Abstract 2032: Regulation of MUC1 expression by activated EGFR and PPARγ in human uterine and pancreatic cancer cell lines

Many epithelial tumors including endometrial and pancreatic cancers, overexpress the high molecular weight, transmembrane mucin, MUC1, on their cell surface. Overexpression and aberrant glycosylation of MUC1 makes tumor cells poorly adherent, increases drug resistance and promotes cancer cell metastasis. MUC1 has three distinct domains: an extracellular domain (ECD) composed of a tandem repeat region rich in serine, threonine and proline; a transmembrane domain (TM) and; a short cytoplasmic tail domain (CT) involved in a variety of signal transduction events. Previous studies (Wang et al. 2010. Mol. Endocrinol. 24: 1368-1379) demonstrated that the Peroxisome Proliferator Activated Receptor γ (PPARγ) agonist, rosiglitazone severely inhibits progesterone stimulated MUC1 expression. Two independent approaches were used to determine if rosiglitazone as well as inhibitors of Epidermal Growth Factor Receptor (EGFR) tyrosine kinase activity reduced MUC1 expression in the human uterine epithelial cell line, HES, the uterine adenocarcinoma cell line, HEC-1A, and in the human pancreatic adenocarcinoma cell lines, HPAFII and CAPAN2. EGFR activation by Epidermal Growth Factor (EGF) stimulated (1.5-2 fold) MUC1 protein expression 1.5-2.0 fold in both uterine and pancreatic cancer cells, while treatment with EGFR tyrosine kinase inhibitor, AG1478, reduced both basal and stimulated MUC1 protein expression. Furthermore, the PPARγ agonist, rosiglitatzone, markedly (> 90%) reduced EGFR-driven MUC1 expression detected by antibodies directed against the MUC1 ECD and CT. A combination of biochemical and molecular biological assays have been used to identify the transcriptional and signal transduction pathways activated by EGFR leading to increased MUC1 expression and the impact of AG1478 and rosiglitazone on these events. Understanding the molecular basis of how these agents reduce MUC1 expression may offer novel therapeutic avenues to improve cancer chemotherapies.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2032. doi:10.1158/1538-7445.AM2011-2032

Paracrine factors produced by bone marrow stromal cells induce apoptosis and neuroendocrine differentiation in prostate cancer cells

BACKGROUND

Preferential bony metastasis of human prostate cancer (PCa) cells contributes to disease mortality and morbidity. Local factors in bone stromal extracellular matrix microenvironment affect tumor growth through paracrine interactions between tumor and stromal cells.

METHODS

Using co-culture and medium transfer, we used several methods to assess interactions between PCa and bone stromal cells using three PCa cell lines: PC3, LNCaP, and the LNCaP derivative, C4-2B.

RESULTS

Co-culture of LNCaP and C4-2B cells with bone marrow stromal cell lines, HS27a and HS5, decreased cell number, as did culture with conditioned medium (CM) harvested from these two cell lines suggesting a soluble paracrine factor was responsible. PC3 cell growth was unaffected. CM harvested from bone stromal cell lines triggered apoptosis in LNCaP and C4-2B cell lines, but not in PC3 cells. Surviving C4-2B cells grown in bone stromal cell CM over several days were growth arrested, suggesting presence of a growth inhibitor. Apoptosis induced by CM was dose-dependent. Flow cytometry demonstrated that over a 5-day culture period in stromal cell CM, LNCaP, and C4-2B cell lines, but not PC3 cells, underwent greater apoptosis than parallel cultures in SF medium. The LNCaP and C4-2B cells showed morphology and biomarker expression consistent with transdifferentiation towards a neuroendocrine phenotype after exposure to stromal cell CM.

CONCLUSIONS

The reactive bone stromal microenvironment initially is hostile to PCa cells producing widespread apoptosis. Activation of transdifferentiation in a subset of apoptotic resistant cells may support phenotypic adaptation during disease progression in bone, eventually favoring lethal disease.

Cytokine and progesterone receptor interplay in the regulation of MUC1 gene expression

Mucin 1 (MUC1), a transmembrane mucin expressed at the apical surface of uterine epithelia, is a barrier to microbial infection and enzymatic attack. MUC1 loss at implantation sites appears to be required to permit embryo attachment and implantation in most species. MUC1 expression is regulated by progesterone (P) and proinflammatory cytokines, including TNFα and interferon γ (IFNγ). TNFα and IFNγ are highly expressed in uterine tissues under conditions where MUC1 expression is also high and activate MUC1 expression via their downstream transcription factors, nuclear factor (NF) κB and signal transducers and activators of transcription. P receptor (PR) regulates MUC1 gene expression in a PR isoform-specific fashion. Here we demonstrate that interactions among PR isoforms and cytokine-activated transcription factors cooperatively regulate MUC1 expression in a human uterine epithelial cell line, HES. Low doses of IFNγ and TNFα synergistically stimulate MUC1 promoter activity, enhance PRB stimulation of MUC1 promoter activity and cooperate with PRA to stimulate MUC1 promoter activity. Cooperative stimulation of MUC1 promoter activity requires the DNA-binding domain of the PR isoforms. MUC1 mRNA and protein expression is increased by cytokine and P treatment in HES cells stably expressing PRB. Using chromatin immunoprecipitation assays, we demonstrate efficient recruitment of NFκB, p300, SRC3 (steroid receptor coactivator 3), and PR to the MUC1 promoter. Collectively, our studies indicate a dynamic interplay among cytokine-activated transcription factors, PR isoforms and transcriptional coregulators in modulating MUC1 expression. This interplay may have important consequences in both normal and pathological contexts, e.g. implantation failure and recurrent miscarriages.

Peroxisome proliferator-activated receptor gamma activation inhibits progesterone-stimulated human MUC1 expression

Mucin 1 (MUC1) is a type I transmembrane glycoprotein abundantly expressed on nearly all epithelial tissues and overexpressed by many cancer cells. Previous studies from our lab showed that progesterone receptor (PR)B is a strong stimulator of MUC1 gene expression. It is reported that liganded peroxisome proliferator-activated receptor gamma (PPARgamma) stimulates Muc1 expression in murine trophoblast. Here, we demonstrate that although the PPARgamma ligand, rosiglitazone, stimulates the murine Muc1 promoter in HEC1A, a human uterine epithelial cell line, rosiglitazone alone, has no significant effect on basal human MUC1 promoter activity. In fact, rosiglitazone treatment antagonizes progesterone-stimulated human MUC1 promoter activity and protein expression in two human uterine epithelial cell lines and T47D human breast cancer cells. This response is antagonized by the PPARgamma antagonist, GW9662, as well as a dominant-negative form of PPARgamma, demonstrating the response is mediated by PPARgamma. Additional studies indicate that PPARgamma activation does not change PR binding to the MUC1 promoter but generally antagonizes progesterone activity by stimulating PRB degradation and inhibiting progesterone-induced PRB phosphorylation. Collectively, these studies indicate that PPARgamma activation inhibits PRB activity through both acute (phosphorylation) and long-term (PRB degradation) pathways.

MUC1 is a substrate for gamma-secretase

Understanding the underlying mechanisms by which a normal cell avoids the oncogenic potential of MUC1 signaling requires further definition of the pathways by which the MUC1 cytoplasmic tail is processed in both normal and tumor-derived cells. In the present study we describe the processing pathway initiated by TACE/ADAM17 cleavage of MUC1. Utilizing the human uterine epithelial cell line, HES, derived from normal endometrium, we show that endogenous full length MUC1 undergoes regulated intramembranous proteolysis mediated by presenillin-dependent gamma-secretase. Cytokine-stimulated HES cells exposed to gamma-secretase inhibitors accumulated a membrane-associated 15 kDa fragment of the MUC1 C-terminal subunit (CTF15). Inhibitors of TACE/ADAM17-mediated shedding inhibited accumulation of MUC1-CTF15 and MUC1 ectodomain release to a similar extent consistent with MUC1-CTF15 being a product of TACE/ADAM17 action. Reduction of catalytically active gamma-secretase complex by nicastrin siRNA treatment also resulted in CTF15 accumulation. Furthermore, mature nicastrin, the substrate receptor for gamma-secretase, co-immunoprecipitated with CTF15 in the presence of gamma-secretase inhibitors indicating the formation of CTF15: nicastrin complexes. MUC1-CTF15 accumulation in response to gamma-secretase inhibition was demonstrated in both normal and tumor-derived cells from humans and mice indicating that this processing pathway exists in many cell contexts. We did not detect products of MUC1 cleavage by gamma-secretase in the presence of various proteasomal inhibitors indicating that subsequent degradation is either non-proteasomal or extremely efficient. We suggest that this efficient pathway attenuates potential signaling mediated by cytoplasmic tail fragments.

Perlecan domain IV peptide stimulates salivary gland cell assembly in vitro

Treatment of xerostomia would benefit from development of a functional implantable artificial salivary gland. Salivary gland tissue from surgical patients was assessed by histology and immunohistochemistry to establish the phenotype of normal salivary gland cells including the native basement membranes. Ductal and acinar cells were identified in tissue and cultured cells from dispersed tissue. High levels of laminin and perlecan/HSPG2 (heparan sulfate proteoglycan 2) were noted in basement membranes, and perlecan also was secreted and organized by cultured acinar populations, which formed lobular structures that mimicked intact glands when cultured on Matrigel or a bioactive peptide derived from domain IV of perlecan. On either matrix, large acini-like lobular structures grew and formed connections between the lobes. alpha-Amylase secretion was confirmed by staining and activity assay. Biomarkers, including tight junction protein E-cadherin and water channel protein aquaporin 5 found in tissue, were expressed in cultured acinar cells. Cells cultured on Matrigel or domain IV of perlecan peptide organized stress fibers and activated focal adhesion kinase. We report a novel technique to isolate acinar cells from human salivary gland and identify a human peptide sequence in perlecan that triggers differentiation of salivary gland cells into self-assembling acini-like structures that express essential biomarkers and which secrete alpha-amylase.

Multifunctionality of extracellular and cell surface heparan sulfate proteoglycans

Heparan sulfate proteoglycans are a remarkably diverse family of glycosaminoglycan-bearing protein cores that include the syndecans, the glypicans, perlecan, agrin, and collagen XVIII. Members of this protein class play key roles during normal processes that occur during development, tissue morphogenesis, and wound healing. As key components of basement membranes in organs and tissues, they also participate in selective filtration of biological fluids, in establishing cellular barriers, and in modulation of angiogenesis. The ability to perform these functions is provided both by the features of the protein cores as well as by the unique properties of heparan sulfate, which is assembled as a polymer of N-acetylglucosamine and glucuronic acid and modified by specific enzymes to generate specialized biologically active structures. This article discusses the structures and functions of this amazing family of proteoglycans and provides a platform for further study of the individual members.

Expression of human MUC1 during early pregnancy in the human MUC1 transgenic mouse model

Embryo implantation involves direct interaction of the blastocyst with the luminal epithelium of the receptive uterus. MUC1, a transmembrane mucin expressed at the apical surface of uterine epithelia, acts as a barrier to microbial infection and enzymatic attack. Loss of MUC1 is believed to be a prerequisite for a functionally receptive uterus across many species. Human and murine MUC1 regulation by steroid hormones displays important differences. Estrogen (E2) stimulates MUC1 expression in mice, and progesterone (P4) antagonizes E2 action in this regard. MUC1 expression is severely reduced during the receptive uterine state in mice. In contrast, human MUC1 expression is maximal at the receptive or midluteal phase, when P4 levels are high. No information is available regarding regulation of human MUC1 in vivo at the site of embryo attachment. Our aim was to better understand regulation of human MUC1 during early pregnancy in vivo. For this purpose, we used a transgenic mouse carrying full-length human MUC1 gene (Tg(MUC1)79.24Gend) as well as endogenous MUC1 as a model system. Human MUC1 was detected by real-time RT-PCR, Western blotting, and immunohistochemistry during early pregnancy. Our data indicate that human MUC1 persists at reduced (20% relative to Day 1 postcoitum) levels in receptive-phase uteri, including the site of embryo attachment. In contrast, mouse MUC1 was much more severely (>98% relative to Day 1 postcoitum) reduced in the same context. These observations are consistent with distinct regulation between the human and mouse genes. Because these genes are expressed in the same transcriptional context (i.e., mouse uterine epithelia), structural differences between human and murine genes must account for these differences in MUC1 regulation.

HIP/RPL29 antagonizes VEGF and FGF2 stimulated angiogenesis by interfering with HS-dependent responses

HIP/RPL29 is a heparan sulfate (HS) binding protein with diverse activities including modulation of heparanase (HPSE) activity. We examined HIP/RPL29's ability to modulate actions of HS-binding growth factors (HBGFs) in angiogenesis. Between 1 and 2.5 microg/ml (ca. 60-150 nM), HIP/RPL29 inhibited HBGF-stimulated endothelial cell tube formation. Aortic explant outgrowth also was inhibited, but at higher concentrations (40 microg/ml). At this concentration, HIP/RPL29 had no effect on HBGF-stimulated MAPK phosphorylation or VEGF-stimulated receptor-2 phosphorylation at site Y-996. Partial inhibition occurred at VEGF receptor-2 site Y951, associated with cell migration. HBGF displacement from HS-bearing perlecan domain I showed that HIP/RPL29 released 50% of bound HBGF at 20 microg/ml, a dose where endothelial tube formation is inhibited. Similar FGF2 release occurred at pH 5.0 and 7.0, conditions where HPSE is highly and residually active, respectively. We considered that HIP/RPL29 inhibits HPSE-dependent release of HS-bound HBGFs. At pH 5.0, release of soluble HS was inhibited by 64% at concentrations of 5 microg/ml and by 77% at 40 microg/ml, indicating that HIP/RPL29 antagonizes HPSE activity. At concentrations up to 40 microg/ml (ca. 2.5 microM) where angiogenic processes are inhibited, release of FGF2 occurred in the presence of HPSE and HIP/RPL29. The majority of this FGF2 is not bound to soluble HS. Studies of HIP/RPL29 binding to HS indicated that many structural features of HS are important in modulation of HBGF activities. Our findings suggest that inhibition of angiogenic processes by HIP/RPL29 involves attenuation of the formation of soluble, biologically active HBGF:HS complexes that activate HBGF receptors.

The cytoplasmic tail of MUC1: a very busy place

The role of mucin 1 (MUC1) in protecting epithelia from microbial infection, enzymatic digestion, and other irritants has been appreciated for some time. In addition, MUC1 serves as a barrier to embryo implantation. MUC1 is highly abundant in many tumors in which its role in barrier function may serve to protect cells from the host immune system, whereas MUC1 is less abundant in certain other cells-for example, in trophoblasts and hematopoietic cells. Most of the functions of MUC1 depend upon its large, extracellular ectodomain. Nonetheless, a series of studies have demonstrated a surprisingly diverse role for the small, highly conserved cytoplasmic domain of MUC1 in intracellular signaling. These intracellular activities have potential roles in the physiology of both malignant and nonmalignant cells.

Transcriptional control of the expression of MUC1

MUC1 is a multifunctional cell surface glycoprotein that modulates cell adhesion, protects mucosa from infection and enzymatic attack, lubricates cell surfaces, participates in multiple signal-transduction pathways and is overexpressed by many tumors. MUC1 levels change dynamically in various cellular contexts. The primary mechanism for controlling MUC1 expression appears to be transcriptional through a complex combination of often overlapping regulatory motifs that control both tissue specificity and overall rate of transcription. This review will summarize the current knowledge of the factors known to control MUC1 transcriptional regulation, including cytokines, steroid hormones and the growth factors they stimulate, as well as suggest how this information may be exploited in the future to control MUC1 expression in specific biological contexts.

The MUC1 HMFG1 glycoform is a precursor to the 214D4 glycoform in the human uterine epithelial cell line, HES

MUC1, a type I transmembrane glycoprotein expressed on most epithelia and many cancer cells, is involved in embryo implantation and tumor progression. A series of antibodies directed against the MUC1 ectodomain have been used to study MUC1 expression in the female reproductive tract, sometimes with apparently contradictory results. In the current study, we used two monoclonal MUC1 antibodies, 214D4 and HMFG1, to study the relationship between these MUC1 glycoforms in the human uterine epithelial cell line, HES, and human endometrial extracts. In response to tumor necrosis factor stimulation, accumulation of the HMFG1-reactive forms preceded that of the 214D4-reactive forms. Following inhibition of protein synthesis by cycloheximide, HMFG1-reactive species were lost rapidly (metabolic half-life [T(1/2)] = 20 min), while there was no change in the level of the 214D4-reactive forms even after 80 min. HMFG1-reactive forms had smaller oligosaccharide chains than the 214D4-reactive forms, and could not be detected on the cell surface of intact cells or in the shed (media) fraction, although they were readily detected in permeabilized cells. Both 214D4- and HMFG1-reactive species were detected in human endometrial extracts throughout the cycle; however, consistent with the HES cell studies, the HMFG1-reactive species were both smaller and less abundant than the 214D4-reactive species. Consistent with this observation, we found that HMFG1-reactive species were difficult to detect in tissue sections unless predigested with neuraminidase, indicating that these structures are rapidly sialylated during synthesis. In contrast, 214D4-reactive species were robustly detected in both proliferative and secretory stages. Collectively, these studies indicate that the HMFG1-reactive glycoform is a precursor of the 214D4-reactive glycoform in HES cells and normal uterine epithelia. Therefore, discrepancies in patterns of MUC1 expression in other studies may be due to failure to account for these glycoform relationships.

A novel peptide sequence in perlecan domain IV supports cell adhesion, spreading and FAK activation

Perlecan/HSPG2 is a large, multi-domain, multifunctional heparan sulfate proteoglycan with a wide tissue distribution. With the exception of its unique domain I, each of perlecan's other four domains shares sequence similarity to other protein families including low density lipoprotein (LDL) receptor, laminin alpha chain, neural cell adhesion molecule (NCAM), immunoglobulin (Ig) superfamily members, and epidermal growth factor (EGF). Previous studies demonstrated that glycosaminoglycan-bearing perlecan domain I supports early chondrogenesis and growth factor delivery. Other sites in the core protein interact with other matrix molecules and support cell adhesion, although the peptide sequences involved remain unidentified. To identify novel functional motifs within perlecan, we used a bioinformatics approach to predict regions likely to be on the exterior of the folded protein. Unique hydrophilic sequences of about 18 amino acids were selected for testing in cell adhesion assays. A novel peptide sequence (TWSKVGGHLRPGIVQSG) from an immunoglobulin (Ig) repeat in domain IV supported rapid cell adhesion, spreading and focal adhesion kinase (FAK) activation when compared to other peptides, a randomly scrambled sequence of the domain IV peptide or a negative control protein. MG-63 human osteosarcoma cells, epithelial cells and multipotent C(3)H10T1/2 cells, but not bone marrow cells, rapidly, i.e., within 30 min, formed focal adhesions and assembled an actin cytoskeleton on domain IV peptide. Cell lines differentially adhered to the domain IV peptide, suggesting adhesion is receptor specific. Adhesion was divalent cation independent and heparin sensitive, a finding that may explain some previously poorly understood observations obtained with intact perlecan. Collectively, these studies demonstrate the feasibility of using bioinformatics-based strategies to identify novel functional motifs in matrix proteins such as perlecan.

MUC1 expression is repressed by protein inhibitor of activated signal transducer and activator of transcription-y

Mucin 1 (MUC1) is a transmembrane glycoprotein that modulates the interaction between the embryo and the uterine epithelial cell surface. MUC1 also is a tumor marker and has been implicated in the protection of cancer cells from immune cell attack as well as in cell signaling in some tumors. We and others have shown that MUC1 expression is activated by progesterone (P), TNF-alpha, and interferon-gamma (IFN-gamma). Here we demonstrate that MUC1 expression is down-regulated by overexpression of members of the protein inhibitor of activated signal transducer and activator of transcription (PIAS) family, PIAS1, PIAS3, PIASxalpha, PIASxbeta, and PIASy, in human uterine epithelial cell lines HES and HEC-1A and in a breast cancer cell line, T47D. Treatments with P, TNF-alpha, and IFN-gamma were unable to overcome the repression by PIASy. PIASy repression of basal, P-, and TNF-alpha-stimulated MUC1 promoter activity was not dependent on the PIASy sumoylation domain. In contrast, PIASy suppression of IFN-gamma-activated MUC1 promoter activity was dependent on the PIASy sumoylation domain. PIASy and P receptor B were localized to the nucleus upon P treatment, and small interfering RNA knockdown of PIASy resulted in an increase in P-mediated stimulation of MUC1 protein expression. Overexpression of PIASy did not affect P receptor B binding to the MUC1 promoter but surprisingly led to a loss of nuclear receptor corepressor (NCoR), which was recruited to the promoter in response to P. Collectively, these data indicate that PIASy may be a useful target for down-regulation of MUC1 expression in various contexts.

Coculture with prostate cancer cells alters endoglin expression and attenuates transforming growth factor-beta signaling in reactive bone marrow stromal cells

A dynamic interplay between prostate cancer cells and reactive bone stroma modulates growth of metastases within bone. We used microarray analysis to screen for changes in gene expression in bone marrow stromal cells cocultured with prostate cancer cells and found reduced expression of endoglin, a transmembrane glycoprotein that functions as an auxiliary coreceptor for members of the transforming growth factor beta (TGF-beta) family of cytokines. The downstream TGF-beta/bone morphogenetic protein signaling pathway including Smad1 and Smad2/3 also was attenuated, as was Smad-dependent gene transcription. Smad1/5/8-dependent inhibitor of DNA binding 1 expression and Smad2/3-dependent plasminogen activator inhibitor I expression both were decreased and were accompanied by decreased cell proliferation. Small interfering RNA-mediated knockdown of endoglin in HS-5 cells verified that the effects on signaling were a direct result of the attenuation of endoglin. These data illustrate that endoglin acts as a positive regulator of both activin receptor-like kinase 1-induced Smad1/5/8 activation and activin receptor-like kinase 5-induced Smad2/3 activation in bone marrow stromal cells. In addition, the data illustrate that one early event of metastasis upon the arrival of prostate cancer cells into the bone stroma is attenuated endoglin expression in the stromal cells, which subsequently alters Smad signaling and cell proliferation. We hypothesize that coculture of bone marrow stromal cells with prostate cancer cells alters TGF-beta signaling in the stromal cells, ultimately facilitating growth of the cancer cells in the bone compartment. Collectively, these studies suggest that prostate cancer cells modulate TGF-beta responsiveness of bone marrow stroma as one means of facilitating their own growth in bone.

Heparan sulfate proteoglycans and their binding proteins in embryo implantation and placentation

Complex interactions occur among embryonic, placental and maternal tissues during embryo implantation. Many of these interactions are controlled by growth factors, extracellular matrix and cell surface components that share the ability to bind heparan sulfate (HS) polysaccharides. HS is carried by several classes of cell surface and secreted proteins called HS proteoglycan that are expressed in restricted patterns during implantation and placentation. This review will discuss the expression of HS proteoglycans and various HS binding growth factors as well as extracellular matrix components and HS-modifying enzymes that can release HS-bound proteins in the context of implantation and placentation.

Heparanase expression and function during early pregnancy in mice

Embryo implantation is a complex process that involves interactions between cell-surface and extracellular components of the blastocyst and the uterus, including blastocyst adhesion to the uterine luminal epithelium, epithelial basement membrane penetration and stromal extracellular matrix remodeling, angiogenesis, and decidualization. These processes all involve interactions with heparan sulfate (HS) proteoglycans, which harbor various growth factors and cytokines and support cell adhesion. Heparanase (HPSE) is an endo-beta-glucuronidase that cleaves HS at specific sites. HPSE also can act as an adhesion molecule independent of its catalytic activity. Thus, HPSE is a multifunctional molecule contributing to and modulating HS-dependent processes. Exogenously added HPSE improves embryo implantation in mice; however, no information is available regarding the normal pattern of HPSE expression and activity during the implantation process in any system. Using several approaches, including real-time RT-PCR, in situ hybridization, and immunohistochemistry, we determined that uterine HPSE expression increases dramatically during early pregnancy in mice. Heparanase mRNA and protein were primarily expressed in decidua and were rapidly induced at the implantation site. Uterine HPSE activity was characterized and demonstrated to increase >40-fold during early pregnancy. Finally, we demonstrate that the HPSE inhibitor PI-88 severely inhibits embryo implantation in vivo. Collectively, these results indicate that HPSE plays a role in blastocyst implantation and complements previous studies showing a role for HS-dependent interactions in this process.

Perlecan--a multifunctional extracellular proteoglycan scaffold

Perlecan is a large multidomain heparan sulfate proteoglycan of the extracellular matrix. Expression of this proteoglycan changes dynamically during embryo implantation and placentation. Perlecan is expressed by various cells of the embryo including trophectoderm and trophoblast as well as the maternal compartment, including basal lamina underlying uterine epithelia and endothelia and, most dynamically, in developing decidua. Perlecan supports various biological functions, including cell adhesion, growth factor binding, and modulation of apoptosis. Moreover, studies in other systems demonstrate that perlecan expression and activity can be controlled at many levels, including transcription, alternative splicing, and extracellular proteolysis. This review will discuss changes in perlecan expression that occur during embryo implantation and placentation. Furthermore, we propose a model in which perlecan represents an extracellular scaffold protein that supports complex, distinct functions in its full-length form or smaller forms generated by alternative mRNA splicing, extracellular proteolysis, or glycosidase action.

Global growth deficiencies in mice lacking the ribosomal protein HIP/RPL29

Because of their deleterious effects on developing organisms, ribosomal protein (RP) mutations have been poorly described in mammals, and only a few heterozygous mutations have been shown to be viable. This observation is believed to be due to the fact that each RP is an essential component in the assembly of a functional stable ribosome. Here, we created gene targeted mutant mice lacking HIP/RPL29, an RP associated with translationally active ribosomes in eukaryotes. In contrast to other RP mutants, HIP/RPL29 null mice are viable but are up to 50% smaller than their control littermates at weaning age. In null embryos, delayed global growth is first observed around mid-gestation, and postnatal lethality due to low birth weight results in distortion of the Mendelian ratio. Prenatal growth defects are not fully compensated for during adulthood, and null animals display proportionately smaller organs and stature, and reach sexual maturity considerably later when compared with their control siblings. Additionally, HIP/RPL29 null embryonic fibroblasts have decreased rates of proliferation and protein synthesis and exhibit reduced steady state levels of core RPs. Altogether, our findings provide conclusive genetic evidence that HIP/RPL29 functions as an important regulator of global growth by modulating the rate of protein synthesis.

Chondrogenic differentiation on perlecan domain I, collagen II, and bone morphogenetic protein-2-based matrices

Extracellular matrix (ECM) molecules in cartilage cooperate with growth factors to regulate chondrogenic differentiation and cartilage development. Domain I of perlecan (Pln) bears heparan sulfate chains that bind and release heparin binding growth factors (HBGFs). We hypothesized that Pln domain I (PlnDI) might be complexed with collagen II (P-C) fibrils to improve binding of bone morphogenetic protein-2 (BMP-2) and better support chondrogenesis and cartilage-like tissue formation in vitro. Our results showed that P-C fibrils bound more BMP-2 than collagen II fibrils alone, and better sustained BMP-2 release. Polylactic acid (PLA)-based scaffolds coated with P-C fibrils immobilized more BMP-2 than either PLA scaffolds or PLA scaffolds coated with collagen II fibrils alone. Multipotential mouse embryonic mesenchymal cells, C3H10T1/2, were cultured on 2-dimensional P-C fibrils or 3-dimensional P-C/BMP-2-coated (P-C-B) PLA scaffolds. Chondrogenic differentiation was indexed by glycosaminoglycan (GAG) production, and expression of the pro-chondrogenic transcription factor, Sox9, as well as cartilaginous ECM proteins, collagen II, and aggrecan. Immunostaining for aggrecan, perlecan, tenascin, and collagen X revealed that both C3H10T1/2 cells and primary mouse embryonic fibroblasts cultured on P-C-B fibrils showed the highest expression of chondrogenic markers among all treatment groups. Safranin O-Fast Green staining indicated that cartilage-like tissue was formed in the P-C-B scaffolds, while no obvious cartilage-like tissue formed in other scaffolds. We conclude that P-C fibrils provide an improved biomimetic material for the binding and retention of BMP-2 and support chondrogenic differentiation.

MUC1 is a scaffold for selectin ligands in the human uterus

MUC1 is a large, transmembrane mucin glycoprotein abundantly expressed at the apical surface of uterine epithelia in all species examined to date. Loss of MUC1 at the time of embryo implantation occurs in many species; however, this does not appear to be the case in humans. Recent studies indicate that human blastocysts express L-selectin at their external surfaces raising the possibility that selectin ligands expressed at the apical surface of the uterine epithelium support early stages of blastocyst attachment. In the current study, we have used a panel of antibodies specific for selectin ligands to determine if MUC1 functions as a scaffold for these carbohydrate motifs in fertile women. The results demonstrate that MUC1 carries selectin ligands throughout the secretory phase of the menstrual cycle, including the mid-secretory (receptive) phase. Consequently, MUC1 represents a potential ligand for selectins expressed by human blastocysts.

Spatiotemporal distribution of heparan sulfate epitopes during murine cartilage growth plate development

Heparan sulfate proteoglycans (HSPGs) are abundant in the pericellular matrix of both developing and mature cartilage. Increasing evidence suggests the action of numerous chondroregulatory molecules depends on HSPGs. In addition to specific functions attributed to their core protein, the complexity of heparan sulfate (HS) synthesis provides extraordinary structural and functional heterogeneity. Understanding the interactions of chondroregulatory molecules with HSPGs and their subsequent outcomes has been limited by the absence of a detailed analysis of HS species in cartilage. In this study, we characterize the distribution and variety of HS species in developing cartilage of normal mice. Cryo-sections of femur and tibia from normal mouse embryos were evaluated using immunostaining techniques. A panel of unique phage display antibodies specific to particular HS species were employed and visualized with secondary antibodies conjugated to Alexa-fluor dyes. Confocal microscopy demonstrates that HS species are dynamic structures within developing growth plate cartilage and the perichondrium. GlcNS6S-IdoUA2S-GlcNS6S species are down regulated and localization of GlcNS6S-IdoUA-GlcNS6S species within the hypertrophic zone of the growth plate is lost during normal development. Regional differences in HS structures are present within developing growth plates, implying that interactions with and responses to HS-binding proteins also may display regional specialization.