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Inhibition of HOS expression and activities by Wnt pathway
Vladimir S Spiegelman1, Weigang Tang, Masaru Katoh
1AMC Cancer Research Center, Lakewood, Colorado, CO 80214, USA.
Abstract:
BetaTrCP and HOS are closely related F-box proteins, which play key roles in ubiquitination and degradation of beta-catenin and IkappaB through associating with those phosphorylated substrates and recruiting SCF E3 ubiquitin ligase. Here we report that activation of Wnt/beta-catenin signal transduction pathway elevates betaTrCP levels but inhibits expression of HOS in 293T cells. Similar disparity is likely to exist in human colorectal tumors. In the NIH3T3 cells, which express HOS, but not betaTrCP, Wnt/beta-catenin signaling leads to inhibition of HOS promoter activity and NF-kappaB-driven transcription as well as to stabilization of beta-catenin. These results indicate that expression and activities of HOS are negatively regulated by Wnt/beta-catenin pathway.
Insights
The Wnt/beta-catenin pathway regulates beta-transducin repeat-containing protein (betaTrCP) and Homolog of Slimb (HOS) F-box proteins. This pathway elevates betaTrCP and inhibits HOS expression, impacting beta-catenin and NF-kappaB activity.
Area of Science:
- Molecular Biology
- Cell Biology
- Biochemistry
Background:
- BetaTrCP and HOS are F-box proteins crucial for ubiquitination and protein degradation.
- They target phosphorylated beta-catenin and IkappaB, recruiting the SCF E3 ubiquitin ligase complex.
- Dysregulation of these proteins is implicated in various cellular processes and diseases.
Purpose of the Study:
- To investigate the regulatory relationship between the Wnt/beta-catenin signaling pathway and the expression/activity of betaTrCP and HOS.
- To determine how Wnt/beta-catenin signaling influences the stability of beta-catenin and the activity of NF-kappaB in the context of HOS and betaTrCP expression.
Main Methods:
- Utilized 293T and NIH3T3 cell lines to study gene expression and protein activity.
- Analyzed Wnt/beta-catenin pathway activation effects on betaTrCP and HOS levels.
- Assessed HOS promoter activity and NF-kappaB-driven transcription.
- Monitored beta-catenin stabilization.
Main Results:
- Activation of the Wnt/beta-catenin pathway increased betaTrCP levels while decreasing HOS expression in 293T cells.
- In NIH3T3 cells (expressing HOS but not betaTrCP), Wnt/beta-catenin signaling inhibited HOS promoter activity and NF-kappaB transcription.
- Wnt/beta-catenin pathway activation led to beta-catenin stabilization in NIH3T3 cells.
- A similar expression disparity between betaTrCP and HOS may occur in human colorectal tumors.
Conclusions:
- The Wnt/beta-catenin signaling pathway negatively regulates the expression and activity of HOS.
- The pathway's activation influences the balance of betaTrCP and HOS, impacting key cellular signaling cascades.
- These findings suggest a complex interplay between Wnt/beta-catenin signaling and F-box protein regulation relevant to colorectal cancer.