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

HE4, A New Potential Tumor Marker for Early Diagnosis and Predicting of Breast Cancer Progression

Background & Objective:

This study examined the potential of human epididymis protein 4 (HE4) as a marker in early diagnosis or as a prognostic factor for breast cancer (BC) patients.

Methods:

A total of 31 patients diagnosed with BC were enrolled in the study between 2008 and 2018. The mRNA and protein expression levels of HE4 were analyzed by immunohistochemistry (IHC) and real-time polymerase chain reaction (PCR) in the BC tissue and the non-tumoral adjacent tissue. Using ELISA technique, HE4 plasma levels were also measured in 43 BC patients compared to 43 healthy individuals. The correlation between HE4 expression and clinicopathological features was then investigated.

Results:

An increase in HE4 expression was observed at mRNA and protein levels in the BC group compared to the control group (P<0.01, P<0.0001, respectively). In addition, the relative expression of HE4 mRNA in BC patients showed a significant correlation with the differentiation grade of cancer cells (P<0.001). Plasma levels of HE4 was also associated with grade (P<0.0001), stage, and tumor size in BC patients (for both P<0.01). Patients with metastatic BC (P<0.01), lymphatic invasion, and lymph node involvement (for both P<0.05) showed significantly higher plasma levels of HE4 expression than patients without metastasis.

Conclusion:

According to our findings, upregulation of HE4 may be related to invasive BC phenotype. Measuring plasma levels of HE4 could be useful as a screening test in early diagnosis of BC.

Marsupial milk: a fluid source of nutrition and immune factors for the developing pouch young

Marsupials have a very different reproductive strategy to eutherians. An Australian marsupial, the tammar wallaby (Macropus eugenii) has a very short pregnancy of about 26.5 days, with a comparatively long lactation of 300-350 days. The tammar mother gives birth to an altricial, approximately 400 mg young that spends the first 200 days postpartum (p.p.) in its mother's pouch, permanently (0-100 days p.p.; Phase 2A) and then intermittently (100-200 days p.p.; Phase 2B) attached to the teat. The beginning of Phase 3 marks the first exit from the pouch (akin to the birth of a precocious eutherian neonate) and the supplementation of milk with herbage. The marsupial mother progressively alters milk composition (proteins, fats and carbohydrates) and individual milk constituents throughout the lactation cycle to provide nutrients and immunological factors that are appropriate for the considerable physiological development and growth of her pouch young. This review explores the changes in tammar milk components that occur during the lactation cycle in conjunction with the development of the young.

Opossum Mammary Maturation as It Relates to Immune Cell Infiltration and Nutritional Gene Transcription

The mammary gland has evolved to accommodate the developmental needs of offspring in species-specific ways. This is particularly true for marsupials. Marsupial milk content changes dramatically throughout lactation in ways appearing timed with neonatal ontogeny and behavior. Here we investigate morphological restructuring within the mammaries throughout lactation in the gray short-tailed opossum, Monodelphis domestica. Substantial remodeling of the mammaries occurs throughout the first half of active lactation. It is not until the latter half of lactation that opossum mammaries appear histologically similar to active eutherian mammaries. Noteworthy was the presence of eosinophils in early developing mammary tissue, which correlated with elevated abundance of transcripts encoding the chemokine IL-16. The presence and abundance of whey protein transcripts within the opossum mammaries were also quantified. Whey acidic protein (WAP) transcript abundance peaked in the latter half of lactation and remained elevated through weaning. Minimal transcripts for the marsupial-specific Early and Late Lactation Proteins (ELP/LLP) were detected during active lactation. Elevated abundance of LLP transcripts was only detected prior to parturition. Overall, the results support the role of eosinophils in mammary restructuring appearing early in mammalian evolution, and describe key similarities and differences in nutritional protein transcript abundance among marsupial species.

The main WAP isoform usually found in camel milk arises from the usage of an improbable intron cryptic splice site in the precursor to mRNA in which a GC-AG intron occurs

Background

Whey acidic protein (WAP) is a major protein identified in the milk of several mammalian species with cysteine-rich domains known as four-disulfide cores (4-DSC). The organization of the eutherian WAP genes is highly conserved through evolution. It has been proposed that WAP could play an important role in regulating the proliferation of mammary epithelial cells. A bacteriostatic activity was also reported. Conversely to the other mammalian species expressing WAP in their milk, camel WAP contains 4 additional amino acid residues at the beginning of the second 4-DSC domain, introducing a phosphorylation site. The aim of this study was to elucidate the origin of this specificity, which possibly impacts its physiological functions.

Results

Using LC-ESI-MS, we identified in Camelus bactrianus from Kazakhstan a phosphorylated whey protein, exhibiting a molecular mass (12,596 Da), 32 Da higher than the original WAP (12,564 Da) and co-eluting with WAP. cDNA sequencing revealed a transition G/A, which modifies an amino acid residue of the mature protein (V12 M), accounting for the mass difference observed between WAP genetic variants. We also report the existence of two splicing variants of camel WAP precursors to mRNA, arising from an alternative usage of the canonical splice site recognized as such in the other mammalian species. However, the major camel WAP isoform results from the usage of an unlikely intron cryptic splice site, extending camel exon 3 upstream by 12-nucleotides encoding the 4 additional amino acid residues (VSSP) in which a potentially phosphorylable Serine residue occurs. Combining protein and cDNA sequences with genome data available (NCBI database), we report another feature of the camel WAP gene which displays a very rare GC-AG type intron. This result was confirmed by sequencing a genomic DNA fragment encompassing exon 3 to exon 4, suggesting for the GC donor site a compensatory effect in terms of consensus at the acceptor exon position.

Conclusions

Combining proteomic and molecular biology approaches we report: the characterization of a new genetic variant of camel WAP, the usage of an unlikely intron cryptic splice site, and the occurrence of an extremely rare GC-AG type of intron.

Crustins are distinctive members of the WAP-containing protein superfamily: An improved classification approach

Crustins are considered effector molecules of innate immunity in arthropods, and classification schemes have been proposed over the last 10 years. However, classification problems have emerged: for example, proteins that have been well identified as members of a particular category have also been classified as crustins. Therefore, the objective of this manuscript was to analyze and, based on solid arguments, improve the original proposed nomenclature to make crustins a distinctive group of antibacterial proteins. The presence of WAP or 4DSC domain has been considered a distinctive feature of crustins; however, several antibacterial proteins containing WAP domains have been detected in diverse taxonomic groups (including mammals). Here, we present evidence supporting the idea that the Cys-rich region and the 4DSC domain can be considered a signature of crustins and, together with some distance arrangements occurring within this 12-Cys region, yield enough information for the classification of these proteins. Herein, the core characteristics to be considered for classification purposes are the length of the Gly-rich region and the repetitive tetrapeptides occurring within this region; these characteristics are then hierarchically followed by the F and A distances located within the 4DSC domain. Finally, the proposed system considers the crustin signature as the common structure in all members, which is a differentiator from other proteins containing WAP domains, separating crustins as a well-distinguished member of the superfamily of WAP-domain containing proteins.

The tammar wallaby: A marsupial model to examine the timed delivery and role of bioactives in milk

It is now clear that milk has multiple functions; it provides the most appropriate nutrition for growth of the newborn, it delivers a range of bioactives with the potential to stimulate development of the young, it has the capacity to remodel the mammary gland (stimulate growth or signal cell death) and finally milk can provide protection from infection and inflammation when the mammary gland is susceptible to these challenges. There is increasing evidence to support studies using an Australian marsupial, the tammar wallaby (Macropus eugenii), as an interesting and unique model to study milk bioactives. Reproduction in the tammar wallaby is characterized by a short gestation, birth of immature young and a long lactation. All the major milk constituents change substantially and progressively during lactation and these changes have been shown to regulate growth and development of the tammar pouch young and to have roles in mammary gland biology. This review will focus on recent reports examining the control of lactation in the tammar wallaby and the timed delivery of milk bioactivity.

Gene expression in the mammary gland of the tammar wallaby during the lactation cycle reveals conserved mechanisms regulating mammalian lactation

The tammar wallaby (Macropus eugenii), an Australian marsupial, has evolved a different lactation strategy compared with eutherian mammals, making it a valuable comparative model for lactation studies. The tammar mammary gland was investigated for changes in gene expression during key stages of the lactation cycle using microarrays. Differentially regulated genes were identified, annotated and subsequent gene ontologies, pathways and molecular networks analysed. Major milk-protein gene expression changes during lactation were in accord with changes in milk-protein secretion. However, other gene expression changes included changes in genes affecting mRNA stability, hormone and cytokine signalling and genes for transport and metabolism of amino acids and lipids. Some genes with large changes in expression have poorly known roles in lactation. For instance, SIM2 was upregulated at lactation initiation and may inhibit proliferation and involution of mammary epithelial cells, while FUT8 was upregulated in Phase 3 of lactation and may support the large increase in milk volume that occurs at this point in the lactation cycle. This pattern of regulation has not previously been reported and suggests that these genes may play a crucial regulatory role in marsupial milk production and are likely to play a related role in other mammals.

The tammar wallaby: a model system to examine domain-specific delivery of milk protein bioactives

The role of milk extends beyond simply providing nutrition to the suckled young. Milk has a comprehensive role in programming and regulating growth and development of the suckled young, and provides a number of potential autocrine factors so that the mammary gland functions appropriately during the lactation cycle. This central role of milk is best studied in animal models such as marsupials that have evolved a different lactation strategy to eutherians and allow researchers to more easily identify regulatory mechanisms that are not as readily apparent in eutherian species. For example, the tammar wallaby (Macropus eugenii) has evolved with a unique reproductive strategy of a short gestation, birth of an altricial young and a relatively long lactation during which the mother progressively changes the composition of the major, and many of the minor components of milk. Consequently, in contrast to eutherians, there is a far greater investment in development of the young during lactation and it is likely that many of the signals that regulate development of eutherian embryos in utero are delivered by the milk. This requires the co-ordinated development and function of the mammary gland since inappropriate timing of these signalling events may result in either limited or abnormal development of the young, and potentially a higher incidence of mature onset disease. Milk proteins play a significant role in these processes by providing timely presentation of signalling molecules and antibacterial protection for the young and the mammary gland at times when there is increased susceptibility to infection. This review describes studies exploiting the unique reproductive strategy of the tammar wallaby to investigate the role of several proteins secreted at specific times during the lactation cycle and that are correlated with potential roles in the young and mammary gland. Interestingly, alternative splicing of some milk protein genes has been utilised by the mammary gland to deliver domain-specific functions at specific times during lactation.

The hypothalamic-pituitary-ovarian axis and manipulations of the oestrous cycle in the brushtail possum

The main purpose of this review is to provide a comprehensive update on what is known about the regulatory mechanisms of the hypothalamic-pituitary-ovarian axis in the brushtail possum, and to report on the outcomes of attempts made to manipulate by hormonal means, these processes in the possum. Over the last 15 years, several unique features of possum reproductive physiology have been discovered. These include an extended follicular phase despite elevated concentrations of FSH during the luteal phase, and early expression of LH receptors on granulosa cells of small antral follicles, suggesting a different mechanism for the selection of a dominant follicle. The use of routine synchronisation protocols that are effective in eutherians has failed to be effective in possums, and so the ability to reliably synchronise oestrus in this species remains a challenge.

Evolution of lactation: ancient origin and extreme adaptations of the lactation system

Lactation, an important characteristic of mammalian reproduction, has evolved by exploiting a diversity of strategies across mammals. Comparative genomics and transcriptomics experiments have now allowed a more in-depth analysis of the molecular evolution of lactation. Milk cell and mammary gland genomic studies have started to reveal conserved milk proteins and other components of the lactation system of monotreme, marsupial, and eutherian lineages. These analyses confirm the ancient origin of the lactation system and provide useful insight into the function of specific milk proteins in the control of lactation. These studies also illuminate the role of milk in the regulation of growth and development of the young beyond simple nutritive aspects.

Bacteriostatic activity of Whey Acidic Protein (WAP)

We have previously reported the action of whey acidic protein (WAP) inhibiting the proliferation of mouse mammary epithelial cells in the experiments utilizing in vivo and in vitro systems. We report herein the bacteriostatic activity of WAP. Western blot analysis demonstrated successful isolation of WAP from whey fractions of rat milk by column chromatography. The WAP fraction inhibited the growth of Staphylococcus aureus JCM2413 in a dose-dependent manner, but did not inhibit the growth of Escherichia coli. The bacteriostatic activity of WAP was highest at pH 6.6 and was not affected by the presence of 150 mM NaCl. A scanning electron micrograph of bacteria treated with WAP exhibited the disruption of the bacterial cell walls.

Characterization of the tammar wallaby (Macropus eugenii) whey acidic protein gene: new insights into the function of the protein

Whey acidic protein (WAP) belongs to a family of four disulfide core (4-DSC) proteins rich in cysteine residues and is the principal whey protein found in milk of a number of mammalian species. Eutherian WAPs have two 4-DSC domains, whereas marsupial WAPs are characterized by the presence of an additional domain at the amino terminus. Structural and expression differences between marsupial and eutherian WAPs have presented challenges to identifying physiological functions of the WAP protein. We have characterized the genomic structure of tammar WAP (tWAP) gene, identified its chromosomal localization and investigated the potential function of tWAP. We have demonstrated that tWAP and domain III (DIII) of the protein alone stimulate proliferation of a mouse mammary epithelial cell line (HC11) and primary cultures of tammar mammary epithelial cells (Wall-MEC), whereas deletion of DIII from tWAP abolishes this proliferative effect. However, tWAP does not induce proliferation of human embryonic kidney (HEK293) cells. DNA synthesis and expression of cyclin D1 and cyclin-dependent kinase-4 genes were significantly up-regulated when Wall-MEC and HC11 cells were grown in the presence of either tWAP or DIII. These data suggest that DIII is the functional domain of the tWAP protein and that evolutionary pressure has led to the loss of this domain in eutherians, most likely as a consequence of adopting a reproductive strategy that relies on greater investment in development of the newborn during pregnancy.

Three-dimensional structure and ligand binding properties of trichosurin, a metatherian lipocalin from the milk whey of the common brushtail possum Trichosurus vulpecula

Lipocalins are extracellular proteins (17-25 kDa) that bind and transport small lipophilic molecules. The three-dimensional structure of the first lipocalin from a metatherian has been determined at different values of pH both with and without bound ligands. Trichosurin, a protein from the milk whey of the common brushtail possum, Trichosurus vulpecula, has been recombinantly expressed in Escherichia coli, refolded from inclusion bodies, purified and crystallized at two different pH values. The three-dimensional structure of trichosurin was solved by X-ray crystallography in two different crystal forms to 1.9 A (1 A=0.1 nm) and 2.6 A resolution, from crystals grown at low and high pH values respectively. Trichosurin has the typical lipocalin fold, an eight-stranded anti-parallel beta-barrel but dimerizes in an orientation that has not been seen previously. The putative binding pocket in the centre of the beta-barrel is well-defined in both high and low pH structures and is occupied by water molecules along with isopropanol molecules from the crystallization medium. Trichosurin was also co-crystallized with a number of small molecule ligands and structures were determined with 2-naphthol and 4-ethylphenol bound in the centre of the beta-barrel. The binding of phenolic compounds by trichosurin provides clues to the function of this important marsupial milk protein, which is highly conserved across metatherians.

Lactation transcriptomics in the Australian marsupial, Macropus eugenii: transcript sequencing and quantification

BACKGROUND

Lactation is an important aspect of mammalian biology and, amongst mammals, marsupials show one of the most complex lactation cycles. Marsupials, such as the tammar wallaby (Macropus eugenii) give birth to a relatively immature newborn and progressive changes in milk composition and milk production regulate early stage development of the young.

RESULTS

In order to investigate gene expression in the marsupial mammary gland during lactation, a comprehensive set of cDNA libraries was derived from lactating tissues throughout the lactation cycle of the tammar wallaby. A total of 14,837 express sequence tags were produced by cDNA sequencing. Sequence analysis and sequence assembly were used to construct a comprehensive catalogue of mammary transcripts. Sequence data from pregnant and early or late lactating specific cDNA libraries and, data from early or late lactation massively parallel sequencing strategies were combined to analyse the variation of milk protein gene expression during the lactation cycle.

CONCLUSION

Results show a steady increase in expression of genes coding for secreted protein during the lactation cycle that is associated with high proportion of transcripts coding for milk proteins. In addition, genes involved in immune function, translation and energy or anabolic metabolism are expressed across the lactation cycle. A number of potential new milk proteins or mammary gland remodelling markers, including noncoding RNAs have been identified.

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.

The Tammar Wallaby and Fur Seal: Models to Examine Local Control of Lactation

Mammary development and function are regulated by systemic endocrine factors and by autocrine mechanisms intrinsic to the mammary gland, both of which act concurrently. The composition of milk includes nutritional and developmental factors that are crucial to the development of the suckled young, but it is becoming increasingly apparent that milk also has a role in regulating mammary function. This review examines the option of exploiting the comparative biology of species with extreme adaptation to lactation to examine regulatory mechanisms that are present but not readily apparent in other laboratory and livestock species. The tammar wallaby has adopted a reproductive strategy that includes a short gestation (26 d), birth of an immature young, and a relatively long lactation (300 d). The composition of milk changes progressively during the lactation cycle, and this is controlled by the mother and not the sucking pattern of the young. Furthermore, the tammar can practice concurrent asynchronous lactation; the mother provides a concentrated milk high in protein and fat for an older animal that is out of the pouch and a dilute milk low in fat and protein but high in carbohydrates from an adjacent mammary gland for a newborn pouch young. This phenomenon suggests that the mammary gland is controlled locally. The second study species, the Cape fur seal, has a lactation characterized by a repeated cycle of long at-sea foraging trips (up to 28 d) alternating with short suckling periods of 2 to 3 d ashore. Lactation almost ceases while the seal is off shore, but the mammary gland does not progress to apoptosis and involution, most likely because of local control of the mammary gland. Our studies have exploited the comparative biology of these models to investigate how mammary function is regulated by endocrine factors, and particularly by milk. This review reports 3 major findings using these model animals. First, the mammary epithelial cell has an extraordinary intrinsic capacity for survival in our culture model, and the path to either function or death by apoptosis is actively driven. The second outcome is that the route to apoptosis is most likely regulated by specific milk factors. Finally, whey acidic protein, a major milk protein in some species, may play a role in normal mammary development, but that role in vivo may be limited to marsupials. Evolutionary pressure has led to changes in the structure of the protein with an accompanying change in function. Therefore, we propose that a loss of function of this protein in eutherians may relate to a reproductive strategy that is less dependent on lactation.

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.

Ruminants genome no longer contains Whey Acidic Protein gene but only a pseudogene

Whey Acidic Protein (WAP) has been identified in the milk of only a few species, including mouse, rat, rabbit, camel, pig, tammar wallaby, brushtail possum, echidna and platypus. Despite intensive studies, it has not yet been found in the milk of Ruminants. We have isolated and characterized genomic WAP clones from ewe, goat and cow, identified their chromosomal localization and examined the expression of the endogenous WAP sequence in the mammary glands of all three species. The WAP sequences were localized on chromosome 4 (4q26) as expected from comparative mapping data. The three ruminant WAP sequences reveal the same deletion of a nucleotide at the end of the first exon when compared with the pig sequence. Due to this frameshift mutation, the putative proteins encoded by these sequences do not harbor the features of a usual WAP protein with two four-disulfide core domains. Moreover, RT-PCR experiments have shown that these sequences are not transcribed and are, thus, pseudogenes. This loss of functionality of the gene in Ruminants raises the question of the biological role of the WAP. Some putative roles previously suggested for WAP are discussed.

Analysis of the Promoter of Mutated Human Whey Acidic Protein (WAP) Gene

Although whey acidic protein (WAP) has been identified in the milk of a range of species, it has been predicted that WAP is not secreted into human milk as a result of critical point mutations within the coding region. In the present study, we first investigated computationally the promoter region of mutated human WAP genes by comparing with those of other known WAP genes. Computational database analyses showed that the human WAP promoter region was highly conserved, as in other species with milk WAP. Next, we evaluated the activity of the human WAP promoter (2.6 kb) using a reporter gene assay. MCF-7 cells were stably transfected with the hWAP/hGH (human growth hormone) fusion gene, cultured on Matrigel, and treated with lactogenic hormones. Radioimmunoassay detected hGH in the culture medium, indicating that the human WAP promoter was responsible for the lactogenic hormones. The human WAP promoter was significantly more active in MCF-7 cells than the mouse WAP promoter (2.4 kb). The present results provide us with important information on the molecular evolution of milk protein genes.

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.

Positive and negative regulatory elements in the late lactation protein-A gene promoter from the tammar wallaby (Macropus eugenii)

Little is known about the regulation of the marsupial-specific late lactation protein-A (LLP-A) gene, first expressed at mid-lactation in the mammary gland of the tammar wallaby. A genomic clone of LLP-A was sequenced and shown to include seven exons. The LLP-A promoter region of 1969 bp ligated to a secreted alkaline phosphatase (SEAP) gene reporter was co-transfected into CHO-K1 cells with prolactin (PRL) receptor cDNA. Transfected cells cultured with insulin, cortisol and PRL did not secrete SEAP into media. Similarly, this construct was not expressed in the mammary gland of eight lines of transgenic mice. In contrast, when the LLP-A promoter region was reduced to 850 bp, the expression of the SEAP reporter in CHO-K1 cells was constitutive and PRL-independent, despite the presence of two low affinity Stat5 binding sites. The 1969 bp promoter was analyzed using nine serial deletions ligated to the SEAP gene. The expression of these constructs was PRL-independent. Five putative inhibitory elements were identified between -1969 and -1796, -1404 and -1184, -1184 and -992, -992 and -757, and -591 and -425, and a putative enhancer or core transcription element between -425 and-239. These studies indicate that the complex temporal regulation of the LLP-A gene involves elements in its 5'-regulatory region.

Cloning and characterization of 5' upstream promoter region of rat WAP gene

Regulatory regions of genes encoding milk proteins are frequently used to produce in the mammary gland of transgenic animals a variety of pharmaceutically and medically important human proteins. One such example is the whey acidic protein (WAP) promoter region, identified so far in the genome of mouse, rat, rabbit, camel, pig, brushtail possum and Tammar wallaby. The aim of the present study was cloning and characterization of the 5' upstream promoter region of rat WAP gene. Using Genome Walking procedure, we cloned the region extending from -849 to -3671 bp. We have shown that there are two conserved regions highly similar to hypersensitive sites present in mouse and rabbit upstream region of WAP gene with binding sites for STAT5 transcription factor, essential for expression of WAP gene in mammary glands during lactation. We characterized dispersed and tandem repeats in the upstream region of rat WAP gen localized not far away from the translation initiation site.

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.

Inhibitory function of whey acidic protein in the cell-cycle progression of mouse mammary epithelial cells (EpH4/K6 cells)

Although the biological role for whey acidic protein (WAP) in milk has been suggested, its true function is not known. This paper describes evidence for WAP function in the cell-cycle progression of EpH4/K6 (EpH4), mammary epithelial cells in vitro. The forced expression of exogenous WAP significantly impaired the proliferation of EpH4 cells, whereas it did not affect that of NIH3T3 cells. Apoptosis was not enhanced in the EpH4 cells with stable expression of WAP (WAP-clonal EpH4 cells). The analyses of BrdU incorporation revealed that forced WAP expression significantly reduced incorporation of BrdU in WAP-clonal EpH4 cells compared with control cells transfected with empty plasmid. Among G1 cyclins, the level expression of cyclins D1 was significantly lower in the WAP-clonal EpH4 cells than in control cells. The inhibitory action of WAP on the proliferation of EpH4 cells was enhanced by the presence of extracellular matrix (ECM), but not by the presence of a single component comprising ECM. The cultured medium of WAP-clonal EpH4 cells inhibited the proliferation of control cells without WAP expression. The present results indicate that WAP plays a negative regulatory role in the cell-cycle progression of mammary epithelial cells through an autocrine/paracrine mechanism.

Hormone-induced modifications of the chromatin structure surrounding upstream regulatory regions conserved between the mouse and rabbit whey acidic protein genes

The upstream regulatory regions of the mouse and rabbit whey acidic protein (WAP) genes have been used extensively to target the efficient expression of foreign genes into the mammary gland of transgenic animals. Therefore both regions have been studied to elucidate fully the mechanisms controlling WAP gene expression. Three DNase I-hypersensitive sites (HSS0, HSS1 and HSS2) have been described upstream of the rabbit WAP gene in the lactating mammary gland and correspond to important regulatory regions. These sites are surrounded by variable chromatin structures during mammary-gland development. In the present study, we describe the upstream sequence of the mouse WAP gene. Analysis of genomic sequences shows that the mouse WAP gene is situated between two widely expressed genes (Cpr2 and Ramp3). We show that the hypersensitive sites found upstream of the rabbit WAP gene are also detected in the mouse WAP gene. Further, they encompass functional signal transducer and activator of transcription 5-binding sites, as has been observed in the rabbit. A new hypersensitive site (HSS3), not specific to the mammary gland, was mapped 8 kb upstream of the rabbit WAP gene. Unlike the three HSSs described above, HSS3 is also detected in the liver, but similar to HSS1, it does not depend on lactogenic hormone treatments during cell culture. The region surrounding HSS3 encompasses a potential matrix attachment region, which is also conserved upstream of the mouse WAP gene and contains a functional transcription factor Ets-1 (E26 transformation-specific-1)-binding site. Finally, we demonstrate for the first time that variations in the chromatin structure are dependent on prolactin alone.

Pig whey acidic protein gene is surrounded by two ubiquitously expressed genes

A 140-kb pig DNA fragment containing the whey acidic protein (WAP) gene cloned in a bacterial artificial chromosome (BAC344H5) has been shown to contain all of the cis-elements necessary for position-independent, copy-dependent and tissue-specific expression in transgenic mice. The insert from this BAC was sequenced. This revealed the presence of two other genes with quite different expression patterns in pig tissues and in transfected HC11 mouse mammary cells. The RAMP3 gene is located 15 kb upstream of the WAP gene in reverse orientation. The CPR2 gene is located 5 kb downstream of the WAP gene in the same orientation. The same locus organization was found in the human genome. The region between RAMP3 and CPR2 in the human genome contains a WAP gene-like sequence with several points of mutation which may account for the absence of WAP from human milk.

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.