A more specific study showed that GPR81 activation reduced the intracellular cAMP concentration, thereby decreasing the phosphorylation of the transcriptional activator TAZ in the Hippo pathway, promoting TAZ to enter the nucleus and bind TEAD1 (forming the TaZ-Tead1 complex), leading to the activation of PD-L1 expression to provide an effective means for tumor cells to escape the immune system222. This evidence concerns the gene HCAR1 and neoplasm.