IRAK2 downregulation reduces the growth of triple-negative breast cancer cells in vitro and in vivo affecting several key pathways in a cell line-dependent way

Ferraro, Francesca; Zenke, Martin (Thesis advisor); Pradel, Gabriele (Thesis advisor); Maurer, Jochen (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022


Breast cancer stem cells (BCSCs) are considered responsible for the recurrence, resistance, and metastasis of tumors. The research group of PD Dr. Jochen Maurer at the University Hospital of Aachen is working with BCSCs that were isolated from human tumors of triple-negative breast cancer (TNBC), a breast cancer molecular subtype whose tumorigenicity is often driven by BCSCs. The primary BCSCs are highly tumorigenic, recapitulate the tumor of origin when transplanted in immunocompromised mice, and present a suitable model for the validation of targeting strategies. In a former publication of the research group, bi-potential TNBC cell line MDA-MB-468 was used to screen kinases whose downregulation elicited a differentiation response. In particular, it was shown that the downregulation of the kinases ERN1 and ALPK1 decreased MDA-MB-468 proliferation, self-renewal capacity, and tumorigenicity. In the kinase screening, interleukin-1 receptor-associated kinase 2 (IRAK2) was identified, and interestingly, IRAK2 is highly expressed by the primary BCSCs. Therefore, in this thesis, it was investigated if IRAK2 depletion may compromise the growth of BCSCs and MDA-MB-468 and thereby impair cancer progression. This dissertation reports that BCSCs and MDA-MB-468 characterized by IRAK2 downregulation showed decreased proliferation and sphere-forming capacity, evidencing the role of IRAK2 in cellular growth and self-renewal. Moreover, cells presenting IRAK2 knockdown originated smaller xenografts compared to control cells when orthotopically transplanted in immunodeficient mice, suggesting that IRAK2 downregulation may delay tumor progression. At the molecular level, IRAK2 knockdown decreased NF-κB and ERK phosphorylation, the expression of the pro-inflammatory cytokine IL-6, and the expression of the cell cycle regulator cyclin D1. Besides, IRAK2 downregulation reduced the expression of genes involved in the unfolded protein response and autophagy, pathways adopted by cells to manage cellular stress conditions, and affected apoptosis. It was concluded that IRAK2 downregulation might compromise cellular growth by affecting pathways responsible for cellular proliferation and resistance to environmental stress. These pathways were to some extent differently affected by IRAK2 downregulation in BCSCs and MDA-MB-468. The difference observed could be attributed to the cellular heterogeneity, given that the cell lines considered have different phenotypes and belong to different TNBC subtypes, but also to the different mutations and genetic backgrounds characterizing them since they were isolated from different patients. Moreover, the cells displayed different efficiencies of IRAK2 knockdown that could have distinctively influenced the pathways that were considered. Overall, given that IRAK2 downregulation significantly impaired cellular growth and the pathways exploited by cancer cells to survive, the presented findings suggest that IRAK2 could be an interesting target to compromise TNBC aggressiveness.