Phd in GENETICS AND MOLECULAR BIOLOGY

Thesis title: New insight into the catalytic -dependent and -independent roles of METTL3 in sustaining aberrant translation in Chronic Myeloid Leukemia.

RNA modifications play a fundamental role in fine-tuning of gene expression. To date, more than 160 RNA modifications have been discovered in coding and non-coding transcripts. N6- methyladenosine (m6A), in particular, has attracted the interest of researchers around the world because it is the most abundant internal chemical modification in mRNAs and controls every aspect of the post-transcriptional regulation of these molecules. Similar to epigenetic modifications in histones and DNA, m6A is a reversible and dynamic modification installed by "writer", removed by "eraser", and recognized by "reader" proteins. Alterations to m6A pattern have a profound impact on cell differentiation, normal development and human diseases. Alteration of m6A level has been found to be closely associated with the onset, the metastasis and drug resistance of various kinds of cancers; in particular, m6A is an important driver of malignant transformation in the hematopoietic compartment. Acute Myeloid Leukemia (AML) is a clear example of how alteration in m6A level can disrupt normal cellular differentiation and contribute to cancer development. Chronic Myeloid Leukemia (CML) is a myeloproliferative neoplasm characterized by the accumulation of myeloid cells at different stages (blasts) in the blood. CML progression is driven by the presence of tyrosine kinase BCR-ABL1 fusion protein, which deregulates transcription and translation of several signaling pathways. Although progress has been made in the understanding of signal transduction in the BCR-ABL1-mediated transformation, the role of m6A in CML remains unknown. We found that METTL3 and METTL14, that form the main writer complex responsible for m6A deposition within mRNAs, are significantly higher in peripheral blood of CML patients than in healthy controls, moreover their expression in CML cell lines is comparable or even higher than in AML cell lines. Therein, we perturbed the catalytic subunit METTL3 level in CML patients and cell lines highlighting that METTL3 is crucial for proliferation and cell cycle progression of CML cells, both sensitive and resistant to TKIs treatment. In particular, we found that METTL3 regulates translation process both indirectly, by sustaining transcription and translation of MYC, the master regulator of ribosome biogenesis and translation, and directly, by regulating PES1 protein level, a ribosome assembly factor that plays an oncogenic role in several tumors. We propose a model in which the nuclear METTL3/METTL14 methyltransferase complex modifies nascent transcripts whose translation is enhanced by cytoplasmic localization of METTL3, independently from its catalytic activity. In conclusion, our work contributed to unveil the novel role of METTL3 in sustaining the aberrant translation that characterized CML. Furthermore, our results point to METTL3 as a novel relevant oncogene in CML and as a promising therapeutic target for TKI resistant CML.