m(6)A methyltransferase METTL16 mediates immune evasion of colorectal cancer cells via epigenetically regulating PD-L1 expression

Background: The immune checkpoint inhibitors (ICIs) has dramatically changed the therapeutic area of cancers. A great number of patients with CRC exhibit poor response rate to ICI treatment. N6-methyl adenosine (m6A) is closely correlated with the initiation and progression of cancers. To explore the role of methyltransferase-like 16 (METTL16) in CRC treatment. Methods: Clinical samples and different CRC cell lines were collected. The expression of METTL16 and PD-L1 was determined by qPCR, IHC. Ectopic expression of METTL16 was performed in CRC cells. A co-culture system was established using CRC cells and T cells to measure the immune evasion. Cell viability, apoptosis, migration, and invasion were examined by CCK-8, colony formation, flow cytometry, Transwell, and wound healing assay, respectively. The N6-methyl adenosine (m6A) modification of PD-L1 by METTL16 was investigated by methylated RIP (MeRIP) and RNA stability experiment. In vivo xenograft model was established to measure the effects of METTL16 on CRC growth. Results: METTL16 was decreased and PD-L1 was increased in CRC tissues and cell lines. METTL16 enhanced cell proliferation, migration, and invasion, and promoted CRC tumor growth in vivo. METTL16 induced m6A modification and decreased the stability of METTL16 RNA, leading to the suppression of METTL16 level. METTL16 overexpression in CRC cells induced decreased portion of PD-1 positive T cells. Overexpression of METTL16 and inhibition of PD-1 synergistically suppressed in vivo growth of CRC cells. Conclusions: Our work identified the METTL16/PD-L1/PD-1 regulatory axis in CRC development and immune evasion, which represented a promising target for CRC treatment.