p62/SQSTM1 Cooperates with Hyperactive mTORC1 to Regulate Glutathione Production, Maintain Mitochondrial Integrity, and Promote Tumorigenesis

Abstract

p62/sequestosome-1 (SQSTM1) is a multifunctional adaptor protein and autophagic substrate which accumulates in cells with hyperactive mTORC1, such as kidney cells with mutations in the tumor suppressor genes TSC1 or TSC2. Here we report that p62 is a critical mediator of TSC2-driven tumorigenesis, as Tsc2+/− and Tsc2f/f Ksp-CreERT2+ mice crossed to p62−/− mice were protected from renal tumor development. Metabolic profiling revealed that depletion of p62 in Tsc2-null cells decreased intracellular glutamine, glutamate, and glutathione (GSH). p62 positively regulated the glutamine transporter Slc1a5 and increased glutamine uptake in Tsc2-null cells. We also observed p62-dependent changes in Gcl, Gsr, Nqo1 and Srxn1 which were decreased by p62 attenuation and implicated in GSH production and utilization. p62 attenuation altered mitochondrial morphology, reduced mitochondrial membrane polarization and maximal respiration, and increased mitochondrial ROS and mitophagy marker PINK1. These mitochondrial phenotypes were rescued by addition of exogenous GSH and overexpression of Sod2, which suppressed indices of mitochondrial damage and promoted growth of Tsc2-null cells. Finally, p62 depletion sensitized Tsc2-null cells to both oxidative stress and direct inhibition of glutathione biosynthesis by buthionine sulfoximine (BSO). Our findings show how p62 helps maintain intracellular pools of glutathione needed to limit mitochondrial dysfunction in tumor cells with elevated mTORC1, highlighting p62 and redox homeostasis as nodal vulnerabilities for therapeutic targeting in these tumors.

VPS41 recessive mutation causes ataxia and dystonia with retinal dystrophy and mental retardation by inhibiting HOPS function and mTORC1 signaling

“…Interestingly, this results in an inhibition of mTORC1 as opposed to the hyperactivity of mTORC1 seen in many other neurodegenerative diseases. (75)(76)(77). These observations are of particular importance with regards to the design of a possible treatment of HOPS related disorders (69,70,73,78,79).…”

Dynamic Phosphorylation of the C Terminus of Hsp70 Regulates the Mitochondrial Import of SOD2 and Redox Balance

“…The disagreements in these studies may reflect the dose- and time-dependent effects of H 2 O 2 on Akt activation. Indeed, recent studies had demonstrated a transient increase in Akt activity when cells were treated with micromolar doses of H 2 O 2 (Thomas et al, 2007; Lam et al, 2017). In line with this finding, our data show that beyond certain levels, further increases in mitochondrial H 2 O 2 formation decreased SOD2 activity.…”

Estrogen activates pyruvate kinase M2 and increases the growth of TSC2-deficient cells

“…Thus, in the long term, it is possible that, compared to hormonal ablation, metabolically-focused strategies in LAM could have preferable side effect profiles with regard to bone health and biochemical parameters including serum calcium, serum phosphorus and bone specific isoform of alkaline phosphatase [54]. Recent studies have demonstrated therapeutic potentials of targeting dysregulated cellular metabolic pathways including glucose metabolism and autophagy addication using hydroxychloroquine or resveratrol in LAM [25,[55][56][57][58]. However, additional pre-clinical and clinical studies will be needed to test this concept.…”