SINE compounds activate exportin 1 degradation through an allosteric mechanism

Area of Science:

• Molecular Biology
• Structural Biology
• Oncology

Background:

• Overexpression of exportin 1 (XPO1/CRM1) in cancer cells leads to mislocalization of nuclear export cargoes.
• Selective inhibitors of nuclear export (SINEs), such as selinexor, restore nuclear localization by blocking XPO1-cargo interactions.
• SINEs also induce XPO1 degradation mediated by the Cullin-RING E3 ligase (CRL) substrate receptor ASB8.

Purpose of the Study:

• To elucidate the structural basis and mechanism of SINE-induced XPO1 degradation.
• To investigate the role of ASB8 in SINE-mediated XPO1 degradation.
• To determine if synthetic XPO1 inhibitors mimic native cellular degradation pathways.

Main Methods:

• Cryo-electron microscopy (cryo-EM) to determine structures of ASB8 bound to SINE-conjugated XPO1.
• Biochemical assays to assess protein-protein interactions and ubiquitination.
• Investigation of ASB8-mediated degradation induced by endogenous compounds.

Main Results:

• Cryo-EM structures reveal ASB8 binding to a cryptic XPO1 site exposed upon SINE conjugation.
• SINEs bind XPO1 independently of ASB8, initiating an allosteric mechanism for high-affinity ASB8 recruitment.
• SINEs induce XPO1 ubiquitination and degradation via the CRL pathway.
• The endogenous itaconate derivative 4-octyl itaconate also triggers ASB8-mediated XPO1 degradation.

Conclusions:

• SINEs induce XPO1 degradation through a novel allosteric mechanism, distinct from typical molecular glues.
• This mechanism involves ASB8 recruitment to a SINE-bound XPO1.
• Synthetic XPO1 inhibitors leverage a native cellular degradation pathway, expanding targeted protein degradation strategies beyond existing modalities.