The histone deacetylase inhibitor valproic acid inhibits NKG2D expression in natural killer cells through suppression of STAT3 and HDAC3

Lulu Ni,Xuewei Yan,Fei Liu,Dean A Lee,Lixin Wang,Zhongya Ni,Shiguo Zhu,Chao Yao,Chenyuan Gong,Stephanie S Watowich,Xiaowen Zhu

doi:10.1038/srep45266

Abstract

NKG2D is a major activating receptor of NK cells and plays a critical role in tumor immunosurveillance. NKG2D expression in NK cells is inhibited by the histone deacetylase (HDAC) inhibitor valproic acid (VPA) and enhanced by the narrow-spectrum HDAC inhibitor entinostat. We previously demonstrated that entinostat enhanced NKG2D transcription by increasing acetylation of Histones H3 and H4. However, the mechanism by which VPA reduces NKG2D expression in NK cells is not known. We have also shown that NKG2D transcription is regulated by STAT3 phosphorylation. In this study, we investigated regulation of NKG2D expression in NK cells by VPA and entinostat by assessing protein expression, phosphorylation, and interaction of HDACs and STAT3. We find that VPA selectively inhibits STAT3 tyrosine705 phosphorylation, but entinostat does not. STAT3 complexes with HDAC3, and HDAC3 inhibition represses STAT3 phosphorylation and therefore NKG2D expression. NK cells from STAT3 wild-type mice downregulate NKG2D in response to VPA, but not NK cells from STAT3 knockout mice. These results show that VPA is a potent inhibitor of STAT3 phosphorylation and demonstrate that histone acetylation and STAT3 tyrosine705 phosphorylation cooperate in regulating NKG2D expression in NK cells.

Highlights

Natural Killer (NK) cells are large granular lymphocytes that play a critical role in the host defense against viral infection and cancers
We analyzed the increasing percentage ratio of NKG2D expression with valproic acid (VPA) or entinostat compared to untreated control, we found VPA significantly decreased but entinostat significantly increased NKG2D expression (Fig. 1B)
To further determine the effect of VPA, we used varying concentrations of VPA to treat NK cells and found that VPA down-regulated NKG2D expression in NK cells in a dose-dependent manner (Fig. 1C). These results showed that the narrow-spectrum HDAC inhibitors (HDACi) entinostat and the wide-spectrum HDACi VPA exert opposite effects on NKG2D expression in NK cells

Summary

Introduction

Natural Killer (NK) cells are large granular lymphocytes that play a critical role in the host defense against viral infection and cancers. We showed that entinostat enhances the expression of NKG2D in NK cells through inhibiting HDAC1 and HDAC2, thereby increasing acetylation of histones H3 and H4 which result in increased NKG2D transcription. Understanding the mechanism of VPA-induced suppression of NKG2D expression in NK cells would be valuable for developing HDAC as targeted cancer drugs for NK cell immune modulation. We found that HDAC3 was able to be complexed with STAT3; VPA inhibited HDAC3 and resulted in selectively inhibition of STAT3 tyrosine[705] phosphorylation, and subsequent down-regulation of NKG2D expression in NK cells This finding indicates that HDAC3 and STAT3 signaling cooperate in the regulation of NKG2D expression in NK cells, and provides valuable insight for new drug development and clinical applications of HDACi in cancer treatment

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Results

Conclusion