PIP5Kγ-dependent PIP2-pool regulates Hippo pathway through Merlin and LATS1 The Hippo-Salvador signaling pathway is crucial in the regulation of organ size and development. Despite recent findings linking phos-phatidylinositol (4,5)- bisphosphate (PIP2) and its producing enzyme phosphatidylinositol 4-phosphate 5- kinase (PIP5K) to the Hippo pathway, the underlying mechanism is not well understood. In this study, we have demonstrated the role of PIP5Kγ, a member of the PIP5K family, in activating the Hippo pathway in a PIP2-dependent manner. When we introduced PIP5Kγ87 or PIP5Kγ90, which are the two major splice variants of PIP5Kγ, we observed their activation of large tumor suppressor kinase 1 (LATS1) and their inhibition of Yes-associated protein (YAP). Conversely, when we knocked down PIP5Kγ, the opposite effects were observed. Our research also revealed that PIP5Kγ90 interacts with Merlin's band 4.1/ezrin/radixin/moesin (FERM) domain, forming a complex with PIP2 and LATS1 at the PM. Notably, PIP5Kγ90, but not its kinase-deficient mutant, strengthened the interaction between Merlin and LATS1 and recruited LATS1 to the PM. Moreover, the depletion of PIP5Kγ or the use of its inhibitor (UNC3230) increased colony formation in carcinoma cell lines in a YAP- dependent manner. Additionally, we found that PIP5Kγ90 interacts with heat shock cognate 71-kDa protein (Hsc70), which also plays a role in activating the Hippo pathway. In summary, our findings suggest that PIP5Kγ regulates the Hippo-YAP pathway by forming a functional complex with Merlin and LATS1 at the PIP2-rich PM, and it also interacts with Hsc70, contributing to pathway activation. Keywords: Hippo pathway, Merlin, PIP2, PIP5Kγ, Hsc70
