The structure and expression of very closely related members of the alpha 2u globulin gene family

Isolation and characterization of the genes up-regulated in isolated neurons by aged garlic extract (AGE)

Aged garlic extract (AGE) produces neurotrophic effects on cultured fetal rat hippocampal neurons. These studies examined the molecular events triggered by AGE that might account for a suppression of neuronal cell death. Genes differentially expressed by the addition of AGE in primary cultured hippocampal neurons isolated from fetal rat brain were screened using mRNA differential display. Four cDNA clones were significantly enhanced at their transcriptional level; they were designated as #24, #110, #153 and #155. Quantitative reverse transcription-polymerase chain reaction (RT-PCR), as well as dot-blot hybridization combined with RT-PCR, confirmed that the transcription from these four genes was elevated at least twofold, particularly the mRNA of #153, which was increased >20 times 72 h after the addition of AGE. A homology search of the respective cDNA sequences in the DNA database revealed that #153 is an alpha 2-microglobulin-related protein (alpha 2MRP) gene. The others genes were not identified. Induction of the alpha 2MRP gene expression occurred within 24 h after addition of AGE. These findings suggest a possible mechanism by which AGE may regulate gene expression and bring about a neurotrophic effect. Further, our results suggest that alpha 2MRP may function at the initial step of the molecular events triggered by AGE and play an important role in the survival of hippocampal neurons.

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.

Molecular evidence of complex tissue- and sex-specific mRNA expression of the rat alpha(2u)-globulin multigene family

alpha(2u)-Globulin is well known to be a rat protein encoded by a highly homologous multigene family with more than twenty members. We report here the cloning and identification of major alpha(2u)-globulin mRNA species expressed in various tissues. Initially, eight individual clones (PGCL1-8) were obtained from a male preputial gland cDNA library. Data base analysis with BLAST demonstrated six mRNAs to be novel, all clones being characterized by highly conserved sequence motifs as lipocalins. All cDNAs contained an open reading frame of 543 nucleotides and encode 181 amino acid proteins showing 92.5-98.7% and 87.3-98.3% nucleic and amino acid identity, respectively. Denaturing gradient gel electrophoresis (DGGE) with sequence analysis showed that PGCL4 is a major member in the female mammary gland, and in the submaxillary and lachrymal glands of both sexes, while the counterpart in male liver and the coagulate glands was found to be PGCL1. Numbers of cDNA species including PGCL1 and PGCL4 were found in preputial glands, no sex-related difference being observed. These results directly demonstrate complex tissue- and sex-specific expression of alpha(2u)-globulins in terms of mRNA species, providing useful information for understanding regulation of the alpha(2u)-globulin multigene family.

Methyl tert-butyl ether causes alpha2u-globulin nephropathy and enhanced renal cell proliferation in male Fischer-344 rats

Methyl tert-butyl ether (MTBE), a fuel additive blended into unleaded gasoline to decrease carbon monoxide emissions, induces renal tumors in male, but not female, rats exposed by inhalation to > or =3000 ppm MTBE. A number of chemicals that induce male rat-specific renal tumors also cause a syndrome unique to male rats referred to as alpha2u-globulin nephropathy (alpha2u-N). The objective of the present study was to determine if MTBE induces an alpha2u-N and renal cell proliferation in male F-344 rats. Male and female F-344 rats were exposed to MTBE vapors of 0, 413, 1516, or 3013 ppm for 6 hr/day for 10 consecutive days. Significant proximal tubule necrosis and protein droplet accumulation were observed in kidneys from male rats exposed to 1516 and 3013 ppm MTBE. Significantly greater labeling indices were observed in all groups of MTBE-exposed male rats. alpha2u-Globulin immunoreactivity was present in and confined to protein droplets in male rat kidney. A mild dose-related increase in alpha2u concentration in the kidney, as measured by an enzyme-linked immunosorbent assay, was observed in male rats exposed to MTBE, with a statistically significant increase in alpha2u concentration in male rats exposed to 3013 ppm MTBE. There was a strong positive correlation (r = 0.994) with exposure concentration between cell proliferation and alpha2u concentration in male rat kidney. No significant differences were observed in female rats for any of these responses. Further analysis of kidney cytosol failed to demonstrate the accumulation of any protein besides alpha2u in MTBE-exposed male rat kidney. These findings demonstrate that MTBE causes a mild induction of alpha2u-N and enhanced renal cell proliferation in male, but not female, F-344 rats, suggesting a role for alpha2u-N in renal tumorigenesis.

cDNA cloning and sequencing reveal the major horse allergen Equ c1 to be a glycoprotein member of the lipocalin superfamily

The gene encoding the major horse allergen, designated Equus caballus allergen 1 (Equ c1), was cloned from total cDNA of sublingual salivary glands by reverse transcription-polymerase chain reaction using synthetic degenerate oligonucleotides deduced from N-terminal and internal peptide sequences of the glycosylated hair dandruff protein. A recombinant form of the protein, with a polyhistidine tail, was expressed in Escherichia coli and purified by immobilized metal affinity chromatography. The recombinant protein is able to induce a passive cutaneous anaphylaxis reaction in rat, and it behaves similarly to the native Equ c1 in several immunological tests with allergic patients' IgE antibodies, mouse monoclonal antibodies, or rabbit polyclonal IgG antibodies. Amino acid sequence identity of 49-51% with rodent urinary proteins from mice and rats suggests that Equ c1 is a new member of the lipocalin superfamily of hydrophobic ligand-binding proteins that includes several other major allergens. An RNA blot analysis demonstrates the expression of mRNA Equ c1 in liver and in sublingual and submaxillary salivary glands.

Identification of a new acute phase protein

We have previously reported mouse SIP24 protein as a secreted inducible protein produced by quiescent Balb/c 3T3 cells. SIP24 can be produced in response to many factors, including serum, basic fibroblast growth factor, prostaglandin F2 alpha, phorbol ester, and dexamethasone. Here we present evidence to show that SIP24 is the product of mouse 24P3 mRNA. The 24P3 cDNA was originally cloned from an SV40-transformed quiescent mouse primary kidney cell culture, and it has been classified as a new member of the lipocalin protein family. We show that the SIP24/24P3 protein and mRNA increase dramatically in mouse serum and liver during the acute phase response induced by turpentine injection. Injection of mice with dexamethasone caused a modest increase of SIP24/24P3 mRNA in the liver. Tissue distribution studies revealed that SIP24/24P3 is mainly expressed in liver during the acute phase response. SIP24/24P3 was also detected in the brain and the uterus. In mouse BNL (Balb/c normal liver) cells, the production of SIP24/24P3 is stimulated by tumor necrosis factor alpha, which is a major regulator of the expression of other acute phase proteins. From its pattern of regulation, we conclude that SIP24/24P3 is a new type 1 acute phase protein.

Risk assessment of d-limonene: an example of male rat-specific renal tumorigens

The naturally occurring food constituent d-limonene has been found to cause tumors at high doses only in the kidney of the male rat in association with the development of hyaline droplet nephropathy. In contrast, neither kidney tumors nor the associated nephropathy have been found in female rats or mice at much higher doses. Adult male rats produce large quantities of a specific low-molecular-weight protein in the liver, which is known as alpha 2U-globulin (alpha 2U-g). With administration of sufficient doses of d-limonene to male rats, this protein has been found to accumulate excessively in the P2 segment cells of renal proximal tubules, resulting in hyaline droplet formation as a manifestation of protein overload. Hyaline droplet accumulation is the first stage in a unique sequence of nephropathic lesions (also known as alpha 2U-g nephropathy), including granular casts in the outer medulla and linear mineralization in the papilla. The mechanism underlying protein accumulation appears to be the reversible binding of chemical to alpha 2U-g with subsequent prolongation of its half-life in the tubule cell. In the case of d-limonene, the minor metabolite d-limonene-1,2-oxide has been shown to be the primary chemical species that binds reversibly to alpha 2U-g, impeding the normal process of lysosomal proteinase degradation of alpha 2U-g. The ensuing nephropathy is associated with a sustained increase in compensatory renal tubule cell proliferation, which provides the putative mechanistic link with renal tumor formation possibly through tumor promotion of spontaneously initiated cells or enhanced spontaneous mutagenesis. This proposed mechanism has been supported by additional information, including negative genotoxicity tests for d-limonene and its oxide metabolites, experimentally verified tumor promotion, and enhanced cell proliferation primarily in P2 segment tubule cells in male F344 rats, but no such effects in the alpha 2U-g-deficient NBR rat. The mechanism of d-limonene tumor development does not appear to be possible in humans since neither the quantity nor the type of protein that binds d-limonene or d-limonene-1,2-oxide is present. The deduction that the renal tumors induced in male rats are not relevant to human carcinogenicity in the hazard evaluation step of risk assessment completes the evaluation of human risk for d-limonene. Consequently, it can be concluded that d-limonene does not pose any carcinogenic or nephrotoxic risk to humans.(ABSTRACT TRUNCATED AT 400 WORDS)

Interpretation of male rat renal tubule tumors

Based on an analysis of recent scientific studies, a Technical Panel of the U.S. Environmental Protection Agency's (EPA) Risk Assessment Forum recently advised EPA risk assessors against using information on certain male rat renal tubule tumors to assess human risk under conditions specified in a new Forum report. Risk assessment approaches generally assume that chemicals producing tumors in laboratory animals are a potential cancer hazard to humans. For most chemicals, including classical rodent kidney carcinogens such as N-ethyl-N-hydroxyethylnitrosamine, this extrapolation remains appropriate. Some chemicals, however, induce accumulation of alpha 2u-globulin (alpha 2u-g), a low molecular weight protein, in the male rat kidney. The alpha 2u-g accumulation initiates a sequence of events that appears to lead to renal tubule tumor formation. Female rats and other laboratory mammals administered the same chemicals do not accumulate low molecular weight protein in the kidney, and they do not develop renal tubule tumors. Because humans appear to be more like other laboratory animals than like the male rat, in this special situation, the male rat is not a good model for assessing human risk. The Forum report stresses the need for full scrutiny of a substantial set of data to determine when it is reasonable to presume that renal tumors in male rats are linked to a process involving alpha 2u-g accumulation and to select appropriate procedures for estimating human risks under such circumstances.

Changes in hepatic androgen sensitivity and gene expression during aging

The hepatic tissue of the male rat exhibits a gradual decline and ultimate loss in androgen responsiveness during in vivo aging. Appearance of the age-associated androgen insensitivity can be delayed by dietary calorie restriction, an effective means for life-span extension. The androgen receptor mRNA is detectable in the liver only in its androgen-responsive state. Pubertal appearance of hepatic androgen sensitivity is remarkably correlated with the concomitant appearance of a cytoplasmic androgen binding (CAB) protein. Androgen resistance during senescence is associated with the loss of hepatic CAB activity as well. We are investigating the molecular basis for the temporal modulation of this hormone sensitivity through studies on the differential expression of two androgen-responsive marker genes. These are the androgen-repressible SMP-2, and the androgen-inducible alpha 2u-globulin. Androgen resistance of hepatocytes during aging results in repression of the alpha 2u-globulin gene, and derepression of the SMP-2 gene. The structural organizations for both of these genes have been characterized. The role of nuclear transcription factors (androgen receptor and any other transacting factor(s) which may be involved) in the coordinate regulation of alpha 2u-globulin and SMP-2 during aging and nutritional manipulation is being explored to establish the molecular mechanism of andropause in the liver.

Crystallographic refinement of human serum retinol binding protein at 2A resolution

Human serum retinol binding protein (RBP) in complex with retinol has been crystallographically refined to an R-factor of 18.1% with 2A resolution data. The protein topology results in an anti-parallel beta-barrel that encapsulates the retinol ligand. A detailed description of the protein and the binding site is provided. Our structural work has helped to define a family of proteins, many of which are carrier proteins for smaller ligand molecules. We describe the structural basis for the conservation of sequence within the family.

A LINE 1 sequence interrupts the rat alpha 2u globulin gene

The rat alpha 2u globulin gene family is composed of about 25 members with closely related structure. Several of these genes are transcriptionally active in the liver of adult males. We isolated about 50 independent genomic clones from the library and determined complete nucleotide sequences of two. Although they were alike and revealed structural features prerequisite for active genes, one cloned gene was interrupted in the 6th intron with about 900 bp 5' truncated and 3'-terminal triplicated form of LINE 1 sequence flanked by 16 bp complete direct repeat originating from the 6th intron. Within the inserted LINE 1 an excellent splicing acceptor homologue with a precedent lariat junction motif and multiple polyadenylation signals was identified. Thus, the possible production of a chimeric RNA, the last exon of which would be replaced by a part of LINE 1, has to be considered.

Microanalysis of the amino-acid sequence of monomeric beta-lactoglobulin I from donkey (Equus asinus) milk. The primary structure and its homology with a superfamily of hydrophobic molecule transporters

The complete primary structure of donkey beta-lactoglobulin I was determined by pulsed-liquid phase microsequencing of tryptic peptides. The protein has been isolated in monomeric form and it corresponds to monomeric beta-lactoglobulin of type I. With the inclusion of donkey beta-lactoglobulin I there are 13% common residues amongst the members of the beta-lactoglobulin family. Donkey beta-lactoglobulin I is homologous to the retinol-binding protein, bilin-binding protein and five other proteins belonging to the new superfamily of hydrophobic molecule transporters. A rapid method for peptide isolation and the strategy for microsequencing of this protein have been described.

The rat vitamin-D-dependent calcium-binding protein (9-kDa CaBP) gene. Complete nucleotide sequence and structural organization

The structural organization of the entire rat vitamin-D-dependent calcium-binding protein (9-kDa CaBP) gene was determined by analysis of overlapping genomic clones isolated from a rat genomic library using the rat 9-kDa CaBP cDNA [Desplan C., Heidmann O., Lillie J., Auffray C. and Thomasset M. (1983) J. Biol. Chem. 258, 13502-13505]. These clones together span 30 kbp of rat genomic DNA, with the rat 9-kDa CaBP gene lying in the middle. The 9-kDa CaBP gene is 2.5 kbp long and contains three exons interrupted by two introns. The first exon contains almost the entire 5' untranslated region. The second exon codes for the calcium-binding site I, the third exon codes for site II and the 3' untranslated region. Therefore each of the calcium-binding domains is encoded by single, separate exons. The transcription initiation site was identified by S1 nuclease mapping and primer extension. A consensus sequence TATAAA is localized 31 bp upstream from the cap site and the 'CCAAT-box' lies upstream from the transcription start. Single (AC)25 and (AG)23 repeats are present in the second intron together with an Alu-like sequence. Repetitive elements are present 5 kbp upstream from the cap site and in the 3' flanking region. Comparison of the known rat CaBP sequences (9-kDa CaBP, 28-kDa CaBP, S100 protein) shows that the 9-kDa CaBP is more closely related to the S100 protein than to the 28-kDa CaBP. There is no evidence to indicate that 9-kDa CaBP has arisen from the 28-kDa CaBP.

The pyrazine-binding protein and olfaction

1. The present results provide circumstantial evidence, but not a proof, that the Pyrazine-binding Protein is an odorant carrier molecule of fundamental importance. 2. At first sight a role for a secretory protein in olfaction is not obvious. 3. Odorants freely diffuse in air, in water and in lipids, and the use of carrier proteins, would seem superfluous unless a very special combination with the odorant occurs [Gaupp E. (1902) In Anatomie des Frosches, 2nd Edn, pp. 673. Vieweg-Verlag, Braunschweig]. 4. The possibility should be considered that the Pyrazine-binding Protein and the urinary proteins belong to a large family of species-specific secretory molecules which, with the odorant bound, directly stimulate the receptor cell.

Length polymorphism in the 3' noncoding region of rat hepatic alpha 2u-globulin mRNAs

We detected two size classes in rat liver alpha 2u-globulin mRNAs when analyzing cDNA clones, and named the mRNAs corresponding to the cDNA clones having longer and shorter sizes as L-type and S-type, respectively. When sequencing these cDNA clones, a 25 base insertion was present in the L-type at the 6th exon-intron junction. The extra sequence coincided with the 5' part of the reported 6th intronic sequence that is directly contiguous to the 3' part of the 6th exon. The relative abundance of L- and S-type mRNAs in the steady-state liver was determined by a sensitive S1 nuclease analysis using the probe prepared from the L-type cDNA. The same method was also applied for the determination of the L/S ratios during the course of postnatal development and estrogen treatment, all resulting in similar values, of about 0.03. These findings indicated that L-type and S-type mRNAs are generated by an alternative splicing mechanism in the 3' noncoding region of alpha 2u-globulin transcripts. Sequence analysis also elucidated the presence of at least two active genes showing exactly the same pattern of alternative splicing.

Comparison of the 5' upstream putative regulatory sequences of three members of the alpha 2u-globulin gene family

We have isolated and characterized seven members of the alpha 2u-globulin gene family from a rat genomic library. The 5' upstream region (up to 1250 base pairs starting from the EcoRI site in exon 2) of three clones was sequenced. The major transcriptional start points were located 25 base pairs downstream from the 'TATA' box. A very high degree of homology was observed over the entire studied region. Two of the examined genes displayed structural features which suggest that their expression may be impeded. A high degree of homology was observed between the promotor regions of alpha 2u-globulin and those of the major urinary protein (MUP) multigene family of the mouse. A remarkable feature is the variable length of an A-rich region between the putative 'CAAT' and the 'TATA' consensus sequences. The size of this region differs markedly between MUP and alpha 2u-globulin and between different members of the alpha 2u-globulin gene family. Comparison of the alpha 2u-globulin promotor with the corresponding region of other androgen-dependent genes (the C1, C2 and C3 subunits of prostatic steroid binding protein) reveals the presence of an A-rich region of homology located approximately 378 base pairs upstream from the cap site in the alpha 2u-globulin genes. This region compares well with a sequence of putative enhancer function previously demonstrated in the alpha-fetoprotein promotor and in the immunoglobulin heavy chain promoter.

Homology between the pyrazine-binding protein from nasal mucosa and major urinary proteins

Sequence analysis of the pyrazine-binding protein from bovine olfactory mucosa reveals marked homology with a family of proteins of unknown function found in the urine of the adult male mouse and rat. In view of the dramatic biological responses to odorants transmitted in male rodent urines, it is proposed that these proteins play important roles in some aspects of odor transmission and reception.

Electrophoretic variants of alpha 2u-globulin in the livers of adult male rats: a possible polymorphism

Two-dimensional polyacrylamide gel electrophoresis has been used to examine the microsomal fractions from the livers of 32 adult male Alpk/AP (Wistar-derived) rats for the presence of alpha 2u-globulin variants of differing isoelectric point. Three major such isoelectric variants are described. Different combinations of these three forms were found in the population examined, with one-half of the animals expressing all three variants in approximately equal proportions and with one variant being present in all the animals examined. An understanding of the relevance of such different alpha 2u-globulin profiles to the individual animal must now await the assignment of a biological role for alpha 2u-globulin.

Induction of alpha 2u globulin mRNA by phenobarbital in rat liver: characterization of a cDNA clone

A clone has been selected from a cDNA library previously constructed from phenobarbital pre-treated rat liver polysomal poly(A)+ RNA, which was reverse transcribed. The double-stranded cDNA was inserted by GC homopolymeric tailing in the Pst I site of pAT 153, and further cloned in E. coli HB101. This clone, called 2A9, corresponds to a mRNA whose concentration is increased five fold 16 h after phenobarbital treatment. Its length is 1200 nucleotides as revealed by RNA dot and Northern blot analysis respectively. The two strands of a 450 bp fragment from the 2A9 580 bp double-stranded cDNA insert have been sequenced and proven to correspond to alpha 2u globulin mRNA. It shows one single bp difference from the sequence previously published by Unterman et al. (1981, PNAS, 78, 3478). Thus, alpha 2u globulin, a hormone regulated gene product, is inducible by phenobarbital.

Tissue-specific control of alpha 2u globulin gene expression: constitutive synthesis in the submaxillary gland

Synthesis of alpha 2u globulin, previously thought to occur only in the male rat liver, has now been demonstrated in the submaxillary salivary gland. Unlike liver, submaxillary synthesis of alpha 2u globulin mRNA is constitutive--that is, independent of the endocrine state, age and sex. Liver and submaxillary alpha 2u globulin mRNAs are of similar size, and their 5' ends map to the same region of the gene. Isoelectric focusing of in vitro translation products revealed that submaxillary mRNA encodes a more acidic subset of alpha 2u globulins than does liver. Salivary alpha 2u globulin mRNA manifests 5% nucleotide divergence, encoding 20 amino acid substitutions, which specifies a more acidic polypeptide than its hepatic counterpart. Thus the liver and submaxillary gland synthesize alpha 2u globulin from different sets of genes that are subject to very different developmental and hormonal control.