PO-299 In vivo shRNA screening to identify quiescence-related genes required for AML growth

Introduction AML is hierarchically organised with at the apex Leukaemia Stem Cells (LSCs), a rare cell population able to initiate and sustain the tumour growth. LSCs share many functional properties with normal Hematopoietic Stem Cells (HSCs) including self-renewal capacity and quiescence. Quiescent LSCs can survive to radiation and chemotherapy acting as a reservoir for leukaemia relapse, the major cause of death for AML patients. Therefore, LSCs quiescence is critical for leukaemia maintenance and few evidences suggest that quiescence regulation in pre-leukemic phase plays a pivotal role for leukemogenic process as well. Material and methods We analysed the transcriptional deregulations induced by the expression of different leukemic oncogenes in HSCs and we examined the contribution of representative quiescence related genes in AML growth by in vivo RNA interference screening. Results and discussions The transcriptional profile of oncogene-expressing HSCs is enriched in a quiescent stem cell gene signature, compared to normal HSCs. Therefore, we hypothesised that enhancement of the quiescent phenotype in HSCs could be a shared mechanism for leukaemia development and maintenance. The in vivo shRNA screening allowed the identification of genes whose silencing in AML blasts was sufficient to significantly decrease in vitro self-renewal and delay leukaemia growth in vivo . Conclusion We identified quiescence-related genes, commonly deregulated by leukemic oncogenes at pre-leukemic level, which may offer new therapeutic targets in a wide group of AML patients

The E3 ubiquitin ligase WWP1 sustains the growth of acute myeloid leukaemia

The E3 ubiquitin ligase (E3) WWP1 is an oncogenic factor implicated in the maintenance of different types of epithelial cancers. The role of WW domain-containing E3 ubiquitin protein ligase 1 (WWP1) in haematological neoplasms remains unknown. Acute myeloid leukaemia (AML) is characterized by the expansion of malignant myeloid cells blocked at different stages of differentiation. Here we report that the expression of WWP1 is significantly augmented in a large cohort of primary AML patients and in AML cell lines, compared with haematopoietic cells from healthy donors. We show that WWP1 inactivation severely impairs the growth of primary AML blasts and cell lines in vitro. In vivo, we observed a reduced leukaemogenic potential of WWP1-depleted AML cells upon transplantation into immunocompromised mice. Mechanistically, WWP1 inactivation induces the accumulation of its protein substrate p27(Kip1), which ultimately contributes to G(0)/G(1) cell cycle arrest of AML blasts. In addition, WWP1 depletion triggers the autophagy signalling and reduces survival of leukaemic cells. Collectively, our findings provide molecular insights into the anticancer potential of WWP1 inhibition, suggesting that this E3 is a promising biomarker and druggable target in AML