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 4

FAXDC2 is a downstream effector of Wnt signaling, and FAXDC2-regulated genes are enriched for RTK signaling.

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FAXDC2 is a downstream effector of Wnt signaling, and FAXDC2-regulated g...
(A) Expression of a subset of Wnt-regulated genes depends on FAXDC2 (FDR < 10%). Heatmap of fold changes of 3,560 FAXDC2-dependent Wnt-regulated genes (interaction test, FDR < 10%). Left: Gene expression changes (log2 fold changes) between WT and FAXDC2-KO tumors at 0 hours. Right: Gene expression changes following treatment with ETC-159 in both parental HPAF-II tumors (56 vs. 0 hours) and FAXDC2-KO tumors (56 vs. 0 hours). This set of differentially responding genes was partitioned into 6 distinct clusters based on similarities in their response to ETC-159, including 3 clusters of Wnt-repressed genes (A, B, and C) and 3 three clusters of Wnt-activated genes (D, E, and F). (B) Representative genes from 4 clusters in part A show that FAXDC2 knockout blunts or reverses the response to Wnt inhibition (hypergeometric test, FDR < 10%). TPM, transcripts per million. (C) FAXDC2-regulated Wnt-repressed genes in clusters A–C show an enrichment of AP1 family TFBS motifs in their promoters (hypergeometric test, FDR < 10%). (D) RTK signaling pathways are enriched in FAXDC2-regulated Wnt-repressed genes. Data from representative GO Biological Process and Reactome enrichment of Wnt-repressed genes from clusters A–C that were identified in part A (hypergeometric test, FDR < 10%). (E) GO Biological Processes and Reactome enrichment analysis of Wnt-repressed genes in ETC-159–treated AsPC-1 and colorectal cancer PDX tumors shows an upregulation of RTK signaling pathways (hypergeometric test, FDR < 10%). (F) Pharmacologic Wnt inhibition with ETC-159 in HPAF-II xenografts increases protein tyrosine phosphorylation. HPAF-II orthotopic tumor protein lysates from vehicle- or ETC-159–treated mice were separated on a 10% SDS gel. Blots were probed with phosphotyrosine antibodies. Each lane represents tumor lysate from an individual mouse. Asterisks indicate prominent phospho-tyrosine bands. (G and H) Genetic inhibition of Wnt/β-catenin signaling in TCF7L2-KO HT29 and HCT116 xenografts increases protein tyrosine phosphorylation. Protein lysates from WT and TCF7L2-KO HT29 and HCT116 tumors were analyzed for abundance of phosphotyrosine proteins as in F. Each lane contains tumor lysate from an individual mouse.