The crosstalk between AXL and YAP promotes tumor progression through STAT3 activation in head and neck squamous cell carcinoma.

ABSTRACT

Receptor tyrosine kinases (RTKs) and Yes-associated protein (YAP) are critical driving factors in tumors. Currently, the regulation of RTKs in the Hippo-YAP pathway has been recognized as an important issue. However, the relationship between AXL, one of the RTKs, and YAP in head and neck squamous cell carcinoma (HNSCC) remains unknown. In this study, the crosstalk between AXL and YAP was thoroughly investigated in vitro and in vivo. We determined that there was a positive correlation between AXL and YAP in the HNSCC tissue samples and the Cancer Genome Atlas (TCGA) dataset, and high co-expression was associated with poor prognosis. Inhibiting YAP decreased AXL expression in HNSCC cells, while YAP overexpression increased AXL. Moreover, ectopic expression of AXL reversed tumor suppressor phenotypes mediated by YAP silencing. This reversal effect was also confirmed in vivo. In addition, AXL overexpression and Gas6, a ligand of AXL, stimulated YAP dephosphorylation, nuclear translocation, and target gene transcription. AXL inhibition decreased YAP dephosphorylation and nuclear translocation. Mechanistically, Gas6 induced a competitive binding to phosphorylated signal transducers and activators of transcription 3 (STAT3) with large tumor suppressor kinase 1 (LATS1) and inhibited the Hippo pathway. This study revealed a novel non-transcriptional effect of STAT3 in Gas6/AXL-induced YAP activity, suggesting that STAT3 acted as a critical "molecular switch" during the mutual promotion between AXL and YAP, which might be a promising therapeutic target in HNSCC.