Casein kinase 1α–dependent feedback loop controls autophagy in RAS-driven cancers
Jit Kong Cheong, … , Andrew Thorburn, David M. Virshup
Jit Kong Cheong, … , Andrew Thorburn, David M. Virshup
Published March 23, 2015
Citation Information: J Clin Invest. 2015;125(4):1401-1418. https://doi.org/10.1172/JCI78018.
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Research Article Oncology

Casein kinase 1α–dependent feedback loop controls autophagy in RAS-driven cancers

Abstract

Activating mutations in the RAS oncogene are common in cancer but are difficult to therapeutically target. RAS activation promotes autophagy, a highly regulated catabolic process that metabolically buffers cells in response to diverse stresses. Here we report that casein kinase 1α (CK1α), a ubiquitously expressed serine/threonine kinase, is a key negative regulator of oncogenic RAS–induced autophagy. Depletion or pharmacologic inhibition of CK1α enhanced autophagic flux in oncogenic RAS–driven human fibroblasts and multiple cancer cell lines. FOXO3A, a master longevity mediator that transcriptionally regulates diverse autophagy genes, was a critical target of CK1α, as depletion of CK1α reduced levels of phosphorylated FOXO3A and increased expression of FOXO3A-responsive genes. Oncogenic RAS increased CK1α protein abundance via activation of the PI3K/AKT/mTOR pathway. In turn, elevated levels of CK1α increased phosphorylation of nuclear FOXO3A, thereby inhibiting transactivation of genes critical for RAS-induced autophagy. In both RAS-driven cancer cells and murine xenograft models, pharmacologic CK1α inactivation synergized with lysosomotropic agents to inhibit growth and promote tumor cell death. Together, our results identify a kinase feedback loop that influences RAS-dependent autophagy and suggest that targeting CK1α-regulated autophagy offers a potential therapeutic opportunity to treat oncogenic RAS–driven cancers.

Authors

Jit Kong Cheong, Fuquan Zhang, Pei Jou Chua, Boon Huat Bay, Andrew Thorburn, David M. Virshup

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Figure 8

CK1α inhibition synergizes with lysosomal inhibition to induce toxicity in RAS-driven human cancer cells.

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CK1α inhibition synergizes with lysosomal inhibition to induce toxicity ...
(A) D4476:CQ hyperactivates autophagy and inhibits growth of RAS-driven human cancer cells via cell death induction. Cells were treated for 18 hours in culture with 5 μM CQ and 1 μM D4476 as indicated (n = 3 per cell line). (B) Mutant RAS confers specificity to D4476:CQ-induced cytotoxicity. Isogenic HCT-116 cells (with/without mutant K-RAS) were treated with D4476:CQ and analyzed for PI uptake by flow cytometry (n = 3 per cell line). The stacked bar charts represent PI-negative and PI-positive cells in each treatment group. Data are mean ± SD of triplicate experiments. (C) FOXO3A depletion rescues mutant RAS–driven HCT-116 cells from D4476:CQ-induced growth arrest. FOXO3A was specifically depleted in the isogenic HCT-116 cells by two independent siRNAs, as shown in the immunoblots (n = 3 per cell line). Cell number was estimated by crystal violet dye retention, and the bar chart shows fold change in cell growth (relative to siCtrl). One-way ANOVA with Dunnett’s multiple comparison test was used to analyze statistical significance in C; ***P < 0.001.