FOXP4 is a Direct YAP1 Target that Promotes Gastric Cancer Stemness and Drives Metastasis

The Hippo-YAP1 pathway is an evolutionally conserved signaling cascade that controls organ size and tissue regeneration. Dysregulation of Hippo-YAP1 signaling promotes initiation and progression of several types of cancer, including gastric cancer (GC). As the Hippo-YAP1 pathway regulates expression of thousands of genes, it is important to establish which target genes contribute to the oncogenic program driven by YAP1 to identify strategies to circumvent it. Here, we identified a vital role of FOXP4 in YAP1-driven gastric carcinogenesis by maintaining stemness and promoting peritoneal metastasis. Loss of FOXP4 impaired GC spheroid formation and reduced stemness marker expression, while FOXP4 upregulation potentiated cancer cell stemness. RNA-seq analysis revealed SOX12 as downstream target of FOXP4, and functional studies established that SOX12 supports stemness in YAP1-induced carcinogenesis. A small molecule screen identified 42-(2-Tetrazolyl)rapamycin as a FOXP4 inhibitor, and targeting FOXP4 suppressed GC tumor growth and enhanced the efficacy of 5-FU chemotherapy in vivo. Collectively, these findings revealed that FOXP4 upregulation by YAP1 in GC regulates stemness and tumorigenesis by upregulating SOX12. Targeting the YAP1-FOXP4-SOX12 axis represents a potential therapeutic strategy for GC.