Lung cancer is one of the most devastating diseases worldwide with high incidence and mortality. Hippo (Hpo) pathway is a conserved regulator of organ size in both Drosophila and mammals. Emerging evidence has suggested the significance of Hpo pathway in cancer development. In this study, we identify VGLL4 as a novel tumor suppressor in lung carcinogenesis through negatively regulating the formation of YAP-TEAD complex, the core component of Hpo pathway. Our data show that VGLL4 is frequently observed to be lowly expressed in both mouse and human lung cancer specimens. Ectopic expression of VGLL4 significantly suppresses the growth of lung cancer cells in vitro. More importantly, VGLL4 significantly inhibits lung cancer progression in de novo mouse model. We further find that VGLL4 inhibits the activity of the YAP-TEAD transcriptional complex. Our data show that VGLL4 directly competes with YAP in binding to TEADs and executes its growth-inhibitory function through two TDU domains. Collectively, our study demonstrates that VGLL4 is a novel tumor suppressor for lung cancer through negatively regulating the YAP-TEAD complex formation and thus the Hpo pathway.

Whether the Hippo pathway contributes to cell lineage transition under pathological conditions, especially tumorigenesis, remains largely unknown. Here we show that YAP, the major effector of the Hippo pathway, displays a distinct activation pattern in lung adenocarcinoma (ADC) and squamous cell carcinoma (SCC); YAP is initially activated by LKB1 loss in lung ADC, which upregulates ZEB2 expression and represses DNp63 transcription in a default manner. During transdifferentiation, YAP is inactivated, which in turn relieves ZEB2-mediated default repression of DNp63 and triggers squamous differentiation reprogramming. Disruption of the YAP barrier for phenotypic transition significantly accelerates squamous transdifferentiation, whereas constitutive YAP activation conversely inhibits this transition. More importantly, ectopic DNp63 expression rescues the inhibitory effect of YAP on squamous transdifferentiation. These findings have established YAP as an essential barrier for lung cancer cell fate conversion and provided a mechanism for regulating cancer plasticity, which might hold important implication for YAP-targeted therapies.

The Hippo signaling pathway maintains organ size and tissue homeostasis via orchestration of cell proliferation and apoptosis. How this pathway triggers cell apoptosis remains largely unexplored. Here, we identify NR4A1 as a target of the Hippo pathway that mediates the pro-apoptotic and anti-tumor effects of the Hippo pathway whereby YAP regulates the transcription, phosphorylation, and mitochondrial localization of NR4A1. NR4A1, in turn, functions as a feedback inhibitor of YAP to promote its degradation, thereby inhibiting the function of YAP during liver regeneration and tumorigenesis. Our studies elucidate a regulatory loop between NR4A1 and YAP to coordinate Hippo signaling activity during liver regeneration and tumorigenesis and highlight NR4A1 as a marker of Hippo signaling, as well as a therapeutic target for hepatocellular carcinoma.