Modulation of 17ß-Estradiol Signaling on Cellular Proliferation by Caveolin-2.

The sex hormone 17ß-estradiol (E2) exerts pleiotropic effects by binding to the ligand-activated transcription factor estrogen receptor α (ERα). The E2:ERα complex regulates several physiological processes, including cell survival and proliferation, through transcriptional effects (i.e., estrogen responsive element [ERE]-based gene transcription) and non-transcriptional membrane-initiated effects (i.e., the activation of extra-nuclear signaling cascades), which derive from the activation of the pool of ERα that is localized to plasma membrane caveolae. Caveolae are ω-shaped membrane sub-domains that are composed of scaffold proteins named caveolins (i.e., caveolin-1, caveolin-2, and caveolin-3). Although caveolin-3 is exclusively expressed in muscles, caveolin-1 and caveolin-2 are co-expressed in all human tissues. From a functional point of view, caveolin-2 can operate both dependently on and independently of caveolin-1, which is the main coat component of caveolae. Interestingly, while a functional interplay between caveolin-1 and ERα has been reported in the control of E2-induced physiological effects, the role of caveolin-2 in E2:ERα signaling within the cell remains poorly understood. This study shows that siRNA-mediated caveolin-2 depletion in breast ductal carcinoma cells (MCF-7) reduces E2-induced ERα phosphorylation at serine residue 118 (S118), controls intracellular receptor levels, precludes ERα-mediated extra-nuclear activation of signaling pathways, reduces ERα transcriptional activity, and prevents cellular proliferation. Meanwhile, the impact of caveolin-1 depletion on ERα signaling in MCF-7 cells is shown to be similar to that elicited by siRNA-mediated caveolin-2 depletion. Altogether, these data demonstrate that caveolin-2 expression is necessary for the control of E2-dependent cellular proliferation.

Pathogen-free, plasma-poor platelet lysate and expansion of human mesenchymal stem cells.

BACKGROUND: Supplements to support clinical-grade cultures of mesenchymal stem cells (MSC) are required to promote growth and expansion of these cells. Platelet lysate (PL) is a human blood component which may replace animal serum in MSC cultures being rich in various growth factors. Here, we describe a plasma poor pathogen-free platelet lysate obtained by pooling 12 platelet (PLT) units, to produce a standardized and safe supplement for clinical-grade expansion of MSC. METHODS: PL lots were obtained by combining 2 6-unit PLT pools in additive solution (AS) following a transfusional-based procedure including pathogen inactivation (PI) by Intercept technology and 3 cycles of freezing/thawing, followed by membrane removal. Three PI-PL and 3 control PL lots were produced to compare their ability to sustain bone marrow derived MSC selection and expansion. Moreover, two further PL, subjected to PI or not, were also produced starting from the same initial PLT pools to evaluate the impact of PI on growth factor concentration and capacity to sustain cell growth. Additional PI-PL lots were used for comparison with fetal bovine serum (FBS) on MSC expansion. Immunoregulatory properties of PI-PL-generated MSC were documented in vitro by mixed lymphocyte culture (MLC) and peripheral blood mononuclear cells (PBMC) mitogen induced proliferation. RESULTS: PI-PL and PL control lots had similar concentrations of 4 well-described growth factors endowed with MSC stimulating ability. Initial growth and MSC expansion by PI-PL and PL controls were comparable either using different MSC populations or in head to head experiments. Moreover, PI-PL and PL control sustained similar MSC growth of frozen/thawed MSC. Multilineage differentiation of PI-derived and PI-PL-derived MSC were maintained in any MSC cultures as well as their immunoregulatory properties. Finally, no direct impact of PI on growth factor concentration and MSC growth support was observed, whereas the capacity of FBS to sustain MSC expansion in basic medium was irrelevant as compared to PL and PI-PL. CONCLUSION: The replacement of animal additives with human supplements is a basic issue in MSC ex vivo production. PI-PL represents a standardized, plasma-poor, human preparation which appears as a safe and good candidate to stimulate MSC growth in clinical-scale cultures.

Ubiquitin-activating enzyme is necessary for 17ß-estradiol-induced breast cancer cell proliferation and migration.

The sex steroid hormone 17ß-estradiol (E2) regulates breast cancer (BC) cell proliferation and migration through the activation of a plethora of signal transduction cascades (e.g., PI3K/AKT activation) starting after E2 binding to the estrogen receptor alpha (ERα). The activity of the ubiquitin (Ub)-system modulates many physiological processes (e.g., cell proliferation and migration), and recently, a specific inhibitor (Pyr-41) of the Ub-activating enzyme (E1), which works as the activator of the Ub-based signaling, has been identified to prevent the functions of the Ub-system. Here, by using Pyr-41, we studied the involvement of the Ub-system in E2-induced signaling to proliferation and migration of BC cells. Our data indicate that E1 activity is involved in the E2:ERα signaling important for cell proliferation and migration through the modulation of the E2-evoked activation of the PI3K/AKT and the p38/MAPK pathways. These discoveries indicate a new molecular circuitry that can be further explored to define new opportunities for BC treatment.

Altered SDF-1-mediated differentiation of bone marrow-derived endothelial progenitor cells in diabetes mellitus.

In diabetic patients and animal models of diabetes mellitus (DM), circulating endothelial progenitor cell (EPC) number is lower than in normoglycaemic conditions and EPC angiogenic properties are inhibited. Stromal cell derived factor-1 (SDF-1) plays a key role in bone marrow (BM) c-kit(+) stem cell mobilization into peripheral blood (PB), recruitment from PB into ischemic tissues and differentiation into endothelial cells. The aim of the present study was to examine the effect of DM in vivo and in vitro, on murine BM-derived c-kit(+) cells and on their response to SDF-1. Acute hindlimb ischemia was induced in streptozotocin-treated DM and control mice; circulating c-kit(+) cells exhibited a rapid increase followed by a return to control levels which was significantly faster in DM than in control mice. CXCR4 expression by BM c-kit(+) cells as well as SDF-1 protein levels in the plasma and in the skeletal muscle, both before and after the induction of ischemia, were similar between normoglycaemic and DM mice. However, BM-derived c-kit(+) cells from DM mice exhibited an impaired differentiation towards the endothelial phenotype in response to SDF-1; this effect was associated with diminished protein kinase phosphorylation. Interestingly, SDF-1 ability to induce differentiation of c-kit(+) cells from DM mice was restored when cells were cultured under normoglycaemic conditions whereas c-kit(+) cells from normoglycaemic mice failed to differentiate in response to SDF-1 when they were cultured in hyperglycaemic conditions. These results show that DM diminishes circulating c-kit(+) cell number following hindlimb ischemia and inhibits SDF-1-mediated AKT phosphorylation and differentiation towards the endothelial phenotype of BM-derived c-kit(+) cells.

The Protein Arginine Methyltransferases 1 and 5 affect Myc properties in glioblastoma stem cells.

Protein Arginine (R) methylation is the most common post-translational methylation in mammalian cells. Protein Arginine Methyltransferases (PRMT) 1 and 5 dimethylate their substrates on R residues, asymmetrically and symmetrically, respectively. They are ubiquitously expressed and play fundamental roles in tumour malignancies, including glioblastoma multiforme (GBM) which presents largely deregulated Myc activity. Previously, we demonstrated that PRMT5 associates with Myc in GBM cells, modulating, at least in part, its transcriptional properties. Here we show that Myc/PRMT5 protein complex includes PRMT1, in both HEK293T and glioblastoma stem cells (GSCs). We demonstrate that Myc is both asymmetrically and symmetrically dimethylated by PRMT1 and PRMT5, respectively, and that these modifications differentially regulate its stability. Moreover, we show that the ratio between symmetrically and asymmetrically dimethylated Myc changes in GSCs grown in stem versus differentiating conditions. Finally, both PRMT1 and PRMT5 activity modulate Myc binding at its specific target promoters. To our knowledge, this is the first work reporting R asymmetrical and symmetrical dimethylation as novel Myc post-translational modifications, with different functional properties. This opens a completely unexplored field of investigation in Myc biology and suggests symmetrically dimethylated Myc species as novel diagnostic and prognostic markers and druggable therapeutic targets for GBM.

HMGB1-stimulated human primary cardiac fibroblasts exert a paracrine action on human and murine cardiac stem cells.

High Mobility Box 1 Protein (HMGB1) is a cytokine released into the extracellular space by necrotic cells and activated macrophages in response to injury. We recently demonstrated that HMGB1 administration into the mouse heart during acute myocardial infarction induces cardiac tissue regeneration by activating resident cardiac c-kit+ cells (CSCs) and significantly enhances left ventricular function. In the present study it was analyzed the hypothesis that human cardiac fibroblasts (cFbs) exposed to HMGB1 may exert a paracrine effect on mouse and human CSCs. Human cFbs expressed the HMGB1 receptor RAGE. Luminex technology and ELISA assays revealed that HMGB1 significantly enhanced VEGF, PlGF, Mip-1alpha, IFN-gamma, GM-CSF, Il-10, Il-1beta, Il-4, Il-1ra, Il-9 and TNF-alpha in cFbs cell culture medium. HMGB1-stimulated cFbs conditioned media induced CSC migration and proliferation. These effects were significantly higher to those obtained when HMGB1 was added directly to the culture medium. In conclusion, we provide evidence that HMGB1 may act in a paracrine manner stimulating growth factor, cytokine and chemokine release by cFbs which, in turn, modulate CSC function. Via this mechanism HMGB1 may contribute to cardiac tissue regeneration.

Regulation of HMG-CoA reductase expression by hypoxia.

The ability to maintain O(2) homeostasis is essential to the survival of all invertebrate and vertebrate species. The transcriptional factor, hypoxia inducible factor 1 (HIF-1), is the principal regulator of oxygen homeostasis. Under hypoxic condition HIF-1 induces the transcription of several hypoxia-responsive genes by binding to hypoxia-response elements (HRE) in their promoters. In recent years it has been demonstrated that hypoxia could be related to metabolic variations such as hyper-cholesterolemia in mouse models. On the basis of this observation, the present study was performed to verify the involvement of HIF-1, and in particular the effect of chemical and environmental induction of HIF-1alpha (the oxygen sensitive isoform) accumulation in 3-hydroxy 3-methylglutaryl coenzyme A reductase (HMG-CoAR, the key and rate limiting enzyme of cholesterol biosynthetic pathway) regulation. Our results show that HIF-1alpha accumulation is able to increase level and activity of HMG-CoAR by stimulating its transcription. The raised transcription of the reductase could be related to an induction by HIF-1alpha even if a parallel action of SREBP-2 actively translocated to nucleus by the increased level of SCAP cannot be excluded.

Platelet Lysate-Derived Neuropeptide y Influences Migration and Angiogenesis of Human Adipose Tissue-Derived Stromal Cells.

Neuropeptide Y (NPY), a powerful neurotransmitter of the central nervous system, is a key regulator of angiogenesis and biology of adipose depots. Intriguingly, its peripheral vascular and angiogenic powerful activity is strictly associated to platelets, which are source of clinical hemoderivates, such as platelet lysate (PL), routinely employed in several clinical applications as wound healing, and to preserve ex vivo the progenitor properties of the adipose stromal cells pool. So far, the presence of NPY in PL and its biological effects on the adipose stromal cell fraction (ASCs) have never been investigated. Here, we aimed to identify endogenous sources of NPY such as PL-based preparations and to investigate which biological properties PL-derived NPY is able to exert on ASCs. The results show that PL contains a high amount of NPY, which is in part also excreted by ASCs when stimulated with PL. The protein levels of the three main NPY subtype receptors (Y1, Y2, Y5) are unaltered by stimulation of ASCs with PL, but their inhibition through selective pharmacological antagonists, considerably enhances migration, and a parallel reduction of angiogenic features of ASCs including decrease in VEGF mRNA and intracellular calcium levels, both downstream targets of NPY. The expression of VEGF and NPY is enhanced within the sites of neovascularisation of difficult wounds in patients after treatment with leuco-platelet concentrates. Our data highlight the presence of NPY in PL preparations and its peripheral effects on adipose progenitors.

Huntingtin polyQ Mutation Impairs the 17ß-Estradiol/Neuroglobin Pathway Devoted to Neuron Survival.

Among several mechanisms underlying the well-known trophic and protective effects of 17ß-estradiol (E2) in the brain, we recently reported that E2 induces the up-regulation of two anti-apoptotic and neuroprotectant proteins: huntingtin (HTT) and neuroglobin (NGB). Here, we investigate the role of this up-regulation. The obtained results indicate that E2 promotes NGB-HTT association, induces the localization of the complex at the mitochondria, and protects SK-N-BE neuroblastoma cells and murine striatal cells, which express wild-type HTT (i.e., polyQ7), against H2O2-induced apoptosis. All E2 effects were completely abolished in HTT-knocked out SK-N-BE cells and in striatal neurons expressing the mutated form of HTT (mHTT; i.e., polyQ111) typical of Huntington's disease (HD). As a whole, these data provide a new function of wild-type HTT which drives E2-induced NGB in mitochondria modulating NGB anti-apoptotic activity. This new function is lost by HTT polyQ pathological expansion. These data evidence the existence of a novel E2/HTT/NGB neuroprotective axis that may play a relevant role in the development of HD therapeutics.

Dynamin II is required for 17ß-estradiol signaling and autophagy-based ERα degradation.

17ß-estradiol (E2) regulates diverse physiological effects, including cell proliferation, by binding to estrogen receptor α (ERα). ERα is both a transcription factor that drives E2-sensitive gene expression and an extra-nuclear localized receptor that triggers the activation of diverse kinase cascades. While E2 triggers cell proliferation, it also induces ERα degradation in a typical hormone-dependent feedback loop. Although ERα breakdown proceeds through the 26S proteasome, a role for lysosomes and for some endocytic proteins in controlling ERα degradation has been reported. Here, we studied the role of the endocytic protein dynamin II in E2-dependent ERα signaling and degradation. The results indicate that dynamin II siRNA-mediated knock-down partially prevents E2-induced ERα degradation through the inhibition of an autophagy-based pathway and impairs E2-induced cell proliferation signaling. Altogether, these data demonstrate that dynamin II is required for the E2:ERα signaling of physiological functions and uncovers a role for autophagy in the control of ERα turnover.

Clathrin Heavy Chain Interacts With Estrogen Receptor α and Modulates 17ß-Estradiol Signaling.

17ß-estradiol (E2)-induced signaling and control of estrogen receptor (ER)α degradation both play a major role in breast cancer cell proliferation. We recently reported the involvement of lysosomal function in both E2-dependent ERα breakdown and E2-induced cell proliferation and thus hypothesized a role for endocytic proteins in ERα signaling. An small interfering RNA screen identified proteins that regulate intracellular endocytic traffic and whose silencing alters E2-induced ERα degradation. One such protein was the clathrin heavy chain (CHC), whose role in E2:ERα signaling to cell proliferation is unknown. Here, we show that CHC physically interacts with ERα in the cytoplasm of breast cancer cells and regulates E2-induced cell proliferation. Surprisingly, the CHC:ERα interaction is required to sustain E2 signaling but is dispensable for ERα degradation. Our data also demonstrate that many membrane trafficking proteins contribute to the regulation of ERα degradation, thus unraveling the contribution of endocytic proteins in E2:ERα signaling.

Estrogen receptor α L429 and A430 regulate 17ß-estradiol-induced cell proliferation via CREB1.

17ß-Estradiol (E2)-dependent cell proliferation requires both estrogen receptor α (ERα)-based integrated control of gene transcription and kinase pathways activation. Such coordination of intracellular E2:ERα-dependent signaling mechanisms is finely tuned by receptor association with specific partner proteins. Recently, we identified the leucine (L) 429 and alanine (A) 430 within the ERα ligand binding domain as important residues for receptor non-covalent interaction to ubiquitinated species [i.e., ERα ubiquitin-binding surface (ERα UBS)] and for E2-induced ERα activation. To date, if these two ERα amino acids are involved in the control of E2-dependent pathways required for cell proliferation is unknown. Here, by using stably expressing ERα mutated in L429 and A430 (i.e., L429A,A430G-LAAG) cell lines, we show that L429 and A430 are critical for E2-induced cell proliferation, PI3K/AKT pathway activation, and ERα-mediated transcriptional changes. Moreover, we demonstrate that these two receptor structural determinants direct the E2-induced PI3K/AKT/CREB1 pathway activation and CREB1-mediated transcriptional activity that in turn control the hormone-induced cell proliferation. As a whole, our data demonstrate for the first time that the ERα UBS contributes to the modulation of E2-induced ERα-mediated cell proliferation and provide a novel connection between the receptor structure and the functional molecular mechanisms by which E2:ERα complex can regulate cell processes.

Lysosomal function is involved in 17ß-estradiol-induced estrogen receptor α degradation and cell proliferation.

The homeostatic control of the cellular proteome steady-state is dependent either on the 26S proteasome activity or on the lysosome function. The sex hormone 17ß-estradiol (E2) controls a plethora of biological functions by binding to the estrogen receptor α (ERα), which is both a nuclear ligand-activated transcription factor and also an extrinsic plasma membrane receptor. Regulation of E2-induced physiological functions (e.g., cell proliferation) requires the synergistic activation of both transcription of estrogen responsive element (ERE)-containing genes and rapid extra-nuclear phosphorylation of many different signalling kinases (e.g., ERK/MAPK; PI3K/AKT). Although E2 controls ERα intracellular content and activity via the 26S proteasome-mediated degradation, biochemical and microscopy-based evidence suggests a possible cross-talk among lysosomes and ERα activities. Here, we studied the putative localization of endogenous ERα to lysosomes and the role played by lysosomal function in ERα signalling. By using confocal microscopy and biochemical assays, we report that ERα localizes to lysosomes and to endosomes in an E2-dependent manner. Moreover, the inhibition of lysosomal function obtained by chloroquine demonstrates that, in addition to 26S proteasome-mediated receptor elimination, lysosome-based degradation also contributes to the E2-dependent ERα breakdown. Remarkably, the lysosome function is further involved in those ERα activities required for E2-dependent cell proliferation while it is dispensable for ERα-mediated ERE-containing gene transcription. Our discoveries reveal a novel lysosome-dependent degradation pathway for ERα and show a novel biological mechanism by which E2 regulates ERα cellular content and, as a consequence, cellular functions.

Xenoestrogens alter estrogen receptor (ER) α intracellular levels.

17ß-estradiol (E2)-dependent estrogen receptor (ER) α intracellular concentration is a well recognized critical step in the pleiotropic effects elicited by E2 in several target tissues. Beside E2, a class of synthetic and plant-derived chemicals collectively named endocrine disruptors (EDs) or xenoestrogens bind to and modify both nuclear and extra-nuclear ERα activities. However, at the present no information is available on the ability of EDs to hamper ERα intracellular concentration. Here, the effects of bisphenol A (BPA) and naringenin (Nar), prototypes of synthetic and plant-derived ERα ligands, have been evaluated on ERα levels in MCF-7 cells. Both EDs mimic E2 in triggering ERα Ser118 phosphorylation and gene transcription. However, only E2 or BPA induce an increase of cell proliferation; whereas 24 hrs after Nar stimulation a dose-dependent decrease in cell number is reported. E2 or BPA treatment reduces ERα protein and mRNA levels after 24 hrs. Contrarily, Nar stimulation does not alter ERα content but reduces ERα mRNA levels like other ligands. Co-stimulation experiments indicate that 48 hrs of Nar treatment prevents the E2-induced ERα degradation and hijacks the physiological ability of E2:ERα complex to regulate gene transcription. Mechanistically, Nar induces ERα protein accumulation by preventing proteasomal receptor degradation via persistent activation of p38/MAPK pathway. As a whole these data demonstrate that ERα intracellular concentration is an important target through which EDs hamper the hormonal milieu of E2 target cells driving cells to different outcomes or mimicking E2 even in the absence of the hormone.

The pesticide dichlorvos disrupts mitotic division by delocalizing the kinesin Kif2a from centrosomes.

The molecular mechanism(s) mediating long-term adverse effects of dichlorvos, a widely used insecticide, are still unclear. Our work uncovered a new cellular effect of dichlorvos in cultured human cells, i.e. its capacity to induce extremely aberrant mitotic spindles with monopolar microtubule arrays that were associated with hypercondensed chromosomes and pyknotic chromatin masses. Monopolar spindles produced by dichlorvos treatment were characterized by the delocalization of the depolymerizing kinesin Kif2a from spindle poles. Dichlorvos-induced spindle monopolarity could be reversed by promoting microtubule stabilization through chemical treatment or by inhibiting the depolymerizing function of the kinesin MCAK at kinetochores. These findings demonstrate that dichlorvos inhibits the depolymerizing activity of Kif2a at centrosomes and thereby disrupts the balance of opposing centrosomal and kinetochore forces controlling spindle bipolarity during prometaphase. Dichlorvos-induced defects in spindle bipolarity may be responsible for the previously reported induction of aneuploidy by this chemical. Collectively, these results indicate that environmental chemicals, such as dichlorvos, may promote chromosome instability by interfering with the cell division machinery.

Abnormal kinetochore-generated pulling forces from expressing a N-terminally modified Hec1.

BACKGROUND: Highly Expressed in Cancer protein 1 (Hec1) is a constituent of the Ndc80 complex, a kinetochore component that has been shown to have a fundamental role in stable kinetochore-microtubule attachment, chromosome alignment and spindle checkpoint activation at mitosis. HEC1 RNA is found up-regulated in several cancer cells, suggesting a role for HEC1 deregulation in cancer. In light of this, we have investigated the consequences of experimentally-driven Hec1 expression on mitosis and chromosome segregation in an inducible expression system from human cells. METHODOLOGY/PRINCIPAL FINDINGS: Overexpression of Hec1 could never be obtained in HeLa clones inducibly expressing C-terminally tagged Hec1 or untagged Hec1, suggesting that Hec1 cellular levels are tightly controlled. On the contrary, a chimeric protein with an EGFP tag fused to the Hec1 N-terminus accumulated in cells and disrupted mitotic division. EGFP- Hec1 cells underwent altered chromosome segregation within multipolar spindles that originated from centriole splitting. We found that EGFP-Hec1 assembled a mutant Ndc80 complex that was unable to rescue the mitotic phenotypes of Hec1 depletion. Kinetochores harboring EGFP-Hec1 formed persisting lateral microtubule-kinetochore interactions that recruited the plus-end depolymerase MCAK and the microtubule stabilizing protein HURP on K-fibers. In these conditions the plus-end kinesin CENP-E was preferentially retained at kinetochores. RNAi-mediated CENP-E depletion further demonstrated that CENP-E function was required for multipolar spindle formation in EGFP-Hec1 expressing cells. CONCLUSIONS/SIGNIFICANCE: Our study suggests that modifications on Hec1 N-terminal tail can alter kinetochore-microtubule attachment stability and influence Ndc80 complex function independently from the intracellular levels of the protein. N-terminally modified Hec1 promotes spindle pole fragmentation by CENP-E-mediated plus-end directed kinetochore pulling forces that disrupt the fine balance of kinetochore- and centrosome-associated forces regulating spindle bipolarity. Overall, our findings support a model in which centrosome integrity is influenced by the pathways regulating kinetochore-microtubule attachment stability.

Expression of the kinetochore protein Hec1 during the cell cycle in normal and cancer cells and its regulation by the pRb pathway.

Highly Expressed in Cancer protein 1 (Hec1) is a subunit of the Ndc80 complex, a constituent of the mitotic kinetochore. HEC1 has been shown to be overexpressed in many cancers, suggesting that HEC1 upregulation is involved in the generation and/or maintenance of the tumour phenotype. However, the regulation of Hec1 expression in normal and tumour cells and the molecular alterations promoting accumulation of this protein in cancer cells are still unknown. Here we show that elevated Hec1 protein levels are characteristic of transformed cell lines of different origins and that kinetochore recruitment of this protein is also increased in cancer cell lines in comparison with normal human cells. Using different cell synchronization strategies, Hec1 expression was found to be tightly regulated during the cell cycle in both normal and cancer cells. A limited proteasome-dependent degradation of Hec1 cellular content was observed at mitotic exit, with no evident differences between normal and cancer cells. Interestingly, increased expression of HEC1 mRNA and Hec1 protein was observed after transient silencing of the retinoblastoma gene by siRNA or following microRNA-mediated permanent depletion of the retinoblastoma protein in HCT116 cells. Our data provide evidence for a functional link between Hec1 expression and the pRb pathway. These observations suggest that disruption of pRb function may lead to chromosome segregation errors and mitotic defects through Hec1 overexpression. This may importantly contribute to aneuploidy and chromosomal instability in RB-defective cancer cells.

Thrombin-mediated impairment of fibroblast growth factor-2 activity.

Thrombin generation increases in several pathological conditions, including cancer, thromboembolism, diabetes and myeloproliferative syndromes. During tumor development, thrombin levels increase along with several other molecules, including cytokines and angiogenic factors. Under such conditions, it is reasonable to predict that thrombin may recognize new low-affinity substrates that usually are not recognized under low-expression levels conditions. In the present study, we hypothesized that fibroblast growth factor (FGF)-2 may be cleaved by thrombin and that such action may lead to an impairment of its biological activity. The evidence collected in the present study indicates that FGF-2-induced proliferation and chemotaxis/invasion of SK-MEL-110 human melanoma cells were significantly reduced when FGF-2 was pre-incubated with active thrombin. The inhibition of proliferation was not influenced by heparin. Phe-Pro-Arg-chloromethyl ketone, a specific inhibitor of the enzymatic activity of thrombin, abolished the thrombin-induced observed effects. Accordingly, both FGF-2-binding to cell membranes as well as FGF-2-induced extracellular signal-regulated kinase phosphorylation were decreased in the presence of thrombin. Finally, HPLC analyses demonstrated that FGF-2 is cleaved by thrombin at the peptide bond between residues Arg42 and Ile43 of the mature human FGF-2 sequence. The apparent k(cat)/K(m) of FGF-2 hydrolysis was 1.1 x 10(4) M(-1) x s(-1), which is comparable to other known low-affinity thrombin substrates. Taken together, these results demonstrate that thrombin digests FGF-2 at the site Arg42-Ile43 and impairs FGF-2 activity in vitro, indicating that FGF-2 is a novel thrombin substrate.

Daidzein-sulfate metabolites affect transcriptional and antiproliferative activities of estrogen receptor-beta in cultured human cancer cells.

Daidzein (D), a soy isoflavone, is almost completely metabolized in the gut and liver. This biotransformation converts D to more water-soluble products and may affect its biological activity. The ability of daidzein metabolites to modulate 17beta-estradiol (E2)-sensitive gene transcription, cell growth, and a proapoptotic cascade was determined in human cancer cells devoid of any estrogen receptor (ER) and rendered E2 sensitive after transfection with ERbeta. The data show that D and some but not all of its metabolites 1) induce promoter activity, 2) reduce proliferation, 3) promote p38/mitogen-activated protein kinase (MAPK) phosphorylation, and 4) activate a proapoptotic cascade involving the cleavage of caspase-3 and its substrate poly(ADP-ribose)polymerase (PARP) in human cancer cells in an ERbeta-dependent manner. Pretreatment of cells with ICI 182,780, a pure antiestrogen, completely prevented the actions of D and its metabolites. These findings highlight the important and complex influence of metabolic transformation on key physiological effects of isoflavones and demonstrate the need to take biotransformation into account when assessing the potential health benefits of consuming soy isoflavones.

Survival versus apoptotic 17beta-estradiol effect: role of ER alpha and ER beta activated non-genomic signaling.

The capability of 17beta-estradiol (E2) to induce the non-genomic activities of its receptors (ER alpha and ER beta) and to evoke different signaling pathways committed to the regulation of cell proliferation has been analyzed in different cell cancer lines containing transfected (HeLa) or endogenous (HepG2, DLD1) ER alpha or ER beta. In these cell lines, E2 induced different effects on cell growth/apoptosis in dependence of ER isoforms present. The E2-ER alpha complex rapidly activated multiple signal transduction pathways (i.e., ERK/MAPK, PI3K/AKT) committed to both cell cycle progression and apoptotic cascade prevention. On the other hand, the E2-ER beta complex induced the rapid and persistent phosphorylation of p38/MAPK which, in turn, was involved in caspase-3 activation and cleavage of poly(ADP-ribose)polymerase, driving cells into the apoptotic cycle. In addition, the E2-ER beta complex did not activate any of the E2-ER alpha-activated signal molecules involved in cell growth. Taken together, these results demonstrate the ability of ER beta isoform to activate specific signal transduction pathways starting from plasma membrane that may justify the effect of E2 in inducing cell proliferation or apoptosis in cancer cells. In particular this hormone promotes cell survival through ER alpha non-genomic signaling and cell death through ER beta non-genomic signaling.