A narrative review for the Hippo-YAP pathway in cancer survival and immunity: the Yin-Yang dynamics

The Hippo-YAP pathway is fast becoming a key instrument in regulating cancers. Binary oppositions, also known as the Yin-Yang dynamics in Chinese, have emerged in its effects. Some oppositions are attributable to in vitro and in vivo experimental conditions, some are due to differences between cancers or species, some are derived from its inherent duality endowed by upstream and downstream signaling, and some are yet unresolved mysteries. However, as bewildering they are, few have been noticed and defined so far. In this review, we first look back on the Hippo pathway which was initially identified more than a decade ago. We then focus on tumor biology, especially some latest popular mechanisms that regulate tumor cell survival, such as ferroptosis, autophagy, and apoptosis. The third chapter is concerned with the findings of the relationship between the Hippo pathway and tumor immunity on the microenvironment in which tumor cells progress. In each of these main sections the contradictory points of the Hippo pathway are elucidated and thoroughly examined. On one hand, the Yin-Yang dynamics of the Hippo pathway brings about considerable challenges for current research; on the other hand, this work will generate fresh insight into it and offer opportunities for subsequent drug development for cancer and regenerative medicine.