Medizinische Universität Graz Austria/Österreich - Forschungsportal - Medical University of Graz
Gewählte Publikation:
Hatzl, S.
The role of microRNA-23a in Acute Myeloid Leukemia.
Doktoratsstudium der Medizinischen Wissenschaft; Humanmedizin; [ Dissertation ] Graz Medical University ; 2020. pp. 125
[OPEN ACCESS]
FullText
- Autor*innen der Med Uni Graz:
- Betreuer*innen:
- Reinisch Andreas
- Rinner Beate
- Sill Heinz
- Zebisch Armin
- Altmetrics:
- Abstract:
- Micro-RNAs are small, evolutionary highly preserved non-coding RNAs, which regulate gene expression on a post-transcriptional level. It has been shown that micro-RNAs are functionally involved in the development of malignant diseases by regulating key proteins of carcinogenesis. In this thesis, we wanted to extend our knowledge about micro-RNAs within the process of myeloid leukemogenesis. In the first part of the thesis, we aimed to delineate the role of micro-RNAs in loss of the RAF-kinase inhibitor protein (RKIP). RKIP is a central regulator of the RAS/MAPK/ERK signal-transduction pathway and functions as tumor- and metastasis-suppressor. A somatic loss of RKIP has been described previously in different human malignancies and in acute myeloid leukemia (AML). However, the mechanisms behind this RKIP loss remain unclear so far. By analyzing more than 400 primary patient samples with micro-RNA microarrays and qPCR, we could show a significant correlation between increased expression miR-23a and decreased expression of RKIP. Furthermore, we could functionally show that ectopic overexpression of miR-23a decreased the expression of RKIP in hematopoietic cell lines, whereas a knockdown of miR-23a had the opposite effect. Importantly, we could demonstrate that this regulation is mediated via a direct interaction of miR-23a with the RKIP-3`UTR. We additionally could demonstrate that overexpression of miR-23a enforces the proliferation of hematopoietic cells, which pinpoints a relevance for leukemogenesis. Interestingly, co-transfection of miR-23a with an RKIP construct lacking the 3´UTR binding site was able to rescue this phenotype. This suggests that the leukemogenic effects of miR-23a are truly mediated via a miR-23a/RKIP axis. Finally, we could demonstrate the relevance of the miR-23a/RKIP axis in other cancer entities as well. By analyzing 4000 primary patient samples of different cancers within the cancer and genome atlas, we observed an inverse correlation between miR-23a and RKIP in the majority of cancer subtypes. In conclusion we have identified miR-23a as negative regulator of RKIP in acute myeloid leukemia (AML), and its relevance for cancer research in general. Secondly, we studied the role of miR-23a in AML drug resistance, which is one of the central obstacles in this disease. This is based on the fact that dysregulation of miR-23a has been linked to myeloid leukemogenesis and drug resistance previously. Therefore, we analyzed the role of miR-23a in mediating therapeutic resistance to cytarabine (AraC), which forms the backbone of AML chemotherapy. We could demonstrate that miR-23a overexpressing hematopoietic cell lines showed decreased sensitivity to AraC, whereas knockdown of miR-23a mediates increased sensitivity. Furthermore, we could show that increased expression of miR-23a significantly correlates with relapsed/refractory AML, the leukemic stem cell compartment as well as with inferior treatment outcomes in standard chemotherapy-treated AML patients. Additionally, we could mechanistically show that miR-23a mediates AraC resistance by direct downregulation of topoisomerase 2β (TOP2B). In agreement with these findings, we could show that decreased TOP2B expression correlates with relapsed/refractory AML and inferior AML treatment outcomes as well. In conclusion, we could demonstrate that miR-23a mediates resistance to AraC in AML via modulation of TOP2B. Moreover, we could show that increased expression of miR-23a and decreased expression of TOP2B correlate with inferior treatment outcomes.