Successful cell division is accomplished by the proper formation of the mitotic spindle. Here， we show that EphA2 knockdown causes mitotic errors， including a delay in M-phase progression， asymmetric spindle positioning， multipolar spindles， and cell blebs. It has been known that EphA2 is phosphorylated at Tyr588， which is triggered by the ligand binding， and at Ser897 downstream of growth factor signaling. Upon mitotic entry， EphA2 is phosphorylated at Ser897， accompanied by a reduction in Tyr588 phosphorylation. This EphA2 phosphorylation at Ser897 is inhibited by MEK/ERK and 90 kDa ribosomal S6 kinase (RSK) inhibitors and is induced by the introduction of active cyclin-dependent kinase 1 (C... More
Successful cell division is accomplished by the proper formation of the mitotic spindle. Here， we show that EphA2 knockdown causes mitotic errors， including a delay in M-phase progression， asymmetric spindle positioning， multipolar spindles， and cell blebs. It has been known that EphA2 is phosphorylated at Tyr588， which is triggered by the ligand binding， and at Ser897 downstream of growth factor signaling. Upon mitotic entry， EphA2 is phosphorylated at Ser897， accompanied by a reduction in Tyr588 phosphorylation. This EphA2 phosphorylation at Ser897 is inhibited by MEK/ERK and 90 kDa ribosomal S6 kinase (RSK) inhibitors and is induced by the introduction of active cyclin-dependent kinase 1 (Cdk1) and cyclin B1. EphA2 knockdown-induced M-phase delay and cell blebs are rescued by wild type EphA2 expression but not by Ser897Ala mutant. The Ras homolog gene family member G (RhoG) guanine nucleotide exchange factor Ephexin4 interacts with EphA2 in a Ser897 phosphorylation-dependent manner， and its knockdown delays M-phase progression and causes RhoG delocalization. RhoG knockdown delays M-phase progression， and EphA2 knockdown-induced M-phase delay is partially rescued by the constitutively active RhoG mutant. These results suggest that， in EphA2-expressing cells， EphA2 phosphorylation at Ser897 participates in proper M-phase progression downstream of the Cdk1/MEK/ERK/RSK pathway because of its role in maintaining cortical rigidity via Ephexin4 and RhoG and thereby regulating mitotic spindle formation.-Kaibori， Y. Saito， Y.， Nakayama， Y. EphA2 phosphorylation at Ser897 by the Cdk1/MEK/ERK/RSK pathway regulates M-phase progression via maintenance of cortical rigidity.
