Regulation and Functional Dissection of YAP in Mitosis

Abstract Text
The Hippo pathway controls cell contact inhibition, stem cell self -renewal, and tumorigenesis
through phosphorylating and inactivating the downstream oncoprotein, yes-associated protein
(YAP). The PI, along with others, has demonstrated that YAP promotes oncogenesis by
stimulating cell proliferation and inhibiting apoptosis. YAP is overexpressed or hyperactivated in
many types of cancers. Current studies involving YAP focus on determining its
overall oncogenic role in various organs/tissues as well as its role in crosstalk with other
signaling pathways. While these studies provide important insight into the oncogenic properties
of YAP, however, the underlying molecular mechanisms through which YAP exerts its
oncogenic function are poorly understood. The long-term goal of this project is to elucidate the
regulatory mechanisms of the Hippo-YAP signaling pathway in mitotic cell-cycle control and
oncogenic transformation, thus providing potential therapeutic targets.
Our preliminary studies demonstrate that during mitosis YAP is phosphorylated on novel sites
and activated in a CDK1-dependent manner. Importantly, mitotic phosphorylation is required for
YAP-driven cellular transformation. We have found that YAP is required for the activation of the
spindle checkpoint during mitosis. Furthermore, overexpression of YAP, but not of the non -
phosphorylatable mutant, hyper-activates the spindle checkpoint and causes mitotic defects.
Based on these preliminary studies, we hypothesize that CDK1-mediatd mitotic phosphorylation
of YAP is biologically significant in the regulation of the spindle checkpoint activation and
subsequent oncogenic transformation. Our central hypothesis will be tested through the
following three specific aims: Aim 1: Determine the molecular mechanism of YAP
regulation/activation during mitosis; Aim 2: Determine the role of YAP and its phosphorylation in
mitotic progression, the spindle checkpoint, and aneuploidy; Aim 3: Determine the functional
significance of YAP phosphorylation on its targets. Successful completion of these studies will
not only reveal novel roles of YAP in mitosis and genome instability, but will also shed light on
the mechanisms involved in YAP-driven oncogenesis.