The tRNA methyltransferase NSun2 stabilizes p16INK4 mRNA by methylating the 3′-untranslated region of p16

The impact of methylation of the 3′-untranslated region (UTR) of a messenger RNA (mRNA) remains largely unknown. Here we show that NSun2, a transfer RNA methyltransferase, inhibits the turnover of p16 INK4 mRNA. Knockdown of NSun2 reduces p16 expression by shortening the half-life of the p16 mRNA, while overexpression of NSun2 stabilizes the p16 mRNA. In vitro methylation assays show that NSun2 methylates the p16 3′UTR at A988. Knockdown of NSun2 reduces the stability of the EGFP-p16 chimeric reporter transcripts bearing wild-type p16 3′UTR, but not p16 3′UTR with a mutant methylation site. Methylation by NSun2 prevents the association of p16 3′UTR with HuR, AUF1 and Ago2/RISC, and prevents the recruitment of EGFP-p16 3′UTR chimeric transcripts to processing bodies. In response to oxidative stress, NSun2 is essential for elevating p16 expression levels. We conclude that NSun2-mediated methylation of the p16 3′UTR is a novel mechanism to stabilize p16 mRNA. The expression of the tumour suppressor p16 is frequently lost in cancer. Zhang et al . show in cultured cells that p16 mRNA levels are stabilised by methylation of the 3′-untranslated region by the tRNA methyltransferase NSun2, revealing a new mechanism for regulating p16.