Nicotinamide nucleotide transhydrogenase (NNT) deficiency dysregulates mitochondrial retrograde signaling and impedes proliferation

Abstract

To study the physiological roles of NADH and NADPH homeostasis in cancer, we studied the effect of NNT knockdown on physiology of SK-Hep1 cells. NNT knockdown cells show limited abilities to maintain NAD+ and NADPH levels and have reduced proliferation and tumorigenicity. There is an increased dependence of energy production on oxidative phosphorylation. Studies with stable isotope tracers have revealed that under the new steady-state metabolic condition, the fluxes of TCA and glycolysis decrease while that of reductive carboxylation increases. Increased [α-ketoglutarate]/[succinate] ratio in NNT-deficient cells results in decrease in HIF-1α level and expression of HIF-1α regulated genes. Reduction in NADPH level leads to repression of HDAC1 activity and an increase in p53 acetylation. These findings suggest that NNT is essential to homeostasis of NADH and NADPH pools, anomalies of which affect HIF-1α- and HDAC1-dependent pathways, and hence retrograde response of mitochondria.

Nicotinamide nucleotide transhydrogenase regulates mitochondrial metabolism in NSCLC through maintenance of Fe-S protein function

“…This is in direct contrast to what was observed in a model of adrenal adenocarcinoma (Chortis et al, 2018), though it was previously established that NNT regulation of global oxidation is critical to adrenal physiology and NNT deficiency manifests with adrenal insufficiency in patients (Roucher-Boulez et al, 2016; Meimaridou et al, 2018). This indicates that while NNT serves to supplement the NADPH pool across tissue types (Lopert and Patel, 2014; Fisher-Wellman et al, 2015; Ronchi et al, 2016; Meimaridou et al, 2018), its functional contribution to redox homoeostasis may vary, especially with regards to malignancy (Gameiro et al, 2013; Ho et al, 2017; Chortis et al, 2018; Li et al, 2018).…”

“…Through subsequent studies, NNT has been established as a significant contributor to the mitochondrial NADPH pool (Fisher-Wellman et al, 2015; Ronchi et al, 2016; Francisco et al, 2018). The importance of NNT has also been evaluated in malignancy, where NNT is shown to contribute to the maintenance of redox homeostasis in several cancers (Gameiro et al, 2013; Ho et al, 2017; Chortis et al, 2018; Li et al, 2018).…”

NNT Regulates Mitochondrial Metabolism in NSCLC Through Maintenance of Fe-S Protein Function

“…Though, it was previously established that NNT regulation of global oxidation is critical to adrenal physiology and NNT deficiency manifests with adrenal insufficiency in patients (Roucher-Boulez et al, 2016. This indicates that while NNT serves to supplement the NADPH pool across tissue types (Lopert and Patel, 2014, Fisher-Wellman et al, 2015, Ronchi et al, 2016, its functional contribution to redox homoeostasis may vary, especially with regards to malignancy (Gameiro et al, 2013, Ho et al, 2017, Li et al, 2018.…”

“…It has been shown in disparate cancer cell lines that disruption of redox homeostasis following the loss of NNT expression induces metabolic rewiring, marked by changes in fuel utility (Gameiro et al, 2013, Ho et al, 2017. In an endothelial cell line derived from the ascitic fluid of a patient with liver adenocarcinoma, NNT knockdown was associated with reduced flux of both glucose and glutamine carbon through the TCA cycle coupled with a shift towards reductive glutamine metabolism (Ho et al, 2017). This is in contrast to melanoma cells, which exhibit increased glucose flux through the TCA cycle at the expense of reductive glutamine metabolism (Gameiro et al, 2013).…”

“…Through subsequent studies NNT has been established as a significant contributor to the mitochondrial NADPH pool (Fisher-Wellman et al, 2015, Ronchi et al, 2016, Francisco et al, 2018. The importance of NNT has also been evaluated in malignancy, where NNT is shown to contribute to the maintenance of redox homeostasis in several cancers (Gameiro et al, 2013, Ho et al, 2017, Li et al, 2018.…”