Investigation on the molecular pathways interacting with the oncogene Notch1 in the survival and chemoresistance of human haematological malignancies

Notch pathway plays a pivotal role in regulating cell proliferation, survival, differentiation and apoptosis; accordingly, the relevance of its involvement in a variety of malignancies has been demonstrated. Particularly in T-cell acute lymphoblastic leukemia, Notch1 pathway deregulation plays a causative role. Notch1 mutations or Notch pathway abnormal activation are detectable in nearly the 60% of T-ALL patients and cell lines [Weng AP,2004]. Besides, FBW7 gene homozygous mutations were detected in 8.6% of T-ALL patients; FBW7 encodes an ubiquitin ligase that targets Notch1 for proteasome-dependent degradation [O’Neil J,2007]. Recent works indicate a role for Notch signaling in other, non-lymphoid hematological malignancies, such as acute myeloid leukemias [Thoda S,2001] and multiple myeloma [Nefedova Y,2008; Jundt F,2004; Houde C,2004]. Emerging data show that Notch interacts with various pathways playing a critical role in cancer, such as C-MYC, PI3K/Akt, PTEN and NF-κB. Besides, several evidences indicate a possible role for Notch in the control of expression and functions of chemokine receptors: this could account for possible Notch role in controlling tumor cell migration, invasion and metastases. The relevance and breadth of Notch activities in leukemias have led investigators to study the effect of Notch inhibition in cellular models, mainly through γ-secretase inhibitors (GSis). The goal is to identify a possible Notch-based therapy for such hematological malignancies. The majority of the cell lines and patient samples under study are resistant to GSi treatments, preventing the use of Notch as a major target for the development of molecularly tailored antileukemic drugs [Weng AP,2004; O’Neil J,2007]. Understanding the molecular mechanism accounting for Notch signaling effects and GSi-resistance in leukemic cells is likely to provide new insights for the development of innovative therapies. To address this goal, this thesis work aims to elucidate the mechanisms thorough which Notch interacts with its major identified partners, and to identify new components of Notch signaling pathway.