Inhibition of p70 S6 kinase activity by A77 1726 induces autophagy and enhances the degradation of superoxide dismutase 1 (SOD1) protein aggregates

• Published in: Cell death & disease Vol. 9; no. 3; pp. 407 - 16
• Main Authors: Sun, Jing, Mu, Yarong, Jiang, Yuanyuan, Song, Ruilong, Yi, Jianxin, Zhou, Jingsong, Sun, Jun, Jiao, Xinan, Prinz, Richard A, Li, Yi, Xu, Xiulong
• Format: Journal Article
• Language: English
• Published: England Springer Nature B.V 14.03.2018; Nature Publishing Group UK
• Subjects: Amino Acid Motifs; AMP; AMP-activated protein kinase; AMP-Activated Protein Kinase Kinases; Amyotrophic lateral sclerosis; Aniline Compounds - pharmacology; Animals; Autophagy; Autophagy - drug effects; Autophagy-Related Protein 7 - genetics; Autophagy-Related Protein 7 - metabolism; Autophagy-Related Protein-1 Homolog - genetics; Autophagy-Related Protein-1 Homolog - metabolism; Cell Line; Crotonates; Hydroxybutyrates - pharmacology; Inflammation; Kinases; Leflunomide; Localization; MAP Kinase Kinase Kinases - genetics; MAP Kinase Kinase Kinases - metabolism; Mice; Motor neurons; Nitriles; p70 S6 kinase; Phagocytosis; Phagosomes; Phosphates; Phosphorylation; Protein Aggregates - drug effects; Protein folding; Protein Kinases - genetics; Protein Kinases - metabolism; Protein-serine/threonine kinase; Proteins; Proteolysis - drug effects; Rapamycin; Ribosomal Protein S6 Kinases, 70-kDa - antagonists & inhibitors; Ribosomal Protein S6 Kinases, 70-kDa - chemistry; Ribosomal Protein S6 Kinases, 70-kDa - genetics; Ribosomal Protein S6 Kinases, 70-kDa - metabolism; siRNA; Superoxide dismutase; Superoxide Dismutase-1 - genetics; Superoxide Dismutase-1 - metabolism; TAK1 protein; Toluidines; TOR protein; TOR Serine-Threonine Kinases - genetics; TOR Serine-Threonine Kinases - metabolism
• ISSN: 2041-4889; 2041-4889
• DOI: 10.1038/s41419-018-0441-0

Autophagy plays a central role in degrading misfolded proteins such as mutated superoxide dismutase 1 (SOD1), which forms aggregates in motor neurons and is involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). Autophagy is activated when UNC-51-like kinase 1 (ULK1) is phosphorylated at S555 and activated by AMP-activated protein kinase (AMPK). Autophagy is suppressed when ULK1 is phosphorylated at S757 by the mechanistic target of rapamycin (mTOR). Whether p70 S6 kinase 1 (S6K1), a serine/threonine kinase downstream of mTOR, can also regulate autophagy remains uncertain. Here we report that inhibition of S6K1 by A77 1726, the active metabolite of an anti-inflammatory drug leflunomide, induced mTOR feedback activation and ULK1 phosphorylation in NSC34 cells, a hybrid mouse motoneuron cell line. Unexpectedly, A77 1726 did not suppress but rather induced autophagy by increasing AMPK and ULK1 phosphorylation. Similar observations were made with PF-4708671, a specific S6K1 inhibitor, or with S6K1 siRNA. Further studies showed that A77 1726 induced AMPK phosphorylation by activating the TGF-β-activated kinase 1 (TAK1). Functional studies revealed that A77 1726 induced co-localization of mutant SOD1 protein aggregates with autophagosomes and accelerated SOD1 protein degradation, which was blocked by inhibition of autophagy through autophagy-related protein 7 (ATG7) siRNA. Our study suggests that S6K1 inhibition induces autophagy through TAK1-mediated AMPK activation in NSC34 cells, and that blocking S6K1 activity by a small molecule inhibitor such as leflunomide may offer a new strategy for ALS treatment.