Degradation of FBXO31 by APC/C is regulated by AKT- and ATM-mediated phosphorylation

Area of Science:

• Cellular Biology
• Molecular Oncology
• Biochemistry

Background:

• FBXO31 is a tumor suppressor involved in degrading cell-cycle regulators like cyclin D1 and MDM2.
• Loss of heterozygosity at 16q24.3, encoding FBXO31, occurs in various solid tumors.
• FBXO31 levels increase after genotoxic stress, but the regulatory mechanism is unclear.

Purpose of the Study:

• To elucidate the mechanism regulating FBXO31 protein levels.
• To investigate how FBXO31 is degraded under normal conditions and stabilized following genotoxic stress.

Main Methods:

• Investigated FBXO31 degradation using proteasomal assays.
• Utilized co-immunoprecipitation to study protein interactions.
• Analyzed the role of specific phosphorylation sites (Ser33, Ser278) using kinase inhibitors and site-directed mutagenesis.
• Examined FBXO31 regulation in response to genotoxic stress.

Main Results:

• FBXO31 is proteasomally degraded in a cell-cycle-dependent manner by the APC/C complex, facilitated by coactivators CDH1 and CDC20 binding to its D-box motif.
• AKT-mediated phosphorylation of FBXO31 at Ser33 is required for its degradation.
• Genotoxic stress induces ATM-mediated phosphorylation of FBXO31 at Ser278, disrupting its interaction with CDH1/CDC20 and preventing degradation.
• These findings reveal a dual phosphorylation mechanism controlling FBXO31 stability.

Conclusions:

• FBXO31 levels are tightly regulated by a phosphorylation-dependent switch controlling its interaction with the APC/C degradation machinery.
• AKT and ATM kinases play opposing roles in regulating FBXO31 stability, impacting its tumor suppressor function.
• Understanding this regulation provides insights into cancer development and potential therapeutic strategies targeting FBXO31.