SUMOylation of large tumor suppressor 1 at Lys751 attenuates its kinase activity and tumor-suppressor functions.

Large tumor suppressor (Lats) plays a critical role in maintaining cellular homeostasis and is the core to mediate Hippo growth-inhibitory signaling pathway. SUMOylation is a reversible and dynamic process that regulates a variety of cell functions. Here, we show that SUMOylation of Lats1 affects its kinase activity specifically towards Hippo signaling. Small ubiquitin-like modifier (SUMO) 1 interacts with and directly SUMOylates Lats1, whereas loss of SUMOylation pathway function disrupts Lats1 SUMOylation. Among potential SUMOylation sites on hLats1, K751 and K830 are conversed and essential for maintaining the transcriptional output of Hippo signaling, whereas K751 mutation more significantly abolishes SUMO1-induced Lats1 SUMOylation than K830 mutation. Though Lats1 SUMOylation at K751 affects neither its subcellular distribution nor its interactions with YAP and TAZ, it significantly destabilizes the phosphorylated Lats1 (Thr1079 but not Ser909), resulting in the attenuation of Lats1 kinase activity and inhibition of Hippo signaling. Moreover, HepG2 hepatocellular carcinoma cells express significantly more SUMOylated Lats1 than LO2 normal human hepatic cells, and in HepG2 cells or HepG2 cells xenografts, Lats1 SUMOylation at K751 consistently attenuates Lats1 kinase activity and subsequently suppresses Hippo signaling, resulting in not only the promotion of cell proliferation and colony formation but also the suppression of cell apoptosis. Together, we demonstrate that Lats1 SUMOylation at K751 suppresses its kinase activity and subsequently attenuates its tumor-suppressor functions. Thus, this study provides additional insight into how Hippo signaling is regulated and highlights the potentially critical role of Lats1 SUMOylation in tumor development.