M6A Demethylase ALKBH5 Regulates PD-L1 Expression and Tumor Immunoenvironment in Intrahepatic Cholangiocarcinoma

  • Cancer Res. 2021 Sep 15;81(18):4778-4793. doi: 10.1158/0008-5472.CAN-21-0468.
Xinyao Qiu   #  1 ,  Shuai Yang   #  1 ,  Shan Wang   #  1 ,  Jianmin Wu   #  2 ,  Bo Zheng  3  4 ,  Kaiting Wang  5 ,  Siyun Shen  3  4 ,  Seogsong Jeong  6 ,  Zhixuan Li  3  4 ,  Yanjing Zhu  3  4 ,  Tong Wu  3  4 ,  Xuan Wu  7 ,  Rui Wu  8 ,  Weiwei Liu  9 ,  Hong-Yang Wang  10  3  4 ,  Lei Chen  10  3  4
Affiliations
  • 1. Fudan University Shanghai Cancer Center, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China.
  • 2. Institute of Metabolism and Integrative Biology, Fudan University, Shanghai, China.
  • 3. The International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China.
  • 4. National Center for Liver Cancer, Shanghai, China.
  • 5. School of Life Sciences, Fudan University, Shanghai, China.
  • 6. Department of Liver Surgery, Renji Hospital, School of Medicine, Shanghai JiaoTong University, Shanghai, China.
  • 7. Department of Laboratory Medicine, The Tenth People's Hospital of Shanghai, Tongji University, Shanghai, China.
  • 8. Department of Biliary Surgery I, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China.
  • 9. Department of Laboratory Medicine, The Tenth People's Hospital of Shanghai, Tongji University, Shanghai, China. [email protected] [email protected] [email protected].
  • 10. Fudan University Shanghai Cancer Center, Department of Oncology, Shanghai Medical College, Fudan University, Shanghai, China. [email protected] [email protected] [email protected].
  • # Contributed equally.
PMID: 34301762 DOI: 10.1158/0008-5472.CAN-21-0468
Abstract

N6-methyladenosine (m6A) has been reported as an important mechanism of posttranscriptional regulation. Programmed death-ligand 1 (PD-L1) is a primary immune inhibitory molecule expressed on tumor cells that promotes immune evasion. Here we report ALKBH5 as an important m6A demethylase that orchestrates PD-L1 expression in intrahepatic cholangiocarcinoma (ICC). Regulation of PD-L1 expression by ALKBH5 was confirmed in human ICC cell lines. Sequencing of the m6A methylome identified PD-L1 mRNA as a direct target of m6A modification whose levels were regulated by ALKBH5. Furthermore, ALKBH5 and PD-L1 mRNA were shown to interact. ALKBH5 deficiency enriched m6A modification in the 3'UTR region of PD-L1 mRNA, thereby promoting its degradation in a YTHDF2-dependent manner. In vitro and in vivo, tumor-intrinsic ALKBH5 inhibited the expansion and cytotoxicity of T cells by sustaining tumor cell PD-L1 expression. The ALKBH5-PD-L1-regulating axis was further confirmed in human ICC specimens. Single-cell mass cytometry analysis unveiled a complex role of ALKBH5 in the tumor immune microenvironment by promoting the expression of PD-L1 on monocytes/macrophages and decreasing the infiltration of myeloid-derived suppressor-like cells. Analysis of specimens from patients receiving anti-PD1 immunotherapy suggested that tumors with strong nuclear expression patterns of ALKBH5 are more sensitive to anti-PD1 immunotherapy. Collectively, these results describe a new regulatory mechanism of PD-L1 by mRNA epigenetic modification by ALKBH5 and the potential role of ALKBH5 in immunotherapy response, which might provide insights for Cancer immunotherapies. SIGNIFICANCE: This study identifies PD-L1 mRNA as a target of ALKBH5 and reveals a role for ALKBH5 in regulating the tumor immune microenvironment and immunotherapy efficacy.

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