Exploring the Role of DNMT1 in RNA m⁵C Methylation (RNA-BS-SEQ NSUN2 Knock down)

DNA methyltransferase 1 (DNMT1) is an enzyme known for DNA methylation maintenance. However, point mutations in its RFTS domain lead to late-onset neurodegeneration such as the autosomal dominant cerebellar ataxia-deafness and narcolepsy (ADCA-DN) disorder. Here we demonstrated that wild-type DNMT1 also has the capability to bind to mRNA transcripts and facilitate 5-methylcytosine (m5C) RNA methylation by recruiting NOP2/Sun RNA methyltransferase 2 (NSUN2). RNA m5C methylation, in turn, promotes RNA stability for those genes modulating mitochondrial function. When DNMT1 RFTS domain is mutated in the case of ADCA-DN disorder, it triggers aberrant DNMT1-RNA interaction and significantly elevated m5C RNA methylation and RNA stability for a portion of metabolic genes. Consequently, increased levels of metabolic RNA transcripts contribute to cumulative oxidative stress, mitochondrial dysfunction, and neurological symptoms. Collectively, our results highlight a novel role for DNMT1 in regulating both DNA and RNA methylation as well as mitochondrial function, shedding light on the pathogenic mechanism of DNMT1 mutation-induced neurodegeneration. HeLa cells were transfected with small interfering RNA (siRNA) targeting NSUN2 using Lipofectamine RNAiMAX (Thermo Fisher Scientific) according to the manufacturer's instructions. Following transfection, cells were collected for RNA extraction and RNA bisulfite sequencing (RNA-BS-seq).