Defining the roles of YAP/TAZ in controlling cell fate decisions following abnormal mitosis

Abstract

Mitosis is a critically important and time sensitive cellular process that proceeds rapidly, typically completing in 15-45 minutes. Mechanisms have evolved to measure the duration of mitosis, resulting in the identification of aberrant cells that spend too long in mitosis. If non-transformed cells undergo a mitosis that exceeds 90 minutes, then the resulting daughter cells activate a durable G1 arrest and cease proliferating. The underlying mechanism acting to time the duration of mitosis is unknown. Here, we demonstrate that cells activate the Hippo pathway upon entry into mitosis, which initiates degradation of the pro-growth transcriptional co-activators YAP and TAZ. Consequently, prolonged mitosis leads to decreased YAP/TAZ levels in the following G1, thus enforcing cell cycle arrest. We reveal that inactivation of the Hippo pathway, which is common in solid tumors, is sufficient to restore YAP/TAZ levels following a prolonged mitosis, and cells born from this prolonged mitosis can progress through the cell cycle. We also demonstrate that Hippo pathway inactivation alters cell fate decisions in response to mitotic arrest. Antimitotics (e.g. Taxol) have long been used to permanently arrest cells in mitosis, which frequently results in mitotic cell death. It has long been recognized that some cancer cells are resistant to antimitotics; this resistance can arise from cells escaping mitosis into the G1 phase in a process termed mitotic slippage. The mechanisms underlying these cell fate decisions are poorly understood. Here, we demonstrate that inactivation of the Hippo pathway promotes mitotic slippage and overall survival in cells treated with antimitotics by increasing antiapoptotic protein expression. Our data suggest that inactivation of the Hippo pathway may promote resistance to antimitotic therapies by favoring the survival and proliferation of cells that have experienced a prolonged mitosis. Interestingly, we find that restoring Hippo signaling to cancer cells that are resistant to antimitotic therapies sensitizes them to antimitotics and promotes mitotic cell death. Overall, we illuminate a broad role for Hippo signaling in determining cell fate during mitosis and identify a novel mechanism by which resistance to antimitotic therapies can arise.