JNK Signaling Promotes Bladder Cancer Immune Escape by Regulating METTL3-Mediated m6A Modification of PD-L1 mRNA

The RNA N-6-methyladenosine (m(6)A) writer methyltransferase-like 3 (METTL3) is upregulated in many types of cancer and promotes cancer progression by increasing expression of several oncogenes. Therefore, a better understanding of the mechanisms regulating METTL3 expression and the key targets of METTL3 in cancer cells could provide new therapeutic targets. In this study, we found that activated JNK signaling is associated with increased METTL3 expression in bladder cancer. Knockdown of JNK1 or administration of a JNK inhibitor impaired the binding of c-Jun with the METTL3 promoter, thereby decreasing the expression of METTL3 and global RNA m(6)A levels. Moreover, RNA m(6)A sequencing indicated enrichment of m(6)A in the 3'-UTR of immune checkpoint PD-L1 mRNA, which could be recognized by the m(6)A reader IGF2BP1 to mediate RNA stability and expression levels of PD-L1. Inhibition of JNK signaling suppressed m6A abundance in PD-L1 mRNA, leading to decreased PD-L1 expression. Functionally, METTL3 was essential for bladder cancer cells to resist the cytotoxicity of CD8(+) T cells by regulating PD-L1 expression. Additionally, JNK signaling contributed to tumor immune escape in a METTL3-dependent manner both in vitro and in vivo. These data reveal the JNK/METTL3 axis as a mechanism of aberrant m(6)A modification and immune regulation in bladder cancer. Significance: The identification of a novel m(6)A-dependent mechanism underlying immune system evasion by bladder cancer cells reveals JNK signaling as a potential target for bladder cancer immunotherapy. [GRAPHICS]

Automated summary

This study reveals that activated JNK signaling is associated with increased expression of METTL3 in bladder cancer. JNK signaling regulates METTL3 expression and global RNA m(6)A levels. Additionally, m(6)A modification is enriched in the 3'-UTR of PD-L1 mRNA, and it is recognized by the m(6)A reader protein IGF2BP1 to mediate the stability and expression levels of PD-L1.