Identification of link protein during follicle development and cumulus cell cultures in rats

Analysis of a limb-specific regulatory element in the promoter of the link protein gene

Link protein is encoded by the Hapln1 gene and is a prototypical protein found in the cartilage matrix. It acts as an important component of the endochondral skeleton during early development. To study its transcriptional regulation, promoter fragments derived from the link protein gene were coupled to the β-galactosidase reporter and used to study in vivo transgene expression in mice. In day 15.5 mouse embryos, a link promoter fragment spanning -1020 to +40 nucleotides demonstrated highly specific β-galactosidase staining of skeletal structures, including the appendicular and axial cartilaginous tissues. Two shorter promoter fragments, spanning -690 to +40 and -315 to +40 nucleotides, demonstrated limb- and genitalia-specific expression resembling that of homeodomain-regulated tissues. Bioinformatic analysis revealed a highly conserved, Hox-like binding site (HLBS) at approximately -220 bp of the promoter, shared by both constructs, which contained the Hox-core consensus sequence TAATTA. Electromobility shift assays demonstrated binding of Hox-B4 recombinant protein to the HLBS, which was eliminated with nucleotide substitutions within the core-binding element. Co-transfection analysis of the HLBS demonstrated a 22-fold transcriptional activation by HoxA9 expression, which was ablated with a substitution within the core HLBS element. Together these findings establish promoter regions within the link protein gene that are important for in vivo expression and identify the potential role of homeodomain-containing proteins in controlling cartilage and limb gene expression.

Molecular organization and mechanical properties of the hyaluronan matrix surrounding the mammalian oocyte

Successful ovulation and oocyte fertilization are essential prerequisites for the beginning of life in sexually reproducing animals. In mammalian fertilization, the relevance of the protein coat surrounding the oocyte plasma membrane, known as zona pellucida, has been widely recognized, while, until not too long ago, the general belief was that the cumulus oophorus, consisting of follicle cells embedded in a hyaluronan rich extracellular matrix, was not essential. This opinion was based on in vitro fertilization procedures, in which a large number of sperms are normally utilized and the oocyte can be fertilized even if depleted of cumulus cells. Conversely, in vivo, only very few sperm cells reach the fertilization site, arguing against the possibility of a coincidental encounter with the oocyte. In the last two decades, proteins required for HA organization in the cumulus extracellular matrix have been identified and the study of fertility in mice deprived of the corresponding genes have provided compelling evidence that this jelly-like coat is critical for fertilization. This review focuses on the advances in understanding the molecular interactions making the cumulus environment suitable for oocyte and sperm encounter. Most of the studies on the molecular characterization of the cumulus extracellular matrix have been performed in the mouse and we will refer essentially to findings obtained in this animal model.

Periovulatory expression of hyaluronan and proteoglycan link protein 1 (Hapln1) in the rat ovary: hormonal regulation and potential function

Periovulatory follicular matrix plays an important role in cumulus-oocyte complex (COC) expansion, ovulation, and luteal formation. Hyaluronan and proteoglycan link protein 1 (HAPLN1), a component of follicular matrix, was shown to enhance COC expansion in vitro. However, the regulatory mechanisms of periovulatory expression of Hapln1 and its role in periovulatory granulosa cells have not been elucidated. We first determined the periovulatory expression pattern of Hapln1 using pregnant mare serum gonadotropin/human chorionic gonadotropin (PMSG/hCG)-primed immature rat ovaries. Hapln1 expression was transiently induced both in intact ovaries and granulosa cells at 8 h and 12 h after hCG injection. This in vivo expression of Hapln1 was recapitulated by culturing preovulatory granulosa cells with hCG. The stimulatory effect of hCG was blocked by inhibition of protein kinase A, phosphatidylinositol-dependent kinase, p38 MAPK, epidermal growth factor signaling, and prostaglandin synthesis, revealing key mediators involved in LH-induced Hapln1 expression. In addition, knockdown of Runx1 and Runx2 expression by small interfering RNA or inhibition of RUNX activities by dominant-negative RUNX decreased hCG or agonist-induced Hapln1 expression. Chromatin immunoprecipitation assays verified the in vivo binding of RUNX1 and RUNX2 to the Hapln1 promoter in periovulatory granulosa cells. Luciferase reporter assays revealed that mutation of the RUNX binding sites completely obliterated the agonist-induced activity of the Hapln1 promoter. These data conclusively identified RUNX proteins as the crucial transcription regulators for LH-induced Hapln1 expression. Functionally, treatment with HAPLN1 increased the viability of cultured granulosa cells and decreased the number of the cells undergoing apoptosis, whereas knockdown of Hapln1 expression decreased granulosa cells viability. This novel finding indicates that HAPLN1 may promote periovulatory granulosa cell survival, which would facilitate their differentiation into luteal cells.

Formation of the ovarian follicular antrum and follicular fluid

The formation of the follicular antrum and follicular fluid has received scant attention from researchers, yet both are important processes in follicular development. The central hypothesis on follicular fluid formation suggests that production by granulosa cells of hyaluronan and the chondroitin sulfate proteoglycan versican generates an osmotic gradient. This gradient draws in fluid derived from the thecal vasculature. Inter-alpha-trypsin inhibitor is also present in follicular fluid at least in species with large follicles, and inter-alpha-trypsin inhibitor and versican could additionally bind or cross-link with hyaluronan, resulting in the retention of these molecules within the follicular antrum. Barriers to the movement of fluid across the membrana granulosa are apparently minimal, as even relatively large serum proteins are present in follicular fluid. Despite the relative permeability of the follicular wall, aquaporins are present in granulosa cells and could be actively involved in the transport of water into the follicle. The formation of an antrum also requires movement of granulosa cells relative to each other to allow the fluid to accumulate. This presumably involves remodeling of cell-cell junctions and in species with small follicles may involve death of centrally located granulosa cells. Remodeling of the stroma and thecal layers also accompanies growth and expansion of the antrum and presumably involves similar processes that accompany growth of other glands.

Gene expression microarray profiles of cumulus cells in lean and overweight-obese polycystic ovary syndrome patients

The aim of this work was to study gene expression patterns of cultured cumulus cells from lean and overweight-obese polycystic ovary syndrome (PCOS) patients using genome-wide oligonucleotide microarray. The study included 25 patients undergoing in vitro fertilization and intra-cytoplasmic sperm injection: 12 diagnosed with PCOS and 13 matching controls. Each of the groups was subdivided into lean (body mass index (BMI) < 24) and overweight (BMI > 27) subgroups. The following comparisons of gene expression data were made: lean PCOS versus lean controls, lean PCOS versus overweight PCOS, all PCOS versus all controls, overweight PCOS versus overweight controls, overweight controls versus lean controls and all overweight versus all lean. The largest number of differentially expressed genes (DEGs), with fold change (FC) |FC| >or= 1.5 and P-value < 0.01, was found in the lean PCOS versus lean controls comparison (487) with most of these genes being down-regulated in PCOS. The second largest group of DEGs originated from the comparison of lean PCOS versus overweight PCOS (305). The other comparisons resulted in a much smaller number of DEGs (174, 109, 125 and 12, respectively). In the comparison of lean PCOS with lean controls, most DEGs were transcription factors and components of the extracellular matrix and two pathways, Wnt/beta-catenin and mitogen-activated protein kinase. When comparing overweight PCOS with overweight controls, most DEGs were of pathways related to insulin signaling, metabolism and energy production. The finding of unique gene expression patterns in cumulus cells from the two PCOS subtypes is in agreement with other studies that have found the two to be separate entities with potentially different pathophysiologies.

Higher expression of hyaluronan binding protein 1 (HABP1/p32/gC1qR/SF2) during follicular development and cumulus oocyte complex maturation in rat

Ovulation is a complex process of releasing a fertilizable oocyte and depends on the proper formation of an extracellular hyaluronan rich matrix by the cumulus oocyte complex (COC). The formation of a HA rich matrix is dependent on the synthesis and organization of HA in the presence of several biomolecules that mediate its crosslinking. To gain an insight into the follicular maturation and COC expansion, we have studied the expression of hyaluronan binding protein 1 (HABP1), which is known to interact specifically with hyaluronan. The level of HABP1 increased markedly during ovulation after gonadotropin stimulation, and the overexpression was seen in mural granulosa cells, expanding cumulus cells and follicular fluid. However, HABP1 could not be detected in the luteal cells of corpus luteum after ovulation. Such increased expression of HABP1 was observed both during in vivo and in vitro conditions of COC expansion. The level of HABP1 transcript was upregulated up to fivefold after COC expansion as compared to compact COC. Immunofluorescence analysis showed HABP1 to be localized in the cytoplasm and extracellular matrix, suggesting its role in ECM organization. The cultured expanded COC treated with hyaluronidase for different time periods showed the gradual dispersion of COC, which coincide with the loss of HABP1 from the matrix suggesting that HABP1 is bound to hyaluronan. These results indicate that HABP1 expressed in rat COCs during maturation may facilitate the formation of the HA matrix in the extracellular space around the oocyte with cumulus expansion during maturation.

Molecular mechanisms of ovulation: co-ordination through the cumulus complex

Successful ovulation requires that developmentally competent oocytes are released with appropriate timing from the ovarian follicle. Somatic cells of the follicle sense the ovulatory stimulus and guide resumption of meiosis and release of the oocyte, as well as structural remodelling and luteinization of the follicle. Complex intercellular communication co-ordinates critical stages of oocyte maturation and links this process with release from the follicle. To achieve these outcomes, ovulation is controlled through multiple inputs, including endocrine hormones, immune and metabolic signals, as well as intrafollicular paracrine factors from the theca, mural and cumulus granulosa cells and the oocyte itself. This review focuses on the recent advances in understanding of molecular mechanisms that commence after the gonadotrophin surge and culminate with release of the oocyte. These mechanisms include intracellular signalling, gene regulation and remodelling of tissue structure in each of the distinct ovarian compartments. Most critical ovulatory mediators exert effects through the cumulus cell complex that surrounds and connects with the oocyte. The convergence of ovulatory signals through the cumulus complex co-ordinates the key mechanistic processes that mediate and control oocyte maturation and ovulation.

Luteinizing hormone-induced RUNX1 regulates the expression of genes in granulosa cells of rat periovulatory follicles

The LH surge induces specific transcription factors that regulate the expression of a myriad of genes in periovulatory follicles to bring about ovulation and luteinization. The present study determined 1) the localization of RUNX1, a nuclear transcription factor, 2) regulation of Runx1 mRNA expression, and 3) its potential function in rat ovaries. Up-regulation of mRNA and protein for RUNX1 is detected in preovulatory follicles after human chorionic gonadotropin (hCG) injection in gonadotropin-treated immature rats as well as after the LH surge in cycling animals by in situ hybridization and immunohistochemical and Western blot analyses. The regulation of Runx1 mRNA expression was investigated in vitro using granulosa cells from rat preovulatory ovaries. Treatments with hCG, forskolin, or phorbol 12 myristate 13-acetate stimulated Runx1 mRNA expression. The effects of hCG were reduced by inhibitors of protein kinase A, MAPK kinase, or p38 kinase, indicating that Runx1 expression is regulated by the LH-initiated activation of these signaling mediators. In addition, hCG-induced Runx1 mRNA expression was inhibited by a progesterone receptor antagonist and an epidermal growth factor receptor tyrosine kinase inhibitor, whereas amphiregulin stimulated Runx1 mRNA expression, demonstrating that the expression is mediated by the activation of the progesterone receptor and epidermal growth factor receptor. Finally, knockdown of Runx1 mRNA by small interfering RNA decreased progesterone secretion and reduced levels of mRNA for Cyp11a1, Hapln1, Mt1a, and Rgc32. The hormonally regulated expression of Runx1 in periovulatory follicles, its involvement in progesterone production, and regulation of preovulatory gene expression suggest important roles of RUNX1 in the periovulatory process.

Expression of hyaluronan synthases and corresponding hyaluronan receptors is differentially regulated during oocyte maturation in cattle

In response to the gonadotropin surge, the compact cumulus-oocyte complex (COC) undergoes expansion by synthesis of the mucopolysaccharide hyaluronan (HA) accompanying oocyte maturation. The objective of the present study was to quantify mRNA transcripts of the HA synthase (HAS) 1, HAS2, and HAS3 and the HA-receptors CD44 and RHAMM (receptor for HA-mediated motility). Additionally, we determined the histological localization of HA and its receptor, CD44, in maturing bovine COCs and cultured granulosa cells (GCs). Full-length transcript of bovine HAS2 and a part of the bovine RHAMM sequence has been made available. Real-time reverse transcriptase-polymerase chain reaction was used for individual mRNA expressions of bovine COCs in comparison to follicular GC gonadotropin treatment. Localization of CD44 and HA were done by immunohistochemistry and biotinylated HA-binding protein, respectively. Gonadotropins caused a rapid, 120-fold increase of HAS2 mRNA, whereas a delayed, 2-fold up-regulation of HAS3 mRNA was observed. The HAS1 transcripts were barely detected. Expression of CD44 mRNA greatly increased during in vitro maturation of COCs, indicating an important role when compared to an unchanged, steady-state RHAMM expression. As a consequence, HA was locally enriched after COC expansion, but only limited change was observed in the GCs. In cultured GCs, HAS2 expression was stimulated through FSH application, followed by the effective treatments of FSH+LH and LH. Treatment with LH induced the highest increase of the CD44 receptor, followed by FSH and FSH+LH treatments. These results suggest that HAS2 is mainly responsible for rapid HA synthesis in bovine COCs and GCs. In bovine COCs, the transcriptional up-regulation of both HAS2 and the receptor CD44 appear to be important prerequisites for initiating HA-mediated effects during final oocyte development and sperm-egg interaction.

A hyaluronan binding link protein gene family whose members are physically linked adjacent to chondroitin sulfate proteoglycan core protein genes: the missing links

We describe a vertebrate hyaluronan and proteoglycan binding link protein gene family (HAPLN), consisting of four members including cartilage link protein. The encoded proteins share 45-52% overall amino acid identity. In contrast to the average sequence identity between family members, the sequence conservation between vertebrate species was very high. Human and mouse link proteins share 81-96% amino acid sequence identity. Two of the four link protein genes (HAPLN2 and HAPLN4) were restricted in expression to the brain/central nervous system, while one of the four genes (HAPLN3) was widely expressed. Genomic structures revealed that all four HAPLN genes were similar in exon-intron organization and were also similar in genomic organization to the 5' exons for the CSPG core protein genes. Strikingly, all four HAPLN genes were located immediately adjacent to the four CSPG core protein genes creating four pairs of CSPG-HAPLN genes within the mammalian genome. Furthermore, the two brain-specific HAPLN genes (HAPLN2 and HAPLN4) were physically linked to the brain-specific CSPG genes encoding brevican and neurocan, respectively. The tight physical association of the HAPLN and CSPG genes supports a hypothesis that the first HAPLN gene arose as a partial gene duplication event from an ancestral CSPG gene. There is some degree of coordinated expression of each gene pair. Collectively, the four HAPLN genes are expressed by most tissue types, reflecting the fundamental importance of the hyaluronan-dependent extracellular matrix to tissue architecture and function in vertebrate species. Comparison of the genomic structures for the HAPLN, CSPG genes and other members of the link module superfamily provide strong support for a common evolutionary origin from an ancestral gene containing one link module encoding exon.

Follicle-stimulating hormone and insulin-like growth factor I synergistically induce up-regulation of cartilage link protein (Crtl1) via activation of phosphatidylinositol-dependent kinase/Akt in rat granulosa cells

FSH and IGF-I are both important determinants of follicle development and the process of cumulus cell-oocyte complex expansion. FSH stimulates the phosphorylation of Akt by mechanisms involving phosphatidylinositol 3-kinase (PI3-K), a pattern of response mimicking that of IGF-I. Cartilage link protein (Crtl1) is confined to the cartilaginous lineage and is assembled into a macroaggregate complex essential for hyaluronan-rich matrix stabilization. The present studies were performed to determine the actions of FSH and IGF-I on Crtl1 production in rat granulosa cells. Primary cultures of granulosa cells were prepared from 24-d-old rats. After treatments, cell extracts and media were prepared, and the Crtl1 level was determined by immunoblotting analysis using anti-Crtl1 antibodies. Here we showed that 1) treatment with FSH (> or = 25 ng/ml) or IGF-I (> or = 25 ng/ml) for 4 h increased Crtl1 production; 2) maximal stimulatory effects of FSH or IGF-I were observed at 100 or 50 ng/ml, respectively; 3) FSH caused a concentration-dependent increase in IGF-I-induced Crtl1 production and vice versa; 4) FSH and IGF-I also up-regulate the expression of Crtl1 mRNA; 5) FSH- and IGF-I-dependent Crtl1 production were abrogated by PI3-K inhibitors (LY294002 and wortmannin), and inhibition of Crtl1 production by p38 mitogen-activated protein kinase inhibitor (SB202190) was partial (approximately 30%), suggesting that PI3-K and, to a lesser extent, p38 mitogen-activated protein kinase are critical for the response. Our study represents the first report that FSH amplifies IGF-I-mediated Crtl1 production, possibly via PI3-K-Akt signaling cascades in rat granulosa cells.

Link protein as an enhancer of cumulus cell-oocyte complex expansion

To investigate the specific components involved in regulating cumulus cell-oocyte complex (COC) expansion in an in vitro mouse experiment, freshly-isolated COC were cultured in the presence of various combinations of FSH (1.0 microg/ml), proteins of the inter-alpha-inhibitor (I alpha I) family (a light chain, also known as bikunin, heavy chains [HC1 + HC2] and I alpha I [0.01-2.0 microg/ml]) and link protein (LP) (0.016-10 microg/ml) for 24 h and were observed for expansion of their cumulus cells (percent of COC with + 3 and + 4 expansion and average projected area). The COC were videotaped in real time at the initiation of culture and after 24 h of culture. FSH alone did not stimulate cumulus expansion under serum-free conditions; however, treatment with I alpha I (0.1-2.0 microg/ml) or heavy chains (10 microg/ml), but not bikunin (10 micro g/ml), in the presence of FSH significantly increased COC expansion, with maximal promotion occurring at 1.0 microg/ ml of I alpha I. Addition of LP (2.0 micro g/ml) to the medium containing I alpha I (1.0 microg/ml) and FSH resulted in significantly higher expansion levels than were observed in response to I alpha I alone, although LP alone (10 microg/ml) had no or very little effect by itself. Anti-I alpha I or anti-LP polyclonal antibody, which inhibits binding of I alpha I and LP, respectively, to hyaluronic acid (HA), markedly reduced expansion of the surrounding cumulus cell extracellular matrices. Therefore, in vitro, LP might serve, in part, to enhance the COC expansion possibly by stabilizing HA-I alpha I (or heavy chains) complex on the surrounding cumulus cell matrices.

Identification of a hyaluronic acid (HA) binding domain in the PH-20 protein that may function in cell signaling

The macaque sperm surface protein PH-20 is a hyaluronidase, but it also interacts with hyaluronic acid (HA) to increase internal calcium ( [Ca(2+)](i) ) in the sperm cell. A region of the PH-20 molecule, termed Peptide 2 (aa 205-235), has amino acid charge homology with other HA binding proteins. The Peptide 2 sequence was synthesized and two recombinant PH-20 proteins were developed, one containing the Peptide 2 region (G3, aa 143-510) and one without it (E12, aa 291-510). On Western blots, affinity-purified anti-Peptide 2 IgG recognized the 64 kDa band corresponding to PH-20 in acrosome intact sperm and, under reducing conditions, recognized the whole 67 kDa PH-20 and the endoproteolyzed N-terminal fragment of PH-20. HA conjugated to a photoaffinity substrate specifically bound to sperm surface PH-20. Indirect immunofluorescence demonstrated that Fab fragments of anti-Peptide 2 IgG bound to the head of live sperm. Biotinylated HA was bound by Peptide 2 and by sperm extracts in a microplate binding assay, and this binding was inhibited by Fab fragments of anti-Peptide 2 IgG. Biotinylated HA bound to the G3 protein and this binding was inhibited by anti-Peptide 2 Fab, but HA did not bind to the E12 protein. Fab fragments of anti-Peptide 2 IgG inhibited the increase in [Ca(2+)](i) induced in macaque sperm by HA. Our results suggest that the Peptide 2 region of PH-20 is involved in binding HA, which results in the cell signaling events related to the elevation of [Ca(2+)](i) during sperm penetration of the cumulus.

Characterization of binding properties of urinary trypsin inhibitor to cell-associated binding sites on human chondrosarcoma cell line HCS-2/8

Urinary trypsin inhibitor (UTI) forms membrane complexes with UTI-binding proteins (UTI-BPs) and initiates modulation of urokinase-type plasminogen activator (uPA) expression, which results in UTI-mediated suppression of cell invasiveness. It has been established that suppression of uPA expression and invasiveness by UTI is mediated through inhibition of protein kinase C-dependent signaling pathways and that human chondrosarcoma cell line HCS-2/8 expresses two types of UTI-BPs; a 40-kDa UTI-BP (UTI-BP(40)), which is identical to link protein (LP), and a 45-kDa UTI-BP (UTI-BP(45)). Here we characterize binding properties of UTI-BPs.UTI complexes in the cells. In vitro ligand blot, cell binding and competition assays, and Scatchard analyses demonstrate that both UTI-BP(40) and UTI-BP(45) bind (125)I-UTI. A deglycosylated form of UTI (NG-UTI), from which the chondroitin-sulfate side chain has been removed, binds only to UTI-BP(40). Additional experiments, using various reagents to block binding of (125)I-UTI and NG-UTI to the UTI-BP(40) and UTI-BP(45) confirm that the chondroitin sulfate side chain of UTI is required for its binding to UTI-BP(45). Analysis of binding of (125)I-UTI and NG-UTI to the cells suggests that low affinity binding sites are the UTI-BP(40) (which can bind NG-UTI), and the high affinity sites are the UTI-BP(45). In addition, UTI-induced suppression of phorbol ester stimulated up-regulation of uPA is inhibited by reagents that were shown to prevent binding of UTI to the 40- and 45-kDa proteins. We conclude that UTI must bind to both of the UTI-BPs to suppress uPA up-regulation.

Defect in SHAP-hyaluronan complex causes severe female infertility. A study by inactivation of the bikunin gene in mice

Hyaluronan (HA) associates with proteins and proteoglycans to form the extracellular HA-rich matrices that significantly affect cellular behaviors. So far, only the heavy chains of the plasma inter-alpha-trypsin inhibitor (ITI) family, designated as SHAPs (serum-derived hyaluronan-associated proteins), have been shown to bind covalently to HA. The physiological significance of such a unique covalent complex has been unknown but is of great interest, because HA and the ITI family are abundant in tissues and in plasma, respectively, and the SHAP-HA complex is formed wherever HA meets plasma. We abolished the formation of the SHAP-HA complex in mice by targeting the gene of bikunin, the light chain of the ITI family members, which is essential for their biosynthesis. As a consequence, the cumulus oophorus, an investing structure unique to the oocyte of higher mammals, had a defect in forming the extracellular HA-rich matrix during expansion. The ovulated oocytes were completely devoid of matrix and were unfertilized, leading to severe female infertility. Intraperitoneal administration of ITI, accompanied by the formation of the SHAP-HA complex, fully rescued the defects. We conclude that the SHAP-HA complex is a major component of the HA-rich matrix of the cumulus oophorus and is essential for fertilization in vivo.

Suppression of urokinase expression and invasiveness by urinary trypsin inhibitor is mediated through inhibition of protein kinase C- and MEK/ERK/c-Jun-dependent signaling pathways

Urinary trypsin inhibitor (UTI), a Kunitz-type protease inhibitor, interacts with cells as a negative modulator of the invasive cells. Human ovarian cancer cell line, HRA, was treated with phorbol ester (PMA) to evaluate the effect on expression of urokinase-type plasminogen activator (uPA), since the action of uPA has been implicated in matrix degradation and cell motility. Preincubation of the cells with UTI reduced the ability of PMA to trigger the uPA expression at the gene level and at the protein level. UTI-induced down-regulation of PMA-stimulated uPA expression is irreversible and is independent of a cytotoxic effect. Down-regulation of uPA by UTI is mediated by its binding to the cells. We next asked whether the mechanism of inhibition of uPA expression by UTI was due to interference with the protein kinase C second messenger system. An assay for PKC activity demonstrated that UTI does not directly inhibit the catalytic activity of PKC and that PMA translocation of PKC from cytosol to membrane was inhibited by UTI, indicating that UTI inhibits the activation cascade of PKC. PMA could also activate a signaling pathway involving MEK1/ERK2/c-Jun-dependent uPA expression. When cells were preincubated with UTI, we could detect suppression of phosphorylation of these proteins. Like several types of PKC inhibitor, UTI inhibited PMA-stimulated invasiveness. We conclude that UTI markedly suppresses the cell motility possibly through negative regulation of PKC- and MEK/ERK/c-Jun-dependent mechanisms, and that these changes in behavior are correlated with a coordinated down-regulation of uPA which is likely to contribute to the cell invasion processes.