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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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 6

FAXDC2 is downstream of Wnt/β-catenin in the regulation of RTK signaling.

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FAXDC2 is downstream of Wnt/β-catenin in the regulation of RTK signalin...
(A) Stabilized β-catenin prevents multiple RTKs from moving to the cell surface upon treatment with ETC-159. Cell surface abundance of EGFR, ERBB2, and EPHA2 was assessed as before in HPAF-II cells with or without stabilized β-catenin. Cells were treated with DMSO or 100 nM ETC-159 for 72 hours before staining with fluorescent tagged antibodies. Each histogram represents ~50,000 cells. Data are representative of 3 independent experiments, and 2 replicates are shown. (B) Knockdown of FAXDC2 prevents Wnt inhibition–mediated increase in EGFR cell surface abundance. HPAF-II cells were transfected with a pool of 4 siRNAs or 2 independent siRNAs (si6 and si7) against FAXDC2 for 24 hours, followed by treatment with ETC-159 for 72 hours. The cells were then stained with Alexa Fluor 488–conjugated anti-EGFR antibody and analyzed by flow cytometry. Data are representative of 3 independent experiments, and 2 replicates are shown. (C and D) Knockout of FAXDC2 in HPAF-II tumors prevents Wnt inhibition–mediated increase in tyrosine phosphorylation and p-EPHA2 levels. Protein lysates from HPAF-II or FAXDC2-KO tumor xenografts from vehicle- or ETC-159–treated mice were separated on 10% SDS gels and transferred to a PVDF membrane. Membranes were probed with anti-phosphotyrosine or –p-EphA2 antibodies. Each lane represents lysate from an individual tumor. (E) Overexpression of FAXDC2 in FAXDC2-KO tumors rescues the Wnt inhibition–mediated increase in tyrosine phosphorylation. Protein lysates from FAXDC2-KO or FAXDC2-OE tumor xenografts from vehicle- or ETC-159–treated mice were probed with phosphotyrosine antibodies. Each lane represents lysate from an individual tumor. (F–H) FAXDC2 knockout prevents the Wnt inhibition–mediated increase in EGFR and Eph family receptor tyrosine kinase abundance. Protein lysates from HPAF-II or FAXDC2-KO tumors from mice treated with vehicle or ETC-159 were analyzed as in C. Data are shown from 2 independent FAXDC2-KO clones, clone 3 (F and G) and clone 12 (H). Each lane represents lysate from an individual tumor.