Casein kinase 1α–dependent feedback loop controls autophagy in RAS-driven cancers
Jit Kong Cheong, Fuquan Zhang, Pei Jou Chua, Boon Huat Bay, Andrew Thorburn, David M. Virshup
Jit Kong Cheong, Fuquan Zhang, Pei Jou Chua, Boon Huat Bay, Andrew Thorburn, David M. Virshup
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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.