Function and Mechanism of the Hippo-PI5P4K Axis for Growth Control

PROJECT SUMMARY Our long-term goal is to decipher the molecular mechanisms underlying PI5P4K-driven growth and to elucidate how their dysregulation contributes to breast tumorigenesis. In this proposal, we will set out to provide a comprehensive understanding of a new signaling network that is critical to integrate metabolic information and determine how the related proteins and pathways interact to maintain cellular homeostasis. Phosphatidylinositol-5-phosphate 4-kinases (PI5P4Ks) are a family of non-canonical phosphoinositide kinases which we have shown to be critical for preserving nutrient availability and fuel growth yet how they are regulated themselves is largely unknown. Using a comprehensive in vitro kinase screen, we have discovered the core kinases of the Hippo pathway, MST1 and MST2 as direct negative regulators of the PI5P4Ks as well as the lipid substrate of the PI5P4Ks, PI-5-P to interact with the Hippo adaptor protein MOB1 which in turn effects the activity of the Hippo downstream effector YAP. The Hippo pathway is known to be important for development, growth and organogenesis, and dysregulation of this pathway leads to tumor progression. While PI5P4Ks have been linked to tumor growth, exactly how the PI5P4Ks are regulated is poorly understood. Furthermore, how the PI5P4Ks actually command cell growth under both physiological conditions and pathological contexts such as breast cancer is incomplete. To answer these important questions, we will perform the following Aims: In Aim 1 we will use very feasible biophysical and structural biology to determine atomic-resolution details of the interface between PI-5-P and MOB1 and quantitate how PI-5-P regulates MOB1 binding to other Hippo pathway components in vitro. In Aim 2 we will investigate how the activity of the PI5P4Ks control the activation of the MOB-LATS complex downstream of MST1/2, exploring one potential mechanism for PI5P4K tumorigenic properties. In Aim 3 we will establish the biological significance of the PI5P4K-Hippo axis in breast cancer using a panel of TNBC cell lines, novel mouse breast tumor models, and patient breast tumor samples. This project seeks to combine quantitative structural biology with molecular cell genetics to decipher how PI-5- P regulates the Hippo pathway for breast cancer cell growth. Given that PI5P4Ks are exciting ‘druggable’ targets for breast cancer, characterizing how PI5P4Ks connect to the Hippo pathway reveals a possible strategy for future anti-cancer therapies.