Nuclear Localization of Yes-Associated Protein is Associated With Tumor Progression in Cutaneous Melanoma

Abstract

Yes-associated protein (YAP), an effector molecule of the Hippo signaling pathway, is expressed at high levels in cutaneous melanoma. However, the role of YAP in melanoma progression according to cellular localization is poorly understood. Tissues from 140 patients with invasive melanoma were evaluated by immunohistochemistry. Flow cytometry, western blotting, viability assays, wound healing assays, verteporfin treatment, and xenograft assays were conducted using melanoma cell lines B16F1 and B16F10 subjected to Yap^S127A transfection and siYap knockdown. Nuclear YAP localization was identified in 63 tumors (45.0%) and was more frequent than cytoplasmic YAP in acral lentiginous and nodular subtypes (P =.007). Compared with cytoplasmic YAP melanomas, melanomas with nuclear YAP had higher mitotic activity (P =.016), deeper invasion (P <.001), and more frequently metastasized to lymph nodes (P <.001) and distant organs (P <.001). Patients with nuclear YAP melanomas had poorer disease-free survival (P <.001) and overall survival (P <.001). Nuclear YAP was an independent risk factor for distant metastasis (hazard ratio: 3.206; 95% CI: 1.032-9.961; P =.044). Proliferative ability was decreased in siYapB16F1 (P <.001) and siYapB16F10 (P =.001) cells and increased in Yap^S127AB16F1 (P =.003) and Yap^S127AB16F10 (P =.002) cells. Cell cycle analysis demonstrated relative G1 retention in siYapB16F1 (P <.001) and siYapB16F10 (P <.001) cells and S retention in Yap^S127AB16F1 cells (P =.008). Wound healing assays showed that Yap knockdown inhibited cell invasion (siYapB16F1, P =.001; siYapB16F10, P <.001), whereas nuclear YAP promoted it (Yap^S127AB16F, P <.001; Yap^S127AB16F1, P =.017). Verteporfin, a direct YAP inhibitor, reduced cellular proliferation in B16F1 (P =.003) and B16F10 (P <.001) cells. Proliferative effects of nuclear YAP were confirmed in xenograft mice (P <.001). In conclusion, nuclear YAP in human melanomas showed subtype specificity and correlated with proliferative activity and proinvasiveness. It is expected that YAP becomes a useful prognostic marker, and its inhibition may be a potential therapy for melanoma patients.