Importin-β and CRM1 control a RANBP2 spatiotemporal switch essential for mitotic kinetochore function

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Small ubiquitin-related modifier (SUMO) conjugation is a key post-translational modification regulating protein function.
• RAN Binding Protein 2 (RANBP2) acts as a SUMO E3 ligase and stabilizer, implicated in cancer.
• The RANBP2-SUMO-RANGAP1 complex localizes to the mitotic spindle and kinetochores during mitosis.

Purpose of the Study:

• To investigate the regulatory mechanisms governing the localization of the RANBP2-SUMO-RANGAP1 complex.
• To determine the role of nuclear transport receptors in this localization process.
• To elucidate how this localization impacts kinetochore functions during mitosis.

Main Methods:

• Proximity ligation assays were employed to study protein interactions.
• Inducible cell lines were generated to control the expression of nuclear transport receptors.
• Kinetochore functions, including SUMO conjugation and fiber stability, were assessed.

Main Results:

• Nuclear transport receptors importin-β and CRM1 are essential for regulating RANBP2-SUMO-RANGAP1 localization.
• Overexpression of these receptors differentially affects the timing of RANBP2 localization.
• Kinetochore functions, such as SUMO-conjugated topoisomerase-IIα accumulation and kinetochore fiber stability, are consequently altered.

Conclusions:

• Nuclear transport receptors provide a novel mechanism to control the functional state of kinetochores.
• The timely deposition of RANBP2 at kinetochores, regulated by nuclear transport, is critical for mitotic progression.
• This study reveals a new layer of regulation in kinetochore-microtubule interactions mediated by SUMOylation and nuclear transport.