Dottorato in MEDICINA MOLECOLARE

Titolo della tesi: Pin1 targeting: a new potential approach to overcome Platinum resistance in ovarian cancer by maximizing Notch3-negative regulators activity

High-grade Serous Ovarian Cancer (HGSOC) is the most common histological subtype of Ovarian Cancer (OC) and is one of the most lethal female-related disease malignancies. Its curative and survival trends have not changed over the past decades because of the insurgence of recurrence connected with resistance to Platinum (PT)-based chemotherapies. Therefore, finding novel targetable biomarkers to evade or reverse these events is urgently required. Given its role in tumorigenesis in OC, the Notch3 (N3) signalling pathway has emerged as a promising candidate for novel specific targeted therapies. Consequently, the prediction of the interaction between N3 and its regulators, through the exploitation of its post-translational modification (PTMs), is emerging as an innovative approach. In this backdrop, the appealing candidates as fine-tuner of N3 stability are i) the peptidyl-prolyl cis/trans isomerase Pin1, previously identified in our lab as a N3-positive regulator in T-cell acute lymphoblastic leukaemia, and ii) the GSK-3β kinase and the E3 ligase WWP2, both identified as N3-negative regulators through the induction of its proteasomal degradation. However, what impact each interactor may have on N3 and on each other is still largely unknown in OC. Therefore, the main aims of the present project are: 1. To investigate the Pin1-N3 crosstalk and the functional relevance of this axis in the response to PT-based therapies; 2. To dissect the key molecular onco-suppressive mechanisms of WWP2 and GSK-3β activities on N3 intracellular domain (N3ICD), in order to understand whether the Pin1-dependent stabilization of N3 could specifically interfere with their function. First, via functional studies we demonstrated the N3 involvement in PT-drug resistance, by using in vitro and in vivo OC models. Interestingly, a significant correlation between high Pin1/N3 protein levels was shown in HGSOC primary tumours, which was consistent with a worse prognosis. Moreover, we observed that Pin1 targeting affects N3 expression and function under PT-treatment, both in vitro and in vivo, finally leading to re-sensitization to PT-drugs. Next, we performed mechanistic studies demonstrating the antagonistic role of Pin1 in preventing both the WWP2 and GSK-3β activities, through “distinct” processes mainly resulted from masking/hiding specific consensus sites on N3ICD. All in all, the final goal of the present project is to deepen our knowledge of N3 post-translational regulation, via Pin1-WWP2/GSK3β activity, finally identifying new molecular targets aimed at developing novel therapeutic strategies to maximize the efficacy of Platinum-based therapies for N3-dependent OC-bearing patients.