The Hippo effector TAZ promotes cancer stemness by transcriptional activation of SOX2 in head neck squamous cell carcinoma

The Hippo-TAZ signaling has emerged as a fundamental regulator underlying cancer stem cells (CSCs) stemness which intricately associates with local recurrence and metastatic spreading in head neck squamous cell carcinoma (HNSCC). However, the precise downstream targets of TAZ responsible for HNSCC CSCs maintenance remain largely underexplored. Here, we identified Sex determining region Y box 2 (SOX2) as a putative downstream target of TAZ to promote CSCs maintenance and tumorigenicity in HNSCC. Both TAZ and SOX2 were significantly enriched in CSCs subpopulation (CD44(+)CD133(+)) isolated from Cal27 and Fadu cells via fluorescence-activated cell sorting. TAZ knockdown significantly reduced expression of SOX2 at both mRNA and protein levels, whereas its ectopic overexpression markedly increased its abundance in HNSCC cells. Moreover, reintroduction of ectopic SOX2 abolished, at least in part, the reduced tumorsphere formation and tumorigenicity in vivo induced by TAZ knockdown. Mechanistically, transcriptional complex formed by TAZ and TEAD4 was recruited to two binding sites in SOX2 promoter, which in turn facilitated transcription of SOX2 in HNSCC cells. In addition, the abundance of TAZ and SOX2 was positively correlated in HNSCC clinical samples, and both upregulations of TAZ and SOX2 associated with the worst survival. Taken together, our data reveal a previously unknown mechanistic linkage between TAZ and SOX2 and identify SOX2 as a direct downstream target of TAZ in modulating CSCs self-renewal and maintenance in HNSCC. These findings suggest that targeting TAZ-SOX2 axis might be a promising therapeutic strategy for HNSCC.