The cholesterol biosynthesis enzyme FAXDC2 couples Wnt/β-catenin to RTK/MAPK signaling
Babita Madan, … , Enrico Petretto, David M. Virshup
Babita Madan, … , Enrico Petretto, David M. Virshup
Published January 23, 2024
Citation Information: J Clin Invest. 2024;134(6):e171222. https://doi.org/10.1172/JCI171222.
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Research Article Metabolism Oncology

The cholesterol biosynthesis enzyme FAXDC2 couples Wnt/β-catenin to RTK/MAPK signaling

Abstract

Wnts, cholesterol, and MAPK signaling are essential for development and adult homeostasis. Here, we report that fatty acid hydroxylase domain containing 2 (FAXDC2), a previously uncharacterized enzyme, functions as a methyl sterol oxidase catalyzing C4 demethylation in the Kandutsch-Russell branch of the cholesterol biosynthesis pathway. FAXDC2, a paralog of MSMO1, regulated the abundance of the specific C4-methyl sterols lophenol and dihydro-T-MAS. Highlighting its clinical relevance, FAXDC2 was repressed in Wnt/β-catenin–high cancer xenografts, in a mouse genetic model of Wnt activation, and in human colorectal cancers. Moreover, in primary human colorectal cancers, the sterol lophenol, regulated by FAXDC2, accumulated in the cancerous tissues and not in adjacent normal tissues. FAXDC2 linked Wnts to RTK/MAPK signaling. Wnt inhibition drove increased recycling of RTKs and activation of the MAPK pathway, and this required FAXDC2. Blocking Wnt signaling in Wnt-high cancers caused both differentiation and senescence; and this was prevented by knockout of FAXDC2. Our data show the integration of 3 ancient pathways, Wnts, cholesterol synthesis, and RTK/MAPK signaling, in cellular proliferation and differentiation.

Authors

Babita Madan, Shawn R. Wadia, Siddhi Patnaik, Nathan Harmston, Emile Tan, Iain Bee Huat Tan, W. David Nes, Enrico Petretto, David M. Virshup

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Figure 1

Wnt signaling represses the cholesterol biosynthesis enzyme FAXDC2.

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Wnt signaling represses the cholesterol biosynthesis enzyme FAXDC2. (A) ...
(A) Wnt inhibition upregulates genes regulating cholesterol biosynthesis. Pharmacologic Wnt inhibition with ETC-159 in HPAF-II orthotopic xenografts upregulates 4,350 genes that are grouped into temporal clusters (n = 4–6 mice per group). GO Biological Process and Reactome analysis of the Wnt-repressed genes highlights processes including cholesterol biosynthesis, vesicle-mediated transport, and EGFR/VEGF signaling (hypergeometric test, FDR < 10%). (B) Wnt signaling represses genes encoding enzymes in the cholesterol biosynthesis pathway. Left: Wnt inhibition with ETC-159 increases expression of multiple cholesterol biosynthesis pathway genes in 3 independent systems: HPAF-II and AsPC-1 orthotopic xenografts and cells in culture and colorectal PDX (14) (n = 4–6 tumors per group). Boxed genes show significant change in expression (FDR < 0.10). Right: Cholesterol biosynthesis pathway. (C) Wnt inhibition increases FAXDC2 expression in multiple Wnt-addicted cancer models: ETC-159–treated HPAF-II, AsPC-1 orthotopic tumors, and Wnt-addicted colorectal and pancreatic cancer PDX models have 2- to 10-fold higher FAXDC2 expression compared with control tumors. Relative expression from RNA-Seq in TPM or quantitative reverse transcription PCR (qRT-PCR) is shown. Each data point represents an independent tumor, n = 5–6 per group (hypergeometric test, FDR < 10%, or Mann-Whitney test). (D) ETC-159 treatment increases FAXDC2 protein abundance in tumors. Protein lysates from HPAF-II and AsPC-1 orthotopic xenografts from vehicle- or ETC-159–treated mice were probed with FAXDC2 or GAPDH antibodies. Each lane represents tumor lysate from an individual mouse. (E) Stabilized β‑catenin suppresses FAXDC2 expression despite upstream Wnt inhibition by ETC-159. Mice bearing xenografts from control HPAF-II cells or cells expressing stabilized β‑catenin were treated with ETC-159 or vehicle for 56 hours. FAXDC2 and AXIN2 mRNA were quantitated by qRT-PCR and normalized to both ACTB and EPN1. AXIN2 upregulation is a control for stabilized β‑catenin activity. (F) Genetic inhibition of Wnt signaling by TCF7L2 knockout in HT29 and HCT116 colon cancer xenografts increases FAXDC2 expression 2- to 8-fold in comparison with WT controls. (E and F) Each data point represents an independent tumor. Unpaired t test was used to calculate P values.