CSR1 induces cell death through inactivation of CPSF3

Area of Science:

• Oncology
• Molecular Biology
• Gene Regulation

Background:

• Cellular stress response 1 (CSR1) is a tumor suppressor gene implicated in prostate cancer.
• CSR1 hypermethylation occurs in over 30% of prostate cancers, leading to its silencing.
• The precise mechanism by which CSR1 suppresses tumor growth remains unclear.

Purpose of the Study:

• To elucidate the molecular mechanism underlying CSR1's tumor-suppressive function.
• To identify proteins that interact with CSR1.
• To investigate the functional consequences of CSR1-protein interactions on cellular processes.

Main Methods:

• Yeast two-hybrid screening of a prostate cDNA library to identify CSR1-interacting proteins.
• Biochemical assays to confirm binding affinity and map interaction domains.
• Subcellular localization studies (immunofluorescence) to track protein translocation.
• In vitro and in vivo polyadenylation assays.
• Small interfering RNA (siRNA) knockdown of target genes.
• Site-directed mutagenesis to create non-binding CSR1 mutants.

Main Results:

• Cleavage and polyadenylation-specific factor 3 (CPSF3) was identified as a high-affinity binding partner for CSR1.
• The CSR1-CPSF3 interaction domain was mapped to amino acids 440–543 of CSR1.
• CSR1 binding induced CPSF3 translocation from the nucleus to the cytoplasm.
• CPSF3 translocation inhibited polyadenylation activity both in vitro and in vivo.
• Downregulation of CPSF3 phenocopied CSR1's tumor-suppressive effects, inducing cell death.
• A CSR1 mutant defective in CPSF3 binding failed to induce CPSF3 translocation, inhibit polyadenylation, or cause cell death.

Conclusions:

• CSR1 suppresses prostate tumor growth through a novel mechanism involving the sequestration of CPSF3.
• CSR1 hijacks CPSF3, a key RNA processing enzyme, leading to its nuclear-to-cytoplasmic translocation.
• This interaction disrupts mRNA polyadenylation, ultimately inducing cancer cell death.