Primary structure of rabbit lung uteroglobin as deduced from the nucleotide sequence of a cDNA

Double-stranded cDNA was synthesized from partially purified uteroglobin mRNA from rabbit lung. A cDNA coding for lung uteroglobin was then cloned in the plasmid pUC18 and both the nucleotide sequence and the derived amino acid sequence were determined. This allowed us to demonstrate unequivocally that uteroglobins from lung and uterus are identical proteins.     

Hormonal control of uteroglobin secretion in rabbit uterus. Inhibition of uteroglobin synthesis and messenger ribonucleic acid accumulation by oestrogen and anti-oestrogen administration

Investigations were conducted to quantify activity of uteroglobin mRNA and secretion of uteroglobin in rabbit uterus after administration of progesterone and 5alpha-dihydrotestosterone, either alone or concomitantly with oestradiol-17beta and tamoxifen, a non-steroidal anti-oestrogen. Poly(A)-containing mRNA was isolated from the uterine tissue by extraction with phenol/chloroform, precipitation with ethanol and chromatography on oligo(dT)-cellulose. Cell-free translation in vitro of the poly(A)-containing mRNA was carried out in a wheat-germ lysate, and the product isolated by specific immuno-precipitation with anti-uteroglobin antiserum purified by affinity chromatography. Radioimmunoassay was utilized to determine uteroglobin content in the uterine flushings and tissue preparations. When given for 5 days, both progesterone (1mg/kg per day) and 5alpha-dihydrotestosterone (25mg/kg per day) elicited a marked induction of uteroglobin secretion, which was accompanied with accumulation of uteroglobin mRNA in the tissue. Concomitant administration of oestradiol-17beta (50mug/kg per day) or tamoxifen (12.5mg/kg per day) significantly decreased both progesterone- and 5alpha-dihydrotestosterone-induced uteroglobin secretion, with a parallel decrease in the uteroglobin-mRNA activity. The decline in the uteroglobin content of the uterine flushes brought about by oestradiol-17beta or tamoxifen administration was not due to inhibition of secretion of this protein by the endometrial cells, since a simultaneous decrease occurred in the tissue uteroglobin content. After a 5-day pretreatment with progesterone (1mg/kg per day), administration of oestradiol-17beta (50mug/kg per day) during the ensuing 4 days greatly accelerated the decay of the uteroglobin content in the uterine fluid.     

Uteroglobin mRNA from the lung of the hare (Lepus capensis): cell-free translation and properties

Poly(A)-containing RNA was obtained from the lung of hares (Lepus capensis) and uteroglobin mRNA was characterized by cell-free translation and molecular hybridization to a rabbit uteroglobin cDNA probe. In the cell-free system, hare uteroglobin mRNA was preferentially translated as compared to the whole lung mRNA and it directed the synthesis of a precursor, preuteroglobin, containing about twenty additional amino acids. Hare uteroglobin mRNA was about 40 nucleotides larger than the homologous rabbit one, as analyzed by electrophoresis on agarose gel. Thermal stability of the hybrids formed between rabbit or hare uteroglobin mRNAs and the rabbit cDNA probe indicated differences in the nucleotide sequence of both mRNAs. The levels of uteroglobin mRNA and uteroglobin synthesis in lung are about two-fold higher in hare than in rabbit lung.     

Variable expression of the uteroglobin gene following the administration of norethisterone and its A-ring reduced metabolites

Enzyme-mediated A-ring reduction of norethisterone (NET) results in the transformation of a molecule with potent intrinsic progestational activity into neutral derivatives with estrogen-like effects. To ascertain whether these structural modifications of NET are able to modify the uteroglobin (U) gene (G) expression, a series of experiments assessing the UG products after the administration of NET and its reduced A-ring metabolites were conducted in prepubertal female rabbits. Synthesis of endometrial uteroglobin and its specific mRNA were studied in animals following the administration of NET, 5 alpha-dihydro NET,3 beta,5 alpha-tetrahydro NET and progesterone. Animals treated with either estradiol or vehicle alone served as controls. The uteroglobin content in uterine flushings and cytosols was determined by immunodiffusion and polyacrilamide gel electrophoresis techniques and by a specific double-antibody radioimmunoassay, while the U mRNA synthesis was assessed by its molecular hybridization to [alpha 32P]d-ATP uteroglobin cDNA. NET induced a significant increase of the uterine content of uteroglobin similar to that observed with progesterone with a simultaneous increase on U mRNA synthesis. On the contrary, 5 alpha-NET and 3 beta,5 alpha-NET induced very little, if any uteroglobin synthesis with a concomitantly low U mRNA production as compared with NET; thus exhibiting a similar effect to that observed in estradiol-treated animals. The overall results were interpreted as demonstrating that the enzyme mediated structural changes of NET which occur at the target organs induce variable expression of the uteroglobin gene. The data indicate that the rabbit uteroglobin gene products are suitable molecular markers to evaluate the hormonal potency of contraceptive synthetic progestins and their derivatives.     

Tissue-specific expression, hormonal regulation and 5''-flanking gene region of the rat Clara cell 10 kDa protein: comparison to rabbit uteroglobin.

The amino acid sequence of rat Clara Cell 10 kDa secretory protein (CC10) shows 55% identity to rabbit uteroglobin. In order to define the relationship between rat CC10 and rabbit uteroglobin in detail, the tissue-specific expression and hormonal regulation of rat CC10 mRNA was analyzed. We report that like rabbit uteroglobin, rat CC10 mRNA is expressed in lung and esophagus, as well as in uteri of estrogen- and progesterone-treated females. Expression of CC10 mRNA in lung is regulated by glucocorticoids. The similarity in expression pattern of rat CC10 mRNA and rabbit uteroglobin mRNA is reflected by a striking similarity in the 5'-flanking regions of the two genes. Despite this overall similarity, two regions of 0.3 kb and 2.1 kb are absent in the rat CC10 upstream gene region. The larger region includes a cluster of hormone receptor binding sites, believed to be responsible for differential regulation of rabbit uteroglobin by glucocorticoids and progesterone. Thus, while the sequence identities in the coding and 5'-flanking regions point towards a common ancestor for the uteroglobin and CC10 gene, later events (deletions/insertions) might have caused species-specific differences in their regulation.     

Uterine and lung uteroglobins in the rabbit: Two similar proteins with differential hormonal regulation

Previous studies have shown that several rabbit tissues contain proteins which cross-react in the radioimmunoassay for uteroglobin, a progestin-regulated protein in rabbit uterus (Torkkeli et al. (1977) Mol. Cell. Endocrinol. 9, 101–118). In the present study, a uteroglobin-like protein was purified to an apparent homogeneity from an extra-uterine tissue, rabbit lung, by successive chromatographies on hydroxyapatite, Sephadex G-75, SP-Sephadex, DEAE-cellulose and CM-cellulose. The final preparation behaved homogeneously in various polyacrylamide gel electrophoretic systems and in isoelectric focusing. The uteroglobin-like protein isolated from the lung had very similar physico-chemical and immunological properties to those of uteroglobin present in the rabbit uterine fluid. The two proteins had: (i) the same molecular weight, of approx. 13 000, with a two subunit structure (each approx. M_r 7000); (ii) identical behavior in polyacrylamide gel electrophoresis under non-denaturing and denaturing conditions; (iii) the same isoelectric point at pH 5.4; (iv) absence of carbohydrate in the molecule; (v) very similar amino acid compositions; (vi) lack of tryptophan among the amino acids; (vii) the same N-terminal amino acid (glycine), and (viii) indistinguishable immunological characteristics. Collectively, these data strongly suggest that uterine and lung uteroglobins are identical proteins.In contrast to the induction of the uterine uteroglobin by steroids with progestational activity, the synthesis of extra-uterine uteroglobins was not affected by these steroid hormones to any major extent. In keeping with the concept that lung is a target tissue for glucocorticoid action, cortisol and dexamethasone were capable of increasing the concentration of lung uteroglobin 3-fold (from 3 to 9 μg/mg soluble protein). These compounds did not, however, alter the secretion of the uterine protein. Administration of high doses of testosterone and 5α-dihydrotestosterone elevated significantly the content of both uterine and lung uteroglobin. Only approx. one-fifth of the adult pulmonary uteroglobin levels were present in lungs of newborn rabbits indicating that developmental changes occur in the lung uteroglobin content.     

Recombinant rabbit uteroglobin expressed at high levels in E. coli forms stable dimers and binds progesterone

In order to express uteroglobin in Escherichia coli we have constructed a DNA coding for complete mature rabbit uteroglobin by fusing genomic sequences from the second exon of the gene to an incomplete cDNA. This DNA was inserted into various positions of the polylinker cloning region of pDS expression vectors and the uteroglobin gene was expressed in E. coli by IPTG induction. Four different uteroglobin-derived proteins were produced containing 1, 3, 5 and 7 more N-terminal amino acids than the naturally occurring mature protein. The yield of soluble protein strongly increased with increasing length of the N-terminal additions. Protein and RNA analysis showed that this variation is most likely due to progressively higher translation efficiencies of the larger recombinants. UG7, the most efficiently synthesized recombinant protein, carrying seven additional N-terminal amino acids, was purified and further characterized. Like natural uteroglobin, UG7 forms a dimer and binds progesterone with an affinity indistinguishable to the natural protein. This bacterially produced protein can be used for detailed structure-function investigations of uteroglobin.     

Isolation and characterization of uteroglobin from the lung of the hare (Lepus capensis)

Uteroglobin has been purified from hare lung by gel filtration and chromatography on carboxymethyl-cellulose. Hare uteroglobin appears homogeneous by electrophoresis under both denaturing and nondenaturing conditions. Its chemical and immunological properties as well as its ability to bind progesterone are compared to those of rabbit uteroglobin. The two proteins have the same N-terminal residue (glycine) and both lack tryptophan but differ in amino acid composition. Sodium dodecyl sulfate-gel electrophoresis shows that hare uteroglobin is composed of two subunits of identical Mr (about 7000) held together by disulfide bridges. The amino acid composition indicates a subunit composed of 65-67 residues, which is compatible with the apparent Mr observed. Thus, hare uteroglobin appears to be slightly smaller than the rabbit protein. Hare uteroglobin partially reacts with anti-rabbit uteroglobin in a radioimmunoassay and also binds progesterone, although this binding is relatively unaffected by dithiothreitol. The synthesis of hare uteroglobin in the uterus appears to be rather insensitive to ovarian steroid hormones.     

Primary structure and androgen regulation of a 20-kilodalton protein specific to rat ventral prostate

Nuclear and cytosolic forms of a 20-kdalton rat ventral prostate protein were purified and partially sequenced from their N-termini. Isolated nuclei were treated with micrococcal nuclease and extracted in 0.6 M NaCl, and proteins were separated by affinity chromatography on Matrex gel green A, ammonium sulfate fractionation, and fast protein liquid chromatography on Superose 12. The 43 amino acid N-terminal sequence of the nuclear 20-kdalton protein was identical with the cytosolic protein except it lacked 7 N-terminal amino acids present in the cytosolic form. The DNA sequence of a full-length complementary DNA clone isolated from a ventral prostate gt11 library extended the N-terminal sequence of the cytosolic form by an additional nine amino acids from the predicted initiation methionine. The cDNA included the nucleotide sequence for the 43 amino acid N-terminal sequence of the purified 20-kdalton protein and predicted molecular weights of 16,686, 17,521, and 18,650, respectively, for the nuclear, cytoplasmic, and nonprocessed proteins. Northern blot analyses of reproductive tract tissue RNAs using the 20-kdalton protein cDNA as probe revealed a single mRNA species of 0.92 kb detectable only in extracts of rat ventral prostate. Expression of the 0.92-kb mRNA was androgen dependent since the mRNA was undetectable in extracts obtained 4 days after castration and was restored 16 h after restimulation with androgen.     

Prolactin enhances uteroglobin gene expression by uteri of immature rabbits

The effect of prolactin on uteroglobin production by immature rabbits was studied with neonatal (1 day old) and juvenile (14 days old) does. The animals were divided into 11 treatment groups for each age category and exposed to a 9-day injection protocol. Each day the animals received a subcutaneous injection of oestradiol-17 beta and/or ovine prolactin and/or progesterone, or were sham-injected. Juvenile animals, which received 100 micrograms oestradiol/kg 24 h-1, plus progesterone or plus prolactin and progesterone, produced detectable amounts of uteroglobin in the uterine secretions (0.034 +/- 0.010 mg uteroglobin/mg total protein and 0.098 +/- 0.03 l mg uteroglobin/mg total protein, respectively). None of the animals in the other juvenile treatment groups or any of the neonatal groups produced uteroglobin. From this survey it was apparent that uteroglobin secretion could be induced by exogenous oestradiol and progesterone in rabbits treated as early as 14 days of age, and that the added supplementation of prolactin enhanced the response to the ovarian steroids. As a result, additional juvenile animals were injected with 100 micrograms oestradiol +/- prolactin + progesterone and the effects of these two treatments were quantitated as follows: uteroglobin mRNA levels by slot-blot hybridization; endometrial surface area by computerized image analysis; and oestrogen, progesterone and prolactin receptors by immunocytochemistry. Prolactin modified the response of the juvenile rabbit uterus to oestradiol + progesterone for all parameters tested.     

Amino-acid and cDNA nucleotide sequences of human Clara cell 10 kDa protein

A human lung cDNA expression library was screened by using a rabbit antiserum specific for a human Clara cell 10 kDa protein. The cDNA from two positive clones was sequenced by the dideoxy chain termination method. The nucleotide and primary amino-acid sequence deduced therefrom are presented. The N-terminal amino-acid sequence of the Clara cell 10 kDa protein, purified from bronchoalveolar lavage, was also determined. The deduced and experimentally determined sequences were identical where data for both were available. From the amino-acid composition, deduced and experimentally determined amino-acid sequences, it was determined that the 10 kDa protein in bronchoalveolar lavage consists of two identical 70-amino-acid long polypeptide chains joined by two cystine residues. The size of mRNA for the protein was found to be about 0.6 kb and the monomeric nascent protein, obtained by in vitro translation of lung mRNA was about 7.3 kDa in size. The 10 kDa protein recovered from bronchoalveolar lavage has 61% sequence identity with rabbit uteroglobin, the two proteins have common predicted secondary structures with marked surface differences when comparing predicted and actual structure determined by X-ray diffraction. The differences imply similarity of structure but, not identity of function.     

Construction and identification by positive hybridization-translation of a bacterial plasmid containing a rat growth hormone structural gene sequence.

The construction, identification, and use of a recombinant DNA clone containing a growth hormone structural gene sequence is described. A cDNA copy of partially purified pregrowth hormone mRNA from cultured rat pituitary tumor (GC) cells was employed in the construction of a hybrid plasmid, designated pBR322-GH1. The cloned DNA sequence was positively identified by a hybridization-translation procedure which should be applicable to any cloned structural gene sequence. This procedure involved hybridization of cytoplasmic poly(A)-containing RNA from GC cells to the cloned DNA immobilized on nitrocellulose filters, followed by elution of the hybridized RNA and translation in a mRNA-depleted rabbit reticulocyte lysate system. Physical and immunological criteria were employed to show that the translation products were enriched for pregrowth hormone. Hybridization to excess plasmid DNA of [3H]uridine-labeled, size fractionated GC cell cytoplasmic RNA was used to show that all growth hormone-specific RNA sequences are the same size as functional pregrowth hormone mRNA.     

Glucocorticoid and developmental regulation of uteroglobin synthesis in rabbit lung.

The synthesis of uteroglobin in rabbit lung was studied after the administration of glucocorticoids to intact adult animals as well as during the late stages of rabbit development. The synthesis of uteroglobin was compared with levels of translatable uteroglobin mRNA in the lung. Uteroglobin synthesis was determined both by incorporation of [25S]methionine into the protein by lung explants incubated in vitro and by radioimmunoassay measurements of uteroglobin concentration in lung. Lung poly(A)-containing mRNA, isolated by oligo(dT)--cellulose chromatography, was translated in cell-free systems and the activity of uteroglobin mRNA was determined after immunoprecipitation. Dexamethasone administration increased about 2-fold the synthesis of lung uteroglobin compared with the controls. The effect of cortisol was more moderate. Both glucocorticoids did not affect the degradation rate of lung uteroglobin, but produced increases in the translatable levels of uteroglobin mRNA parallel to those observed for uteroglobin synthesis. During the late stages of rabbit development, both the synthesis of lung uteroglobin and the translatable levels of its mRNA increase in parallel about 12-fold in a biphasic fashion. A first increase occurred between 2 days before and 2 days after birth. Starting at 5 days of age, there was a second increase in both parameters, which at 12 days of age reached values close to those observed in adult rabbits. Our results suggest that the rate of lung uteroglobin synthesis could be mainly determined by the translatable levels of its mRNA.     

Partial purification of a binding protein for polychlorinated biphenyls from rat lung cytosol: physicochemical and immunochemical characterization

A binding protein for certain methyl sulfone metabolites of polychlorinated biphenyls (PCB) was partially purified from lung cytosol of untreated female rats. The protein has an Mr of 13,000 and a pI of 5.3 in the absence of reducing agents. In the presence of dithioerythreitol or beta-mercaptoethanol, the protein is split into subunits with a more basic pI. The 13-kDa protein was electroeluted from SDS-polyacrylamide gels, and an antiserum against the protein was raised in rabbit. The immunoglobulin fraction was shown to contain monospecific antibodies against the 13-kDa protein as determined by Western immunoblots. The antibodies retained partially purified binding protein labeled with radioactive ligand when subjected to protein A-Sepharose chromatography and caused a shift in the elution of the labeled protein from Sephadex G-75 and a shift in its sedimentation behavior on sucrose gradients. Due to striking similarities in physicochemical characteristics of the 13-kDa protein and a protein purified from rabbit lung and uterus, uteroglobin, the anti 13-kDa protein antibodies were tested for cross-reactivity. As judged by Western immunoblots, the anti 13-kDa protein antibodies did not cross-react with uteroglobin and the two proteins, although similar, do not seem to be identical. The 13-kDa protein is proposed to be responsible for the accumulation of certain methylsulfonyl-PCBs in lung tissue of rats. Monospecific antibodies against the 13-kDa protein should constitute immunochemical probes of great value in attempts to elucidate the physiological role of the protein as well as its possible role in PCB-induced respiratory toxicity.     

Synthesis and characterization of a DNA complementary to pre-uteroglobin mRNA.

Uteroglobin, a progesterone-induced uterine protein of the rabbit, is synthesized in cell-free systems as a precursor containing 21 additional amino-acids at its N-terminal end. The mRNA for pre-uteroglobin has been purified from the membrane-bound polysomes of induced endometrium and used as template for the synthesis of a full copy complementary DNA. Final purification of the cDNA was based on hybridization to the template mRNA up to a low value of r0t (0.01 M . s) and digestion of the non-hybridized cDNA by S1 nuclease. A comparison of the hybridization kinetics of the pre-uteroglobin cDNA and rabbit globin cDNA to their respective templates indicates a nucleotide sequence complexity of 650 for pre-uteroglobin mRNA, in agreement with the values obtained by sucrose gradient centrifugation and polyacrylamide gel electrophoresis in formamaide. The melting temperature of the hybrids of pre-uteroglobin cDNA to its template reflects the absence of mismatched sequences. This cDNA has been used to quantify pre-uteroglobin mRNA sequences in the endometrial RNA from control animals and from animals treated sequentially with estradiol and progesterone. In agreement with the induction of uteroglobin-synthesizing activity, there is a dramatic increase in the uterine content of pre-uteroglobin mRNA after hormonal treatment. Part of this effect can be accounted for by hormonally induced cell proliferation. When expressed on a DNA basis there is a 50--100-fold increase in the cellular content of pre-uteroglobin mRNA following hormonal treatment.