Although immune checkpoint blockade (ICB) therapy has revolutionized cancer treatment, many patients do not respond or develop resistance to ICB. N6-methylation of adenosine (m6A) in RNA regulates many pathophysiological processes. Here, we show that deletion of the m6A demethylase Alkbh5 sensitized tumors to cancer immunotherapy. Alkbh5 has effects on m6A density and splicing events in tumors during ICB. Alkbh5 modulates Mct4/Slc16a3 expression and lactate content of the tumor microenvironment and the composition of tumor-infiltrating Treg and myeloid-derived suppressor cells. Importantly, a small-molecule Alkbh5 inhibitor enhanced the efficacy of cancer immunotherapy. Notably, the ALKBH5 gene mutation and expression status of melanoma patients correlate with their response to immunotherapy. Our results suggest that m6A demethylases in tumor cells contribute to the efficacy of immunotherapy and identify ALKBH5 as a potential therapeutic target to enhance immunotherapy outcome in melanoma, colorectal, and potentially other cancers.

An impressive clinical success has been observed in treating a variety of cancers using immunotherapy with programmed cell death-1 (PD-1) checkpoint blockade. However, limited response in most patients treated with anti-PD-1 antibodies remains a challenge, requiring better understanding of molecular mechanisms limiting immunotherapy. In colorectal cancer (CRC) resistant to immunotherapy, mismatch-repair-proficient or microsatellite instability-low (pMMR-MSI-L) tumors have low mutation burden and constitute~85% of patients. Here, we show that inhibition of N 6-methyladenosine (m 6 A) mRNA modification by depletion of methyltransferases, Mettl3 and Mettl14, enhanced response to anti-PD-1 treatment in pMMR-MSI-L CRC and melanoma. Mettl3or Mettl14-deficient tumors increased cytotoxic tumor-infiltrating CD8 + T cells and elevated secretion of IFN-c, Cxcl9, and Cxcl10 in tumor microenvironment in vivo. Mechanistically, Mettl3 or Mettl14 loss promoted IFN-c-Stat1-Irf1 signaling through stabilizing the Stat1 and Irf1 mRNA via Ythdf2. Finally, we found a negative correlation between METTL3 or METTL14 and STAT1 in 59 patients with pMMR-MSI-L CRC tumors. Altogether, our findings uncover a new awareness of the function of RNA methylation in adaptive immunity and provide METTL3 and METTL14 as potential therapeutic targets in anticancer immunotherapy.

N6,2′-O-dimethyladenosine (m6Am) is an abundant RNA modification located adjacent to the 5′-end of the mRNA 7-methylguanosine (m7G) cap structure. m6A methylation on 2′-O-methylated A at the 5′-ends of mRNAs is catalyzed by the methyltransferase Phosphorylated CTD Interacting Factor 1 (PCIF1). The role of m6Am and the function of PCIF1 in regulating host–pathogens interactions are unknown. Here, we investigate the dynamics and reprogramming of the host m6Am RNA methylome during HIV infection. We show that HIV infection induces a dramatic decrease in m6Am of cellular mRNAs. By using PCIF1 depleted T cells, we identify 2237 m6Am genes and 854 are affected by HIV infection. Strikingly, we find that PCIF1 methyltransferase function restricts HIV replication. Further mechanism studies show that HIV viral protein R (Vpr) interacts with PCIF1 and induces PCIF1 ubiquitination and degradation. Among the m6Am genes, we find that PCIF1 inhibits HIV infection by enhancing a transcription factor ETS1 (ETS Proto-Oncogene 1, transcription factor) stability that binds HIV promoter to regulate viral transcription. Altogether, our study discovers the role of PCIF1 in HIV–host interactions, identifies m6Am modified genes in T cells which are affected by viral infection, and reveals how HIV regulates host RNA epitranscriptomics through PCIF1 degradation.

Background Hydrogen Sulfide (H 2 S), a third member of gasotransmitter family along with nitric oxide (NO) and carbon monoxide (CO), exerts a wide range of cellular and molecular actions in our body. There is a large body of evidence suggesting that H 2 S plays an important role in cancer metastasis; however, the molecular mechanisms of H 2 S-mediated acceleration of cancer metastasis remain unknown. Methods We examined the promote effects of H 2 S on phenotype of gastric cancer (GC) cells (including those of express wild type CD36 and mutant CD36) in vitro and in vivo . GC patients' samples were used for clinical translational significance evaluation. Findings H 2 S triggered lipid metabolism reprogramming by significantly up-regulating the expression of the fatty-acid receptor CD36 (CD36) and directly activating CD36 in GC cells. Mechanistically, a disulfide bond located between cysteine (Cys)333 and Cys272 within the CD36 protein structure that was labile to H 2 S-mediated modification. The long chain-fatty acid (LC-FA) binding pocket was capped by a turn in the CD36 protein, located between helical and sheet structures that were stabilized by the Cys333-Cys272. This limited the secondary binding between LC-FAs and lysine (Lys)334. Breaking the Cys333-Cys272 disulfide bond restored the second LC-FA binding conformation of CD36. Targeting CD36 in vivo blocked H 2 S-promoted metastasis and improved animal survival. Interpretation These findings identify that the Cys333-Cys272 disulfide bond disrupted the integrity of the second LC-FA binding conformation of CD36. Therefore, CD36 can directly activate LC-FA access to the cytoplasm by acting as a direct target molecule for H 2 S.

Mannosyl (alpha-1,6-)-Glycoprotein beta-1,6-N-acetyl-glucosaminyltransferase (MGAT5) is exclusively expressed in gastric carcinoma, and plays an essential role in cancer progression, but no targeted drug is available so far. The potential anti-cancer effect of Hydrogen Sulfide (H2S), has not been widely recognized. It intrigued broad interest to explore the clinical benefits of cancer therapy, with the current understanding of molecular mechanisms of H2S which remains very limited. In this study, we identify that H2S is an effective inhibitor of MGAT5, leading to reduce the expression of exclusively abnormal glycoprotein processes in gastric carcinoma. H2S specifically dissociation of karyopherin subunit alpha-2 (KPNA2) with Jun proto-oncogene (c-Jun) interaction, and blocking c-Jun nuclear translocation, and downregulation of MGAT5 expression at the level of gene and protein. Consequently, H2S impairs growth and metastasis in gastric carcinoma by targeting inhibits MGAT5 activity. In an animal tumor model study, H2S is well tolerated, inhibits gastric carcinoma growth and metastasis. Our preclinical work therefore supports that H2S acts as a novel inhibitor of MGAT5 that block tumorigenesis in gastric carcinoma. SIGNIFICANCE: This study shows that H2S can effective targeting inhibits MGAT5 activity, and demonstrates promising antitumor efficacy. These findings gain mechanistic insights into the anti-cancer capacity of H2S and may provide useful information for the clinical explorations of H2S in cancer treatment.