Lactoferrin gene promoter in human and mouse. Analogous and dissimilar characteristics

Induction of lactoferrin gene expression by innate immune stimuli in mouse mammary epithelial HC-11 cells

Lactoferrin (LF) is a multifunctional protein. While its functions and mechanism of actions are actively being investigated, the cellular signals that regulate LF expression have not been as explored. We have previously demonstrated that LF is upregulated by estrogen in the reproductive system. In this study, we show that the expression of LF was stimulated by bacterial lipopolysaccharide (LPS) and double-stranded RNA (dsRNA) in normal mouse mammalian HC-11 cells. When cells were exposed to either LPS or dsRNA, the mRNA and protein of LF were increased in a dose- and time-dependent manner, yet the kinetics of LF induction by dsRNA or LPS were different. The LPS and dsRNA-induced LF was mainly released into the culture medium where it blocked TNF-alpha production in exposed cells. We explored the mechanisms of LF induction by LPS and dsRNA using specific inhibitors and found that the induction could be attenuated by inhibitors to PKC, NF-kappaB, p38 and JNK, but not by an inhibitor to PKA. Interestingly, ERK inhibitor was effective against dsRNA but not against LPS induction of LF. These data suggest that LF was induced by LPS and dsRNA through PKC, NF-kappaB and MAPK pathways which in turn play an inhibitory role in the continuation of innate inflammation.

Single nucleotide polymorphisms (SNPs) in human lactoferrin gene

The lactoferrin protein possesses antimicrobial and antiviral activities. It is also involved in the modulation of the immune response. In a normal healthy individual, lactoferrin plays a role in the front-line host defense against infection and in immune and inflammatory responses. Whether genomic variations, such as single nucleotide polymorphisms (SNPs), have an effect on the structure and function of lactoferrin protein and whether these variations contribute to the different susceptibility of individuals in response to environmental insults are interesting health-related issues. In this study, the lactoferrin gene was resequenced as part of the Environmental Genome Project of the National Institute of Environmental Health Sciences, which operates within the National Institutes of Health. Ninety-one healthy donors of different ethnicities were used to establish common SNPs in the exons of the lactoferrin gene in the general population. The data will serve as a basis from which study the association of lactoferrin polymorphism and disease.

Characterization of the infection-responsive bovine lactoferrin promoter

The concentration of lactoferrin in bovine milk is dramatically increased in response to infection. The high levels of lactoferrin may have a role in the prevention of microbial infection of the mammary gland. However, molecular mechanisms of how the lactoferrin gene is regulated in the mammary gland in response to infection remain unknown. In this study, we isolated and characterized the 5' flanking region of the bovine lactoferrin gene. An 8.2 kilobase (kb) fragment of the bovine lactoferrin gene, containing 4.4 kb of 5' flanking region, exon 1, intron 1, and exon 2, was isolated from a bovine genomic library on two overlapping bacterial artificial chromosome (BAC) clones. Sequence analysis of the isolated lactoferrin gene revealed that the promoter region contains a high GC content, a non-canonical TATA box, multiple stimulating protein 1 (SP1)/GC elements, and other putative binding sites for transcription factors including nuclear factor-kappaB (NF-kappaB), activator protein 1 (AP1), signal transducer and activator of transcriptions 3 and 5 (STAT3 and STAT5), and steroid hormone receptors. To demonstrate that the isolated promoter is functional, 4.4 kb of 5' flanking region was inserted upstream from the firefly luciferase gene and the chimeric construct was transiently transfected into murine mammary epithelial cells. Transfection studies showed that the basal promoter activity is quite potent, being similar in strength to that of the simian virus 40 (SV40) promoter/enhancer. In addition, a 24-h treatment with Escherichia coli lipopolysaccharide (LPS) significantly stimulated its activity up to 2.3-fold in a dose-dependent manner. Furthermore, promoter deletion analysis indicated that the sequence up to -543 was sufficient for basal activity, whereas the sequence up to -1029 was required for maximal basal activity. The basal activity of the promoter is affected by both positive regulatory regions (-2462/-1879 and -1029/-75) and a negative regulatory region (-1407/-1029). LPS-responsive regions of the promoter were localized to the region from -1029 to -543 containing one STAT3 site and two NF-kappaB sites, and the region from -4355 to -2462 containing three AP1 sites and six NF-kappaB sites. Taken together, our findings suggested that the lactoferrin promoter responds to infection via the NF-kappaB pathway.

Differential expression and estrogen response of lactoferrin gene in the female reproductive tract of mouse, rat, and hamster

Lactoferrin, an iron-binding glycoprotein, kills bacteria and modulates inflammatory and immune responses. Presence of lactoferrin in the female reproductive tract suggests that the protein may be part of the mucosal immune system and act as the first line of defense against pathogenic organisms. We have discovered that lactoferrin is a major estrogen-inducible protein in the uterus of immature mice and is up-regulated by physiological levels of estrogen during proestrous in mature mice. In the present study, we examined lactoferrin gene expression and its response to estrogen stimulation in the female reproductive tract of several strains of immature mouse, rat, and hamster. The lactoferrin expression in the cycling adult female rat was also evaluated. Lactoferrin gene polymorphism exists among the different mouse strains. In the three inbred mouse strains studied, lactoferrin gene expression is stimulated by estrogen in the immature uterus, although it is less robust than in the outbred CD-1 mouse. We found that the lactoferrin gene is constitutively expressed in the epithelium of the vagina and the isthmus oviduct; however, it is estrogen inducible in the uterus of immature mice and rats. Furthermore, lactoferrin is elevated in the uterine epithelium of the mature rat during the proestrous and estrous stages of the estrous cycle. Estrogen stimulation of lactoferrin gene expression in the reproductive tract of an immature hamster is limited to the vaginal epithelium. The present study demonstrates differential expression and estrogen responsiveness of the lactoferrin gene in different regions of the female rodent reproductive tract and variation among the rodent species studied.

Lactoferrin gene expression and regulation: an overview

Lactoferrin is highly conserved among human, mouse, bovine, and porcine species. The numbers of amino acids encoded by 15 of the 17 exons in these species are identical, and in 12 locations, they have identical codon interruptions at the intron-exon splice junctions. However, lactoferrin expression is both ubiquitous and species, tissue, and cell-type specific. It is differentially regulated through multiple signaling pathways such as steroid hormone, growth factor, and kinase cascade pathways. Comparing the lactoferrin gene promoters from different species, common and different characteristics are observed. The human, mouse, bovine, porcine, and bubaline (African antelope) promoters all contain a noncanonical TATA box with an adjacent Sp1 site. Both human and mouse have multiple steroid hormone response elements, while none are found in the other species studied, suggesting that the lactoferrin gene is differentially regulated among different species by steroid hormones. Several transcription factors have been identified that are crucial for the expression of the lactoferrin gene during differentiation of the myeloid cells and in estrogen and epidermal growth factor regulation. This article provides an overview on lactoferrin expression and regulation in different species.

Serum and milk lactoferrin concentration and the correlation with some blood components in lactating sows

An increased serum concentration of lactoferrin is associated with inflammatory disease, but there are few reported data on this aspect for lactating sows. Samples of blood and milk were collected from 17 lactating sows under minimum stress conditions and analysed for lactoferrin. Lactoferrin concentrations in serum and milk were positively correlated, being high after farrowing and steadily decreasing throughout 28 days of lactation. A positive linear correlation was observed between lactoferrin concentration and enzyme activities of alanine aminotransferase, lactate dehydrogenase, and hydroxybutyrate dehydrogenase in the serum indicating post-partum inflammation. Serum and milk lactoferrin concentrations, although closely correlated, may be regulated through independent systems activated simultaneously.

Regulation of lactoferrin gene expression by estrogen and epidermal growth factor: molecular mechanism

Lactoferrin (LF) is a member of the transferrin gene family. Its expression in the mouse uterus is regulated by estrogen and epidermal growth factor (EGF). The author et al. cloned the LF gene promoter/enhancer region, and demonstrated that multihormone signaling pathways are involved in modulating LF gene activity. Three short but complex modules, within 400 bp from the transcription initiation site of the mouse LF gene, contain the response elements that are responsible for estrogen, retinoic acid, mitogen, and growth factor stimulation. These elements have been identified and characterized, using reporter constructs transiently transfected into human endometrial carcinoma RL95-2 cells. The author et al. used molecular approaches, such as deletion, insertion, and site-directed mutagenesis, to determine the relationship between the response elements, and to fine-map the crucial nucleotides within them. This article reviews the characterization of the estrogen and EGF response elements of the mouse LF gene promoter.

Cloning and expression of the transferrin and ferritin genes in a marsupial, the brushtail possum (Trichosurus vulpecula)

Transferrin and ferritin cDNAs have been isolated and characterised from the common brushtail possum (Trichosurus vulpecula), the first marsupial examples of these genes. The transferrin cDNA encodes a 711 amino acid pre-protein which shows high levels of amino acid identity with eutherian transferrins (58-60%) and lactoferrins (54-56%). Phylogenetic analysis suggests that the possum transferrin has evolved independently along a pathway distinct from that of the eutherian transferrins and lactoferrins. Possum H-ferritin is a 182 residue protein which shares 86-94% amino acid identity with mammalian, avian and amphibian sequences. Ferritin mRNA was detected in all tissues tested, whereas transferrin was highly expressed in possum liver and mammary gland, and at lower levels in heart, testis and lung. In the possum mammary gland, ferritin mRNA was expressed throughout lactation with higher levels during the first 30 days which coincides with the high iron concentration of milk at this time. The transferrin gene was differentially expressed during lactation with peak mRNA levels detected during the first 6 days of lactation and after day 106 throughout late lactation. The pattern of transferrin mRNA expression in the mammary gland was identical to that of another whey protein, the late lactation protein, suggesting that the transcription of these genes may be regulated by a similar mechanism in this tissue.

Sequence requirements for estrogen receptor binding to estrogen response elements

The estrogen receptor (ER) is a transcription factor that binds to a specific DNA sequence found in the regulatory regions of estrogen-responsive genes, called the estrogen response element (ERE). Many genes that contain EREs have been identified, and most of these EREs contain one or more changes from the core consensus sequence, a 13-nucleotide segment with 10 nucleotides forming an inverted repeat. A number of genes have multiple copies of these imperfect EREs. In order to understand why natural EREs have developed in this manner, we have attempted to define the basic sequence requirements for ER binding. To this end, we measured the binding of homodimeric ER to a variety of nonconsensus EREs. We discovered that an ERE containing even a single change from the consensus may be unable to bind ER. However, an ERE with two changes from the consensus may be capable of binding avidly to ER in the context of certain flanking sequences. We found that changes in the sequences flanking a nonconsensus ERE can greatly alter ER-ERE affinity, either positively or negatively. Careful study of sequences flanking a series of EREs made it possible to develop rules that predict whether ER binds to a given natural ERE and also to predict the relative amounts of binding when comparing two EREs.

Effects of multiple estrogen responsive elements, their spacing, and location on estrogen response of reporter genes

Most highly estrogen-responsive genes possess multiple estrogen-responsive elements (EREs) that act synergistically to activate expression. Synergism between EREs appears to depend on structural features of the EREs and the promoter. To examine the activation process, we cloned single or multiple tandem copies of the consensus ERE into reporter plasmids. These plasmids contained either a chloramphenicol acetyl transferase reporter gene driven by a minimal promoter or a luciferase reporter gene driven by the Simian virus 40 (SV40) promoter. Using MCF-7 human breast cancer cells, we demonstrate that synergism among EREs depends on the number of EREs, their spacing, and the distance of the EREs from the promoter. The induction capacity of EREs falls off slowly with distance from the promoter. Remarkably, multiple EREs can induce effectively and synergize even when they are located more than 2000 nucleotides from the promoter. For EREs located immediately upstream of the promoter, both the distance separating the EREs and the distance to the promoter have to be optimal for synergy. Altering either distance changes the response from synergistic to additive. For distant EREs, presumed to interact by a looping mechanism at the promoter, the length of DNA between the EREs and the promoter is not critical. Synergy among closely spaced EREs that are far from the promoter only requires an optimal distance separating the ERE centers of symmetry. Interestingly, very widely separated EREs can also synergize, presumably also because of their ability to interact by looping. The estrogen response from single or multiple tandem copies of ERE half-palindromes near the SV40 promoter was also tested. The negligible induction capacity of a single half-site was not significantly increased in multiple sites. The biological role of half-EREs is not apparent in the system employed here.

CCAAT Displacement Protein (CDP/cut) Recognizes a Silencer Element Within the Lactoferrin Gene Promoter

Expression of neutrophil secondary granule protein (SGP) genes is coordinately regulated at the transcriptional level, and is disrupted in specific granule deficiency and leukemia. We analyzed the regulation of SGP gene expression by luciferase reporter gene assays using the lactoferrin (LF) promoter. Reporter plasmids were transiently transfected into non–LF-expressing hematopoietic cell lines. Luciferase activity was detected from reporter plasmids containing basepair (bp) −387 to bp −726 of the LF promoter, but not in a −916-bp plasmid. Transfection of a −916-bp plasmid into a LF-expressing cell line resulted in abrogation of the silencing effect. Sequence analysis of this region revealed three eight-bp repetitive elements, the deletion of which restored wild-type levels of luciferase activity to the −916-bp reporter plasmid. Electrophoretic mobility shift assay and UV cross-linking analysis identified a protein of approximately 180 kD that binds to this region in non–LF-expressing cells but not in LF-expressing cells. This protein was identified to be the CCAAT displacement protein (CDP/cut). CDP/cut has been shown to downregulate expression of gp91-phox, a gene expressed relatively early in the myeloid lineage. Our observations suggest that the binding of CDP/cut to the LF silencer element serves to suppress basal promoter activity of the LF gene in non–LF-expressing cells. Furthermore, overexpression of CDP/cut in cultured myeloid stem cells blocks LF expression upon granulocyte colony-stimulating factor–induced neutrophil maturation without blocking phenotypic maturation. This block in LF expression may be due, in part, to the persistence of CDP/cut binding to the LF silencer element.

CCAAT displacement protein (CDP/cut) recognizes a silencer element within the lactoferrin gene promoter

Expression of neutrophil secondary granule protein (SGP) genes is coordinately regulated at the transcriptional level, and is disrupted in specific granule deficiency and leukemia. We analyzed the regulation of SGP gene expression by luciferase reporter gene assays using the lactoferrin (LF) promoter. Reporter plasmids were transiently transfected into non-LF-expressing hematopoietic cell lines. Luciferase activity was detected from reporter plasmids containing base-pair (bp) -387 to bp -726 of the LF promoter, but not in a -916-bp plasmid. Transfection of a -916-bp plasmid into a LF-expressing cell line resulted in abrogation of the silencing effect. Sequence analysis of this region revealed three eight-bp repetitive elements, the deletion of which restored wild-type levels of luciferase activity to the -916-bp reporter plasmid. Electrophoretic mobility shift assay and UV cross-linking analysis identified a protein of approximately 180 kD that binds to this region in non-LF-expressing cells but not in LF-expressing cells. This protein was identified to be the CCAAT displacement protein (CDP/cut). CDP/cut has been shown to downregulate expression of gp91-phox, a gene expressed relatively early in the myeloid lineage. Our observations suggest that the binding of CDP/cut to the LF silencer element serves to suppress basal promoter activity of the LF gene in non-LF-expressing cells. Furthermore, overexpression of CDP/cut in cultured myeloid stem cells blocks LF expression upon granulocyte colony-stimulating factor-induced neutrophil maturation without blocking phenotypic maturation. This block in LF expression may be due, in part, to the persistence of CDP/cut binding to the LF silencer element.

Structure and biological actions of lactoferrin

Lactoferrin is an iron-binding glycoprotein of the transferrin family, first isolated from milk but also found in most exocrine secretions as well as in the secondary granules of neutrophils. The many reports on its antimicrobial and antiinflammatory activity in vitro identify lactoferrin as important in host defense against infection and excessive inflammation. Most if not all lactoferrin actions are mediated through iron sequestration and/or interaction with a large variety of ligands including microbial cell wall components and cellular receptors, through its highly positively charged N-terminus. Lactoferrin exerts its effects on glandular epithelia, secretions, mucosal surfaces as well as in the interstitium and vascular compartments where it has been postulated to participate in iron metabolism, disease defense, and modulation of inflammatory and immune responses. A need to understand the diverse biological actions of lactoferrin and the prospect of a wide variety of potential applications in human health care have stimulated studies of the relation between lactoferrin structure and function, the regulation of lactoferrin secretion and development of large scale production of recombinant human lactoferrin (hLf). This review provides a synthesis of our current understanding of lactoferrin. Space limitations have led us to refer to review articles whenever possible; the reader is advised to use these articles for access to the primary experimental literature.

Estrogen-related receptor, hERR1, modulates estrogen receptor-mediated response of human lactoferrin gene promoter

We have shown previously that estrogen-stimulated transcription from the human lactoferrin gene in RL95-2 endometrium carcinoma cells is mediated through an imperfect estrogen response element (ERE) at the 5 -flanking region of the gene. Upstream from the ERE, a DNA sequence (-418 to -378, FP1) was selectively protected from DNase I digestion by nuclear extracts from endometrial and mammary gland cell lines. In this report, using the electrophoresis mobility shift assay, site-directed mutagenesis, and DNA methylation interference analyses, we show that three different nuclear proteins bind to the FP1 region (C1, C2, and C3 sites). The nuclear receptor, COUP-TF, binds to the C2 site. Mutations in the C1 binding region abolish C1 complex formation and reduce estrogen-dependent transcription from the lactoferrin ERE. When the imperfect ERE of the lactoferrin gene is converted to a perfect palindromic structure, the enhancing effect of the C1 binding element for estrogen responsiveness was abolished. We isolated a complementary DNA (cDNA) clone from an RL95-2 expression library that encodes the C1 site-binding protein. The encoded polypeptide maintains 99% amino acid identity with the previously described orphan nuclear receptor hERR1. A 2.2-kilobase mRNA was detected in RL95-2 cells by the newly isolated cDNA but not by the first 180 base pair of the published hERR1 sequence. By Western analysis, a major 42-kDa protein is detected in the RL95-2 nuclear extract with antibody generated against GST-hERR1 fusion protein. Finally, we show that the hERR1 interacts with the human estrogen receptor through protein-protein contacts.