Comparative sequence analysis of the mRNAs coding for mouse and rat whey protein

The interdependence of mammary-specific super-enhancers and their native promoters facilitates gene activation during pregnancy

Lineage-specific genetic programs rely on cell-restricted super-enhancers, which are platforms for high-density transcription factor occupation. It is not known whether super-enhancers synergize specifically with their native promoters or provide autonomous and independent regulatory platforms. Here, we investigated the ability of the mammary Wap super-enhancer to activate the promoter of the juxtaposed and ubiquitously expressed Tbrg4 gene in the mouse mammary gland. The Wap super-enhancer was fused, alone or in combination with the Wap promoter, to the Tbrg4 gene. While the super-enhancer increased the expression of the Tbrg4 promoter five-fold, the combination of the super-enhancer and promoter resulted in 80-fold gene upregulation, demonstrating lineage-specific promoter-enhancer synergy. Employing ChIP-seq profiling to determine transcription factor binding and identify activating histone marks, we uncovered a chromatin platform that enables the high-level expression of the native promoter-enhancer but not the heterologous promoter. Taken together, our data reveal that lineage-specific enhancer-promoter synergy is critical for mammary gene regulation during pregnancy and lactation.

Establishment of transgenic fibroblasts for producing recombinant human interferon-α and erythropoietin in bovine milk

Human interferon α (IFN-α) and erythropoietin (EPO) have been used for a variety of purposes in clinical medicine. Human IFN-α has been used to treat several types of viral infection and cancer, as well as renal anemia, via stimulation of erythrocyte formation in the bone marrow. Transgenic cattle are excellent candidates for pharmaceutical production for humans due to their ability to produce recombinant proteins in milk. The purpose of the present study was to generate bovine transgenic fibroblasts capable of producing recombinant human IFN-α and EPO proteins in transgenic cattle milk. First, we analyzed the promoter activities of various bovine milk protein genes in HC11 mouse mammary epithelial cells. The bovine milk protein gene promoters were cloned into the Luc gene in a promoter-less pGL3-Basic vector. Presence of the αS1-casein promoter (-175 to +796 nt) resulted in an up to 16-fold increase in luciferase activity compared with that of the promoter-less construct. In addition, the human IFN-α and EPO genes were identified as significantly overexpressed in HC11 cells compared with the promoter-less construct. Together, the present results demonstrate that the construct with the αS1-casein promoter may induce secretion of recombinant human IFN-α and EPO into bovine milk. Furthermore, we generated transgenic fibroblasts expressing human IFN-α and EPO cDNA controlled by the αS1-casein promoter and two screening markers, enhanced green fluorescent protein and neomycin resistance. These transgenic fibroblasts may be a source of somatic cells for generating transgenic cattle that produce recombinant human IFN-α and EPO proteins during lactation.

WFDC1/ps20: a host factor that influences the neutrophil response to murine hepatitis virus (MHV) 1 infection

The whey acidic protein family member, WFDC1/ps20 is a permissivity factor in HIV infection. Herein we describe a contrasting role for ps20 in limiting MHV-1 infection. Intranasal MHV-1 infection produces a respiratory infection in mice. Using ps20 knockout mice we provide evidence that intranasal MHV-1 infection results in increased lung viral titers in ps20^−/− compared to ps20^+/+ mice. Accompanying MHV-1 infection we observe an increase in the number of neutrophils infiltrating the BAL and an increase in the percentage of neutrophils in the lung draining lymph nodes of ps20^−/− compared with ps20^+/+ mice. Gene expression levels for the neutrophil chemoattractants CXCL1 and CXCL2 are elevated in the lungs of ps20^−/− mice post-MHV-1 infection. Characterization of the immune cell profile in naïve ps20^−/− mice revealed an increase in circulating neutrophils compared to ps20^+/+ mice. No notable differences in other immune cell profiles were observed between the ps20^+/+ and ps20^−/− mice. Accordingly, we examined MHV-1 infection of neutrophils and provide evidence that neutrophils isolated from ps20^−/− mice are more susceptible to MHV-1 infection than neutrophils isolated from ps20^+/+ mice. These data suggest roles for ps20 in regulating expression of neutrophil-specific chemotactic factors, thereby potentially modulating neutrophil migration, and in modulating neutrophil susceptibility to MHV-1 infection.

Epigenetic modifications and chromatin loop organization explain the different expression profiles of the Tbrg4, WAP and Ramp3 genes

Whey Acidic Protein (WAP) gene expression is specific to the mammary gland and regulated by lactogenic hormones to peak during lactation. It differs markedly from the more constitutive expression of the two flanking genes, Ramp3 and Tbrg4. Our results show that the tight regulation of WAP gene expression parallels variations in the chromatin structure and DNA methylation profile throughout the Ramp3-WAP-Tbrg4 locus. Three Matrix Attachment Regions (MAR) have been predicted in this locus. Two of them are located between regions exhibiting open and closed chromatin structures in the liver. The third, located around the transcription start site of the Tbrg4 gene, interacts with topoisomerase II in HC11 mouse mammary cells, and in these cells anchors the chromatin loop to the nuclear matrix. Furthermore, if lactogenic hormones are present in these cells, the chromatin loop surrounding the WAP gene is more tightly attached to the nuclear structure, as observed after a high salt treatment of the nuclei and the formation of nuclear halos. Taken together, our results point to a combination of several epigenetic events that may explain the differential expression pattern of the WAP locus in relation to tissue and developmental stages.

Molecular evolution of monotreme and marsupial whey acidic protein genes

Whey acidic protein (WAP), a major whey protein present in milk of a number of mammalian species has characteristic cysteine-rich domains known as four-disulfide cores (4-DSC). Eutherian WAP, expressed in the mammary gland throughout lactation, has two 4-DSC domains, (DI-DII) whereas marsupial WAP, expressed only during mid-late lactation, contains an additional 4-DSC (DIII), and has a DIII-D1-DII configuration. We report the expression and evolution of echidna (Tachyglossus aculeatus) and platypus (Onithorhynchus anatinus) WAP cDNAs. Predicted translation of monotreme cDNAs showed echidna WAP contains two 4-DSC domains corresponding to DIII-DII, whereas platypus WAP contains an additional domain at the C-terminus with homology to DII and has the configuration DIII-DII-DII. Both monotreme WAPs represent new WAP protein configurations. We propose models for evolution of the WAP gene in the mammalian lineage either through exon loss from an ancient ancestor or by rapid evolution via the process of exon shuffling. This evolutionary outcome may reflect differences in lactation strategy between marsupials, monotremes, and eutherians, and give insight to biological function of the gene products. WAP four-disulfide core domain 2 (WFDC2) proteins were also identified in echidna, platypus and tammar wallaby (Macropus eugenii) lactating mammary cells. WFDC2 proteins are secreted proteins not previously associated with lactation. Mammary gland expression of tammar WFDC2 during the course of lactation showed WFDC2 was elevated during pregnancy, reduced in early lactation and absent in mid-late lactation.

Reduction of tumorigenesis and invasion of human breast cancer cells by whey acidic protein (WAP)

Whey acidic protein (WAP) is a major component of whey, which has two or three WAP motif domains characterized by a four-disulfide core (4-DSC) structure similar to the serine protease inhibitor. We have previously found that WAP inhibits the proliferation of mammary epithelial cells in vitro and in vivo [N. Nukumi, K. Ikeda, M. Osawa, T. Iwamori, K. Naito, H. Tojo, Regulatory function of whey acidic protein in the proliferation of mouse mammary epithelial cells in vivo and in vitro, Dev. Biol. 274 (2004) 31-44]. We report herein that WAP also reduces the progression of human breast cancer cells (MCF-7 and MDA-MB-453 cells). We have demonstrated that the forced expression of WAP in MCF-7 cells reduces the proliferation in either the presence or absence of estrogen. The tumor progression of WAP-expressing MCF-7 cells in nude mice is significantly suppressed more than that of mock-MCF-7 cells following the reduced expression of angiopoietin-2 gene. We have confirmed that the invasive activity of breast cancer cells is reduced to approximately 30% of that of mock cells by the forced expression of exogenous WAP through its inhibition of degradation of laminin. These data suggest that WAP has a protease-inhibitory function on the progression of breast cancer cells. It is therefore possible to utilize WAP as therapeutic protein against tumorigenesis of breast cancer.

Characterization of two whey protein genes in the Australian dasyurid marsupial, the stripe-faced dunnart (Sminthopsis macroura)

We report the first isolation and sequencing of genomic BAC clones containing the marsupial milk protein genes Whey Acidic Protein (WAP) and Early Lactation Protein (ELP). The stripe-faced dunnart WAPgene sequence contained five exons, the middle three of which code for the WAPmotifs and four disulphide core domains which characterize WAP. The dunnart ELPgene sequence contained three exons encoding a protein with a Kunitz motif common to serine protease inhibitors. Fluorescence in situ hybridization located the WAPgene to chromosome 1p in the stripe-faced dunnart, and the ELPgene to 2q. Northern blot analysis of lactating mammary tissue of the closely related fat-tailed dunnart has shown asynchronous expression of these milk protein genes. ELPwas expressed at only the earlier phase of lactation and WAPonly at the later phase of lactation, in contrast to beta-lactoglobulin (BLG) and alpha-lactalbumin (ALA) genes, which were expressed in both phases of lactation. This asynchronous expression during the lactation cycle in the fat-tailed dunnart is similar to other marsupials and it probably represents a pattern that is ancestral to Australian marsupials.

A 470 bp WAP-promoter fragment confers lactation independent, progesterone regulated mammary-specific gene expression in transgenic mice

The ability of a 470 bp sub-fragment of the murine whey acidic protein (WAP) promoter in the context of a retroviral expression plasmid to direct gene expression to mammary epithelial cells was analysed in a number of independent transgenic mouse lines. In contrast to previous findings with the genuine 2.5 kb promoter fragment, our studies revealed a highly mammary gland-specific expression detectable only in non-lactating animals. This suggested a mainly progesterone-regulated activity of the short fragment. Therefore, transgene expression was examined in the progesterone-determined estrous cycle and during pregnancy. In accordance with in vitro data from stably transfected cell lines, in both situations expression was upregulated at stages associated with high progesterone levels. Taken together these data provide deeper insight into WAP-promoter regulation and stress the usefulness of the shortened fragment for a lactation independent mammary-targeted expression.

Whey acidic protein (WAP) depresses the proliferation of mouse (MMT) and human (MCF-7) mammary tumor cells

We previously reported that the enforced expression of exogenous whey acidic protein (WAP) significantly inhibited the proliferation of mouse mammary epithelial cells (HC11 and EpH4/H6 cells). This paper presents the first evidence that WAP also depresses the proliferation of mammary tumor cells from mouse (MMT cells) and human (MCF-7 cells). We established WAP-clonal MMT and MCF-7 cell lines, and confirmed the secretion of WAP from the WAP-clonal cells into culture medium. The enforced expression of WAP significantly inhibited the proliferation of MMT and MCF-7 cells in in vitro culture. FACScan analyses revealed that G0/G1 phase cell-cycle progression was disordered and elongated in the WAP-clonal MMT and MCF-7 cells compared to that of the control cells. The expression of cyclin D1 was significantly decreased in the WAP-clonal MMT and MCF-7 cells, suggesting that progression from the G1 to the S phase was delayed in the WAP-clonal cells. The present results indicate that WAP plays a negative regulatory role in the cell-cycle progression of mammary tumor cells via a paracrine mechanism.

Regulatory function of whey acidic protein in the proliferation of mouse mammary epithelial cells in vivo and in vitro

Although possible biological functions of whey acidic protein (WAP) have been suggested, few studies have focused on investigating the function of WAP. This paper describes evidence for WAP function in lobulo-alveolar development in mammary glands in vivo and in the cell cycle progression of mammary epithelial cells in vitro. Ubiquitous overexpression of WAP transgene impaired only lobulo-alveolar development in the mammary glands of transgenic female mice but not other physiological functions, indicating that the inhibitory function of WAP is specific to mammary alveolar cells. The forced expression of WAP significantly inhibited the proliferation of mouse mammary epithelial cells (HC11 cells and EpH4/K6 cells), whereas it did not affect that of NIH3T3 cells. Co-culturing of WAP-clonal cells and control cells using a transwell insert demonstrated that WAP inhibited the proliferation of HC11 cells through a paracrine action but not that of NIH3T3 cells, and that WAP was able to bind to HC11 cells but not to NIH3T3 cells. Apoptosis was not enhanced in the HC11 cells with stable WAP expression (WAP-clonal HC11 cells). BrdU incorporation and FACScan analyses revealed that cell cycle progression from the G0/G1 to the S phase was inhibited in the WAP-clonal HC11 cells. Among G1 cyclins, the expression of cyclin D1 and D3 was significantly decreased in the WAP-clonal HC11 cells. The present results provide the first documented evidence that WAP plays a negative regulatory role in the cell cycle progression of mammary epithelial cells through an autocrine or paracrine mechanism in vivo.

A Novel Protein, Xenopus p20, Influences the Stability of MeCP2 through Direct Interaction

MeCP2 is the founder member of a family of methyl-CpG-binding proteins able to repress transcription from methylated DNA. To date, MeCP2 action seems to involve the delivery on modified DNA of histone deacetylase activity, followed by histone methylating activity. It has been recently demonstrated that MECP2 mutations cause Rett syndrome, a childhood neurological disorder that represents one of the most common causes of mental retardation in females. Here we show that a novel Xenopus laevis protein of 20 kDa, p20, is able to interact in vivo and in vitro with MeCP2. The p20 sequence revealed that it belongs to the family of the WAP (whey acidic protein) proteins, often functioning as a protease inhibitor. Therefore, we asked whether the p20 can influence the MeCP2 half-life. We demonstrate that, indeed, the xp20 not only can significantly increase the stability of an exogenously expressed MeCP2 in Xenopus oocytes but also can stabilize the human endogenous MeCP2. The capability of the mammalian methyl-CpG-binding protein to interact with p20 is confirmed by co-immunoprecipitation experiments performed overexpressing the WAP protein. Glutathione S-transferase pull-down assays reveal that the MeCP2 residues localized between the methyl-binding domain and the transcriptional repression domain is the primary interaction surface. Our data suggest that regulation of MeCP2 metabolism might be of relevant importance; in accordance with this, previous results have shown that some Rett syndrome mutations are characterized by a decrease in MeCP2 stability.

Adolescent vitamin A intake alters susceptibility to mammary carcinogenesis in the Sprague-Dawley rat

We tested the hypothesis that adolescent dietary vitamin A intake impacts mammary gland development and subsequent sensitivity to carcinogenesis. Sprague-Dawley rats were fed a purified diet that was vitamin A deficient, adequate (2.2 mg retinyl palmitate/kg diet), or supranutritional (16 mg retinyl palmitate/kg diet) from 21 to 63 days of age, the period of adolescent mammary gland development. At 73 days of age, rats were given 1-methyl-1-nitrosourea (25 mg/kg body wt i.p.) and monitored for mammary tumors. Tumors appeared earlier and more frequently in rats fed vitamin A-deficient or -supplemented diets. Vitamin A deficiency during adolescence was associated with alveolar mammary gland development and precocious milk protein expression, while supplementation was associated with ductal gland development and suppression of milk protein expression. Differences in circulating estradiol and mammary gland estrogen receptor-alpha, and estrogen-responsive progesterone receptor mRNA were not observed, suggesting that the effects of vitamin A on mammary gland development and carcinogenesis are estrogen independent. Mammary expression of another hormone receptor that regulates milk protein expression, the glucocorticoid receptor, was also unaffected. These results demonstrate that vitamin A intake during adolescence alters mammary gland differentiation and indicate that a narrow range of vitamin A intake during adolescence protects against carcinogenesis.

Novel development of mammary glands in the nursing transgenic mouse ubiquitously expressing WAP gene

Although whey acidic protein (WAP) has been suggested to have some biological functions, its true function has not yet been clearly elucidated. We have generated transgenic mice ubiquitously and highly expressing the WAP gene. The pups born from one female among these transgenic mice showed low growth or died during nursing. This transgenic founder showed novel development of the mammary glands, and demonstrated normal parturition and nursing behavior. The mammary glands showed low-distended ductal structures, and poor development of lobulo-alveolar and acinous formations despite normal nursing, while mammary ducts were rather large in comparison with those of normal lactating females. Although this founder was found to be mosaic for transgenesis, it was shown to be a useful animal model for investigating WAP function.

The comparative biology of whey proteins

Lactational strategies and associated development of the young have been studied in a diverse range of species, and comparative analysis allows common trends and differences to be revealed. The whey fraction contains a vast number of proteins, many of which have not been assigned a function. However, it is expected that an understanding of the comparative biology of these proteins may provide some promise in assigning a function to the major whey proteins. Whey acidic protein is a major component of the whey fraction that has been studied across a range of species, revealing conservation of gene structure, whereas regulation and temporal expression patterns vary. This review focuses primarily on comparative analysis of whey acidic protein, highlighting gene structure, developmental and hormonal regulation, and potential functional roles for this protein. In addition, the contrasting regulation and secretion profiles of several other major whey proteins are discussed.

The murine whey acidic protein promoter directs expression to human mammary tumors after retroviral transduction

The whey acidic protein (WAP) promoter is known to be active in pregnant and lactating mammary epithelial cells as well as mammary tumors of mice. Here we show that a proximal fragment of the murine WAP promoter, including most elements postulated as being responsible for mammary-specific regulation, confers mammary-specific expression upon a marker gene in transgenic mice even though the distal promoter region, known to be important for rat WAP promoter activity, is lacking. The relatively small size of this fragment allows its insertion into a murine leukemia virus-based retroviral vector in place of the viral promoter. Infection of a number of established human mammary and nonmammary cell lines with such a retroviral vector revealed that the WAP promoter was limited in its activity to mammary tumor cell lines. Expression in tumorigenic mammary cells was even more pronounced when these cells were introduced into the mammary fat pads of mice. This is the first demonstration that the WAP promoter is active in human mammary cells and mammary tumor cells in general, and suggests that the extended proximal WAP promoter may be useful for directing therapeutic gene expression to human mammary tumors.

Expression analysis of ruminant α-lactalbumin in transgenic mice: Developmental regulation and general location of importantcis-regulatory elements

The bovine alpha-lactalbumin transgene with 750 bp and 336 bp of the 5' and 3' flanking region, respectively, is developmentally regulated as its endogenous counterpart in transgenic mice. Comparative expression analysis of three 5'-shortened constructs suggests that the region -477/-220 contains important cis-acting transcriptional elements. The level of expression of a long caprine alpha-lactalbumin transgene encompassing 8.5 kb and 9.5 kb of the 5' and 3' flanking region, respectively, was higher but still unrelated to the copy number. Expression of the transgenes and of endogenous milk-protein genes was tissue-specific. In contrast with a recent report, only low amounts of the relevant mRNA were detected in some skin samples, which suggests a possible contamination by mammary tissue.

Differential expression of the whey acidic protein gene during lactation in the brushtail possum (Trichosurus vulpecula)

The whey acidic protein (WAP) is a whey protein found in the milk of a number of species. We have isolated and characterised a WAP cDNA clone from the brushtail possum (Trichosurus vulpecula) and examined its expression in the mammary gland. The amino acid sequences of WAP from the possum and another marsupial, the tammar wallaby, share 69% identity, however, less sequence identity exists between the marsupial and eutherian WAP sequences (30-37%). The possum and tammar WAP genes consist of three four-disulphide core (4-DSC) domains, with a WAP motif at the beginning of each domain. In contrast, the eutherian WAP sequences consist of two 4-DSC domains with the WAP motif only present in the second domain. This WAP motif is also present in a number of protease inhibitors found in a wide range of species. Phylogenetic analysis of marsupial and eutherian WAP sequences suggests that the ancestral WAP gene has three domains and that one of the domains has been deleted from the eutherian gene. The profile of WAP gene expression in the possum mammary gland changed throughout lactation, with WAP mRNA levels reaching a peak between days 106 and 177 of lactation. The level of WAP mRNA in the mammary gland appeared to be correlated with the level of circulating prolactin in the lactating female and was different to that observed for several other whey protein genes. Overlapping expression of the WAP and early lactation protein genes, both of which are putative protease inhibitors, may provide protection of milk immunoglobulins that are required for the prolonged period of passive immune transfer to the marsupial pouch young.

Stat5 phosphorylation status and DNA-binding activity in the bovine and murine mammary glands

The transcription factors Stat5a and Stat5b are mediators of prolactin signalling in mammary epithelial cells, and are thought to play a role in lactogenesis. In cultured cells, activation of Stat5 activity through phosphorylation results in Stat5 binding to the promoters of at least some of the milk protein genes, thereby stimulating their transcription. However, the mammary biology of Stat5 differs between species, and the role of Stat5 in the bovine mammary gland is not fully understood. We have generated an antibody that specifically recognises the phosphorylated forms of Stat5a and Stat5b and used it to compare the levels of phosphorylated Stat5 with Stat5 DNA-binding activity in bovine and murine mammary tissue. Both Stat5 DNA-binding activity and phosphorylation status in the bovine mammary gland were at near-maximal levels at late pregnancy (27-35 days prior to calving), when at least three of the major milk proteins are not highly expressed. In addition, these studies revealed significant animal-to-animal variation in the level of Stat5 activity in both species. The results are consistent with a role in terminal differentiation of mammary epithelial cells. They also suggest that the stimulation of high-level expression of milk protein genes in the bovine mammary gland is not through activation of the prolactin receptor-Jak2-Stat5 pathway.

Regulation of glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1) gene in the mouse mammary gland differs from that of casein genes

Mouse glycosylation-dependent cell adhesion molecule 1 (GlyCAM-1), also known as mC26 and homologous to bovine PP3, is a milk protein synthesized in the mammary gland. Several studies have investigated the regulation of casein, the major milk protein, gene in the mammary gland, but little is known about GlyCAM-1. Here we examined GlyCAM-1 gene expression in mouse mammary epithelial cells. First, we detected GlyCAM-1 expression in mammary epithelial cells in situ by immunohistochemistry; almost all mammary epithelial cells of the lactating mouse expressed GlyCAM-1. Second, mammary epithelial cells were digested with collagenase and cultured with insulin, prolactin and/or glucocorticoid. alpha-Casein and beta-casein genes were expressed following treatment with insulin, prolactin and glucocorticoid. In contrast, GlyCAM-1 expression could not be detected with any combination of these three hormones. We also analyzed changes in the levels of GlyCAM-1 and caseins mRNAs in cultured cells. The addition of hormones to the culture medium increased casein mRNAs, but surprisingly reduced GlyCAM-1 mRNA. Our results suggest that the mechanisms that regulate GlyCAM-1 gene in mammary cells of lactating mice are different from those involved in the regulation of casein genes.

A transgenic mouse model for investigating the response of the upstream region of whey acidic protein (WAP) gene to various steroid hormones

The limitations of studies of clarification of response elements of whey acidic protein (WAP) gene to hormones using mammary cell lines has been shown. We studied the response of the upstream region (2.6 kb) of WAP to various steroid hormones using gonadectomized mWAP/hGH transgenic mice. Ovariectomy or castration for transgenic mice was performed at 10 days or 30 days post partum. Various steroid hormones were administered daily for 10 days to the gonadectomized transgenic mice after they reached 2 months of age. Prior to the hormonal administration and 24 hr after the final administration, blood was collected and the hGH levels in the plasma was measured by RIA. Daily doses of estradiol-17 beta were significantly more effective at increasing hGH levels in transgenic females ovariectomized at 10 days post partum than progesterone of an equal dose. A combined dose of progesterone and of estradiol-17 beta significantly amplified the increase of hGH levels accompanied by the great development of mammary glands, compared to a dose of progesterone alone. Corticosterone induced only a slight increase of hGH, while testosterone had no effect. The doses of gonadal steroid hormones did not induce an increase in hGH levels and development of mammary glands in the castrated transgenic males. The results showed that the response of 5' region of WAP requires at least some extended development of the mammary gland and that the 2.6 kb upstream region of the exogenous WAP gene contained the element responsive to ovarian hormones.

The gene for a novel member of the whey acidic protein family encodes three four-disulfide core domains and is asynchronously expressed during lactation

Secretion of whey acidic protein (WAP) in milk throughout lactation has previously been reported for a limited number of species, including the mouse, rat, rabbit, camel, and pig. We report here the isolation of WAP from the milk of a marsupial, the tammar wallaby (Macropus eugenii). Tammar WAP (tWAP) was isolated by reverse-phase HPLC and migrates in SDS-polyacrylamide gel electrophoresis at 29.9 kDa. tWAP is the major whey protein, but in contrast to eutherians, secretion is asynchronous and occurs only from approximately days 130 through 240 of lactation. The full-length cDNA codes for a mature protein of 191 amino acids, which is comprised of three four-disulfide core domains, contrasting with the two four-disulfide core domain arrangement in all other known WAPs. A three-dimensional model for tWAP has been constructed and suggests that the three domains have little interaction and could function independently. Analysis of the amino acid sequence suggests the protein belongs to a family of protease inhibitors; however, the predicted active site of these domains is dissimilar to the confirmed active site for known protease inhibitors. This suggests that any putative protease ligand may be unique to either the mammary gland, milk, or gut of the pouch young. Examination of the endocrine regulation of the tWAP gene showed consistently that the gene is prolactin-responsive but that the endocrine requirements for induction and maintenance of tWAP gene expression are different during lactation.

Insertion of a casein kinase recognition sequence induces phosphorylation of ovine beta-lactoglobulin in transgenic mice

We have shown that the cellular mechanisms of the mammary gland can be used to produce a phosphorylated form of a normally unphosphorylated milk protein. This was achieved by the insertion of a beta-casein DNA sequence coding for a group of mammary gland casein kinase recognition sites into ovine beta-lactoglobulin. Transgenic mice carrying this modified gene were generated and lactating females were shown to produce a novel beta-lactoglobulin in their milk. The infrared spectrum, reactivity to antiphosphoserine antibody and reduction of electrophoretic mobility on treatment with alkaline phosphatase showed that the novel protein recovered from the milk whey (serum) was phosphorylated and molecular mass determination by mass spectrometry was consistent with the phosphorylation of one or two residues. A similar level of phosphorylation was measured by quantitative infrared spectroscopy. Centrifugation of the milk to pellet the casein micelles showed that most of the phosphorylated beta-lactoglobulin was in the whey and hence not incorporated into casein micelles.

Transgenic animal bioreactors in biotechnology and production of blood proteins

The regulatory elements of genes used to target the tissue-specific expression of heterologous human proteins have been studied in vitro and in transgenic mice. Hybrid genes exhibiting the desired performance have been introduced into large animals. Complex proteins like protein C, factor IX, factor VIII, fibrinogen and hemoglobin, in addition to simpler proteins like alpha 1-antitrypsin, antithrombin III, albumin and tissue plasminogen activator have been produced in transgenic livestock. The amount of functional protein secreted when the transgene is expressed at high levels may be limited by the required posttranslational modifications in host tissues. This can be overcome by engineering the transgenic bioreactor to express the appropriate modifying enzymes. Genetically engineered livestock are thus rapidly becoming a choice for the production of recombinant human blood proteins.

Trout ovulatory proteins are partially responsible for the anti-proteolytic activity found in trout coelomic fluid

After ovulation in salmonids, the eggs are held in the peritoneal cavity and bathed in coelomic fluid. Using a chromogenic peptide substrate, the anti-protease activity of brook trout coelomic fluid was measured. Trypsin, chymotrypsin, and pancreatic elastase activities were significantly inhibited by coelomic fluid containing 5.0, 10.0, and 25.0 microgram of total protein, respectively. Using subtractive cDNA cloning, we have previously characterized a set of ovarian proteins called TOPs (trout ovulatory proteins) that are secreted into the coelomic fluid after ovulation. TOPs are most homologous to mammalian antileukoprotease, a heat- and acid-stable serine protease inhibitor. On the basis of this homology, we hypothesized that the anti-trypsin activity observed in the coelomic fluid was related to the presence of TOPs. In the present study, this hypothesis was supported by the acid- and heat-stability of the anti-trypsin activity present in coelomic fluid. Coelomic fluid could be heated to 50 degrees C or treated at a pH less than 5.2 without a significant decrease in the inhibitory activity. Further, coelomic fluid from which TOPs were immunoprecipitated had significantly less anti-trypsin activity than nonimmunoprecipitated controls. We propose that TOP proteins are uniquely produced by the ovary and secreted into the coelomic fluid to act as protease inhibitors following ovulation.

Genomic organization of the 3'-region of the human MUC5AC mucin gene: additional evidence for a common ancestral gene for the 11p15.5 mucin gene family

The human mucin gene MUC5AC is mapped clustered with MUC2, MUC5B and MUC6 on chromosome 11p15.5. We report here the isolation and characterization of a genomic cosmid clone, designated ELO9, spanning the 3'-region of MUC5AC and the 5'-region of MUC5B, allowing us to conclude that MUC5AC and MUC5B have the same transcriptional orientation. We determined the genomic organization and the entire sequence of the 3'-region of MUC5AC. The comparative molecular analysis of MUC5AC and MUC5B points to a remarkable similarity in the size and the distribution of exons, and in the type of splice sites, supporting the notion that MUC5AC and MUC5B have evolved from a single common ancestral gene. The derivation of the four genes of the 11p15.5 mucin gene family from a single ancestral gene is discussed.

Computer analysis of distribution of putative cis- and trans-regulatory elements in milk protein gene promoters

Multiple alignment of 28 milk protein gene promoters belonging to seven protein superfamilies is described. In these gene promoters three groups of common motifs were found: group I--specific for all milk protein gene promoters; group II--specific only for one gene superfamily; and group III--motifs shared by several gene superfamilies. Motifs of group I and III do not have any preferential location in the promoters, while group II motifs are located in the proximal part, from -36 to -224. Milk protein gene promoters were analysed for presence of putative binding sites for nine transcription factors important for the expression of this group of genes. The transcription factor binding sites for C/EBP, CTF/NF1, MAF and MGF were found in all promoters investigated. The set of putative transcription factor binding sites or response elements for GRE, IRE, PMF, STR and YY1 is unique for every gene superfamily.

Molecular cloning and characterization of lustrin A, a matrix protein from shell and pearl nacre of Haliotis rufescens

A specialized extracellular matrix of proteins and polysaccharides controls the morphology and packing of calcium carbonate crystals and becomes occluded within the mineralized composite during formation of the molluscan shell and pearl. We have cloned and characterized the cDNA coding for Lustrin A, a newly described matrix protein from the nacreous layer of the shell and pearl produced by the abalone, Haliotis rufescens, a marine gastropod mollusc. The full-length cDNA is 4,439 base pairs (bp) long and contains an open reading frame coding for 1,428 amino acids. The deduced amino acid sequence reveals a highly modular structure with a high proportion of Ser (16%), Pro (14%), Gly (13%), and Cys (9%). The protein contains ten highly conserved cysteine-rich domains interspersed by eight proline-rich domains; a glycine- and serine-rich domain lies between the two cysteine-rich domains nearest the C terminus, and these are followed by a basic domain and a C-terminal domain that is highly similar to known protease inhibitors. The glycine- and serine-rich domain and at least one of the proline-rich domains show sequence similarity to proteins of two extracellular matrix superfamilies (one of which also is involved in the mineralized matrixes of bone, dentin, and avian eggshell). The arrangement of alternating cysteine-rich domains and proline-rich domains is strikingly similar to that found in frustulins, the proteins that are integral to the silicified cell wall of diatoms. Its modular structure suggests that Lustrin A is a multifunctional protein, whereas the occurrence of related sequences suggest it is a member of a multiprotein family.

Developing a mammary gland is a stat affair

The mammary gland is a recent acquisition on the phylogenetic scale of organ evolution and is characterized by an unparalleled regenerative capacity. With each pregnancy an expanded lobulo-alveolar compartment rises on the ductal compartment and differentiates to secrete large amounts of milk during lactation. After weaning of the young the entire alveolar compartment undergoes apoptosis and is remodeled to return to a virgin-like state. Evolution recruited old hands from existing signaling pathways to guide and accomplish the extraordinary task of repeatedly building and destroying this highly specialized tissue. Seventy years ago it was known that the presence of estrogen, progesterone, and prolactin (PRL) was essential for ductal and alveolar development. The recent ability to generate mice from which genes have been deleted by homologous recombination has made it possible to gain molecular insight into the signaling pathways used by these hormones to effect mammary differentiation. In the cast of characters progesterone and PRL are on center stage. After binding to its receptor, PRL activates the JAK-STAT pathway leading to transcription of genes which induce alveolar proliferation and differentiation. In vivo experiments have shown that JAK-Stat signaling is mandatory for adult mammary gland development and lactation. Two Stat molecules, Stat3 and Stat5, appear to have opposite functions and their relative activity may serve to control developmental cycles of mammary tissue. While Stat5 activity has been linked to alveolar proliferation and function, Stat3 activity correlates with the loss of alveolar function, cell death and the initiation of mammary tissue remodeling.

Cloning, characterization, and tissue distribution of porcine SPAI, a protein with a transglutaminase substrate domain and the WAP motif

The primary and gene structures and tissue distribution of porcine SPAI-2, a protein that belongs to the WAP protein superfamily and has a sodium-potassium ATPase inhibitory activity, were determined by molecular cloning and Northern analysis. A full-length cDNA clone was isolated from a porcine duodenum cDNA library. The cDNA insert encoded a polypeptide of 187 amino acids, which is composed of three domains: a hydrophobic presequence of 21 amino acids, a prosegment of 105 amino acids ending with Asp126, and the mature SPAI-2 sequence of 61 amino acids beginning with Pro127. The prosegment contained 16 repeats of a hexapeptide that is highly homologous to the repetitive sequence found in the transglutaminase domain of the human elafin, an elastase-specific inhibitor that also belongs to the WAP superfamily. The repetitive sequence was demonstrated to be a good substrate of transglutaminase using a recombinant preparation produced in Escherichia coli. A porcine genomic library was then screened for the SPAI gene. Characterization and sequencing of positive clones indicated that the gene is similar to the elafin gene, having 3 exons encoding the 5'-untranslated region and signal sequence, proSPAI, and 3'-untranslated region, respectively. Northern blot analysis revealed intestine-specific expression of SPAI mRNA; the message was especially abundant in the small intestine. ProSPAI was also found in the circulation. The similarity of proSPAI to elafin in the domain structure, the acid-labile nature of the cleavage site (Asp126-Pro127), and the fact that the major form of SPAI in the plasma is proSPAI strongly suggest that proSPAI is not the precursor but rather it is the native form of SPAI. Like elafin, therefore, SPAI appears to be a new type of biologically active substance with a transglutaminase substrate domain that acts as an anchoring sequence.

Negative regulatory element in the mammary specific whey acidic protein promoter

Expression of the whey acidic protein (WAP) gene is tightly regulated in a tissue and developmental stage specific manner, in that the WAP gene is exclusively expressed in the mammary gland during pregnancy and lactation. Using both deletion and competition analyses, evidence is provided for the existence of a negative regulatory element (NRE) in the WAP promoter located between -413 and -93 with respect to the WAP transcriptional initiation site. This NRE dramatically decreases transcription from linked heterologous promoter-reporter gene constructs. The activity of NRE requires WAP promoter sequences that are 230 bp apart since subfragments of the NRE fail to inhibit transcription of adjoining reporter genes. Nuclear extracts from different cell types, in which the WAP gene is not active, contain a protein or complex that specifically interacts with the entire NRE but not with subfragments of it. The contact points between this protein (NRE binding factor [NBF]) and the NRE element have been partially determined. Mutation of the implicated nucleotides severely reduces the ability of NBF to bind, and such mutated promoter fragments fail to alleviate transcriptional repression in competition experiments. This suggests that NBF binding to the NRE is at least in part responsible for the negative regulation of the WAP promoter. Since NBF is not detectable in the lactating mammary gland, where the WAP gene is expressed, we speculate that it may be a determinant of the expression spectrum of the WAP gene.

Characterization of two novel casein transcripts in rabbit mammary gland

Two clones were isolated from a cDNA library corresponding to mRNAs which accumulate in mid-lactating (14 day) rabbit mammary gland and characterized by DNA sequencing. The two clones sequenced corresponded to two novel casein transcripts (pBRM5 and pBRM42). Relative mRNA abundances for the two clones were assessed by dot-blot analysis. Phylogenetic analysis and comparison of both pBRM5 and pBRM42 with other members of the casein family revealed that the rabbit may be unique among mammals in expressing two alpha s2-casein genes. The presence of two alpha s2-casein genes in the rabbit may be the result of a relatively recent intergenic duplication event.

Structure and function of milk protein genes

Interspecies comparisons of cDNA and mosaic milk protein genes have confirmed their high rate of evolution, but the overall gene organization has been conserved. The three Ca-sensitive casein genes, which share common motifs in the promoter region and contain similar sequences that encode signal peptide and multiple phosphorylation sites, probably derived from a common ancestor. alpha s1- and alpha s2-casein genes, divided into many small exons, undergo complex splicing, and the deleted caseins arise from exon skipping. The four bovine casein genes are clustered on 200 kb of chromosome 6. alpha-Lactalbumin and beta-lactoglobulin pseudogenes occur in ruminants. Study of the expression of native and modified milk protein genes in mammary cell lines and transgenic animals and DNA footprinting have shown the occurrence of important regulatory motifs in the proximal 5' flanking region, including one recognized by a specific mammary nuclear factor. Good stage- and tissue-specific expression has been obtained in transgenic animals with milk protein genes having less than a 3-kb 5' flanking region. Better knowledge of both the structure and function of milk protein genes, which has already allowed the use of powerful techniques for the rapid identification of alleles, offers the potential for the genetic modification of milk composition.

High expression of the caprine beta-casein gene in transgenic mice

An 18-kb caprine genomic DNA fragment, comprising the beta-casein transcription unit with about 3-kb 5' and 6-kb 3' flanking regions, was microinjected into fertilized one-cell murine eggs. All nine lines of transgenic mice obtained expressed the transgene in their mammary glands, as demonstrated by Northern blot analysis of mRNA in miscellaneous tissues, and qualitative and quantitative analysis of caprine beta-casein in milk, using SDS/PAGE, Western blotting and rocket immunoelectrophoresis. Two lines produced milk containing up to 21-24 mg of the exogenous protein/ml, a yield which is roughly twice that found in goat milk. The yield reached at least 40 mg/ml in some progeny of crossbred G1 transgenic mice. Thus, the investigated gene appears to be a good candidate for making hybrid constructs that might promote an efficient production of valuable foreign proteins in milk.

The fatty acid synthase (FAS) gene and its promoter in Rattus norvegicus

Screening of rat liver genomic libraries yielded 5 overlapping clones for rat fatty acid synthase (FAS). From these clones we determined the 18,170 bp sequence of the rat FAS together with 5,028 bp of the 5'-flanking region and 515 bp of the 3'-adjacent genomic sequence. The two FAS transcripts which differ only in the positions of their polyadenylation/termination sites consist of one untranslated and 42 translated exons. Surprisingly, the substrate binding site for enoyl reductase, one of the FAS component functions, is interrupted by an intron. The sizes and the boundaries of the individual domains could be mapped in relation to the exon/intron structure of the gene. These eight partial functions coincide with discrete units of exons. The acyl carrier protein with its prosthetic 4'-phosphopantetheine group is located within a single exon supporting the idea that rat FAS has evolved by gene fusion. Using primer extension the main transcription start site of the FAS mRNA in both hepatic and mammary gland tissues was located at 5,028 bp in the sequence determined. As expected of a gene which is pretranslationally regulated the 5'-flanking region contains, in addition to TATA and CAAT boxes, consensus sequences for several DNA binding proteins.

A gene deleted in Kallmann's syndrome shares homology with neural cell adhesion and axonal path-finding molecules

Kallmann's syndrome (clinically characterized by hypogonadotropic hypogonadism and inability to smell) is caused by a defect in the migration of olfactory neurons, and neurons producing hypothalamic gonadotropin-releasing hormone. A gene has now been isolated from the critical region on Xp22.3 to which the syndrome locus has been assigned: this gene escapes X inactivation, has a homologue on the Y chromosome, and shows an unusual pattern of conservation across species. The predicted protein has significant similarities with proteins involved in neural cell adhesion and axonal pathfinding, as well as with protein kinases and phosphatases, which suggests that this gene could have a specific role in neuronal migration.

The WDNM1 gene product is a novel member of the 'four-disulphide core' family of proteins

It has been previously demonstrated that the WDNM1 gene is downregulated in metastatic rat mammary adenocarcinomas. Detailed analysis of the structure of WDNM1 mRNA reveals the presence of two transcripts generated by alternative splicing of a single exon. The unspliced version possesses an in-frame termination codon which encodes a predicted protein of 18 amino acids. The spliced version encodes a predicted protein of 60 amino acids which exhibits strong homology to a family of proteins possessing a conserved arrangement of cysteine residues. This family includes several proteinase inhibitors suggesting that WDNM1 could encode a product with proteinase inhibiting capacity. Possible modulation in the level of this protein product could be related to overall proteinase activity of specific tumour cells which, in turn, could influence the invasive and metastatic potential of such cell populations.

Some monotreme milk "whey" and blood proteins

1. Electrophoretic studies are made of mature phase milk "whey" proteins and blood serum proteins of echidna (Tachyglossus aculeatus) and platypus (Ornithorhynchus anatinus). The echidna milk bands are designated A-M, those of platypus A-G. Some of the proteins are isolated and characterized. 2. Echidna band A protein has some similarity to high cystine "whey" proteins. Band E protein (apparent Mr 21,000) may be a beta-lactoglobulin-like protein. Band M is lysozyme. Band C is serum albumin. Bands G-K are transferrins. 3. Platypus milk bands A, C, D, F and G are isolated. Bands F and G are transferrins. 4. Lactose synthase and lytic activities are examined.

Generation of polyclonal antibodies against purified rat whey acidic proteins and the synthesis of a tracer fusion protein suitable for use in radioimmunoassays

Rodent milk consists mainly of caseins and whey proteins. A major component of the latter group is the whey acidic proteins (WAP) the gene for which has been cloned recently and shown to contain several potential glucocorticoid receptor binding sites. Studies on the regulation of this gene by glucocorticoids would be greatly enhanced by the availability of a radioimmunoassay for WAP. Rat milk was obtained from lactating Sprague-Dawley rats and the WAP purified to homogeneity by ammonium sulphate fractionation, gel filtration and ion exchange chromatography. Rabbit polyclonal antibodies were raised against the purified WAP and used to probe a Western blot of whey proteins. The major band recognized by the antibody corresponded in molecular weight to purified WAP. Problems associated with radiolabelling the tyrosine-free WAP molecule necessitated the fusion of a tyrosine containing protein with the rat milk protein. A rat WAP cDNA clone was ligated to the glutathione transferase gene, the fusion protein expressed in Escherichia coli and purified by a one-step procedure on a glutathione affinity column. Purified WAP readily displaced the radiolabelled recombinant tracer in a radioimmunoassay.

Growth control and differentiation in mammary epithelial cells

Growth and differentiation of the mammary gland are controlled by various hormones and other environmental factors. The role of hormones and growth factors in mammary development is discussed with regard to animal species, physiological stages, and the various experimental systems in vitro. In the female embryo, mammary morphogenesis is induced by the mesenchyme and is hormone independent, whereas androgens cause the partial necrosis of mammary epithelium in the male. Ductal growth during adolescence requires estrogen and prolactin or growth hormone. During pregnancy, progesterone participates in the development of the lobuloalveolar structure of the gland. After parturition, changes in the hormonal environment lead to production and secretion of milk. Proliferation and differentiation of mammary epithelium can be induced in culture systems. Insulin and epidermal growth factor (EGF) stimulate mammary cell proliferation in vitro. EGF is required for the optimal growth of the mammary gland during pregnancy. EGF also appears to play an important role in mammary tumorigenesis in certain mouse strains. Production of milk proteins can be induced in vitro by the synergistic interactions of prolactin, insulin, and glucocorticoids and is inhibited by EGF and progesterone. Complete or partial sequencing of several milk protein genes and comparative analysis have led to identification of a sequence of high homology and conservation in the 5' flanking region that is likely to be involved in the regulation of milk protein gene expression.

Influence of some dietary chemopreventive agents on the expression of functional differentiation of the mouse mammary gland in vitro

The purpose of the present studies was to determine the influence of the chemopreventive agents selenium, 4-(hydroxyphenyl)-retinamide (4-HPR) and beta-carotene, on functional differentiation (lactogenesis) of the mouse mammary gland cells. The hormone-induced expression of the milk-protein genes, beta-casein, epsilon-casein and the whey acidic protein (WAP) was used as molecular marker of differentiation of the mammary cells in organ culture medium containing insulin, prolactin, aldosterone and hydrocortisone. Quantitative determination of the cellular concentration of the respective mRNA was ascertained by molecular hybridization of RNA to the specific cloned cDNA probes using both the solution and the filter hybridization methods. Selenium at 100 nm concentration caused a pronounced inhibition of accumulation of the respective mRNAs. The retinoid, 4-HPR, also caused a dose-dependent inhibition of expression of these mRNA sequences. In contrast, concentrations of the 3 mRNAs in beta-carotene-treated glands remained similar to those observed in glands cultured in medium containing the hormones and hexane (the latter being the solvent for beta-carotene). The significant antagonistic action of selenium and 4-HPR, however, was reversible after removal of the chemicals from the culture medium. Thus, among the 3 chemicals tested, selenium and retinoid can cause an adverse effect on functional differentiation (lactogenesis) of the mammary cells. This inhibitory effect, however, was reversible. beta-Carotene, on the other hand, caused no apparent antagonistic effect on expression of the milk-protein genes in the isolated whole mammary organ in culture.

Characterization of a heterogeneous camel milk whey non-casein protein

A milk protein, occurring in the whey fraction, has been characterized from camel milk. Determination of the primary structure reveals the existence of two related types of chain with residue differences in at least the N-terminal region. A fragment representing an N-terminal part of the protein was also recovered (heterogeneous at the same positions). The absence of cysteine residues in the protein shows that no disulphide bridges are present. The pattern of fragments and a parent protein resembles that for casein and its fragments, showing that fragments and a multiplicity of forms may be typical for different milk proteins.