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 7

FAXDC2 knockout prevents Wnt inhibition–induced MAPK activation, cellular differentiation, and senescence.

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FAXDC2 knockout prevents Wnt inhibition–induced MAPK activation, cellul...
(A and B) FAXDC2 is required for MAPK activation. Xenografts from 2 independent FAXDC2-KO clones had reduced ERK phosphorylation with no further increase upon ETC-159 treatment. Protein lysates were prepared as a master mix and loaded on independent gels. Load control of A is shared with Figure 6D and of B with Figure 6H. (C) FAXDC2 overexpression mediates sustained ERK activation. Western blot analysis of protein lysates from indicated xenografts. Each lane represents tumor lysate from an individual mouse. (D) Knockout of FAXDC2 reduced the growth of HPAF-II subcutaneous xenografts, with further reduction upon Wnt inhibition. n = 5–6 mice per group. (E) Overexpression of FAXDC2 delayed implantation and reduced growth of HPAF-II xenografts. n = 5–6 mice per group. (F and G) Wnt inhibition caused an increase in senescence-associated β-galactosidase in HPAF-II tumors that was diminished in the FAXDC2-KO tumors. (F) Representative images are shown. Scale bars: 100 μm. (G) Percentage of positively stained area (blue) was quantitated. Each dot represents quantitation of a tumor section from an individual mouse. P values were calculated by Mann-Whitney U test. (H and I) FAXDC2 knockout blunts the differentiation response to Wnt inhibition. (H) Expression of selected differentiation markers in tumors assessed by RNA-Seq. Each data point represents an individual tumor (hypergeometric test, FDR <10%). (I) FAXDC2 knockout blunts the Wnt inhibition–mediated increase in mucin expression as assessed by Alcian blue staining. Scale bars: 50 μm. (J–L) The Wnt/MAPK axis is present in non-malignant mouse pancreas. (J and K) Genetic activation and subsequent pharmacologic inhibition of Wnt signaling in mouse pancreas led to reciprocal regulation of Faxdc2 expression. Pancreas from control or ETC-159–treated WT and Ptf1αCre Rnf43–/– Znrf3–/– mice was analyzed for (J) Tcf7 and (K) Faxdc2 (Gm12248) expression by qRT-PCR. Data are from 2 independent biological experiments; each dot represents an individual mouse. P values were calculated by the Mann-Whitney U test. (L) Wnt activation reduced p-ERK levels in the mouse pancreas as assessed by IHC. Representative image of anti–p-ERK–stained pancreas. Scale bars: 100 μm.