New insights about the role of the nadph oxidase nox4 in hepatocarcinogenesis
- Autores: Irene Peñuelas Haro
- Directores de la Tesis: Maria Isabel Fabregat Romero (dir. tes.), Esther Bertran i Rodríguez (dir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2021
- Idioma: inglés
- Tribunal Calificador de la Tesis: Francesc Ventura Pujol (presid.), Patricia Sancho Andrés (secret.), Laia Caja Puigsubirà (voc.)
- Programa de doctorado: Programa de Doctorado en Biomedicina por la Universidad de Barcelona
- Materias:
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- Resumen
The NADPH oxidase (NOX) family has emerged in the last years as an important source of reactive oxygen species (ROS) in signal transduction. The isoform NOX4 has been implicated in a variety of physiological and pathological processes. In recent works, our research group found that silencing NOX4 expression in hepatocellular carcinoma (HCC) cells increases their proliferative capacity in vitro and enhances their tumorigenic potential in xenografts mice, resulting in earlier onset of tumor formation and increase in tumor size. NOX4 also regulated other cellular processes that occur later in progression and that favor tumor metastasis, such as migration and invasion. In this thesis, we aim to determine the molecular mechanisms regulated by NOX4 in liver cells that could explain its tumor suppressor functions. A proteomic analysis, by comparing HCC control cells with cells where NOX4 had been silenced or overexpressed, allowed the identification of changes in the levels of proteins whose expression is under the control of the transcription factors MYC and NRF2. The activation of both transcription factors inversely correlated with NOX4 levels. Importantly, the increase in cell proliferation and migration upon silencing NOX4 were reverted when silencing MYC expression. Moreover, silencing NOX4 induced changes in the amount and dynamics of the mitochondria, increase in the protein levels of complex IV and V and higher ATP levels, which was mediated by MYC activation. In addition, cell metabolism emerged as one of the highest affected processes in the proteomic analysis. Silencing NOX4 levels in HCC cells increased both glycolysis and oxidative phosphorylation pathways, while NOX4 overexpression showed opposite effects. A detailed transcriptomic and metabolomic analysis indicated that NOX4 could be also regulating fatty acid metabolism. Importantly, the inverse correlation between NOX4 and MYC, as well as with some key metabolic enzymes was observed in human HCC samples. Furthermore, NOX4 loss altered the cellular redox balance that produced increase in NRF2 activity, which was responsible for MYC activation. Low levels of NOX4 induced the expression of NOX1/NOX2 ROS-producing enzymes, which contributed to oxidative stress and consequently to NRF2 activation. Analogously, NOX4 silencing reduces proteasomal activity, which may impact on NRF2 degradation, therefore contributing to its constitutive activation. Importantly, the catalytic activity of NOX4 was required for some of the effects observed. In conclusion, the liver tumor suppressor functions of NOX4 could be explained through its essential roles in regulating redox and metabolic cell homeostasis in a NRF2/Myc-dependent fashion.
