Alpha fetoprotein and albumin gene transcripts are detected in distinct cell populations of the brain and kidney of the developing rat

Renal type a intercalated cells contain albumin in organelles with aldosterone-regulated abundance

Albumin has been identified in preparations of renal distal tubules and collecting ducts by mass spectrometry. This study aimed to establish whether albumin was a contaminant in those studies or actually present in the tubular cells, and if so, identify the albumin containing cells and commence exploration of the origin of the intracellular albumin. In addition to the expected proximal tubular albumin immunoreactivity, albumin was localized to mouse renal type-A intercalated cells and cells in the interstitium by three anti-albumin antibodies. Albumin did not colocalize with markers for early endosomes (EEA1), late endosomes/lysosomes (cathepsin D) or recycling endosomes (Rab11). Immuno-gold electron microscopy confirmed the presence of albumin-containing large spherical membrane associated bodies in the basal parts of intercalated cells. Message for albumin was detected in mouse renal cortex as well as in a wide variety of other tissues by RT-PCR, but was absent from isolated connecting tubules and cortical collecting ducts. Wild type I MDCK cells showed robust uptake of fluorescein-albumin from the basolateral side but not from the apical side when grown on permeable support. Only a subset of cells with low peanut agglutinin binding took up albumin. Albumin-aldosterone conjugates were also internalized from the basolateral side by MDCK cells. Aldosterone administration for 24 and 48 hours decreased albumin abundance in connecting tubules and cortical collecting ducts from mouse kidneys. We suggest that albumin is produced within the renal interstitium and taken up from the basolateral side by type-A intercalated cells by clathrin and dynamin independent pathways and speculate that the protein might act as a carrier of less water-soluble substances across the renal interstitium from the capillaries to the tubular cells.

T-STAG: resource and web-interface for tissue-specific transcripts and genes

T-STAG (tissue-specific transcripts and genes) is a resource and web-interface, designated to analyze tissue/tumor-specific expression patterns in human and mouse transcriptomes. It integrates our refined prediction of specific expression patterns both in genes as well as in individual isoforms with man–mouse orthology data. In combination with the features for combining/contrasting the genes expressed in different tissues, T-STAG implicates important biological applications, such as the detection of differentially expressed genes in tumors, the retrieval of orthologs with significant expression in the same tissue etc. Additionally, our refined categorization of expressed sequence tags (ESTs) according to the normalization of cDNA libraries allows searching for putative low-abundant transcripts. The results are tightly linked to our visualization tools, GeneNest (expression patterns of genes) and SpliceNest (gene structure and alternative splicing). The user-friendly interface of T-STAG offers a platform for comprehensive analysis of tissue and/or tumor-specific expression patterns revealed by the EST data. T-STAG is freely accessible at .

Cargo from tumor-expressed albumin inhibits T-cell activation and responses

In this study, we show that rodent albumin is expressed by and cell surface localized on at least some murine tumor cells. We have been able to purify this tumor-expressed albumin from in vivo grown tumor masses. The tumor-expressed albumin, unlike normal serum albumin purified from blood, is capable of inhibiting T-cell activation, proliferation, and function in both in vitro and in vivo settings. Tumor-expressed albumin does not appear to affect antigen processing or presentation by professional antigen-presenting cells. The activity appears to lie in relatively small, lipid-like moieties that are presumably cargo for tumor-expressed albumin, and that activity can be removed from the albumin by lipid removal or treatment with lipase. Thus, we herein report of a novel form of tumor-induced immune suppression attributable to lipid-like entities, cloaked by albumin produced by tumors.

Biological roles of alpha-fetoprotein during pregnancy and perinatal development

The use of alpha-fetoprotein (AFP) as a serum marker in cancer actually predates its employment in the detection of congenital defects; however, the latter use of AFP as a fetal defect marker has propelled its clinical utilization. Although the serum-marker capacity of AFP has long been exploited, less is known of the biological activities of this oncofetal protein during fetal and perinatal development. In the present review, the biological activities of AFP are discussed in light of this glycoprotein's presence in various biological fluid compartments: embryonic and fetal tissues, serum, urine, and reproductive fluids. After a review of the histochemical detection of AFP in various cells and tissues during development, AFP concentrations within various biological fluids were discussed in the context of gestational age and anatomic location. Discussion follows concerning the relationships and roles of AFP in developmental events such as erthyropoiesis, histogenesis/organogenesis, and ligand binding and in developmental disorders such as hypothyroidism, folate deficiencies, and acquired immunodeficiency disorder (AIDS). Based on its association with so many types of birth defects, malformations, and congenital anomalies, AFP can be viewed as a molecular "troubleshooter" until signal transduction pathways are established during pregnancy and prenatal development. The review concludes with a discussion of the place of AFP in the rapidly expanding field of proteomics.

Alteration in albumin level during modified muscular activity

We have previously reported that albumin protein is increased in the atrophied muscle induced by hindlimb immobilization. The purpose of this study was to evaluate the effects of several disuse models on albumin protein and mRNA levels in mice skeletal muscle and to investigate whether the elevated amount of albumin returns to control level by muscular activity increased by hindlimb remobilization. Western blot analysis revealed that hindlimb immobilization, denervation, and tenotomy, except for hindlimb unloading, significantly increased albumin levels in soleus muscles by 2.1-, 1.9- and 2.0-fold, respectively (P < 0.001). Immunohistochemical analysis showed that albumin protein accumulates in the widened extracellular space. Reverse transcription-polymerase chain reaction (RT-PCR) assay revealed albumin gene expression to be downregulated in all disuse models relative to control level. During hindlimb remobilization, the amounts of albumin protein appeared to remain higher level after 3 and 7 days and had returned to control level after 14 days and muscle mass, the amounts of myosin heavy chain, and actin proteins seemed to restore control levels after 21 days. These results indicate that the amount of interstitial albumin protein may be modulated by muscular activity.

Initiation of mammalian liver development from endoderm by fibroblast growth factors

The signaling molecules that elicit embryonic induction of the liver from the mammalian gut endoderm or induction of other gut-derived organs are unknown. Close proximity of cardiac mesoderm, which expresses fibroblast growth factors (FGFs) 1, 2, and 8, causes the foregut endoderm to develop into the liver. Treatment of isolated foregut endoderm from mouse embryos with FGF1 or FGF2, but not FGF8, was sufficient to replace cardiac mesoderm as an inducer of the liver gene expression program, the latter being the first step of hepatogenesis. The hepatogenic response was restricted to endoderm tissue, which selectively coexpresses FGF receptors 1 and 4. Further studies with FGFs and their specific inhibitors showed that FGF8 contributes to the morphogenetic outgrowth of the hepatic endoderm. Thus, different FGF signals appear to initiate distinct phases of liver development during mammalian organogenesis.

TGF-beta1 in liver fibrosis: an inducible transgenic mouse model to study liver fibrogenesis

Transforming growth factor-beta1 (TGF-beta1) is a powerful stimulus for collagen formation in vitro. To determine the in vivo effects of TGF-beta1 on liver fibrogenesis, we generated transgenic mice overexpressing a fusion gene [C-reactive protein (CRP)/TGF-beta1] consisting of the cDNA coding for an activated form of TGF-beta1 under the control of the regulatory elements of the inducible human CRP gene promoter. Two transgenic lines were generated with liver-specific overexpression of mature TGF-beta1. After induction of the acute phase response (15 h) with lipopolysaccharide (100 microgram ip), plasma TGF-beta1 levels reached >600 ng/ml in transgenic animals, which is >100 times above normal plasma levels. Basal plasma levels of uninduced transgenic animals were about two to five times above normal. As a consequence of hepatic TGF-beta1 expression, we could demonstrate marked transient upregulation of procollagen I and procollagen III mRNA in the liver 15 h after the peak of TGF-beta1 expression. Liver histology after repeated induction of transgene expression showed an activation of hepatic stellate cells in both transgenic lines. The fibrotic process was characterized by perisinusoidal deposition of collagen in a linear pattern. This transgenic mouse model gives in vivo evidence for the important role of TGF-beta1 in stellate cell activation and liver fibrogenesis. Due to the ability to control the level of TGF-beta1 expression, this model allows the study of the regulation and kinetics of collagen synthesis and fibrolysis as well as the degree of reversibility of liver fibrosis. The CRP/TGF-beta1 transgenic mouse model may finally serve as a model for the testing of antifibrogenic agents.

Albumin gene expression during mouse odontogenesis

Albumin protein is present in developing teeth of several species. Oligomer primers and cRNA probes specific for albumin were designed to perform RT-PCR, and for in situ hybridization, respectively. In situ hybridization failed to reveal albumin expression in any tooth cells, however, albumin PCR products were amplified from tissues adhering to the roots of developing teeth from four-week-old mice. It is concluded that this source is not the primary source of albumin protein found in developing enamel, because of the location and level of expression of albumin mRNA in periodontal tissue.

Expression of serum albumin and of alphafetoprotein in murine normal and neoplastic primitive embryonic structures

Alphafetoprotein (AFP), a major serum protein synthesized during the embryo-fetal and postnatal period (in the yolk sac, then in the liver), is also an oncoprotein. The intracellular presence of AFP and of serum albumin (SA) in normal and neoplastic neural crest and neural tube derivatives was previously demonstrated. In this work we have studied the comparative expression of AFP and SA in primitive neuroectoblastic structures of mouse embryos (6 and 7 days "post coitum") and mouse teratocarcinomas (derived from the PCC4 cell line). Using immunofluorescence technique, antibodies to SA gave a positive reaction in embryos of 7 days, while AFP was not detected during this period. By mRNA in situ hybridization, SA mRNA gave a strong signal in both 6 and 7 day embryos, whereas AFP mRNA gave a weak signal only in 7-day embryos. The distribution of SA and AFP and their mRNAs was investigated in primitive neuroectoblastic structures of the teratocarcinomas by in situ hybridization and immunostaining. Only SA protein was detectable by immunostaining. SA mRNA gave a strong signal in differentiating structures as well as in undifferentiated cell clusters. AFP mRNA was observed only in differentiating structure. Dot-blot hybridization indicated that the level of SA transcripts was at least 6-fold higher than that of AFP transcripts in the teratocarcinomas investigated. In teratocarcinoma-bearing mice injected intraperitoneally with 125I-radiolabeled SA and AFP, significant accumulations of both SA and AFP were demonstrated in the tumors, SA being about 3-fold higher than that of AFP after normalization to quantity of uptake in liver. External in vivo photoscanning confirmed this relationship of accumulated radiolabeled proteins. The last observation could be useful in vivo for diagnosis of teratocarcinoma. We conclude that the expression of SA relative to AFP and the external cellular uptake of SA relative to AFP are similar in normal embryonic developing tissues and in the corresponding morphologically neoplastic tissues of the teratocarcinomas. The same SA:AFP relationship constitutes an oncofetal marker of primitive neuroectoblastic structures.

Age-dependent uptake and retrograde axonal transport of exogenous albumin and transferrin in rat motor neurons

This study presents evidence for retrograde axonal transport of exogenous albumin and transferrin in adult brainstem motor neurons, whereas plasma proteins are not transported in neonatal motor neurons. The plasma protein uptake in motor neurons was dose-dependent, suggesting a nonspecific (fluid-phase) uptake mechanism. Further evidence for nonspecific uptake of exogenous transferrin in the motor neuron was found in the presence of transferrin receptor only on the soma and not on the axon terminal. The immunoreaction product of the exogenous plasma proteins was localized as perinuclear granules in association with the lysosomal system, as verified by staining for the lysosomal marker cathepsin D and by ultrastructural examinations. The results suggest that albumin and transferrin derived from hepatic synthesis gain access to motor neurons nonspecifically by retrograde axonal transport, whereas transferrin derived from intracerebral synthesis specifically gains access to motor neurons due to receptor-mediated uptake at the soma of the neuron. The lack of plasma proteins in developing motor neurons suggests that retrograde axonal transport of plasma proteins has no significance for developing axons. Plasma proteins have a potential for transporting toxic metals to motor neurons. Intraneuronal uptake of aluminum-transferrin either by nonspecific uptake in axon terminals or by receptor-mediated uptake at the soma may have a role in the pathogenesis of the motor neuron disease amyotrophic lateral sclerosis.

Subcutaneous sarcomas of probable neuronal origin in a transgenic mouse strain containing an albumin promoter-fused simian virus 40 large T antigen gene

Frequent development of subcutaneous neurogenic sarcomas was observed in a hepatocellular carcinoma-producing transgenic mouse strain harboring an albumin-promoted simian virus 40 (SV40) large T antigen gene. Found unexpectedly in 19 out of 306 mice (6.2%) by 6 months of age, all the sarcomas were similar and were characterized as neurogenic on the basis of histological features including Homer-Wright type rosette formation, the presence of dense core granules of 100-200 nm diameter under the electron microscope, expression of neuron specific enolase, S-100 protein, and catecholamines, and nerve cell-like differentiation in culture in response to But2cAMP. Immunohistochemical study revealed tiny clusters of SV40 T antigen-expressing cells with neurogenic character in normal-appearing adult mouse subcutis as candidate progenitors of the sarcomas. The tumor cells strongly expressed large T antigen but did not express albumin or albumin mRNA at the detection sensitivity used. Transient transfection assay (CAT assay), however, revealed the presence of transcriptional factor(s) acting on the albumin promoter in tumor cells. Thus, the present investigation suggested the presence of specifically differentiated neurogenic cells in the mouse subcutis with aberrant expression of the transgene.

ATBF1, a multiple-homeodomain zinc finger protein, selectively down-regulates AT-rich elements of the human alpha-fetoprotein gene

ATBF1 is a 306-kDa protein containing four homeodomains, 17 zinc finger motifs, and several segments potentially involved in transcriptional regulation (T. Morinaga, H. Yasuda, T. Hashimoto, K. Higashio, and T. Tamaoki, Mol. Cell. Biol. 11:6041-6049, 1991). At least one of the homeodomains of ATBF1 binds to an AT-rich element in the human alpha-fetoprotein (AFP) enhancer (enhancer AT motif). In the present work, we analyzed the transcriptional regulatory activity of ATBF1 with respect to the enhancer AT motif and similar AT-rich elements in the human AFP promoter and the human albumin promoter and enhancer. Gel retardation assays showed that ATBF1 binds to the AFP enhancer AT motif efficiently; however, it binds weakly or not at all to other AT-rich elements in the AFP and albumin regulatory regions studied. Alterations of the enhancer AT motif by site-specific mutagenesis resulted in the loss of binding of ATBF1. Cotransfection experiments with an ATBF1 expression plasmid and the chloramphenicol acetyltransferase (CAT) gene fused to AFP promoter or enhancer fragments showed that ATBF1 suppressed the activity of AFP enhancer and promoter regions containing AT-rich elements. This suppression was reduced when the mutated AT motifs with low affinity to ATBF1 were linked to the CAT gene. The ATBF1 suppression of AFP promoter and enhancer activities appeared to be due, at least in part, to competition between ATBF1 and HNF1 for the same binding site. In contrast to the AFP promoter and enhancer, the albumin promoter and enhancer were not affected by ATBF1, although they contain homologous AT-rich elements. These results show that ATBF1 is able to distinguish AFP and albumin AT-rich elements, leading to selective suppression of the AFP promoter and enhancer activities.

ATBF1, a multiple-homeodomain zinc finger protein, selectively down-regulates AT-rich elements of the human alpha-fetoprotein gene

ATBF1 is a 306-kDa protein containing four homeodomains, 17 zinc finger motifs, and several segments potentially involved in transcriptional regulation (T. Morinaga, H. Yasuda, T. Hashimoto, K. Higashio, and T. Tamaoki, Mol. Cell. Biol. 11:6041-6049, 1991). At least one of the homeodomains of ATBF1 binds to an AT-rich element in the human alpha-fetoprotein (AFP) enhancer (enhancer AT motif). In the present work, we analyzed the transcriptional regulatory activity of ATBF1 with respect to the enhancer AT motif and similar AT-rich elements in the human AFP promoter and the human albumin promoter and enhancer. Gel retardation assays showed that ATBF1 binds to the AFP enhancer AT motif efficiently; however, it binds weakly or not at all to other AT-rich elements in the AFP and albumin regulatory regions studied. Alterations of the enhancer AT motif by site-specific mutagenesis resulted in the loss of binding of ATBF1. Cotransfection experiments with an ATBF1 expression plasmid and the chloramphenicol acetyltransferase (CAT) gene fused to AFP promoter or enhancer fragments showed that ATBF1 suppressed the activity of AFP enhancer and promoter regions containing AT-rich elements. This suppression was reduced when the mutated AT motifs with low affinity to ATBF1 were linked to the CAT gene. The ATBF1 suppression of AFP promoter and enhancer activities appeared to be due, at least in part, to competition between ATBF1 and HNF1 for the same binding site. In contrast to the AFP promoter and enhancer, the albumin promoter and enhancer were not affected by ATBF1, although they contain homologous AT-rich elements. These results show that ATBF1 is able to distinguish AFP and albumin AT-rich elements, leading to selective suppression of the AFP promoter and enhancer activities.

Odontogenic tumors in mice carrying albumin-myc and albumin-rats transgenes

Odontogenic tumors that produce abnormal tooth-like structures are repeatedly observed in mandibles of mice that carry both albumin-myc and albumin-ras transgenes. The earliest lesions appear among the periodontal ligament mesenchymal cells, but later lesions include an epithelial component. Subsequent tumor development recapitulates the process of normal tooth formation, which requires multiple sequential cell signals, and results in cell differentiation, matrix secretion, and mineralization. Tumor cells with epithelial morphology produce ras oncoprotein, consistent with an epithelial origin of these tumors. As albumin regulatory sequences direct oncogene expression in these mice, our findings also suggest that some of the albumin present in normal teeth may be locally produced and have a role in tooth mineral formation. The reproducibility of this phenotype makes these mice an excellent model for studies of both normal and neoplastic odontogenesis.

Chemistry and biology of alpha-fetoprotein

Alpha-Fetoprotein (AFP) is a product of specific fetal tissues and of neoplastic cells of hepatocyte or germ cell origin in adults. This protein belongs to a gene family that is phylogenetically most closely related to serum albumin. Its primary, secondary, and tertiary structural aspects appear similar to the three-domain concept proposed for the latter protein. The primary sequence of AFP departs most widely from serum albumin in the first 135 amino acid residues, with about 42% of the remaining 590 residues of the human proteins being identical. Some evidence exists that there are limited sequence differences in the AFP of a given animal species. AFP shows considerable charge heterogeneity that appears to relate mostly to its glycoid moiety. The proteins of some species such as the rat show more pronounced heterogeneities than that of humans. The variations in extent and type of glycosylations are evidenced by differences in the binding to various lectins. These interactions are being extensively explored in attempts to differentiate the sources of the protein produced by various normal and neoplastic cells and may provide valuable diagnostic methods. AFP, like serum albumin, shows relatively strong binding affinities for a variety of ligands. The most notable difference is the strong preferential binding of polyunsaturated fatty acids by AFP. This protein may play a role in transporting these substances to developing and to malignant cells. Various agents affect the synthesis of this protein both by specific fetal tissues and by neoplastic cells. Marked differences in the responses of cells, particularly those of neoplastic types, are indicative of variations in the genetic factors responsible for control of its synthesis. The subject of the genomic repression of the synthesis of AFP seen in fetal life upon maturation of the liver and the reoccurrence of synthesis upon malignant conversion of hepatocytes and of certain germ cells are of particular interest. The regulation of the closely related AFP and albumin genes is providing a powerful and attractive model to examine molecular events in the activation and inactivation of specific genes during development and in oncogenic processes. Extensive measurements of AFP during pregnancy and in the course of neoplasias, notably hepatoma, are being made to aid in following changes in such developments. Various specific physiological roles for this protein are also being proposed. One of these is its possible action in the regulation of immune processes.(ABSTRACT TRUNCATED AT 400 WORDS)

Expression patterns of mRNAs for alpha-fetoprotein and albumin in the developing rat: the ontogenesis of hepatocyte heterogeneity

In developing and normal adult rat liver the expression patterns of the mRNAs for alpha-fetoprotein (AFP) and albumin (ALB) were analysed by in situ hybridization using specific 35S-labelled complementary DNA probes. In the developing liver AFP and ALB mRNA are found from embryonic day (ED) 11 and 12, respectively, onward. At ED 20 the first signs of a zonal distribution of these mRNAs across the liver lobule can be observed, AFP mRNA concentration being higher in the pericentral area and ALB mRNA concentration higher in the periportal area. This distribution pattern of reciprocal, overlapping gradients of mRNA can be clearly recognized in the neonatal period. In the adult liver AFP mRNA can no longer be detected and similar to the neonatal situation, ALB mRNA is expressed across the entire porto-central distance decreasing in concentration going from the portal to the central area. Transient extra-hepatic expression of AFP mRNA is found in the embryonic heart and in the epithelial lining of intestine and lung; furthermore, AFP and ALB mRNA are found to be transiently expressed in the developing renal tubules. Similar expression patterns have been observed for other liver-characteristic mRNAs (Moorman et al., 1990), suggesting that common regulatory factors are operative during development.

Atlantic salmon (Salmo salar) serum albumin: cDNA sequence, evolution, and tissue expression

Atlantic salmon serum albumin is one of the most abundant proteins in salmon liver, representing 1.6% of all clones in a cDNA library made from salmon liver RNA. The DNA from a number of clones was sequenced to reveal an open reading frame of 1,827 bases encoding a 608-amino-acid protein. The sequenced 5' untranslated region is 69 bases long and the 3' untranslated region contains two putative polyadenylation signals and poly(A) tail. Sequence analysis of different clones indicates the presence of a second cDNA for salmon serum albumin. Multiple alignments of salmon serum albumin deduced amino acid sequence with Xenopus laevis, rat, bovine, and human serum albumins shows significant conservation of cysteine residues. The triple domain structure of serum albumin proteins is maintained. Unlike mammalian systems where serum albumin expression appears to be specific to liver only, salmon serum albumin is expressed in muscle also.

Expression patterns of mRNAs for ammonia-metabolizing enzymes in the developing rat: the ontogenesis of hepatocyte heterogeneity

The expression patterns of the mRNAs for the ammonia-metabolizing enzymes carbamoylphosphate synthetase (CPS), glutamine synthetase (GS) and glutamate dehydrogenase (GDH) were studied in developing pre- and neonatal rat liver by in situ hybridization. In the period of 11 to 14 embryonic days (ED) the concentrations of GS and GDH mRNA increases rapidly in the liver, whereas a substantial rise of CPS mRNA in the liver does not occur until ED 18. Hepatocyte heterogeneity related to the vascular architecture can first be observed at ED 18 for GS mRNA, at ED 20 for GDH mRNA and three days after birth for CPS mRNA. The adult phenotype is gradually established during the second neonatal week, i.e. GS mRNA becomes confined to a pericentral compartment of one to two hepatocytes thickness, CPS mRNA to a large periportal compartment being no longer expressed in the pericentral compartment and GDH mRNA is expressed over the entire porto-central distance, decreasing in concentration going from central to portal. Comparison of the observed mRNA distribution patterns in the perinatal liver, with published data on the distribution of the respective proteins, points to the occurrence of posttranslational, in addition to pretranslational control mechanisms in the period of ontogenesis of hepatocyte heterogeneity. Interestingly, during development all three mRNAS are expressed outside the liver to a considerable extent and in a highly specific way, indicating that several organs are involved in the developmentally regulated expression of the mRNAs for the ammonia-metabolizing enzymes, that were hitherto not recognized as such.