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Scaffold attachment factor B1: an intrinsic inhibitor of androgen receptor downregulated in prostate cancer
11] Department of Biochemistry and Molecular Biology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA [2] Department of Urology, Mayo Clinic College of Medicine, Rochester, MN 55905, USA [3] Mayo Clinic Cancer Center, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
Abstract:
The androgen receptor (AR) is a pleiotrophic transcription factor that regulates expression of a large number of genes involved in many diverse cellular processes. The AR activation pathways have been studied extensively. However, the molecular mechanism and biological significance of AR inhibitory signals remain poorly understood. Mukhopadhyay et al. have now identified the nuclear matrix protein scaffold attachment factor B1 (SAFB1) as a novel AR corepressor. The authors found that SAFB1 physically associates with AR protein and inhibits AR transcriptional activity and androgen-sensitive gene expression. SAFB1 had no effect on chromatin occupancy of AR, but silencing of SAFB1 abolished recruitment MST1, a known AR repressor, at AR target loci. They also showed that SAFB1 interacts with EZH2, SUZ12 and EED, three core components of the Polycomb repressive complex 2 (PRC2), which catalyzes the gene repression histone modification H3 lysine 27 trimethylation (H3K27me3). The authors further showed that forced expression of SAFB1 increases H3K27me3 at AR target loci and this effect requires EZH2. Finally, the authors demonstrated that expression of SAFB1 is downregulated in human prostate cancer (PCa) specimens and SAFB1 knockdown results in an aggressive phenotype of PCa. These findings identify SAFB1 as an important node for integration of multiple inhibitory signals of AR, which represents a viable pathway for therapeutic intervention of PCa.
Insights
Scaffold attachment factor B1 (SAFB1) is a novel androgen receptor (AR) corepressor that inhibits AR activity and prostate cancer progression. SAFB1 downregulation in prostate cancer promotes aggressive phenotypes, suggesting therapeutic potential.
Area of Science:
- Molecular Biology
- Cancer Biology
- Epigenetics
Background:
- The androgen receptor (AR) is crucial for normal cellular processes, but its dysregulation drives prostate cancer.
- Understanding AR inhibitory signals is vital for developing effective cancer therapies.
- The role of nuclear matrix proteins in AR regulation is largely unexplored.
Purpose of the Study:
- To identify novel regulators of androgen receptor (AR) signaling.
- To elucidate the molecular mechanisms underlying AR inhibition.
- To investigate the role of scaffold attachment factor B1 (SAFB1) in prostate cancer.
Main Methods:
- Co-immunoprecipitation to assess protein-protein interactions.
- Chromatin immunoprecipitation (ChIP) to analyze protein binding and histone modifications.
- RNA interference (RNAi) to silence SAFB1 expression.
- Analysis of SAFB1 expression in human prostate cancer tissues.
Main Results:
- Scaffold attachment factor B1 (SAFB1) physically associates with the androgen receptor (AR) and inhibits its transcriptional activity.
- SAFB1 silencing disrupts the recruitment of AR repressors and Polycomb repressive complex 2 (PRC2) components to AR target genes.
- SAFB1 expression is reduced in prostate cancer, and its knockdown promotes an aggressive cancer phenotype.
- SAFB1-mediated repression involves EZH2 and H3K27 trimethylation at AR target loci.
Conclusions:
- SAFB1 acts as a novel AR corepressor, integrating multiple inhibitory signals.
- SAFB1 plays a critical role in suppressing AR-driven gene expression and prostate cancer progression.
- SAFB1 represents a potential therapeutic target for prostate cancer treatment.
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