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Cancer Immunol Res. 2018 Nov 6. pii: canimm.0071.2018. doi: 10.1158/2326-6066.CIR-18-0071. [Epub ahead of print]

PARP1 Suppresses the Transcription of PD-L1 by Poly(ADP-Ribosyl)ating STAT3.

Author information

1
College of Pharmaceutical Sciences, Zhejiang University.
2
Zhejiang University.
3
Department of Reproductive Endocrinology, Women's Hospital, School of Medicine, Zhejiang University.
4
College of Pharmaceutical Sciences, Pharmacology and Toxicology.
5
Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University.
6
College of Pharmaceutical Sciences, Zhejiang University yang924@zju.edu.cn.

Abstract

Studies have pointed to a role of PARP1 in regulating gene expression through poly(ADP-ribosyl)ating, sequence-specific, DNA-binding transcription factors. However, few examples exist that link this role of PARP1 to the immunogenicity of cancer cells. Here, we report that PARP1 poly(ADP-ribosyl)ates STAT3 and subsequently promotes STAT3 de-phosphorylation, resulting in reduced transcriptional activity of STAT3 and expression of PD-L1. In this study, we showed that PARP1 silencing or pharmacological inhibition enhanced the transcription of PD-L1 in cancer cells, which was accompanied by the upregulation of PD-L1 protein expression, both in the cytoplasm and on the cell surface. This induction of PD-L1 was attenuated in the absence of the transcription factor STAT3. Cell-based studies indicated that PARP1 interacted directly with STAT3 and caused STAT3 poly(ADP-ribosyl)ation. STAT3's activation of PD-L1 transcription was abolished by the over-expression of wild-type PARP1 but not mutant PARP1, which lacks catalytic activity. PARP1 downregulation or catalytic inhibition enhanced the phosphorylation of STAT3, which was reversed by the ectopic expression of wild-type PARP1 but not by mutated PARP1. An inverse correlation between PARP1 and PD-L1 was also observed in clinical ovarian cancer samples. Overall, our study revealed PARP1-mediated poly(ADP-ribosyl)ation of STAT3 as a key step in inhibiting the transcription of PD-L1, and this mechanism exists in a variety of cancer cells.

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