PTGS2 and hepatocellular carcinoma: For example, in HSCs, the enterohepatic circulation of DCA, synergizing with the TLR2 agonist, lipoteichoic acid, a component of Gram-positive gut microbes, induces the senescence-associated secretory phenotype, which suppresses anti-tumor immunity and promotes tumor-promoting factors, such as cyclooxygenase-2 (COX-2), followed by COX-2-mediated prostaglandin E2 (PGE2) inhibition of antitumor immunity through PGE2 receptor subtype 4 (EP4), resulting in HCC in mice (Yoshimoto et al., 2013; Loo et al., 2017).