Background: Epithelial-mesenchymal transition (EMT) is prevalent in human cancer and facilitates tumor metastasis and therapy resistance by enhancing cancer cell motility, invasiveness, survival, and immune evasion. However, the molecular mechanisms underlying the cellular changes during EMT remain largely elusive, making it challenging to simultaneously target these diverse malignant phenotypes. Results: Here, we show that the EMT-inducing ZEB transcription factors directly repressed WWC1 (also known as KIBRA), a key upstream activating component of the Hippo signaling pathway. The EMT program thus inherently downregulated WWC1, leading to impaired Hippo signaling and constitutive activation of the downstream effector and transcriptional coactivator YAP. The YAP-dependent transcriptional program promotes manifold cellular phenotypes that resemble those induced during EMT. Indeed, pharmacological inhibition of YAP suppressed EMT-stimulated cell migration and invasion, apoptosis resistance, and cell size growth, identifying active YAP as a common essential mediator of multiple EMT-associated phenotypes. Moreover, YAP activation directly induced transcription of B7 family immune checkpoint proteins VSIR (VISTA) and PD-L2, and rendered cancer cells resistant to effector CD8 T cells. Conclusions: Collectively, the results suggest that EMT intrinsically activates YAP by repressing WWC1, providing a non-genetic mechanism for pervasive YAP activation in cancer. Activated YAP, in turn, critically contributes to diverse EMT-enhanced malignant phenotypes and immune evasion. Therefore, pharmacological targeting of YAP may suppress various EMT-associated malignant properties and improve the efficacy of anti-PD-1 immunotherapy, offering a promising therapeutic strategy against cancer cells exhibiting EMT characteristics.

Epithelial-mesenchymal transition (EMT) is prevalent in human cancer, and facilitates tumor metastasis and therapy resistance by enhancing cancer cell motility, invasiveness, survival, and immune evasion. However, the molecular mechanisms underlying the cellular changes during EMT remain largely elusive, making it challenging to simultaneously target these diverse malignant phenotypes. Here, we showed that the EMT-inducing ZEB transcription factors directly repressed WWC1 (also known as KIBRA), a key upstream activating component of the Hippo signaling pathway. The EMT program thus inherently downregulated WWC1, leading to impaired Hippo signaling and constitutive activation of the downstream effector and transcriptional coactivator YAP. The YAP-dependent transcriptional program promotes manifold cellular phenotypes that resemble those induced during EMT. Indeed, pharmacological inhibition of YAP suppressed EMT-stimulated cell migration and invasion, apoptosis resistance, and cell size growth, identifying active YAP as a common essential mediator of multiple EMT-associated phenotypes. Moreover, YAP activation directly induced transcription of B7 family immune checkpoint proteins VSIR (VISTA) and PD-L2, and rendered cancer cells resistant to effector CD8 T cells. Collectively, the results suggest that EMT intrinsically activates YAP by repressing WWC1, providing a non-genetic mechanism for pervasive YAP activation in cancer. Activated YAP in turn critically contributes to diverse EMT-enhanced malignant phenotypes and immune evasion. Therefore, pharmacological targeting of YAP may suppress various EMT-associated malignant properties and improve the efficacy of anti-PD-1 immunotherapy, offering a promising therapeutic strategy against cancer cells exhibiting EMT characteristics.