The Hippo Pathway Component TAZ Promotes Immune Evasion in Human Cancer through PD-L1

The Hippo pathway component WW domain-containing transcription regulator 1 (TAZ) is a transcriptional coactivator and an oncogene in breast and lung cancer. Transcriptional targets of TAZ that modulate immune cell function in the tumor microenvironment are poorly understood. Here, we perform a comprehensive screen for immune-related genes regulated by TAZ and its paralog YAP using NanoString gene expression profiling. We identify the immune checkpoint molecule PD-L1 as a target of Hippo signaling. The upstream kinases of the Hippo pathway, mammalian STE20-like kinase 1 and 2 (MST1/2), and large tumor suppressor 1 and 2 (LATS1/2), suppress PD-L1 expression while TAZ and YAP enhance PD-L1 levels in breast and lung cancer cell lines. PD-L1 expression in cancer cell lines is determined by TAZ activity and TAZ/YAP/TEAD increase PD-L1 promoter activity. Critically, TAZ-induced PD-L1 upregulation in human cancer cells is sufficient to inhibit T-cell function. The relationship between TAZ and PD-L1 is not conserved in multiple mouse cell lines, likely due to differences between the human and mouse PD-L1 promoters. To explore the extent of divergence in TAZ immune-related targets between human and mouse cells, we performed a second NanoString screen using mouse cell lines. We show that many targets of TAZ may be differentially regulated between these species. These findings highlight the role of Hippo signaling in modifying human/murine physiologic/pathologic immune responses and provide evidence implicating TAZ in human cancer immune evasion.Significance: Human-specific activation of PD-L1 by a novel Hippo signaling pathway in cancer immune evasion may have a significant impact on research in immunotherapy. Cancer Res; 78(6); 1457-70. ©2018 AACR.