Destruction of DDIT3/CHOP protein by wild-type SPOP but not prostate cancer-associated mutants

Area of Science:

• Molecular Biology
• Cancer Genetics
• Cellular Stress Response

Background:

• Next-generation sequencing reveals frequent SPOP gene mutations in prostate cancer, implicating it in disease development.
• SPOP functions as an adaptor protein in the CUL3-RBX1 E3 ubiquitin ligase complex, regulating substrate ubiquitination and degradation.
• Endoplasmic reticulum (ER) stress and the transcription factor DDIT3 are critical in apoptotic pathways.

Purpose of the Study:

• To investigate the role of SPOP in regulating DDIT3 protein levels.
• To determine if prostate cancer-associated SPOP mutations affect DDIT3 degradation.
• To elucidate the link between SPOP mutations, DDIT3 homeostasis, and ER stress in prostate cancer.

Main Methods:

• Utilized next-generation sequencing data to identify SPOP mutations in prostate cancer.
• Employed biochemical assays to identify DDIT3 as a substrate of the SPOP-CUL3-RBX1 E3 ubiquitin ligase complex.
• Investigated the impact of wild-type and mutant SPOP on DDIT3 ubiquitination and degradation via the ubiquitin-proteasome pathway.

Main Results:

• Identified DDIT3 as a direct substrate recognized and degraded by the SPOP-CUL3-RBX1 E3 ubiquitin ligase complex.
• Demonstrated that SPOP recognizes a specific degron within the DDIT3 transactivation domain.
• Showcased that prostate cancer-associated SPOP mutants exhibit impaired ability to degrade DDIT3, leading to its accumulation.

Conclusions:

• SPOP plays a crucial role in regulating DDIT3 protein homeostasis through targeted degradation.
• Dysregulation of DDIT3 degradation by mutant SPOP may contribute to ER stress and prostate cancer progression.
• This study provides novel insights into the molecular mechanisms linking SPOP mutations to ER stress pathways in prostate cancer.