ERK regulates calpain 2-induced androgen receptor proteolysis in CWR22 relapsed prostate tumor cell lines
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Updated: Jun 18, 2026
A Bioluminescent and Fluorescent Orthotopic Syngeneic Murine Model of Androgen-dependent and Castration-resistant Prostate Cancer
Published on: March 6, 2018
Honglin Chen1, Stephen J Libertini, Yu Wang
1Department of Medical Microbiology and Immunology, University of California, Davis, California 19616, USA.
Abstract:
Androgen ablation therapy is effective in treating androgen-dependent prostate tumors; however, tumors that can proliferate in castrate levels of androgen eventually arise. We previously reported that in CWR22Rv1 (Rv1) cells, the protease calpain 2 can cleave the androgen receptor (AR) into a constitutively active approximately 80,000 low molecular weight (LMW) form. In this study, we further dissect the mechanisms that produce the AR LMW forms using Rv1 cells and the related CWR22-R1 (R1) cells. The 39-amino acid insertional mutation in the Rv1-AR (E3DM-AR) sensitizes this AR to calpain 2 proteolysis. R1 cells encode the same AR molecule as the parental CWR22 xenograft. Using calpain 2 small interfering RNA and calpeptin, we find that calpain 2 plays a role in the generation of the LMW-AR in R1 cells. Furthermore, LMW-AR expression is regulated by the activation of calpain 2 by ERK 1 and 2. Inhibition of ERK phosphorylation or small interfering RNA-mediated decrease of ERK expression reduces LMW-AR levels in R1 cells. Conversely, activation of the MAPK pathway results in increased ERK phosphorylation and increased levels of LMW-AR. Finally, analyses of human tumor samples found that LMW-AR levels are higher in tumors that have an increased calpain/calpastatin ratio and/or increased levels of phospho-ERK (pERK). This suggests that a higher calpain/calpastatin ratio collaborates with activated ERK to promote the generation of the LMW-AR.
Insights
Calpain 2 and ERK signaling generate a low molecular weight androgen receptor (AR) form in prostate cancer cells. This AR form is linked to tumor growth and may be a therapeutic target.
Area of Science:
- Molecular Biology
- Cancer Research
- Cell Signaling
Background:
- Androgen ablation therapy is a standard treatment for prostate cancer, but resistance eventually develops.
- The androgen receptor (AR) is a key driver of prostate cancer growth.
- Previous work identified calpain 2 protease activity generating a constitutively active low molecular weight AR (LMW-AR) form.
Purpose of the Study:
- To further investigate the mechanisms responsible for generating LMW-AR forms.
- To explore the role of calpain 2 and ERK signaling in LMW-AR production.
- To correlate LMW-AR levels with clinical parameters in human prostate tumors.
Main Methods:
- Utilized CWR22Rv1 (Rv1) and CWR22-R1 (R1) prostate cancer cell lines.
- Employed small interfering RNA (siRNA) targeting calpain 2 and ERK.
- Used calpeptin (a calpain inhibitor) and assessed ERK phosphorylation.
- Analyzed human prostate tumor samples for calpain/calpastatin ratios and phospho-ERK (pERK) levels.
Main Results:
- Calpain 2 was confirmed to play a role in LMW-AR generation in R1 cells.
- Activation of ERK 1 and 2 by the MAPK pathway regulates calpain 2 activity and LMW-AR levels.
- Inhibition of ERK phosphorylation or ERK expression reduced LMW-AR.
- Human tumors with higher calpain/calpastatin ratios and/or increased pERK showed higher LMW-AR levels.
Conclusions:
- Calpain 2 activity, modulated by ERK signaling, is crucial for producing LMW-AR.
- The calpain/calpastatin ratio and activated ERK collaborate in LMW-AR generation.
- LMW-AR may represent a therapeutic target in advanced prostate cancer.
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