PD-L1 promotes myofibroblastic activation of hepatic stellate cells by distinct mechanisms selective for TGF-O receptor I versus II

Intrahepatic cholangiocarcinoma (ICC) contains abundant myofibroblasts derived from hepatic stellate cells (HSCs) through an activation process mediated by TGF-O. To determine the role of programmed death-ligand 1 (PD-L1) in myofibroblastic activation of HSCs, we disrupted PD-L1 of HSCs by shRNA or anti-PD-L1 antibody. We find that PD-L1, produced by HSCs, is required for HSC activation by stabilizing TGF-O receptors I (TORI) and II (TORII). While the extracellular domain of PD-L1 (amino acids 19-238) targets TORII protein to the plasma membrane and protects it from lysosomal degradation, a C-terminal 260-RLRKGR-265 motif on PD-L1 protects TORI mRNA from degradation by the RNA exosome complex. PD-L1 is required for HSC expression of tumor-promoting factors, and targeting HSC PD-L1 by shRNA or Cre/loxP recombination suppresses HSC activation and ICC growth in mice. Thus, myofibroblast PD-L1 can modulate the tumor microenvironment and tumor growth by a mechanism independent of immune suppression.

Automated summary

PD-L1 plays an important role in the activation process of HSCs, promoting HSC activation by stabilizing TORI and TORII. PD-L1 also regulates HSC expression of tumor-promoting factors by protecting TORI mRNA and TORII protein. Targeting HSC PD-L1 suppresses HSC activation and growth of intrahepatic cholangiocarcinoma.