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 3

A FOXO3 autophagy gene transactivation signature after CK1α depletion or inhibition.

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A FOXO3 autophagy gene transactivation signature after CK1α depletion or...
(A) A subset of autophagy-related genes is dysregulated upon CK1α depletion. Autophagy transcriptome changes were assessed in HCT-116 and T24 cells (n = 3 per cell line) 24 hours following CK1α knockdown. The percentage of differentially regulated genes is indicated, using a 1.5-fold cut off. (B) Transcriptome profiling identifies enhanced expression of FOXO3A-responsive genes upon CK1α depletion. Representative Venn diagram from three independent experiments depicts overlapping upregulated genes in CK1α-depleted HCT-116 and T24 cells (n = 3 per cell line). Genes previously shown to be regulated by FOXO3A are indicated in bold. (C) CK1α knockdown for 48 hours increases expression of FOXO3A-responsive autophagy-related genes as assessed by qPCR (n = 3 per cell line). (D) D4476 increases expression of FOXO3A-responsive autophagy-related genes. Indicated cell lines were treated with DMSO or D4476 for 6 hours prior to analysis by qPCR (n = 3 per cell line). One-way ANOVA with Dunnett’s multiple comparison test was used to analyze statistical significance in C and D; **P < 0.01; ***P < 0.001.