Clusterin expression can be modulated by changes in TCF1-mediated Wnt signaling

Area of Science:

• Molecular biology
• Cell signaling
• Cancer research

Background:

• Clusterin (CLU) is implicated in various physiological and disease states.
• Wnt signaling pathway components, APC and c-MYC, influence CLU levels.
• Investigating Wnt signaling's role in regulating CLU variants is crucial.

Purpose of the Study:

• To determine if Wnt signaling activity regulates CLU mRNA and protein variants.
• To identify which Wnt pathway components mediate CLU expression changes.
• To characterize the specific CLU variant regulated by Wnt signaling.

Main Methods:

• Abrogation of Wnt signaling using over-expressed E-cadherin cytoplasmic domain.
• Over-expression of dominant-negative TCF1 and TCF4 transcription factors.
• Analysis of CLU mRNA variants via real-time RT-PCR and 5'-end RACE.
• Immunofluorescence to detect cytoplasmic CLU protein levels.

Main Results:

• Wnt signaling abrogation increased cytoplasmic CLU protein levels.
• Dominant-negative TCF1, but not TCF4, induced intra- and extracellular CLU protein.
• Only one of three CLU mRNA variants responded to TCF1 over-expression.
• This CLU mRNA variant was shorter at the 5'-end, encoding a secreted protein.

Conclusions:

• The Wnt signaling pathway specifically regulates a distinct CLU mRNA variant via TCF1.
• This TCF1-regulated CLU transcript produces a shorter intracellular isoform (60 kDa) secreted as ~80 kDa.
• CLU appears to be a secondary target gene within the Wnt signaling pathway.