RÉSUMÉ
Thrombospondin-1 (TSP-1) is a multifunctional matrix protein with antitumor activities due in part to its ability to inhibit angiogenesis, which in turn contributes to determine the fate of many tumours. Previous studies have shown that TSP-1 expression supports normal kidney angiostasis, and decreased TSP-1 levels contribute to the angiogenic phenotype of renal cell carcinomas (RCC). The loss of the von Hippel-Lindau tumour suppressor gene (VHL) in these tumours favours stabilization of the Hypoxia Inducible Factors (HIF), which in turn contribute to adapt tumour cells to hostile environments promoting tumour progression. However, HIF-independent regulation of certain genes might also be involved. We have previously shown that TSP-1 is regulated in hypoxia in clear cell RCC (ccRCC) in a HIF-independent manner; however, the effect of VHL protein (pVHL) on TSP-1 expression has not been evaluated. Our results proved that pVHL loss or mutation in its alpha or beta domain significantly decreased TSP-1 levels in ccRCC in a HIF-independent manner. Furthermore, this regulation proved to be important for ccRCC cells behaviour showing that decreased TSP-1 levels rendered ccRCC cells more migratory. This data substantiates a unique regulation pattern for TSP-1 in a pVHL-dependent manner, which may be relevant in the aggressiveness of ccRCC.
Sujet(s)
Néphrocarcinome/anatomopathologie , Régulation de l'expression des gènes tumoraux , Tumeurs du rein/anatomopathologie , Protéines tumorales/physiologie , Thrombospondine-1/biosynthèse , Protéine Von Hippel-Lindau supresseur de tumeur/physiologie , Lignée cellulaire tumorale , Mouvement cellulaire , Milieux de culture sans sérum , Régulation négative , Techniques de knock-down de gènes , Humains , Sous-unité alpha du facteur-1 induit par l'hypoxie/physiologie , Jonctions intercellulaires/métabolisme , Mutation faux-sens , Invasion tumorale , Protéines tumorales/biosynthèse , Protéines tumorales/génétique , Domaines protéiques/génétique , Interférence par ARN , ARN messager/biosynthèse , ARN messager/génétique , ARN tumoral/biosynthèse , ARN tumoral/génétique , Petit ARN interférent/génétique , Thrombospondine-1/génétique , Protéine Von Hippel-Lindau supresseur de tumeur/antagonistes et inhibiteurs , Protéine Von Hippel-Lindau supresseur de tumeur/génétiqueRÉSUMÉ
The fine regulation of mitochondrial function has proved to be an essential metabolic adaptation to fluctuations in oxygen availability. During hypoxia, cells activate an anaerobic switch that favors glycolysis and attenuates the mitochondrial activity. This switch involves the hypoxia-inducible transcription factor-1 (HIF-1). We have identified a HIF-1 target gene, the mitochondrial NDUFA4L2 (NADH dehydrogenase [ubiquinone] 1 alpha subcomplex, 4-like 2). Our results, obtained employing NDUFA4L2-silenced cells and NDUFA4L2 knockout murine embryonic fibroblasts, indicate that hypoxia-induced NDUFA4L2 attenuates mitochondrial oxygen consumption involving inhibition of Complex I activity, which limits the intracellular ROS production under low-oxygen conditions. Thus, reducing mitochondrial Complex I activity via NDUFA4L2 appears to be an essential element in the mitochondrial reprogramming induced by HIF-1.