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 2

CK1α knockdown or inactivation elevates basal autophagy and autophagic flux in a mutant RAS–dependent manner.

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CK1α knockdown or inactivation elevates basal autophagy and autophagic f...
(A) CK1α depletion increases basal autophagy and autophagic flux in isogenic HCT-116 cells (with/without mutant K-RAS). Cells were analyzed 48 hours after RNAi treatment. (B) CK1α inhibition increases basal autophagy and autophagic flux in a mutant RAS–specific manner. Cells were exposed to vehicle control (Veh Ctrl; DMSO) or 5 μM D4476 for 6 hours. Fold change in LC3B-II protein expression after CQ addition over the indicated duration was assessed without or with CK1α knockdown (A) or without or with CK1α inhibition (B). Values are mean ± SD from 3 independent experiments. Fold expression change in the proteins of interest after normalization is indicated below protein blots. mu, mutant. Cell lines with mutant RAS: SW480, DLD-1, HCT-116K–RAS WT/mu, and T24; with WT K-RAS: HT-29 and HCT-116K–RAS WT/–.