Introduction
Emerging evidences indicate the involvement of a dynamic network connecting cellular bioenergetics, inflammatory response and redox homeostasis in tumor progression. Since there is a considerable overlap of signaling mediators involved in these interactions, the role of pro-inflammatory IL-1b in connecting these events in Glioblastoma multiforme (GBM) was investigated.
Methods
Nucleosomal scanning assay (NuSA) was performed in glioma cells to determine the effect of SIRT6 (Sirtuin 6) on positional stability of nucleosomes on HK2 promoter in the presence IL-1b. The role of SIRT6-HK2 axis in IL-1b treated glucose deprived cells was determined by Western blot analysis, co-immunoprecipitation and ChIP (chromatin immune-precipitation) upon knock-down and over-expression of SIRT6 or HK2.
Results
IL-1β induced expression of Hexokinase 2 (HK2) - the enzyme that catalyzes the first committed step of glycolysis, was accompanied by heightened SIRT6 levels. SIRT6 served as negative regulator of HK2, and IL-1β-induced HIF-1α (Hypoxia inducible factor 1a) prevented SIRT6 abundance and consequently its availability for regulating HK2 transcription. While treatment with IL-1b alone had no effect on glioma cell viability, massive cell death was observed in IL-1b treated cells under glucose deprivation in a ROS dependent manner. This was accompanied by increase in HK2, Nrf2 and Xanthine oxidoreductase (XOR) levels. SIRT6 not only promoted IL-1b induced death under glucose deprivation by regulating ROS levels, but also affected NRF2 expression and its interaction with HK2. Importantly, SIRT6 mediated HK2-Nrf2 interaction was crucial for regulation of XOR promoter activity. Interestingly, XOR inhibition further elevated IL-1b and HIF-1a levels under glucose deprived inflammatory conditions. Taken together, IL-1b induced SIRT6 not only regulates HK2 transcription but is also involved in maintaining cellular redox homeostasis.
Conclusion
Relative abundance of SIRT6 determines tumor cell fate by modulating metabolic and redox status of cells,