METTL3/IGF2BP3 axis inhibits tumor immune surveillance by upregulating N6-methyladenosine modification of PD-L1 mRNA in breast cancer

Abstract

Background Continual expression of PD-L1 in tumor cells is critical for tumor immune escape and host T cell exhaustion, however, knowledge on its clinical benefits through inhibition is limited in breast cancer. N6-methyladenosine (m6A) plays a crucial role in multiple biological activities. Our study aimed to investigate the regulatory role of the m6A modification in PD-L1 expression and immune surveillance in breast cancer. Methods MeRIP-seq and epitranscriptomic microarray identified that PD-L1 is the downstream target of METTL3. MeRIP-qPCR, absolute quantification of m6A modification assay, and RIP-qPCR were used to examine the molecular mechanism underlying METTL3/m6A/IGF2BP3 signaling axis in PD-L1 expression. B-NDG and BALB/c mice were used to construct xenograft tumor models to verify the phenotypes upon METTL3 and IGF2BP3 silencing. In addition, breast cancer tissue microarray was used to analyze the correlation between PD-L1 and METTL3 or IGF2BP3 expression. Results We identified that PD-L1 was a downstream target of METTL3-mediated m6A modification in breast cancer cells. METTL3 knockdown significantly abolished m6A modification and reduced stabilization of PD-L1 mRNA. Additionally, METTL3-mediated PD-L1 mRNA activation was m6A-IGF2BP3-dependent. Moreover, inhibition of METTL3 or IGF2BP3 enhanced anti-tumor immunity through PD-L1-mediated T cell activation, exhaustion, and infiltration both in vitro and in vivo. PD-L1 expression was also positively correlated with METTL3 and IGF2BP3 expression in breast cancer tissues. Conclusion Our study suggested that METTL3 could post-transcriptionally upregulate PD-L1 expression in an m6A-IGF2BP3-dependent manner to further promote stabilization of PD-L1 mRNA, which may have important implications for new and efficient therapeutic strategies in the tumor immunotherapy.

Crosstalk among m6A RNA methylation, hypoxia and metabolic reprogramming in TME: from immunosuppressive microenvironment to clinical application

“…VHL deficiency regulates m 6 A methylation levels in ICOS through a HIF-1α-dependent glycolytic pathway and inhibits T cell maturation [ 70 ]. Interestingly, the METTL3/IGF2BP3 axis promotes tumor immune escape via m 6 A modification of PD-L1 mRNA and suppression of T cell activation in breast cancer [ 130 ]. These findings suggest that m 6 A methylation in tumor cells could remodel TME and mediate immune escape by affecting T cell functions.…”

The role of Insulin-like growth factor 2 mRNA-binding proteins (IGF2BPs) as m6A readers in cancer

“…m 6 A demethylase ALKBH5 inhibits metastasis of gastric cancer through modulating expression of downstream target, PKMYT, and IGF2BP3 stabilize the mRNA stability of PKMYT1 by recognizing its m 6 A modification sites 179 . m 6 A methyltransferase METTL3 post-transcriptionally mediates PD-L1 mRNA activation in breast cancer with m 6 A-IGF2BP3-dependent manner 180 . Thus, m 6 A readers play important roles in m 6 A writers or erasers-mediated the stability of targets mRNA.…”

The Role of m6A RNA Methylation in Cancer: Implication for Nature Products Anti-Cancer Research

“…PD-L1, the ligand of PD-1, is highly expressed in many cancers and is closely associated with mortality in cancer patients, establishing the role of PD-1 in cancer-induced immunosuppression. METTL3 enhances the stability of PD-L1 mRNA, promotes the expression of PD-L1 and induces tumor immunosuppression by relying on m6A modification ( Wan et al, 2022 ). However, METTL3 is low expression in triple negative breast cancer (TNBC) and strongly associated with short-distance-metastasis-free survival.…”