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Biomedical subjects

L Magnelli

Publications and source records attributed to L Magnelli.

At least 19 recordsLinked to original sources
PubMed2003

Down-regulation of platelet-derived growth factor receptor signaling during myogenesis.

Cell differentiation is often associated with a block in the cell cycle. Growth factor signaling has been reported to be impaired in differentiated cells, due to the withdrawal of growth factors or to transcriptional down-regulation of their receptors. Our proposal is that the down regulation of growth factor signaling may be achieved through an alternative pathway: the decrease of growth factor receptor activation and the ensuing inhibition of intracellular pathways leading the cell to division. Here we report that platelet-derived growth factor receptor (PDGFr) signaling is down-regulated during muscle differentiation, although its expression level remains unchanged. PDGFr signaling inhibition is achieved through a decrease in the receptor tyrosine phosphorylation level, in particular of Tyr716, Tyr751, Tyr857 and Tyr1021, leading to down-regulation of intracellular signaling pathways. Furthermore, during myogenesis, the expression level of several phosphotyrosine phosphatases (PTPs) increases and most of them shift toward the reduced/activated state. We propose a causal link between the down-regulation of PDGFr tyrosine phosphorylation and the increases in PTP specific activity during myogenesis.

Animals↗
PubMed2001

Inducible nitric oxide synthase expression in benign and malignant cutaneous melanocytic lesions.

Nitric oxide (NO) is synthesized by nitric oxide synthases (NOS) and plays an important role in tumour growth. In this study, inducible NOS (iNOS) expression was evaluated by immunohistochemistry in 34 melanocytic naevi (13 common melanocytic naevi, six Spitz naevi, and 15 so-called 'dysplastic naevi'), ten cutaneous melanomas in situ, 50 stage I invasive melanomas, and eight subcutaneous metastases of melanoma. In addition, four samples of melanocytic naevi and four samples of invasive melanomas were collected in order to perform western blot and northern blot analysis. By immunohistochemistry, melanocytic naevi never expressed iNOS. Among cases of melanoma in situ, two were negative, seven displayed staining in less than 20% of melanoma cells, and positivity was observed in 21-50% of melanoma cells in only one case. iNOS expression was detected in 46 out of 50 invasive melanomas (92%). Among these cases, 18 showed positivity in less than 20% of melanoma cells, 18 showed positivity in 21-50% of melanoma cells, and ten showed iNOS expression in more than 50% of cells. Statistical analysis revealed a significant difference in iNOS expression between melanocytic naevi and cutaneous melanomas (p<0.001). In addition, iNOS expression was significantly higher in invasive melanomas than in melanomas in situ (p=0.01). Among primary cutaneous melanomas, no significant correlation was found between iNOS expression and histopathological parameters (histotype, level, thickness and presence of regression/inflammatory infiltrate) and disease-specific survival. In subcutaneous melanoma metastases, iNOS expression was diffuse in more than 50% of cells. Statistical analysis revealed that subcutaneous melanoma metastases showed greater iNOS immunoreactivity than invasive melanomas (p=0.02). Molecular analyses confirmed that iNOS mRNA and protein were highly expressed in melanoma samples. In conclusion, iNOS was constantly absent in melanocytic naevi, whereas it was frequently expressed in melanomas, with up-regulation of the enzyme paralleling tumour progression. These data suggest that iNOS may play a role in the malignant transformation of melanocytes and in tumour growth. In addition, iNOS may be useful as an immunohistochemical marker for malignant melanocytic lesions.

Adult↗
PubMed2000

Regulation of urokinase/urokinase receptor interaction by heparin-like glycosaminoglycans.

We show here that the interaction between the urokinase-type plasminogen activator and its receptor, which plays a critical role in cell invasion, is regulated by heparan sulfate present on the cell surface and in the extracellular matrix. Heparan sulfate oligomers showing a composition close to the dimeric repeats of heparin (glucosamine-NSO(3)(6-OSO(3))-iduronic acid(2-OSO(3))) n = 5 and n > 5, where iduronic acid may alternate with glucuronic acid, exhibit affinity for urokinase plasminogen activator and confer specificity on urokinase/urokinase receptor interaction. Cell surface clearance of heparan sulfate reduces the affinity of such interaction with a parallel decrease of specific urokinase binding in the presence of an unaltered expression of receptor. Transfection of human urokinase plasminogen activator receptor in normal Chinese hamster ovary fibroblasts and in Chinese hamster ovary cells defective for the synthesis of sulfated glycosaminoglycans results in specific urokinase/receptor interaction only in nondefective cells. Heparan sulfate/urokinase and receptor/urokinase interactions exhibit similar K(d) values. We concluded that heparan sulfate functions as an adaptor molecule that confers specificity on urokinase/receptor binding.

Animals↗
PubMed2000

Molecular polarity in endothelial cells and tumor-induced angiogenesis.

Endothelial cells expose receptors for vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) at the abluminal, basal surface that work as basic regulators of tumor-induced angiogenesis. Their specific localization makes them susceptible to the activity of tumor-released stimulatory factors, like VEGF/VPF, which induce proliferation of the endothelial cell toward the extracellular matrix. At the same time, VEGF/VPF stimulates endothelial cells to expose tissue factor (TF), the high-affinity transmembrane receptor and cofactor for cellular initiation of the plasma coagulation protease cascades through the extrinsic pathway, so generating thrombin. Thrombin exerts a number of activities: it forms an extracellular fibrin barrier from the VEGF/VPF-dependent fibrinogen extravasation; it activates progelatinase-A (pro-MMP-2), which destroys the basal membrane, allowing proliferation of endothelial cells (ECs) in the novel tumoral fibrin matrix; finally, it induces EC proliferation, potentiating the VEGF effect. Another important factor exposed at the abluminal endothelial cell surface is membrane type 1 matrix metalloproteinase (MT1-MMP), a membrane-bound metalloproteinase, which also activates progelatinase-A, allowing an alternative pathway to that of thrombin to destroy the basal membrane. In addition, we will see that MT1-MMP is also engaged in a direct, cell-associated fibrinolytic activity, essential for tubulogenesis of the novel outsprouting capillary.

Blood-Brain Barrier↗
PubMed1999

Inhibitory effect of full-length human endostatin on in vitro angiogenesis.

Endostatin, a C-terminal product of collagen XVIII, is a very powerful angiogenesis inhibitor. In vivo experiments in mice indicate that endostatin dramatically reduces tumor mass without causing the onset of any resistance to the treatment. Recently, a 12-aa shorter human endostatin has been purified from plasma, but is ineffective in in vitro angiogenesis assays. Here we report that the full-length human recombinant endostatin has a potent inhibitory activity in in vitro angiogenesis assays. Two powerful angiogenic factors were used to stimulate endothelial cells: FGF-2 and VEGF-165. Endostatin prevented cell growth both in the basal condition and after stimulation with FGF-2 or VEGF-165. Migration of microvascular endothelial cells toward FGF-2 or VEGF-165 was impaired, both when cells were pretreated with the inhibitor and when endostatin was added together with the growth factors. Furthermore, experiments of inhibition of proliferation performed on nonmicroendothelial cells showed that endostatin was ineffective. This study indicates that human endostatin is a potent angiogenesis inhibitor and suggests its use in human anticancer therapy.

Capillaries↗
PubMed1998

Chronic treatment of human fibroblasts cultures with diacylglycerol induces down-regulation of p53 functional activity.

We found that many spontaneous human tumors exhibit increased levels of endocellular diacylglycerol (DAG) which is synthesized de novo as a byproduct of glycolysis. It has been shown that DAG mimics phorbol esters as a full tumor promoter in mouse skin carcinogenesis. A short term DAG treatment activates protein kinase C (PKC), while a long term "chronic" treatment down-regulates PKC. We show here that chronic treatment of human fibroblast with DAG induces p53 down-regulation and inhibition of p53 functional activity, and protection from UV-induced apoptosis. As PKC phosphorylation is necessary for p53 functional activity, we propose that chronic DAG treatment mimics the same event occurring in vivo for the effect of glycolysis in tumor progression.

Animals↗
PubMed1998

Redundant down-regulation pathways for p53.

The aim of this review is to underline the redundancy of down-regulation pathways for p53, at the light of the two more important degradative systems: calpains and ubiquitin-dependent pathways. The MDM2 feed-back loop is also illustrated, as well as the phosphorylative/dephosphorylative regulation of the latent and active p53 isoforms. The mechanisms prolonging p53 half life, following irradiation, are also discussed.

Animals↗
PubMed1998

Cox-2, iNOS and p53 as play-makers of tumor angiogenesis (review).

Cyclooxygenases (COXs) are key enzymes in the conversion of arachidonic acid to prostaglandins (PGs) and other eicosanoids. Nitric oxide synthase (NOS) is the enzyme that catalyzes the formation of nitric oxide (NO), a regulator of vascular permeability, from the guanidino nitrogen atom of L-arginine. Two isoforms of both enzymes occur: a constitutive one, Cox-1 and the inducible counterpart Cox-2; also NOS has a constitutive counterparts (cNOS) and an inducible form, called iNOS. The inducible isoforms of both enzymes are of maximum interest. It has been recently shown that cyclooxygenase-2 (Cox-2) is inducible by a variety of stimuli and that eicosanoids, mainly of the PGE2 species, are inducers of basic regulator of angiogenesis, including VEGF/VPF, bFGF, TGF-beta, PDGF, and endothelin-1. In addition, iNOS is inducible by Cox-2. p53 down-regulates the angiogenic process at various levels: it induces thrombospondin-1, a powerful antiangiogenic factor, down-regulates VEGF and NOS and, in addition, down-regulates hypoxia-induced angiogenesis, either inducing apoptosis or enhancing antiangiogenetic factors. It is noteworthy how important the p53 oncosuppressor is in the angiogenesis of solid tumor growth. Cox-2, iNOS and p53 are thus fundamental play-makers of the angiogenic process: they are discussed in detail and a tentative hierarchical cascade is proposed.

Animals↗
PubMed1998

Acetylation and phosphorylation of the carboxy-terminal domain of p53: regulative significance.

Three fundamental domains are conventionally distinguished on the p53 molecule: an NH2 domain involved in transcription, a central core domain involved in specific DNA binding to the consensus sequences, and a carboxy-terminal domain of about 30 amino acids working as a basic regulatory domain, exhibiting aspecific DNA binding, tetramerization, and nuclearization. The presence of an unmodified carboxy-terminus does not allow the specific transactivation transcriptional function of the p53 protein. Therefore, for the activation of the protein function the carboxy-terminus must be modified. In the present commentary we discuss the role of two covalent modification events occurring at the carboxy-terminus, namely phosphorylation and acetylation, as well as the specific role of these events in the functional regulation of p53 molecule.

Acetylation↗
PubMed1997

The old and the new in p53 functional regulation.

The gene termed p53 is one of the most extensively studied for the past 18 years and the amount of literature published on this gene reflects its relevance in the field of molecular oncology; thus, loss or mutation of this oncosuppressor gene is probably the molecular lesion most frequently observed in human tumors. The aim of this minireview is to report, discuss, and interpret some recent observations on this topic: (I) The relationship with the Ataxia-Telangectasia gene and with the signaling enzyme phosphatidylinositol 3-kinase (PI3K). (II) The relationship between DNA damage, p53, and sensitivity to anticancer therapies. (III) The gain of function caused by mutations that transform the oncosuppressor p53 gene into a dominant transforming oncogene and (IV) The phosphorylative regulation of p53 and its relationship with the mitogenic signaling cascade involving protein kinase C and tumor promoters.

Ataxia Telangiectasia↗
PubMed1997

Complex interplay among apoptosis factors: RB, p53, E2F, TGF-beta, cell cycle inhibitors and the bcl2 gene family.

Apoptosis is a fundamental cell program as important as growth, differentiation and quiescence. It regulates tissue development, homeostasis and it is a basic defence against cancer. The cell can undertake multiple apoptotic pathways, where different elements are involved. In this report, we would like to stress particularly that the p53/RB pathway and its complex, interplay with the bcl2 gene family, where paramount elements of apoptosis regulation are operating. It is generally believed that bcl2 blocks apoptosis at the level of the activation of ICE-(Interleukin Converting Enzymes)-like proteases [1,2]. The interconnection between apoptosis and cell cycle is very important and complex and we will start the story from this very up-to-date point of view.

Animals↗
PubMed1996

Herpes simplex virus thymidine kinase/ganciclovir-mediated apoptotic death of bystander cells.

An emerging strategy for cancer gene therapy involves the transfer of the herpes simplex virus thymidine kinase (HSV-tk) gene into tumor cells, rendering them susceptible to the cytotoxic effects of ganciclovir. The observation that HSV-tk-expressing cells can also induce cell death in neighboring cells, which do not express HSV-tk, has been called the bystander effect. Gap junction-mediated transfer of cytotoxic molecules to bystander cells may be an important mechanism of bystander cell death, although others have suggested a role for phagocytosis. In this study, we evaluated the mode of cell death in bystander cells. We detected apoptosis in bystander cells and found that bystander cell death could be inhibited by BCL2 expression. We determined that ganciclovir incubations for 10 h were sufficient to induce cell death in most bystander cells cocultured with HSV-tk-expressing cells. During this period, no phagocytosis was detected, although it was obvious at later stages.

3T3 Cells↗