PIP5K Mediates PI(4,5)P2/Merlin/LATS1 Signaling Activation and Interplays with Hsc70 in Hippo-YAP Pathway Regulation

The type I phosphatidylinositol 4-phosphate 5-kinase (PIP5K) family produces the critical lipid regulator phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) in the plasma membrane (PM). Here, we investigated the potential role of PIP5K gamma, a PIP5K isoform, in the Hippo pathway. The ectopic expression of PIP5K gamma 87 or PIP5K gamma 90, two major PIP5K gamma splice variants, activated large tumor suppressor kinase 1 (LATS1) and inhibited Yes-associated protein (YAP), whereas PIP5K gamma knockdown yielded opposite effects. The regulatory effects of PIP5K gamma were dependent on its catalytic activity and the presence of Merlin and LATS1. PIP5K gamma knockdown weakened the restoration of YAP phosphorylation upon stimulation with epidermal growth factor or lysophosphatidic acid. We further found that PIP5K gamma 90 bound to the Merlin's band 4.1/ezrin/radixin/moesin (FERM) domain, forming a complex with PI(4,5)P2 and LATS1 at the PM. Notably, PIP5K gamma 90, but not its kinase-deficient mutant, potentiated Merlin-LATS1 interaction and recruited LATS1 to the PM. Consistently, PIP5K gamma knockdown or inhibitor (UNC3230) enhanced colony formation in carcinoma cell lines YAP-dependently. In addition, PIP5K gamma 90 interacted with heat shock cognate 71-kDa protein (Hsc70), which also contributed to Hippo pathway activation. Collectively, our results suggest that PIP5K gamma regulates the Hippo-YAP pathway by forming a functional complex with Merlin and LATS1 at the PI(4,5)P2-rich PM and via interplay with Hsc70.