Contribution of the Rho GTPase Rnd3 in the regulation of Glioma cell motility and invasion
[eng] Introduction GBMs constitute the most common CNS tumours, representing 14.2% of all tu-mours and 50.1% of malignant tumours. They stand among the most devastating hu-man cancers, characterized by a median overall survival of only 15 months. The chal-lenges in managing GBMs stem from several de...
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| Formato: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2025 |
| País: | España |
| Recursos: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/694847 |
| Acesso em linha: | http://hdl.handle.net/10803/694847 |
| Access Level: | acceso abierto |
| Palavra-chave: | Glioblastoma Rho GTPases Rnd3 Cell motility Cytoskeleton Motilitat cel·lular Citoesquelet Rho GTPasas Motilidad celular Citoesqueleto Bioquímica i Biologia Molecular 57 577 |
| Resumo: | [eng] Introduction GBMs constitute the most common CNS tumours, representing 14.2% of all tu-mours and 50.1% of malignant tumours. They stand among the most devastating hu-man cancers, characterized by a median overall survival of only 15 months. The chal-lenges in managing GBMs stem from several defining hallmarks, such as their en-hanced invasiveness and intratumoural heterogeneity, which includes the presence of a subpopulation of GSCs particularly resistant to radio- and chemotherapy. These fac-tors complicate complete resection and render the tumours highly resistant to current available therapies, resulting in modest responsiveness to standard treatment protocols involving radiotherapy and TMZ. In light of this landscape, extensive efforts have been directed toward characteriz-ing the molecular alterations underlying the aggressive nature of GBM. Among the identified alterations, abnormalities in receptor tyrosine kinases are prominent, with approximately 70% of GBM patients exhibiting alterations in at least one RTK, in-cluding EGFR, PDGFR, FGFR, and cMET. Oncogenic signalling emanating from RTKs affects various cellular cascades involved in cell proliferation, survival, and notably, cellular motility. Within this context, Rho GTPases emerge as pivotal regula-tors of the actin cytoskeleton. Among these proteins, the antagonistic proteins Rac1 and RhoA are the best characterised. While the former governs the formation of pro-invasive lamellipodia at the leading edge of cells, the latter modulates stress fibres (SF) and focal adhesion (FA) formation, and actomyosin contractility. A third member of this family, Rnd3, is an atypical Rho GTPase, constitutively bound to GTP and a well-known RhoA antagonist. The role of Rnd3 in cancer seems to be largely dependent on cellular context, with studies reporting divergent effects on cell motility and proliferation. In this thesis, we have investigated the molecular mechanisms gov-erning GBM cell motility, focusing on the interplay between RTKs and Rho GTPases, especially Rnd3. Research content Firstly, we focused on studying the impact of oncogenic RTK signalling on cellu-lar motility. The use of a panel of TKIs targeting EGFR, PDGFR/VEGFR, and c-MET revealed that inhibiting these RTKs results in a dramatic reorganization of the cellular cytoskeleton, promoting a phenotype characterized by the formation of SFs and FAs, which led to decreased cellular motility. These effects were reversed when disrupting the RhoA/ROCK signalling axis, suggesting that aberrant RTK activation sustains a Rho GTPase balance favouring the pro-invasive activity of Rac1 over RhoA; a balance that is reversed upon RTK inhibition, leading to the formation of structures typical of RhoA signalling and favouring a less invasive phenotype. Taken the antagonistic role of Rnd3 upon RhoA/ROCK activity, we then decided to focus on the specific contribution of this protein to the invasive phenotype of GBM. Inhibition of RTKs revealed that Rnd3 expression is indeed under the control of RTK signalling. Rnd3-mediated silencing essentially recapitulated all the observed effects promoted by RTK inhibition of actin cytoskeleton dynamics and cell motility. Con-versely, moderate Rnd3 overexpression prevented TKI-induced cytoskeleton reorgani-zation; altogether indicating that Rnd3 is an important mediator of the invasive pheno-type in GBM cells. In atypical Rho GTPases, canonical nucleotide cycling mechanisms diminish in importance compared to other regulatory mechanisms such as post-translational modi-fications and cellular expression modulation. Therefore, we conducted a bioin-formatic analysis to explore putative TFs involved in Rnd3 regulation. In this context, our data suggest a potential involvement of the AP-1 complex and JNK, as well as a potential implication of Rnd3 in the response to oxidative stress. Conclusion In conclusion, the evidence gathered in this thesis highlights the Rho GTPase Rnd3 as a significant player in the invasive context of GBM cells and opens the door to fu-ture lines of research delving into the regulatory mechanisms of its expression and its potential implication in the oxidative stress response. |
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