Andrea Basile

Reciprocal regulation of Notch and PI3K/Akt signalling in T‐ALL cells In Vitro

Notch signalling plays an important role in hematopoiesis and in the pathogenesis of T‐ALL. Notch is known to interact with Ras and PTEN/PI3K (phosphoinositide‐3 kinase)/Akt pathways. We investigated the interaction of Notch with these pathways and the possible reciprocal regulation of these signalling systems in T‐ALL cells in vitro. Our analyses indicate that the PI3K/Akt pathway is constitutively active in the four T‐ALL cell lines tested. Akt phosphorylation was not altered by the sequestration of growth factors, that is, Akt activation seems to be less dependent on but not completely independent of growth factors, possibly being not subject to negative feedback regulation. PTEN expression was not detected in 3/4 cell lines tested, suggesting the loss of PTEN‐mediated Akt activation. Inhibition of the PI3K/Akt pathway arrests growth and enhances apoptosis, but with no modulation of expression of Bax‐α and Bcl‐2 proteins. We analysed the relationship between Notch‐1 and the PI3K/Akt signalling and show that inhibition of the Akt pathway changes Notch expression; Notch‐1 protein decreased in all the cell lines upon treatment with the inhibitor. Our studies strongly suggest that Notch signalling interacts with PI3K/Akt signalling and further that this occurs in the absence of PTEN expression. The consequences of this to the signalling outcome are yet unclear, but we have uncovered a significant inverse relationship between Notch and PI3K/Akt pathway, which leads us to postulate the operation of a reciprocal regulatory loop between Notch and Ras‐PI3K/Akt in the pathogenesis of T‐ALL. J. Cell. Biochem. 103: 1405–1412, 2008.

Notch signaling deregulation in multiple myeloma: A rational molecular target

Despite recent therapeutic advances, multiple myeloma (MM) is still an incurable neoplasia due to intrinsic or acquired resistance to therapy. Myeloma cell localization in the bone marrow milieu allows direct interactions between tumor cells and non-tumor bone marrow cells which promote neoplastic cell growth, survival, bone disease, acquisition of drug resistance and consequent relapse. Twenty percent of MM patients are at high-risk of treatment failure as defined by tumor markers or presentation as plasma cell leukemia. Cumulative evidences indicate a key role of Notch signaling in multiple myeloma onset and progression. Unlike other Notch-related malignancies, where the majority of patients carry gain-of-function mutations in Notch pathway members, in MM cell Notch signaling is aberrantly activated due to an increased expression of Notch receptors and ligands; notably, this also results in the activation of Notch signaling in surrounding stromal cells which contributes to myeloma cell proliferation, survival and migration, as well as to bone disease and intrinsic and acquired pharmacological resistance. Here we review the last findings on the mechanisms and the effects of Notch signaling dysregulation in MM and provide a rationale for a therapeutic strategy aiming at inhibiting Notch signaling, along with a complete overview on the currently available Notch-directed approaches.

First principle calculations of the optical properties of a neutral oxygen vacancy in Ge-doped silica

Abstract We report ab initio configuration interaction calculations of the optical properties of a neutral oxygen vacancy in Ge-doped silica. This defect center, V(SiGe), is assumed to involve a missing O atom between a Si and a Ge atom with formation of a direct SiGe bond, SiGe. Several calculations have been performed using cluster models to obtain a reliable estimate of the excitation energy. The lowest fully allowed singlet–singlet transition in V(SiGe) occurs in a spectral region around 7.3 eV according to the calculations, i.e. not too far from the absorption band at 7.6 eV attributed to a V(SiSi) center in pure silica. The emission properties of V(SiGe) and the reasons for the similar transition energy in V(SiSi) and V(SiGe) centers are discussed.

Targeting Notch as a Therapeutic Approach for Human Malignancies

BACKGROUND Notch is a multifaceted protein that plays a fundamental role in fetal development and tissue homeostasis by directing many cellular functions, including cell growth and differentiation, cell fate determination and regulation of stem cells maintenance. The Notch family consists of four receptors (Notch 1-4) and five ligands (Jagged1-2 and Delta-like 1-3-4) widely expressed in human tissues. Given the crucial contribution of Notch signaling in many physiological processes, it is not surprising that a variety of human malignancies is characterized by a dysregulation of one or more components of this pathway. METHODS In this review, we are going to provide a broad overview on the role of Notch pathway in solid and hematological malignancies and a survey on possible Notch-directed therapeutic strategies. RESULTS We present the most recent findings indicating that Notch signaling dysregulation in human cancers may be due to genetic and epigenetic alterations or to the interactions with other oncogenic pathways. Furthermore, Notch activity may have an oncogenic or a tumor suppressor effect. Finally, we describe the latest preclinical and clinical studies concerning the different pharmacological approaches targeting Notch. CONCLUSION The provided evidence confirms the importance of Notch pathway in human malignancies indicating that a strong rationale exists for the development of a Notch-tailored therapy.

A Numb–Mdm2 fuzzy complex reveals an isoform-specific involvement of Numb in breast cancer

Numb functions as an oncosuppressor by inhibiting Notch signaling and stabilizing p53. This latter effect depends on the interaction of Numb with Mdm2, the E3 ligase that ubiquitinates p53 and commits it to degradation. In breast cancer (BC), loss of Numb results in a reduction of p53-mediated responses including sensitivity to genotoxic drugs and maintenance of homeostasis in the stem cell compartment. In this study, we show that the Numb–Mdm2 interaction represents a fuzzy complex mediated by a short Numb sequence encompassing its alternatively spliced exon 3 (Ex3), which is necessary and sufficient to inhibit Mdm2 and prevent p53 degradation. Alterations in the Numb splicing pattern are critical in BC as shown by increased chemoresistance of tumors displaying reduced levels of Ex3-containing isoforms, an effect that could be mechanistically linked to diminished p53 levels. A reduced level of Ex3-less Numb isoforms independently predicts poor outcome in BCs harboring wild-type p53. Thus, we have uncovered an important mechanism of chemoresistance and progression in p53-competent BCs.

Cancer Cells Exploit Notch Signaling to Redefine a Supportive Cytokine Milieu

Notch signaling is a well-known key player in the communication between adjacent cells during organ development, when it controls several processes involved in cell differentiation. Notch-mediated communication may occur through the interaction of Notch receptors with ligands on adjacent cells or by a paracrine/endocrine fashion, through soluble molecules that can mediate the communication between cells at distant sites. Dysregulation of Notch pathway causes a number of disorders, including cancer. Notch hyperactivation may be caused by mutations of Notch-related genes, dysregulated upstream pathways, or microenvironment signals. Cancer cells may exploit this aberrant signaling to “educate” the surrounding microenvironment cells toward a pro-tumoral behavior. This may occur because of key cytokines secreted by tumor cells or it may involve the microenvironment through the activation of Notch signaling in stromal cells, an event mediated by a direct cell-to-cell contact and resulting in the increased secretion of several pro-tumorigenic cytokines. Up to now, review articles were mainly focused on Notch contribution in a specific tumor context or immune cell populations. Here, we provide a comprehensive overview on the outcomes of Notch-mediated pathological interactions in different tumor settings and on the molecular and cellular mediators involved in this process. We describe how Notch dysregulation in cancer may alter the cytokine network and its outcomes on tumor progression and antitumor immune response.