Biomedical subjects

Silvia Giordano

Publications and source records attributed to Silvia Giordano.

9 recordsLinked to original sources

PubMed2025

Heat shock factor 2 regulates oncogenic gamma-herpesvirus gene expression by remodeling the chromatin at the ORF50 and BZLF1 promoter.

The Human gamma-herpesviruses Kaposi's sarcoma herpesvirus (KSHV) and Epstein-Barr virus (EBV) are causally associated to a wide range of cancers. While the default infection program for these viruses is latent, sporadic lytic reactivation supports virus dissemination and oncogenesis. Despite its relevance, the repertoire of host factors governing the transition from latent to lytic phase is not yet complete, leaving much of this complex process unresolved. Here we show that heat shock factor 2 (HSF2), a transcription factor involved in regulation of stress responses and specific cell differentiation processes, promotes gamma-herpesvirus lytic gene expression. In lymphatic endothelial cells infected with KSHV and in gastric cancer cells positive for EBV, ectopic HSF2 enhances the expression of lytic genes; While knocking down HSF2 significantly decreases their expression. HSF2 overexpression is accompanied by decreased levels of repressive histone marks at the promoters of the lytic regulators KSHV ORF50 and EBV BZLF1, both characterized by poised chromatin features. Our results demonstrate that endogenous HSF2 binds to the promoters of KSHV ORF50 and EBV BZLF1 genes and shifts the bivalent chromatin state towards a more transcriptionally permissive state. We detected HSF2 binding to the ORF50 promoter in latent cells, in contrast, in lytic cells, HSF2 occupancy at the ORF50 promoter is lost in conjunction with its proteasomal degradation. These findings identify HSF2 as a regulator of gamma-herpesvirus lytic gene expression in latency and offer new insights on the function of this transcription factors at poised gene promoters, improving our understanding of its role in differentiation and development.

Humans↗

PubMed2004

Reactive oxygen species mediate Met receptor transactivation by G protein-coupled receptors and the epidermal growth factor receptor in human carcinoma cells.

Cross-communication between the Met receptor tyrosine kinase and the epidermal growth factor receptor (EGFR) has been proposed to involve direct association of both receptors and EGFR kinase-dependent phosphorylation. Here, we demonstrate that in human hepatocellular and pancreatic carcinoma cells the Met receptor becomes tyrosine phosphorylated not only upon EGF stimulation but also in response to G protein-coupled receptor (GPCR) agonists. Whereas specific inhibition of the EGFR kinase activity blocked EGF- but not GPCR agonist-induced Met receptor transactivation, it was abrogated in the presence of a reducing agent or treatment of cells with a NADPH oxidase inhibitor. Both GPCR ligands and EGF are further shown to increase the level of reactive oxygen species within the cell. Interestingly, stimulation of the Met receptor by either GPCR agonists, EGF or its cognate ligand HGF, resulted in release of Met-associated beta-catenin and in its Met-dependent translocation into the nucleus, as analyzed by small interfering RNA-mediated knockdown of the Met receptor. Our results provide a new molecular explanation for cell surface receptor cross-talk involving the Met receptor and thereby link the wide diversity of GPCRs and the EGFR to the oncogenic potential of Met signaling in human carcinoma cells.

Animals↗

PubMed2003

Hepatocyte growth factor and its receptor are required for malaria infection.

Plasmodium, the causative agent of malaria, must first infect hepatocytes to initiate a mammalian infection. Sporozoites migrate through several hepatocytes, by breaching their plasma membranes, before infection is finally established in one of them. Here we show that wounding of hepatocytes by sporozoite migration induces the secretion of hepatocyte growth factor (HGF), which renders hepatocytes susceptible to infection. Infection depends on activation of the HGF receptor, MET, by secreted HGF. The malaria parasite exploits MET not as a primary binding site, but as a mediator of signals that make the host cell susceptible to infection. HGF/MET signaling induces rearrangements of the host-cell actin cytoskeleton that are required for the early development of the parasites within hepatocytes. Our findings identify HGF and MET as potential targets for new approaches to malaria prevention.

Actins↗

PubMed2003

Expression of the human oestrogen receptor-alpha gene is regulated by promoter F in MG-63 osteoblastic cells.

(O)estrogen receptor-alpha (ERalpha), a hormone-dependent transcription factor belonging to the steroid/thyroid-hormone-receptor superfamily, plays an essential role in the development and maintenance of the skeleton. Here we report the analysis of an unexplored sequence inside the bone-specific distal promoter F (PF) with respect to the regulation of ERalpha gene expression in bone. This sequence, 785 bp in size, is localized upstream of the assigned transcription start site of exon F, at -117140 bp from the originally described transcription start site +1. It contains a TA reach box, a conventional CAAT box and potential regulatory elements for many transcription factors, including Cbfa1 [OSE2 (osteoblast-specific element) core binding factor], GATA-1 [(A/T)GATA(A/G) binding protein], Sox5 [sex-determining region Y (SRY)-type HMG bOX protein, belonging to a subfamily of DNA-binding proteins with an HMG domain], Sry, AP1 (activator protein 1) and CP2 (activator of gamma-globin). It is able to strongly activate the luciferase reporter gene in MG-63 osteoblastic-like cells, but not in MCF7 breast-cancer cells. This is in agreement with different transcripts that we found in the two cell types. The footprinting and electrophoretic mobility-shift assays (EMSAs) showed that, inside the region analysed, there were some sequences that specifically reacted to nuclear proteins isolated from MG-63 cells. In particular, we identified two regions, named PF a and PF b, that do not present binding sites for known transcription factors and that are involved in a strong DNA-protein interaction in MG-63, but not in MCF7, cells. The analysis of three transcription factors (GATA-1, Sry and Sox) that might bind the identified footprinted areas suggested a possible indirect role of these proteins in the regulation of ERalpha gene expression in bone. These data provide evidence for different promoter usage of the ERalpha gene through the recruitment of tissue-specific transcription activators and co-regulators.

Base Sequence↗

PubMed2003

Negative receptor signalling.

Binding of external factors to cell membrane receptors triggers intracellular signalling pathways that ultimately determine if the cell proliferates, differentiates or undergoes apoptosis. Activated receptors also initiate a cascade of events, called negative receptor signalling, that decreases the amplitude of positive signals and modulates the level of cell stimulation. Recent studies have revealed that negative signalling by receptor tyrosine kinases involves coordinated action of ubiquitin ligases (i.e. Cbl), adaptor proteins (i.e. Grb2 and CIN85), inhibitory molecules (i.e. Sprouty), cytoplasmic kinases (i.e. activated Cdc42-associated kinase) and phosphoinositol metabolites. These inhibitory signals are essential for normal cell functioning, and their deregulation often results in human diseases.

Adaptor Proteins, Vesicular Transport↗

PubMed2003

Hypoxia promotes invasive growth by transcriptional activation of the met protooncogene.

Hypoxia unleashes the invasive and metastatic potential of tumor cells by largely unknown mechanisms. The Met tyrosine kinase, a high affinity receptor for hepatocyte growth factor (HGF), plays a crucial role in controlling invasive growth and is often overexpressed in cancer. Here we show that: (1) hypoxia activates transcription of the met protooncogene, resulting in higher levels of Met; (2) hypoxic areas of tumors overexpress Met; (3) hypoxia amplifies HGF signaling; (4) hypoxia synergizes with HGF in inducing invasion; (5) the proinvasive effects of hypoxia are mimicked by Met overexpression; and (6) inhibition of Met expression prevents hypoxia-induced invasive growth. These data show that hypoxia promotes tumor invasion by sensitizing cells to HGF stimulation, providing a molecular basis to explain Met overexpression in cancer.

Base Sequence↗

PubMed2002

CD100/Plexin-B1 interactions sustain proliferation and survival of normal and leukemic CD5+ B lymphocytes.

Growth and survival of chronic B-cell tumors are favored by the malignant cell's capacity to respond to selected microenvironmental stimuli provided by nontumoral bystander cells. To investigate which mechanisms operate in these crosstalks and whether they are malignancy-related or reproduce the mechanisms used by normal B cells we have studied the expression and functional role of semaphorin CD100 (now called Sema4D) in chronic lymphocytic leukemia (CLL) cells and normal CD5+ B cells. We demonstrate here that (1) leukemic and normal CD5+ B lymphocytes uniformly express CD100; (2) the CD100 high-affinity receptor Plexin-B1 is expressed by bone marrow stromal cells, follicular dendritic cells, and activated T lymphocytes, and is thus available to CD100+ lymphocytes in different specific microenvironments; and (3) upon interaction between CD100 and Plexin-B1 both CLL and normal CD5+ B cells increase their proliferative activity and extend their life span. These findings establish that Plexin-B1 is an easily accessible receptor for CD100 within the immune system. The encounter of CD100+ leukemic cells with Plexin-B1 may promote the proliferation and survival of malignant cells. The crosstalk operated by the CD100/Plexin-B1 interaction is not malignancy related but reproduces a mechanism used by normal CD5+ B cells.

Animals↗

PubMed2002

The endophilin-CIN85-Cbl complex mediates ligand-dependent downregulation of c-Met.

Ligand-dependent downregulation of tyrosine kinase receptors is a critical step for modulating their activity. Upon ligand binding, hepatocyte growth factor (HGF) receptor (Met) is polyubiquitinated and degraded; however, the mechanisms underlying HGF receptor endocytosis are not yet known. Here we demonstrate that a complex involving endophilins, CIN85 and Cbl controls this process. Endophilins are regulatory components of clathrin-coated vesicle formation. Through their acyl-transferase activity they are thought to modify the membrane phospholipids and induce negative curvature and invagination of the plasma membrane during the early steps of endocytosis. Furthermore, by means of their Src-homology 3 domains, endophilins are able to bind CIN85, a recently identified protein that interacts with the Cbl proto-oncogene. Cbl, in turn, binds and ubiquitinates activated HGF receptor, and by recruiting the endophilin-CIN85 complex, it regulates receptor internalization. Inhibition of complex formation is sufficient to block HGF receptor internalization and to enhance HGF-induced signal transduction and biological responses. These data provide further evidence of a relationship between receptor-mediated signalling and endocytosis, and disclose a novel functional role for Cbl in HGF receptor signalling.

Adaptor Proteins, Signal Transducing↗

PubMed2002

The semaphorin 4D receptor controls invasive growth by coupling with Met.

Semaphorins are cell surface and soluble signals that control axonal guidance. Recently, semaphorin receptors (plexins) have been discovered and shown to be widely expressed. Their biological activities outside the nervous system and the signal transduction mechanism(s) they utilize are largely unknown. Here, we show that in epithelial cells, Semaphorin 4D (Sema 4D) triggers invasive growth, a complex programme that includes cell#150;cell dissociation, anchorage-independent growth and branching morphogenesis. Interestingly, the same response is also controlled by scatter factors through their tyrosine kinase receptors, which share striking structural homology with plexins in their extracellular domain. We found that in cells expressing the endogenous proteins, Plexin B1 (the Sema 4D Receptor) and Met (the Scatter Factor 1/ Hepatocyte Growth Factor Receptor) associate in a complex. In addition, binding of Sema 4D to Plexin B1 stimulates the tyrosine kinase activity of Met, resulting in tyrosine phosphorylation of both receptors. Finally, cells lacking Met expression do not respond to Sema 4D unless exogenous Met is expressed. This work identifies a novel biological function of semaphorins and suggests the involvement of an unexpected signalling mechanism, namely, the coupling of a plexin to a tyrosine kinase receptor.

Amino Acid Sequence↗