Hippo pathway induces PIEZO1 expression to promote oral squamous cell carcinoma cell proliferation

Most cancer cells are exposed to extracellular environments, such as extracellular matrix, which commonly becomes stiffer along with transformation. It is conceivable that tumorous extracellular environments would be changing to affect tumor cell behavior. It has been reported that Hippo pathway responds to the extracellular environments and induces the nuclear localization of transcription activator, yes-associated protein (YAP), resulting in stimulating cell proliferation. Its pathway also regulates gene expression, but the precise molecule to meditate cell proliferating effect of Hippo pathway in oral squamous cell carcinoma (OSCC) is not well understood. Here, we examined the effects of YAP-mediated Hippo pathway in OSCC tumorigenesis. Loss-of-function experiments using siRNA or an inhibitor, and immunohistochemical analyses of tissue specimens obtained from OSCC specimens demonstrated that YAP-mediated Hippo pathway was involved in OSCC cell proliferation. We identified Piezo-type mechanosensitive ion channel component 1 (PIEZO1), a Ca2+ channel, as a downstream molecule of Hippo pathway and showed that elevated PIEZO1 expression was required for PIEZO1 agonist-dependent Ca2+ entry and cell proliferation in OSCC cells. Furthermore, the experiments using three-dimensional culture and suspension culture revealed that PIEZO1, of which expression was regulated by YAP-mediated Hippo pathway, was involved in OSCC cellular growth. Immunohistochemically, YAP overexpression with nucleus and/or cytoplasm was detected with both PIEZO1 and Ki-67 expression at high frequencies in tumor lesion, but not in non-tumor region, of OSCC specimens. These results suggest that the YAP-mediated Hippo/PIEZO1 axis, which might be activated by the tumorous extracellular environments, promotes OSCC tumor cell growth. Microarray analyses were performed using HSC-4 cells cultured in 2D culture, and transfected without or with LATS2 siRNA in suspension culture. Compare1: HSC-4 cells cultured in 2D culture were compared with HSC-4 cells cultured in suspension culture. Compare2: HSC-4 cells transfected with siLATS2 were compared with HSC-4 cells transfected with control siRNA in suspension culture