved to be down-regulated in diabetic rats simultaneously.

CONCLUSION

Our results suggest that down-regulation of alpha-2u globulin may be associated with an abnormal β-oxidation of long-chain fatty acids during diabetes. The decreased expression of A2-fragment in renal mitochondria of diabetic nephropathy may reduce fatty acid β-oxidation, which leads to a diminished energy supply from mitochondria to kidney tissue and the deposition of a large number of fatty acids in the kidney, ultimately causing and aggravating kidney damage. In conclusion, these findings may be helpful for understanding the molecular mechanism of diabetic nephropathy.

Major urinary protein regulation of chemical communication and nutrient metabolism

The major urinary protein (MUP) family members contain a conserved β-barrel structure with a characteristic central hydrophobic pocket. They are secreted by the liver and excreted into the urine. MUPs bind via their central pockets to volatile pheromones or other lipophilic molecules, and regulate pheromone transportation in the circulation, excretion in the kidney, and release into the air from urine marks. MUPs are highly polymorphic, and the MUP profiles in urine function as individual identity signatures of the owners. The MUP signatures are detected by the main and accessory olfactory systems and trigger adaptive behavioral responses and/or developmental processes. Circulating MUPs serve as a metabolic signal to regulate glucose and lipid metabolism. Recombinant MUP1 markedly ameliorates hyperglycemia and glucose intolerance in mice with type 2 diabetes. MUP1 suppresses hepatic gluconeogenesis and promotes energy expenditure in skeletal muscle by stimulating mitochondrial biogenesis and function. MUPs are unique members of the lipocalin superfamily that mediate both chemical and metabolic signaling.

Initial studies of the cytoplasmic FABP superfamily

Our colleagues and we have determined the complete primary structure of a low molecular weight cytoplasmic FABP (also known as z-protein) that binds to LCFAs with high affinities, obtained from rat liver. At the same time, we were the first to propose that rat FABP1, bovine FABP8 (MP-2), bovine CRBP and rat CRABP constituted a protein superfamily in 1982. Since then, extensive investigation of structures, functions and expressions has been carried out on a whole family of FABPs. Analyses of rat heart FABP; FABP1, FABP3 and alpha(2U)-globulin expressed in rat kidney; discovery of ileal FABP6 (I-15P); and first application of FABP2 as a diagnostic marker also stand out in particular.

Cell-specific biomarkers in renal medicine and research

Histopathology is the gold standard for defining renal injury, but it is invasive, time-consuming and expensive, plus it is seldom used in subjects with mild renal injury. Using biomarkers linked to distinct, defined cell types and tissues provides a direct link to histopathology without its drawbacks, plus it provides increased sensitivity, and specificity. The nephron consists of several sections, each with its own specific biomarkers; therefore, by the use of a battery of tests injuries can be localised to distinct areas of it. Using urine samples simplifies repeated sampling from the same subject or animal leading to better defined toxicokinetics and disease monitoring.Serum creatinine is the most widely used renal biomarker in spite of its known shortcomings. Cell-specific biomarkers are more specific and sensitive and have been known for over 40 years, but they are still underused in renal medicine and research. In particular, while many studies have shown cell-specific biomarkers to be valuable in diagnosis, there are few studies where they have been used to guide therapy or linked to quantitative changes in the kidney. Furthermore, the great majority of cell-specific biomarkers are from the proximal tubule, which may have hindered research into the study of conditions where the distal tubules are affected. Recently, the range of biomarkers and their applications has been expanded by the introduction of indicators of cellular regeneration.This chapter will discuss how using biomarkers with a known cellular origin, renal effects may be found earlier and at lower levels of injury. Their use in both renal medicine and drug research will be presented. Knowledge of these existing markers lays the foundation for evaluation, comparison, and characterisation of new markers that will be identified in the future.

Subcellular Distribution and Protein Binding of Perfluorooctanoic Acid in Rat Liver and Kidney

Perfluorooctanoic acid (PFOA) is an organic fluorochemical, and its elimination in rats is markedly sex-dependent. Liver and kidney are two primary tissues of distribution of PFOA in rats. In this study, the subcellular distribution of PFOA in male and female rat liver and kidney was examined. The results demonstrated that PFOA content in the liver cytosol of the female rat was significantly higher (49 +/- 6% of total radioactive residues, TRR) than in the male liver (26 +/- 5% TRR), whereas PFOA distribution in the heavier subcellular fractions, especially the nuclei and cell debris fraction, was marginally higher in male rat liver. In rat kidney, more than 70% of PFOA was distributed in the cytosolic fraction, with no significant difference between sexes. The degree of protein binding of PFOA in rat liver and kidney cytosol was analyzed by two different chromatographic methods. The percentage of protein-bound PFOA in the liver cytosol was found to be approximately 55% in both male and female rats. In contrast, significantly more PFOA was bound to cytosolic proteins in the kidney of male rats (42 +/- 6% TRR) than in females (17 +/- 5% TRR). Ligand blotting analysis revealed that multiple proteins from the liver cytosol, nuclei, and mitochondria fractions were capable of specific binding to PFOA.

Fabp3 as a biomarker of skeletal muscle toxicity in the rat: comparison with conventional biomarkers

Fatty acid binding protein 3 (Fabp3) has been used as a serological biomarker of cardiac injury, but its utility as a preclinical biomarker of injury to skeletal muscle is not well described. Fabp3 concentrations were determined for tissues from Sprague-Dawley rats and found to occur at highest concentrations in cardiac muscle and in skeletal muscles containing an abundance of type I fibers, such as the soleus muscle. Soleus is also a primary site of skeletal muscle (SKM) injury caused by lipid-lowering peroxisome proliferator-activated receptor alpha (PPAR-alpha) agonists. In rats administered repeat doses of a PPAR-alpha agonist, the kinetics and amplitude of plasma concentrations of Fabp3 were consistent with plasma compound concentrations and histopathology findings of swollen, hyalinized, and fragmented muscle fibers with macrophage infiltration. Immunohistochemical detection of Fabp3 revealed focal depletion of Fabp3 protein from injured SKM fibers which is consistent with increased serum Fabp3 concentrations in treated rats. We then assessed the predictivity of serological Fabp3 for SKM necrosis in short duration toxicology studies. Rats were treated with various doses of 27 different compounds, and the predictivity of serological biomarkers was assessed relative to histology in individual rats and in treatment groups. Under these study conditions, Fabp3 was the most useful individual biomarker based on concordance, sensitivity, positive and negative predictive values, and false negative rate. In addition, the combination of Fabp3 and aspartate aminotransferase (AST) had greater diagnostic value than the conventional combination of creatine kinase-MM isoenzyme (CK) and AST.

Studies of the FABP family: a retrospective

Following my research on the role played by soluble proteins in their function as hydrophobic ligand carriers acting through squalene epoxidase, Dr Odani and I started to work together on low molecular lipid binding proteins. As a result of this collaboration, in 1982 we managed to determine the complete primary structure of Z-protein in rat liver. This was the first report ever to give the complete amino acid sequence of a fatty acid binding protein (FABP). This gave momentum to further such research, and now extensive exploration has been carried out on a whole family of homologous intracellular hydrophobic ligand binding proteins, the product of the expression of an ancient gene family in numerous organisms. Takahashi et al. have determined the primary structures of mammalian FABP family protein in liver, intestine, heart, kidney, and skin through amino acid sequencing as well as through determination of the cDNA sequence. Out of all my research on the FABP family, I believe, my initial study on FABP in liver, my work on kidney FABP, heart type FABP and my discovery of an I-15P (BAPB) and I-FABP application as a diagnostic marker stand out in particular.

Binding of perfluorooctanoic acid to rat liver-form and kidney-form alpha2u-globulins

Perfluorooctanoic acid (PFOA) is an organic fluorochemical and is reported to have a long half-life in human blood. Its urinary elimination in rats is markedly sex-dependent, and characterized by significantly longer plasma half-life of PFOA in male rats than in females. It has been postulated that male-specific PFOA binding protein(s) is responsible for the long half-life of PFOA in male rats. In this paper, two male rat specific proteins, liver- and kidney-form alpha2u-globulins (A2U(L) and A2U(K)), were purified from male rat urine and kidney, respectively. The binding of these two nroteins to PFOA was investigated using ligand blotting, electrospray ionization mass spectrometry and fluorescence competitive binding assay. The results revealed that both A2U(L) and A2U(K) were able to bind PFOA in vitro under physiological conditions, and that PFOA and a fluorescent-labeled fatty acid shared the same binding site on both A2U(L) and A2U(K). The binding affinities, however, are relatively weak. The estimated dissociation constants are in the 10(-3) M range, indicating that bindings of PFOA to either A2U(L) or A2U(K) cannot adequately explain the sex-dependent elimination of PFOA in rats, and it is unlikely that PFOA-A2U(K) binding would induce A2U nephropathy as seen with, for example, 1,4-dichlorobenzene.

Expression of heart-type fatty acid-binding protein in human gastric carcinoma and its association with tumor aggressiveness, metastasis and poor prognosis

OBJECTIVE

Fatty acid-binding proteins (FABPs) are involved in lipid metabolism by intracellular transport of long-chain fatty acids. Heart-type (H-) FABP has been reported to inhibit cell growth and induce cell differentiation, but to our knowledge the significance of H-FABP expression in human gastric carcinoma has not been elucidated. The aim of the current study was to examine the expression of H-FABP and its relation to clinicopathologic parameters and fatty acid synthase (FAS) status of gastric carcinoma, since gastric cancer shows increased expression of FAS.

METHODS

Immunohistochemistry with anti-H-FABP antibody was performed in 669 gastric carcinomas and 60 tubular adenomas of the stomach. H-FABP-positive and H-FABP-negative carcinomas were analyzed for their clinicopathologic characteristics and FAS status.

RESULTS

None of the adenomas expressed H-FABP, whereas 127 of 669 carcinomas (19.0%) were positive for the protein. H-FABP positivity was associated with the depth of invasion (p <0.0001), vascular invasion (p <0.0001), lymph node metastasis (p <0.0001), hepatic metastasis (p=0.0011), stage of the carcinoma (p <0.0001) and FAS status of the carcinoma (p=0.0476). A higher survival rate was noted in H-FABP-negative cases compared with H-FABP-positive cases (p=0.0004).

CONCLUSIONS

A subset of human gastric carcinoma expresses H-FABP and its expression is associated with FAS status, disease progression, tumor aggressiveness and poor patient survival.

Major urinary proteins, alpha(2U)-globulins and aphrodisin

The major urinary proteins (MUPs) are proteins secreted by the liver and filtered by the kidneys into the urine of adult male mice and rats, the MUPs of rats being also referred to as alpha(2U)-globulins. The MUP family also comprises closely related proteins excreted by exocrine glands of rodents, independently of their sex. The MUP family is an expression of a multi-gene family. There is complex hormonal and tissue-specific regulation of MUP gene expression. The multi-gene family and its outflow are characterized by a polymorphism which extends over species, strains, sexes, and individuals. There is evidence of evolutionary conservation of the genes and their outflow within the species and evidence of change between species. MUPs share the eight-stranded beta-barrel structure lining a hydrophobic pocket, common to lipocalins. There is also a high degree of structural conservation between mouse and rat MUPs. MUPs bind small natural odorant molecules in the hydrophobic pocket with medium affinity in the 10(4)-10(5) M(-1) range, and are excreted in the field, with bound odorants. The odorants are then released slowly in air giving a long lasting olfactory trace to the spot. MUPs seem to play complex roles in chemosensory signalling among rodents, functioning as odorant carriers as well as proteins that prime endocrine reactions in female conspecifics. Aphrodisin is a lipocalin, found in hamster vaginal discharge, which stimulates male copulatory behaviour. Aphrodisin does not seem to bind odorants and no polymorphism has been shown. Both MUPs and aphrodisin stimulate the vomeronasal organ of conspecifics.

Hepatic alpha 2 mu-globulin localizes to the cytosol of rat proximal tubule cells

BACKGROUND

Alpha 2 mu-Globulin (A2), an 18.6 kD protein of hepatic origin, accumulates in the proximal tubule as an abundant, 15.5 kD cleavage product termed "A2-fragment" (A2-f). A2-f facilitates proximal tubule fatty acid oxidation, presumably by binding hydrophobic ligands. This requires some A2-f to enter the cytosol of the renal epithelial cell (REC). The localization of A2/A2-f in the proximal tubule cell was evaluated in this study.

METHODS

Immunoblot analysis of renal cortical homogenates separated by differential centrifugation and quantitative immunoelectron microscopy (IEM) was performed to localize A2/A2-f using an affinity-purified antibody that detects both proteins. To evaluate A2 as a physiologically relevant ligand, the accumulation of A2-f in the female rat kidney (normally devoid of A2-f) was examined after the induction of hepatic A2 synthesis. Ligand binding, uptake, and degradation assays were used to assess A2 processing by RECs in vitro.

RESULTS

Although A2 and A2-f were detected in the "lysosomal" fraction, only A2-f was found in the soluble protein fraction. IEM confirmed the presence of significant signal in the vesicular and lysosomal as well as the cytosolic compartments. In contrast, both beta 2 mu globulin (B2) and cathepsin B were restricted to endosomes. In the female rat, induction of hepatic A2 production resulted in A2-f accumulation in the renal cortex. In RECs in culture, uptake of A2 and B2 demonstrated nonsaturable, nondisplacable surface binding and similar uptake rates. Compared with B2, A2 was markedly resistant to degradation.

CONCLUSIONS

A fraction of A2 escapes lysosomal degradation, permitting A2-f to accumulate in the cytosol of the proximal tubule epithelial cell. A2 may represent an unusual example of a physiologic protein capable of accumulating in a distant cell type.

Lipid-binding proteins in rat and human kidney

BACKGROUND

The kidney metabolizes actively lipophilic molecules. Several species of lipid-binding proteins (LBPs) have been well characterized, including fatty acid-binding proteins (FABPs), acyl-CoA binding protein (ACBP), sterol carrier protein 2 (SCP2), cellular retinol binding protein (CRBP), and phosphatidylinositol transfer protein (PITP).

METHODS

To clarify which LBPs are expressed in isolated rat glomeruli (RG), cultured rat mesangial cells (RMC) and human kidney, RT-PCR, immunoblot analysis and immunohistochemistry were performed.

RESULTS

Protein and mRNA expression of heart type (H-) FABP was found in RMC, but not in RG. Immunohistochemistry using antihuman H-FABP antibody revealed that an H-FABP like protein was present in the capillary wall and distal tubules of human glomeruli. Immunoblot analysis using the antibody showed that a 110-kDa protein related to H-FABP was present in human isolated glomeruli but not in any other tissues tested including blood, liver, and heart, and that the 14-kDa protein, H-FABP itself was localized in the distal tubules of human kidney. mRNA for SCP2, ACBP and PITP was detected in RG and RMC. CRBP and mRNA was detected in RG but not RMC.

CONCLUSIONS

A variety of lipid-binding proteins are present in rat glomeruli. In human glomeruli, a novel 110-kDa H-FABP-related protein is localized specifically in the capillary wall.

Normal function and lack of fibronectin accumulation in kidneys of Clara cell secretory protein/uteroglobin deficient mice

Clara cell secretory protein (CCSP), also known as uteroglobin (Ug), is a 16-kDa homodimeric protein of unknown function. Within rodent species, CCSP is expressed predominantly by nonciliated Clara cells that line conducting airways of the lung. To investigate in vivo functions for CCSP, we established mice homozygous for a null allele of the CCSP gene (CCSP-/-). We previously showed no overt phenotypic consequences associated with CCSP deficiency when CCSP-/- mice are maintained in the absence of environmental stress. However, CCSP-/- mice show an oxidant-sensitive phenotype that cannot be attributed to alterations in the inflammatory response when challenged by inhaled oxidant gases. The current study was undertaken to determine whether CCSP deficiency results in pathological changes to the kidney. This study was prompted by the recent description of severe systemic disease and kidney fibrosis/dysfunction in an independent line of CCSP-deficient mice, termed Ug-/- (Zhang et al, Science 276:1408-1412, 1997). CCSP-/- mice show normal growth and reproductive performance when maintained in two independent genetic backgrounds, inbred 129 and congenic C57BL/6. Strain 129 CCSP-/- mice have normal kidney function, as assessed by urinary glucose, lactate dehydrogenase, and glomerular filtration rate; they show no kidney fibrosis or abnormalities in fibronectin accumulation and no histological abnormalities in proximal convoluted tubules or glomeruli at either light or electron microscopic levels. CCSP deficiency is associated with mild proteinurea involving a modest increase in mouse major urinary protein-1. We conclude that CCSP (Ug) deficiency, per se, is not the cause of severe renal pathology and systemic disease reported for Ug-/- mice.

Ascorbic acid deficiency decreases the renal level of kidney fatty acid-binding protein by lowering the alpha2u-globulin gene expression in liver in scurvy-prone ODS rats

The evidence for the role of ascorbic acid in gene expression or protein synthesis in vivo is limited. To investigate this role of ascorbic acid, we surveyed proteins whose tissue levels are changed by ascorbic acid deficiency by using ODS rats with a hereditary defect in ascorbic acid biosynthesis. Male ODS rats (7 wk old, body weight approximately 130 g) were fed a basal diet containing ascorbic acid (300 mg/kg diet) or an ascorbic acid-free diet for 14 d. Ascorbic acid deficiency decreased a renal protein with an apparent molecular mass of 17 kDa. The amino-terminal amino acid sequence of 16 residues of this 17-kDa protein was identical to a kidney fatty acid-binding protein known to be generated by proteolytic degradation of alpha2u-globulin, a major urinary protein of adult male rats. alpha2u-Globulin is synthesized in liver, secreted into blood and excreted into urine, but partially reabsorbed by renal proximal tubules. It exists in kidney in a proteolytically modified form. Ascorbic acid deficiency lowered the renal level of kidney fatty acid-binding protein to 53% (P < 0.05) and lowered the serum level of alpha2u-globulin to 52% (P < 0.05) of the level of the control group, but did not affect the amount of alpha2u-globulin excreted into urine. The hepatic level of alpha2u-globulin mRNA of the ascorbic acid-deficient rats was significantly lower (30%) than that of the control rats. These results suggest that in male ODS rats, ascorbic acid deficiency decreases the renal level of kidney fatty acid-binding protein by lowering alpha2u-globulin gene expression in liver.

Purification and identification of allergenic alpha (2u)-globulin species of rat urine

Amino-acid compositional and sequence analyses as well as mass spectrometric determinations of purified rat urine proteins, previously termed prealbumin and alpha(2)-euglobulin, have revealed a high homology between the two forms which have now been identified as alpha(2)-globulin species. The "prealbumin' fraction was found to correspond to alpha(2u)-globulin originating from salivary gland and the 'alpha(2)-euglobulin' fraction was identical with the major urinary protein (MUP) or alpha(2u)-globulin. The results indicate that the two major protein fractions of rat urine constitute different forms of the same parent protein, alpha(2u)-globulin, having no amino-acid sequence resemblance to prealbumin (transthyretin) of rat serum.

Acute nephrotoxicity of a carcinogenic iron chelate. Selective inhibition of a proteolytic conversion of alpha 2U-globulin to the kidney fatty acid-binding protein

The mechanism of acute nephrotoxicity of an iron chelate in vivo has been investigated. Administration of a renal carcinogen ferric nitrilotriacetate (Fe-NTA) (15 mg Fe/kg body weight, intraperitoneally) led to selective loss of a renal protein with an apparent molecular mass of 17 kDa. Analysis of the 17 kDa protein by NH2-terminal sequence demonstrated its identity over 16 NH2-terminal residues as a kidney fatty acid-binding protein (k-FABP) that is a proteolytically modified form of alpha 2U-globulin, a major urinary protein of adult male rats. An immunochemical study using anti-alpha 2U-globulin polyclonal antibodies confirmed that a single injection of Fe-NTA led to a decrease in k-FABP levels. However, a 19-kDa protein identical to the alpha 2U-globulin progressively appeared in the kidney, suggesting that the proteolytic processing of alpha 2U-globulin in the renal proximal tubules was suppressed by the treatment with Fe-NTA. By monitoring k-FABP and its precursor alpha 2U-globulin, it was determined that repeated exposure to Fe-NTA caused suppression of both proteolytic and endocytotic activity of the kidney. The implications of these data in relation to the nephrotoxicity of Fe-NTA are discussed.

The primary structure of a basic (pI 9.0) fatty acid-binding protein from liver of Gallus domesticus

The complete amino acid sequence of a basic (pI 9.0) fatty acid-binding protein purified from liver of Gallus domesticus was determined by automated Edman degradation of tryptic, CNBr/HFBA and Staphylococcus aureus protease peptides. The protein contains 125 amino acid residues which correspond to a molecular mass of 14094. The identification of the blocked N-terminus Ac-Ala required digestion of a SV-8 peptide with the acylamino acid-releasing enzyme prior to sequence analysis. Sequence comparison shows that chicken liver basic-FABP has a significant similarity to other proteins belonging to the superfamily of intracellular lipid molecule binding proteins. Moreover, these sequence data confirm that basic-FABP probably binds its substrate in a slightly different way when compared with other FABPs. Basic-FABP was submitted to the EMBL Data Library with an accession number of P80226.

Characterization and binding properties of human fetal lung fatty acid-binding proteins

When delipidated Mr > 10,000 cut-off human fetal lung cytosol was separated on gel filtration and ion-exchange chromatography on Auto-FPLC system, two fatty acid-binding proteins (FABPs) of pI 6.9 and pI 5.4 were purified to homogeneity. On Western blotting analysis with the anti-human fetal lung pI 6.9 FABP, these two proteins showed immunochemical cross reactivity with each other and with purified hepatic FABPs but not with cardiac or gut FABP. These two FABPs have identical molecular mass of 15.2 kDa, which is slightly higher than that of the hepatic proteins (14.2 kDa). Carbohydrate covalently linked to FABPs, that may substantially add to the molecular mass, was not detected in the purified protein preparations. Amino acid analysis revealed that both the proteins have same amino acid composition each containing one Trp residue that is lacking in hepatic FABP. Different isoforms of lung FABP exhibited different binding ability for their natural ligands. These proteins bind palmitoyl CoA with higher affinity than oleic acid. pI 6.9 FABP can more rapidly and efficiently transfer fatty acid than can pI 5.4 FABP from unilammelar liposomes. Thus these FABPs may play a critical role in fatty acid transport during human fetal lung development.

Hepatic fatty acid-binding protein mRNA is regulated by growth hormone

Hepatic fatty acid-binding protein (FABP) is one of several abundant proteins which may participate in fatty acid uptake and utilization. Using differential hybridization to screen for growth hormone-responsive gene products, a complementary deoxyribonucleic acid (cDNA) was isolated which proved to be a hepatic FABP cDNA fragment. Hypophysectomy caused a 60% reduction in hepatic FABP messenger ribonucleic acid (mRNA) levels in rat liver, and growth hormone administration to hypophysectomized rats resulted in restoration of the expression of hepatic FABP mRNA. Other pituitary hormones did not alter these changes in expression. The response to growth hormone occurred within 4 hours of administration. During development, expression of hepatic FABP mRNA in rat liver was low in late fetal life, with increases to 40% of adult values by day 2 of life. Significant increases to adult levels did not occur until after day 25, when weaning is essentially completed. Alteration of hepatic FABP mRNA expression by growth hormone in rat liver may be important in the complex regulation of fatty acid uptake and metabolism.

Immunohistochemical distribution of heart-type fatty acid-binding protein immunoreactivity in normal human tissues and in acute myocardial infarct

The cellular distribution of heart-type fatty acid-binding protein (H-FABP) immunoreactivity was examined in normal human tissues using a polyclonal antibody against human H-FABP. Immunoreactivity was detected in cardiomyocytes of both ventricles and atria as well as in all striated muscles investigated. In addition, staining was frequently observed in parietal cells of the stomach, renal epithelial cells, acinar and ductal cells of the breast, ductal cells of the salivary gland, corpus luteum, and Leydig cells of the testis. Adipocytes and vascular endothelial cells were positive but other tissues and cells examined were negative. Old infarcts of the heart replaced by fibrous connective tissues were not labelled. Necrotic cardiomyocytes and morphologically normal cardiomyocytes in acute ischaemic lesions 1 h after onset showed reduced or no H-FABP immunoreactivity. Thus, decreased immunoreactivity for H-FABP may be a good histological marker of damaged cardiomyocytes.

Characterization of cardiac fatty-acid-binding protein from human placenta. Comparison with placenta hepatic types

When a 105,000 x g supernatant of human placenta was incubated with [1-14C]oleate and subjected to Sephadex G-75 gel filtration and HPLC, two fatty-acid-binding protein (FABP) peaks were obtained. One of these, when further purified by carboxymethyl-cellulose, gave one 15.3-kDa FABP with pI5.3. The other, when chromatographed on DEAE cellulose, separated into two 14.2-kDa FABP with pI6.9 and 5.4. Purity of the proteins was checked by SDS/PAGE. Molecular mass, pI, immunochemical properties and amino acid compositions all indicated that 15.3-kDa FABP was of the cardiac type, whereas both 14.2-kDa FABP were of the hepatic type. Cardiac FABP did not cross-react with hepatic proteins. When tested for the acceptor/donor properties of these FABP, hepatic types were found to be better candidates than cardiac in uptaking fatty acids from liposomes. Cardiac FABP, on the other hand, acted in a more efficient way as a donor, indicating a distinct role of these proteins in human placenta, which furnishes a multiorgan system for the developing fetus.

Cytoplasmic fatty acid binding protein: significance for intracellular transport of fatty acids and putative role on signal transduction pathways

The cellular transport of long-chain fatty acid moieties is thought to be mediated by a plasmalemmal and a cytoplasmic fatty acid binding protein (FABPPM and FABPC, respectively) and a cytoplasmic acyl-coenzyme A binding protein (ACBP). Their putative main physiological significance is the assurance that long-chain fatty acids and derivatives, either in transit through membranes or present in intracellular compartments, are largely complexed to proteins. FABPC distinguishes from the other proteins in that distinct types of FABPC exist and that these are found in a variety of tissues in remarkable abundance, with some cells containing more than one type In addition, liver type FABPC binds not only fatty acids, but also several other hydrophobic ligands, including heme, bilirubin, prostaglandin E1 and lipoxygenase metabolites of arachidonic acid. Calculations made for rat cardiomyocytes reveal that the presence of FABPC substantially enhances the cytoplasmic solubility as well as the maximal diffusional flux of fatty acids in these cells. Apart from this putative function in the bulk transport of ligands, FABPC may also function in the fine-tuning of cellular events by modulating the metabolism of hydrophobic compounds implicated in the regulation of cell growth and differentiation.

Pheromone binding to two rodent urinary proteins revealed by X-ray crystallography

The principal protein excreted in male rat urine, urinary alpha 2-globulin and the homologous mouse protein, major urinary protein, have been well characterized, although their functions remain unclear. Male rat urine affects the behaviour and sexual response of female rats, leading to the proposal that rodent urinary proteins are responsible for binding pheromones and their subsequent release from drying urine. Urinary alpha 2-globulin is also involved in hyaline droplet nephropathy, an important toxicological syndrome in male rats resulting from exposure to a number of industrial chemicals and characterized by the accumulation of liganded urinary alpha 2-globulin in lysosomes in the kidney, followed by the induction of renal cancer. We now report the three-dimensional structures of mouse major urinary protein (at 2.4 A resolution) and rat urinary alpha 2-globulin (at 2.8 A resolution). The results corroborate the role of these proteins in pheromone transport and elaborate the structural basis of ligand binding.