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Selected Publication:
Jonas, K.
Characterization of Novel Non-Coding RNAs Potentially Involved in Breast Carcinogenesis
PhD-Studium (Doctor of Philosophy); Humanmedizin; [ Dissertation ] Medizinische Universität Graz; 2024. pp. 141
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- Authors Med Uni Graz:
- Jonas Katharina
- Advisor:
- Madl Tobias
- Pichler Martin
- Rinner Beate
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- Abstract:
- Breast cancer is the most common type of cancer in women, with the subtype of triple negative breast cancer (TNBC) standing out as particularly aggressive and difficult to treat, which is why it was the focus of this dissertation. In the aim of gaining a better understanding of the carcinogenesis of TNBC, ultimately allowing the development of more efficient treatment strategies, the realm of non-coding RNAs (ncRNAs) holds large potential. Especially a sub-class of short ncRNAs called microRNAs (miRNAs) is frequently deregulated in many cancer types and contributes to cancer hallmarks. The goal of this dissertation was thus to identify novel miRNAs with a role in TNBC, to characterize their molecular mechanisms, and to explore a potential therapeutic utility. Based on a previous miRNA expression screen of 3D breast cancer spheres, two miRNAs were selected that had not been studied in breast cancer prior. These two miRNAs were miR-4646-5p (MIMAT0019707) and miR-4649-5p (MIMAT0019711). We investigated the impact of the miRNAs on several important phenotypic characteristics of TNBC cells by employing synthetic mimics to induce ectopic overexpression, as well as an antisense inhibitor in case of miR-4646-5p. The phenotypic assays revealed that miR-4646-5p overexpression reduced the growth and migration of TNBC cell lines, while inhibition had corresponding opposite effects. Interestingly, we also observed a cell-line-specific induction of apoptosis upon miR-4646-5p overexpression in TNBC cells, and reduced tube formation of endothelial cells, which suggests anti-angiogenic properties of miR-4646-5p. Overexpression of miR-4649-5p reduced the growth, proliferation, and migration of TNBC cells, but had no impact on apoptosis or tube formation. Whole transcriptome analysis revealed diverse underlying mechanisms for the phenotypic effects we observed. For example, miR-4646-5p caused a broad downregulation of tumor-promoting cytokines. Ultimately, we also identify one direct target for each miRNA, the cholesterol transfer protein GRAMD1B for miR-4646-5p and the phosphatidylinositol kinase PIP5K1C for miR-4649-5p, both of which may contribute to the tumor-suppressive properties of the miRNAs. PIP5K1C, for example, is known to promote migration and cell growth, the latter due to downstream effects on PI3K/AKT signaling, which is frequently overactivated in TNBC. Thus, a combination of the miR-4649-5p mimic and pharmacologic PIP5K1C or AKT inhibition showed additive growth-reducing effects. The broad in vitro tumor-suppressive effects of the miRNAs remain to be confirmed in vivo as technical and biological challenges prevented us from doing so within this dissertation. Regarding therapeutic utility, combinatorial approaches may hold more potential than miRNA mimics alone. As miR-4646-5p may modulate the tumor microenvironment through its impact on cytokines, combinations with immune checkpoint inhibitors could be beneficial, whereas for miR-4649-5p in vivo combinations with PI3K or AKT inhibitors like capivasertib are evident.