Abstract
Tissue fibrosis is a pathological condition that is associated with impaired epithelial repair and excessive deposition of extracellular matrix (ECM). Fibrotic lesions increase the risk of cancer in various tissues, but the mechanism linking fibrosis and cancer is unclear. Yes-associated protein (YAP) and the transcriptional coactivator with PDZ-binding motif (TAZ) are core components of the Hippo pathway, which have multiple biological functions in the development, homeostasis, and regeneration of tissues and organs. YAP/TAZ act as sensors of the structural and mechanical features of the cell microenvironment. Recent studies have shown aberrant YAP/TAZ activation in both fibrosis and cancer in animal models and human tissues. In fibroblasts, ECM stiffness mechanoactivates YAP/TAZ, which promote the production of profibrotic mediators and ECM proteins. This results in tissue stiffness, thus establishing a feed-forward loop of fibroblast activation and tissue fibrosis. In contrast, in epithelial cells, YAP/TAZ are activated by the disruption of cell polarity and increased ECM stiffness in fibrotic tissues, which promotes the proliferation and survival of epithelial cells. YAP/TAZ are also involved in the epithelial–mesenchymal transition (EMT), which contributes to tumor progression and cancer stemness. Importantly, the crosstalk with transforming growth factor (TGF)-β signaling and Wnt signaling is essential for the profibrotic and tumorigenic roles of YAP/TAZ. In this article, we review the latest advances in the pathobiological roles of YAP/TAZ signaling and their function as a molecular link between fibrosis and cancer.
Highlights
Fibrosis is a pathological process that is characterized by mesenchymal cell infiltration and proliferation in the interstitial space
The fibrogenic response consists of the following phases: (1) initiation of the response driven by primary injury to the organ, (2) activation of effector cells such as fibroblasts induced by inflammatory mediators, and (3) elaboration of the extracellular matrix (ECM) [1]
transforming growth factor (TGF)-β drives the differentiation of quiescent fibroblasts into matrix-secreting myofibroblasts, which is a key step in tissue fibrosis
Summary
Fibrosis is a pathological process that is characterized by mesenchymal cell infiltration and proliferation in the interstitial space. In addition to the above-mentioned upstream signals, extracellular mechanical cues including ECM stiffness, cell attachment or detachment, and cellular tension are potent regulators of YAP/TAZ. The LATS1/2-dependent regulation of YAP/TAZ activity by stress fiber (F-actin) formation has been reported [25,26]. This finding was confirmed by the observation that the F-actin-capping/severing proteins cofilin, CapZ, and gelsolin restrict the nuclear localization of YAP [27]. Accumulating evidence suggests that YAP/TAZ signaling is linked to the pathophysiology of fibrosis, and aberrant YAP/TAZ activation has been reported in both the epithelial compartment and fibroblasts/myofibroblasts (Table 1)
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