@misc{Turos-Korgul_Laura_Intercellular_2026,
 author={Turos-Korgul, Laura},
 editor={Piwocka, Katarzyna (1970– ) : Supervisor},
 copyright={Rights Reserved - Free Access},
 address={Warsaw},
 howpublished={online},
 school={Nencki Institute of Experimental Biology PAS},
 school={degree obtained: 2026},
 year={2026},
 publisher={Nencki Institute of Experimental Biology PAS},
 language={eng},
 abstract={Intercellular communication, while essential for normal organism function, is also exploited by cancer cells to interact with both malignant and non-malignant cells, thereby promoting tumor growth and adaptation to changing environmental conditions. In myeloid leukemias, including chronic myeloid leukemia (CML), leukemic cells interact directly and indirectly with various types of cells in the bone marrow niche. This contact is essential for the immune evasion, development of resistance, and the persistence of leukemic stem cells (LSC). Among the diverse modes of cell-cell communication, tunneling nanotubes (TNTs) have emerged as a distinct, unconventional type of direct intercellular communication mechanism. TNTs enable the transfer of a wide range of cargo, including mitochondria, vesicles, or proteins, between distant cells. However, despite significant advances in research on TNTs, substantial knowledge gaps persist, limiting our full understanding of these structures, their role in cancer progression and resistance, as well as their potential clinical application. Our previous studies have shown that TNTs are exploited by bone marrow stromal cells (BMSCs) and CML cells to transfer cellular vesicles and proteins from stroma to leukemia cells. This results in the increased resistance of recipient cells to the imatinib drug. Here, we identified CD44 as one of the stromal proteins transferred to leukemia. The general aim of this work was to examine the role of the stroma-derived CD44 protein in CML recipient cells. First, the stroma-to-leukemia CD44 transfer was confirmed using confocal microscopy and flow cytometry. The results showed that the transfer strictly depends on the direct cell-cell contact between stromal and leukemia cells. Moreover, it is mediated by tunneling nanotubes formed between connected cells. The RNA-seq analysis of CML cells that received and did not receive stromal CD44 revealed that CD44 transfer is linked to increased expression of genes related to cell adhesion, extracellular matrix remodeling, and cell migration. This was accompanied by increased activity of matrix metalloproteinases and higher invasiveness of these cells. Notably, in leukemic recipient cells, the endogenous CD44 was also upregulated at both mRNA and protein levels. Stroma-driven upregulation of CD44 in CML cells was associated with the activation of the pro-survival ERK/AP-1 pathway and stroma-mediated protection from tyrosine kinase inhibitors. In vitro, pharmacological targeting of the interaction between CD44 and its main ligand, hyaluronan, disrupted stroma-driven protection and sensitized CML cells to imatinib. An additional aim of this study was to investigate the ultrastructure of TNTs, which are the primary mediators of CD44 transfer. Focused ion beam scanning electron microscopy (FIB-SEM) confirmed the presence of TNTs in the stroma-leukemia co-cultures. However, TNTs identified by confocal microscopy using the current standard criteria do not consistently meet them when examined at higher resolution, using volume electron microscopy. Therefore, it was proposed here that current approaches should be re-evaluated. Furthermore, the presented data contradicted the theory that TNTs are completely open structures, indicating the existence of a specific regulatory system controlling cargo transfer via TNTs. In summary, the studies presented in this dissertation provide new insights into stroma-driven resistance associated with horizontal CD44 protein transfer mediated by TNTs, leading to transcriptional reprogramming of leukemia acceptor cells toward a more invasive and resistant phenotype. Additionally, these findings deepen the understanding of TNTs’ ultrastructure and critically evaluate the criteria and methodologies currently employed for their identification},
 title={Intercellular transfer of CD44 from bone marrow stroma to chronic myeloid leukemia cells as a driver of niche-mediated imatinib resistance : PhD thesis},
 type={Text},
 URL={http://rcin.org.pl/Content/263385/doktorat.pdf},
 keywords={CD44, Chronic myeloid leukemia, Intercellular communication, Microenvironment, TNTs, Tunneling nanotubes},
}