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Biomedical subjects

D I Linzer

Publications and source records attributed to D I Linzer.

At least 19 recordsLinked to original sources
PubMed2001

Reactivation of proliferin gene expression is associated with increased angiogenesis in a cell culture model of fibrosarcoma tumor progression.

Proliferin (PLF) is an angiogenic placental hormone. We now report that PLF gene expression can also occur in a progressive fibrosarcoma mouse tumor cell model. PLF mRNA and protein are detectable at very low levels in cell lines derived from the mild noninvasive stage of tumor development. Expression is greatly augmented in cell lines from the aggressively invasive stage of development, a stage at which the tumor becomes highly angiogenic, and PLF expression remains high in cell lines from the end stage of fibrosarcoma. Activator protein 1 factors present at high levels in the more invasive stages of the tumor may in part allow for increased PLF expression, as cells from the mild stage in which c-jun and junB are stably expressed secrete levels of PLF comparable to that of the advanced stages. Secreted PLF protein is functionally important in tumor cell angiogenic activity, as demonstrated by the reduction of angiogenic activity in fibrosarcoma cell culture medium by immunodepletion of PLF. These results suggest that an extraembryonic genetic program, which has evolved to support fetal growth, may be reactivated in certain tumors and contribute to tumor growth.

Cells, Cultured↗
PubMed2001

Nodal regulates trophoblast differentiation and placental development.

Nodal has been thought to be an embryo-specific factor that regulates development, but nodal is also expressed in the mouse placenta beginning at midgestation, specifically in the spongiotrophoblasts. In an insertional null nodal mutant, not only is embryonic development disrupted, but mouse placental development is also grossly altered with the loss of the diploid spongiotrophoblasts and labyrinth and an expansion of the polyploid giant cell layer. A hypomorphic mutation in nodal results in an expansion of the giant cell and spongiotrophoblast layers, and a decrease in labyrinthine development. Expression of nodal in trophoblast cell cultures is sufficient to inhibit trophoblast giant cell differentiation, demonstrating that nodal can act directly on trophoblasts. The mechanism of nodal action includes the inhibition of junB gene transcription. These results suggest that nodal may be involved in redirecting trophoblast fate towards the midgestational expansion of the labyrinth region while maintaining the thin layer of trophoblast giant cells and the underlying layer of spongiotrophoblasts that form the boundary between the maternal and extraembryonic compartments.

Animals↗
PubMed2001

Murine prolactin-like protein E synergizes with human thrombopoietin to stimulate expansion of human megakaryocytes and their precursors.

The aim of this study was to determine the effect of promegakaryocytopoietic murine hormone prolactin-like protein E (PLP-E) on human megakaryocytopoiesis. Human bone marrow CD34+ cells, cultured in serum-free medium with combinations of thrombopoietin (TPO), stem cell factor (SCF), Flt-3 ligand (Flt-3L), and PLP-E, were analyzed via microscopy, flow cytometry, and clonogenic assay. Unlike the situation with mouse cells, PLP-E alone did not promote human megakaryocyte (MK) differentiation, but instead synergizes with TPO to increase colony-forming unit megakaryocyte (CFU-MK), burst-forming unit erythroid (BFU-E), and and colony-forming unit granulocyte erythroid macrophage mixed (CFU-GEMM) expansion, as well as total MK production. These effects can be attributed to an increase in colony frequency, combined with a significantly greater total cell expansion induced by adding PLP-E along with TPO. The number of cells in each CFU-MK colony is an indication of the maturity of the progenitor population, with larger colonies deriving from a more immature progenitor cell. PLP-E significantly expanded immature, intermediate, and mature CFU-MK subsets at 3 days of culture, as well as the intermediate and mature subsets at day 6. PLP-E combined with TPO induced significant expansion of all CFU-MK subsets at all time points. PLP-E further increased the effect of SCF and Flt-3L on TPO-induced total cell and CFU-MK expansion.PLP-E may act as a survival factor for primitive human megakaryocytic and erythroid progenitors. It appears to preserve the highly proliferative immature fraction of the progenitor compartment but by itself does not promote total cell proliferation or human MK production. PLP-E may prove useful in combination with TPO and other cytokines for ex vivo expansion of hematopoietic progenitors to be used in a clinical setting.

Animals↗
PubMed2000

Placental prolactins and the physiology of pregnancy.

Mammalian pregnancy is characterized by a concerted and widespread series of changes in maternal physiology, many of which are direct responses to the binding of placental hormones to maternal targets. Among these placental hormones are proteins closely related to prolactin. In rodents, a large number of these placental prolactin-related hormones are expressed that have a broad spectrum of activities, including activities on endothelial cells and blood cells.

Animals↗
PubMed2000

Identification of three prolactin-related hormones as markers of invasive trophoblasts in the rat.

An expressed-sequence tag database search has identified three rat cDNA clones in the prolactin/growth hormone family, including a homologue of mouse proliferin-related protein (PRP). The encoded proteins of the two novel clones, designated prolactin-like proteins L (PLP-L) and M (PLP-M), are predicted to be synthesized as precursors of 229 and 227 amino acids, modified by N-linked glycosylation, and secreted as mature glycoproteins of 199 and 200 residues, respectively. Murine homologues to PLP-L and PLP-M were also identified. The open reading frame of rat PRP encodes a precursor protein of 245 amino acids and predicts a secreted 215-amino acid glycoprotein with 81% identity to mouse PRP. All three rat mRNAs are expressed in the placenta, and expression is not detected in other tissues. PLP-L mRNA expression is observed from Days 11-20, with highest levels at Day 13; highest levels of PLP-M are observed from Day 11 until parturition, with peak levels also on Day 13; and highest levels of PRP are also observed from Day 11 until term, with maximal expression on Day 17. All three genes are most highly expressed in invasive trophoblast cells lining the central placental vessel. The identification of molecular markers for endovascular trophoblasts serves to highlight the invasive nature of rodent placentation and may prove useful for future studies of placental function.

Amino Acid Sequence↗
PubMed2000

GATA-2 restricts prolactin-like protein A expression to secondary trophoblast giant cells in the mouse.

An analysis of the pattern of expression of the mouse placental hormone prolactin-like protein A (PLP-A) has revealed that this hormone is expressed exclusively in secondary trophoblast giant cells but not in primary giant cells. Thus, PLP-A serves as a marker for a subset of giant cells. Recent results have indicated that PLP-A binds to and inhibits the activity of natural killer cells, and thus, the localized expression of PLP-A may be important for regulating the activity of this class of T lymphocytes in a restricted region of the implantation site. Previous studies indicated that the transcription factor GATA-2 is required for the trophoblast giant cell-specific expression of two other hormones in the prolactin family, placental lactogen I and proliferin. In the absence of GATA-2, PLP-A continues to be expressed, but in this mutant background, PLP-A mRNA is detected in both primary and secondary giant cells. Thus, GATA-2 contributes both to positive and negative regulation of trophoblast giant cell-specific gene expression, and this factor apparently plays an important role in generating or maintaining the distinct functions of secondary, compared with primary, trophoblast giant cells.

Animals↗
PubMed2000

Inhibition of tumor growth by the antiangiogenic placental hormone, proliferin-related protein.

Proliferin-related protein (PRP) is a potent placental antiangiogenic hormone. To test the antiangiogenic potential of PRP to block tumor growth, we engineered tumor cells to express this hormone. Both SV40-transformed BALB/c mouse 3T3 fibroblasts and rat C6 glioma cells have markedly reduced growth rates as tumors in mice if they express high levels of PRP. In both models, the small tumors that form are largely avascular, whereas control tumors are rich in blood vessels, consistent with PRP limiting tumor growth by preventing neovascularization of the tumors. The antiangiogenic effects of PRP are also detected on human endothelial cells, suggesting that the receptor and signaling pathway of this mouse hormone are conserved between mouse and human and may represent useful targets for the development of antiangiogenic therapeutics. That signaling pathway appears to involve an inhibition of arachidonic acid release, based on the ability of arachidonic acid to overcome the antiangiogenic effects of PRP.

3T3 Cells↗
PubMed1999

Induction of megakaryocyte differentiation by a novel pregnancy-specific hormone.

Maturation of megakaryocytes and subsequent platelet release are normally regulated by a network of cytokines, including thrombopoietin and various interleukins. Because abnormal platelet production and activation have been implicated in gestational pathologies, additional pregnancy-specific cytokines may play important roles in the regulation of megakaryocytopoiesis. Consistent with this hypothesis, we have found that the hormone prolactin-like protein E, a placental hormone that we have recently characterized, targets megakaryocytes through a specific cell surface receptor and induces megakaryocyte differentiation through a gp130-dependent signal transduction pathway.

Animals↗
PubMed1999

Metallothionein is part of a zinc-scavenging mechanism for cell survival under conditions of extreme zinc deprivation.

Metallothionein (MT) is a small cysteine-rich protein thought to play a critical role in cellular detoxification of inorganic species by sequestering metal ions that are present in elevated concentrations. We demonstrate here that metallothionein can play an important role at the other end of the homeostatic spectrum by scavenging an essential metal in a mouse fibroblast cell line that has been cultured under conditions of extreme zinc deprivation (LZA-LTK-). These cells unexpectedly produce constitutively high levels of metallothionein mRNA; however, the MT protein accumulates only when high concentrations of zinc are provided in the media. Until this MT pool is saturated, no measurable zinc remains in the external media. In this case, zinc deprivation leads to amplification of the MT gene locus in the LZA-LTK- cell line. Furthermore, the intracellular zinc levels in the fully adapted cells remain at the normal level of 0.4 fmol zinc/cell, even when extracellular zinc concentration is decreased by 2 orders of magnitude relative to normal media.

3T3 Cells↗
PubMed1999

A novel megakaryocyte differentiation factor from mouse placenta.

Megakaryocyte differentiation and subsequent platelet production are regulated by a network of growth factors and cytokines. We hypothesized that pregnancy-specific regulatory factors also may participate in the modulation of megakaryocytopoiesis and thrombopoiesis. We identified a mouse placental prolactin-like protein hormone with an activity similar to interleukin 6 in targeting megakaryocytes and inducing cell differentiation. The receptor for this placental hormone is present on megakaryocytes from pregnant and nonpregnant female mice and from male mice, and from humans, suggesting that this signaling pathway (if not necessarily this particular ligand) is broadly functional both in terms of physiologic state and evolution. Thus, studying the biologic activities of the large family of placental prolactin-like proteins represents a potentially valuable approach to the discovery of novel hematopoietic signaling pathways.

Animals↗
PubMed1999

Prolactin (PRL)-like protein J, a novel member of the PRL/growth hormone family, is exclusively expressed in maternal decidua.

A search of a nonmouse, nonhuman, expressed sequence tag database for messenger RNAs in the PRL/GH family has identified a novel rat complementary DNA clone. The encoded protein, designated PRL-like protein J (PLP-J), is predicted to be synthesized as a precursor of 211 amino acids, modified by N-linked glycosylation, and secreted as a mature glycoprotein of 182 residues. PLP-J messenger RNA synthesis is limited to early pregnancy with abundant expression on day 7, slightly declining expression on day 9, and no detectable expression by day 11. Unlike most other PRL family members, PLP-J does not appear to be synthesized by placental trophoblasts but, rather, by decidual cells surrounding the implantation site. By sequence similarity to rat PLP-J, a murine clone was identified in a mouse expressed sequence tag database. Mouse PLP-J was used to map the gene to a 700-kb region of mouse chromosome 13 that includes other members of the PRL/GH family.

Amino Acid Sequence↗
PubMed1998

Identification of trophoblast-specific regulatory elements in the mouse placental lactogen II gene.

Placental lactogen II, the major ligand for the PRL receptor during the second half of gestation in rodents, is synthesized specifically by placental trophoblast giant cells. A transient transgenic analysis has been used to localize the giant cell-specific regulatory region within the mouse placental lactogen II gene to sequences between -1340 and -2019 upstream of the transcriptional start site. More precise mapping of the regulatory elements has been accomplished by transfection of promoter constructs into Rcho-1 trophoblast cells, resulting in the characterization of two positive regulatory elements in the -1471 to -1340 region; two other regulatory elements have been implicated but not further characterized, a negative regulatory element between -2019 and -1778 and another positive element within the region from -1340 to -569. Both of the characterized positive regulatory elements are recognized by factors that are enriched in differentiated giant cells compared with proliferative trophoblasts, and these factors are either absent or at low levels in fibroblasts. The complexes that form on the two elements are distinct and neither element competes with the other for factor binding, thus implicating at least two different regulatory elements in late-gestational trophoblast giant cell-specific gene expression.

Animals↗
PubMed1997

Prolactin receptor expression in the developing mouse embryo.

We have examined the developmental pattern of prolactin receptor expression in the mouse by reverse transcription-polymerase chain reaction, in situ hybridization, and radioligand binding and have found two unexpected aspects of temporal regulation. First, high levels of prolactin receptor mRNA were detected in mouse embryos at day 8 and day 18, but levels decreased between these days to a minimum at approximately day 14. In contrast, placental prolactin receptor mRNA levels remained constant throughout this gestational period. Second, on embryonic day 16 the mRNA encoding the long form of the prolactin receptor is more abundant in the fetal liver than any of the short receptor form mRNAs, but by day 18 a switch occurs and the mRNA encoding one of the short receptor forms becomes the predominant receptor mRNA in that tissue. Expression of the receptor mRNA and protein is widespread throughout the fetus, with especially high levels in developing bone and cartilagenous structures, the thymus and pituitary, the tongue and skeletal muscle, and certain regions of the brain. The pattern of expression of prolactin receptor in the fetal mouse suggests an important role for the placental lactogens, the major ligands for fetal prolactin receptors, in fetal growth and development.

Animals↗
PubMed1997

Proliferin transport and binding in the mouse fetus.

Proliferin (PLF), a member of the PRL/GH family secreted by the placenta, can be detected in both the maternal and fetal compartments. We now show that PLF immunoreactivity can be detected in association with the yolk sac, consistent with the transport of PLF across this structure into the amniotic fluid. Furthermore, PLF is transported across the extraembryonic membranes in isolated conceptuses that are placed in culture, and specific binding sites for PLF are detected in these embryos. The major binding sites for PLF in the cultured conceptus correspond to sites at which endogenous PLF localizes in the fetus, including developing vertebral and vascular structures. Similar binding patterns were also detected for PLF that was incubated with fetal sections. Competition and comparative binding studies indicate that the insulin-like growth factor II/mannose 6-phosphate receptor is involved in PLF binding to specific cells in the fetus. These results suggest that in addition to the effects of PLF in the placenta on neovascularization and in the maternal uterus on cell proliferation, PLF may also act at specific sites in the developing fetus.

Animals↗
PubMed1997

The different forms of the prolactin receptor in the rat corpus luteum: developmental expression and hormonal regulation in pregnancy.

The corpora lutea of pregnancy in the rat are highly dependent on the action of PRL and PRL-like hormones to hypertrophy and to produce progesterone needed for the maintenance of gestation. Two forms of the PRL receptor (PRL-R), designated as long (PRL-RL) and short (PRL-RS), have been described in rat tissues. To determine whether both forms are present in the corpus luteum during pregnancy and to examine the developmental and hormonal regulation of their expression, total RNA isolated from corpora lutea at different stages of pregnancy and from highly luteinized granulosa cells subjected to different hormonal treatments were analyzed by semiquantitative RT-PCR. Immunoblotting of luteal proteins from early and late pregnancy was also performed to determine if the pattern of PRL-R proteins follows that of PRL-R messenger RNA (mRNA) expression. In addition, the correlation between the well characterized PRL-regulated gene, 20alpha-hydroxysteroid dehydrogenase (20alpha-HSD), and PRL-R gene expression was investigated during the time of luteolysis. Both PRL-RL and PRL-RS mRNA and protein were expressed in corpora lutea of pregnancy, with the long form being the most dominant at all stages. Whereas no changes in mRNA level of either PRL-RL or PRL-RS were found until day 20 of gestation, a profound decline in PRL-R mRNA and protein for both receptor types occurred at the end of pregnancy. This drop in PRL-R expression was accompanied by a sharp and abrupt expression of 20alpha-HSD mRNA. Studies performed in vivo and in luteinized cells in culture indicate that PRL can up-regulate the expression of the PRL-RL mRNA, an effect prevented by the tyrosine kinase inhibitor, genistein. PRL-RL mRNA was also selectively increased by cAMP. In summary, the results of this investigation have established that: 1) the corpus luteum of pregnancy expresses both the short and long forms of the PRL-R with the long form being more abundant; 2) the mRNA for both forms of the PRL-R remains at constant levels throughout pregnancy but drops before parturition; 3) the decline in PRL-R mRNA at the end of pregnancy is accompanied by a dramatic rise in 20alpha-HSD; 4) PRL is able to increase the expression of PRL-R mRNA; and that 5) both A kinase and tyrosine kinase mediated pathways appear to participate in the up-regulatory mechanism involved in PRL-R mRNA expression.

20-Hydroxysteroid Dehydrogenases↗
PubMed1997

Three new members of the mouse prolactin/growth hormone family are homologous to proteins expressed in the rat.

A search of a mouse expressed sequence tag database for novel messenger RNAs (mRNAs) in the PRL/GH family has identified three clones that are homologous to the rat PRL-like protein A (PLP-A), PRL-like protein B (PLP-B), and decidual/trophoblast PRL-related protein (d/tPRP). Full-length complementary DNA clones for each of these three mouse mRNAs have been sequenced. Mouse PLP-A is predicted to be synthesized as a precursor of 227 residues and secreted as a glycoprotein of 196 amino acids; the secreted protein shares 78% identity with rat PLP-A. The open reading frame for mouse PLP-B encodes a protein of 230 residues; the putative mature glycoprotein of 201 amino acids is 66% identical to rat PLP-B. The third mouse complementary DNA clone encodes a precursor protein of 240 residues and a secreted glycoprotein of 211 amino acids with 64% identity to rat d/tPRP. All three mouse mRNAs are expressed specifically in the placenta or decidua. The highest levels of the PLP-A mRNA are detected on day 12, at which time expression is localized to a subset of trophoblast giant cells, especially those cells that line maternal blood sinuses. PLP-B mRNA levels are high on day 10 in decidual cells and on day 12 in spongiotrophoblasts. The mRNA similar to rat d/tPRP is present at high levels even earlier in gestation (day 8) and is localized to the decidual layer. The identification of PRL-related mRNAs in common between the mouse and rat indicates that the encoded hormones are evolutionarily conserved and, therefore, likely to play important roles in reproductive physiology.

Amino Acid Sequence↗