M phase-specific interaction between SBDS and RNF2 at the mitotic spindles regulates mitotic progression

Abstract

Shwachman-Diamond syndrome (SDS) is an autosomal recessive inherited disorder caused by biallelic mutations in the Shwachman-Bodian-Diamond syndrome (SBDS) gene. SBDS protein is involved in ribosome biogenesis; therefore SDS is classified as a ribosomopathy. SBDS is localized at mitotic spindles and stabilizes microtubules. Previously, we showed that SBDS interacts with ring finger protein 2 (RNF2) and is degraded through RNF2-dependent ubiquitination. In this study, we investigated when and where SBDS interacts with RNF2 and the effects of the interaction on cells. We found that SBDS co-localized with RNF2 on centrosomal microtubules in the mitotic phase (M phase), whereas SBDS and RNF2 localized to the nucleolus and nucleoplasm in the interphase, respectively. The microtubule-binding assay revealed that SBDS interacted directly with microtubules and RNF2 interacted with SBDS bound to microtubules. In addition, SBDS was ubiquitinated and degraded by RNF2 during the M phase. Moreover, RNF2 overexpression accelerated mitotic progression. These findings suggest that SBDS delays mitotic progression, and RNF2 releases cells from suppression through the ubiquitination and subsequent degradation of SBDS. The interaction between SBDS and RNF2 at mitotic spindles might be involved in mitotic progression as a novel regulatory cascade.