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RASSF1A is a tumor suppressor gene that is inactivated by hypermethylation of its promoter region in most types of human cancers. The incidence of spontaneous or induced tumors is significantly higher in Rassf1a(-/-) mice than in wild-type mice, confirming the tumor suppressor function of RASSF1A. RASSF1A promotes apoptosis mainly through its interaction with the proapoptotic serine/threonine STE20-like kinases MST1 and 2. However, Rassf1a(-/-) mice do not show overt signs of deregulated apoptosis, suggesting that other RASSF1A effectors are also critical for tumor suppression. In a proteomics screen, we identified RAN GTPase, MST1 and 2 kinases, and alpha- and gamma-tubulin as RASSF1A-interacting proteins. We show that RASSF1A-induced microtubule hyperstability, a hallmark of RASSF1A expression, is RAN-GTP dependent. RASSF1A promotes the accumulation of the GTP-bound form of RAN via the MST2-induced phosphorylation of RCC1. Depletion of RASSF1A results in mislocalization of RCC1 to the mitotic spindle and spindle poles, leading to mitotic spindle abnormalities and prometaphase block. A similar mitotic delay is also observed with MST2 depletion. These findings reveal a mechanism for how RASSF1A controls microtubule stability and for how its loss compromises the integrity of the mitotic spindle, leading to aneuploidy and tumorigenesis.

Original publication

DOI

10.1016/j.cub.2009.05.064

Type

Journal article

Journal

Curr Biol

Publication Date

28/07/2009

Volume

19

Pages

1227 - 1232

Keywords

Animals, Cell Cycle Proteins, Guanine Nucleotide Exchange Factors, HeLa Cells, Humans, Mice, Mice, Knockout, Microscopy, Fluorescence, Microtubules, Nuclear Proteins, Phosphorylation, Protein-Serine-Threonine Kinases, Proteomics, Spindle Apparatus, Tubulin, Tumor Suppressor Proteins, ran GTP-Binding Protein