PO-356 MicroRNA mediated regulation of morgana, a new oncosuppressor in chronic myeloid leukaemia

Introduction Morgana is a chaperone protein encoded by the CHORDC1 gene. Its deletion is embryonic lethal due to apoptosis of the cells of the inner cell mass. We recently characterised the role of Morgana in myeloid malignancies, as the haploinsufficiency of the protein in mice is able to induce a fatal and transplantable myeloproliferative disease resembling human Atypical Chronic Myeloid Leukaemia (aCML). 5 out of 5 aCML patients and 16% of Philadelphia-positive CML patients express low/undetectable levels of Morgana in their bone marrow. As we never found mutations or deletions of CHORDC1 gene, we decided to investigate if Morgana can be targeted by miRNAs. Five miRNAs are predicted to target Morgana: miR-15a/b and miR-16 sharing the same seed sequence and miR-26a/b. Material and methods HEK-293T cells were used to overexpress miRNAs predicted to target Morgana mRNA. The level of miRNAs overexpression and Morgana mRNA was assessed with qRT-PCR and Morgana protein level with Western Blot at different time points. The seed sequences for the selected miRNAs in the 3’UTR of CHORDC1 gene were than mutagenized to validate the specificity of the binding. Bioinformatic analysis were used to correlate miRNAs and Morgana expression levels in leukaemia and lymphoma. Results and discussions We demonstrated that miRNA-15a/b and miRNA-26a/b are able to bind to Morgana 3’-UTR and, in this way, mediate its mRNA deregulation leading to a reduction of Morgana, both at mRNA and protein level. We were able to highlight an anti-correlation between Morgana and miRNAs expression in haematological tumours: in particular miR-15b in Chronic Lymphocytic Leukaemia and Lymphomas, miR-15a in aCML and CML and miR-26a and miR-16 in Lymphomas. Conclusion Morgana is able to act both as proto-oncogene and as oncosuppressor depending on tissue type and levels of expression as it is frequently found both overexpressed and downregulated. Different approaches to elucidate its mechanisms of regulation failed and we believe that miRNAs are just one of them. Further investigations are needed to clirify how Morgana expression is regulated in different type of tumours.