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Published on: October 27, 2014
Wnt inhibitory factor 1 (WIF1) is a marker of osteoblastic differentiation stage and is not silenced by DNA
Emma K Baker1, Scott Taylor2, Ankita Gupte2
1Stem Cell Regulation Unit, St. Vincent's Institute of Medical Research, Fitzroy, Australia; Department of Medicine, St. Vincent's Hospital, University of Melbourne, Fitzroy, Australia.
Abstract:
Wnt pathway targeting is of high clinical interest for treating bone loss disorders such as osteoporosis. These therapies inhibit the action of negative regulators of osteoblastic Wnt signaling. The report that Wnt inhibitory factor 1 (WIF1) was epigenetically silenced via promoter DNA methylation in osteosarcoma (OS) raised potential concerns for such treatment approaches. Here we confirm that Wif1 expression is frequently reduced in OS. However, we demonstrate that silencing is not driven by DNA methylation. Treatment of mouse and human OS cells showed that Wif1 expression was robustly induced by HDAC inhibition but not by methylation inhibition. Consistent with HDAC dependent silencing, the Wif1 locus in OS was characterized by low acetylation levels and a bivalent H3K4/H3K27-trimethylation state. Wif1 expression marked late stages of normal osteoblast maturation and stratified OS tumors based on differentiation stage across species. Culture of OS cells under differentiation inductive conditions increased expression of Wif1. Together these results demonstrate that Wif1 is not targeted for silencing by DNA methylation in OS. Instead, the reduced expression of Wif1 in OS cells is in context with their stage in differentiation.
Insights
Wnt inhibitory factor 1 (WIF1) is reduced in osteosarcoma (OS), but not due to DNA methylation. WIF1 expression is linked to osteoblast differentiation, not epigenetic silencing in OS tumors.
Area of Science:
- Oncology
- Molecular Biology
- Bone Biology
Background:
- Wnt pathway is crucial for bone health and a target for osteoporosis treatments.
- Wnt inhibitory factor 1 (WIF1) is a negative regulator of Wnt signaling.
- Previous reports suggested epigenetic silencing of WIF1 in osteosarcoma (OS) via DNA methylation.
Purpose of the Study:
- To investigate the mechanism of Wif1 downregulation in osteosarcoma (OS).
- To determine if WIF1 is epigenetically silenced by DNA methylation in OS.
- To understand the relationship between Wif1 expression and OS differentiation.
Main Methods:
- Analysis of Wif1 expression in mouse and human OS cells.
- Treatment of OS cells with histone deacetylase (HDAC) inhibitors and methylation inhibitors.
- Chromatin analysis of the Wif1 locus, including acetylation and H3K4/H3K27 trimethylation states.
- Correlation of Wif1 expression with osteoblast maturation and OS tumor differentiation.
Main Results:
- Wif1 expression is frequently reduced in OS.
- Wif1 downregulation in OS is not caused by DNA methylation.
- HDAC inhibition robustly induced Wif1 expression in OS cells.
- The Wif1 locus in OS exhibits low acetylation and a bivalent H3K4/H3K27 trimethylation state.
- Wif1 expression correlates with late-stage osteoblast differentiation and OS tumor differentiation stage.
Conclusions:
- Wif1 is not epigenetically silenced by DNA methylation in osteosarcoma.
- Reduced Wif1 expression in OS is associated with the tumor's differentiation stage.
- HDAC inhibition can restore Wif1 expression, suggesting a role for histone acetylation.
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