YAP1 and osteosarcoma: Sox2, as an upstream signaling molecule of the Hippo signaling pathway, inhibits the activation factors NF2 (neurofibromin 2) and KIBRA of the Hippo pathway, resulting in decreased YAP phosphorylation and subsequent nuclear accumulation, which promotes the development and progression of osteosarcoma (Basu-Roy et al., 2015).