Targeted Quantitative Profiling of Epitranscriptomic Reader, Writer and Eraser Proteins Revealed Potential Crosstalk between N6-Methyladenosine and Other RNA Modifications

N⁶-methyladenosine (m6A) and its reader, writer, and eraser (RWE) proteins assume crucial roles in regulating the splicing, stability, and translation of mRNA. To our knowledge, no systematic investigations have been conducted about the crosstalk between m6A and other modified nucleosides in RNA. Herein, we modified our recently established liquid chromatography-parallel-reaction monitoring (LC-PRM) method by incorporating stable isotope-labeled (SIL) peptides as internal or surrogate standards for profiling epitranscriptomic RWE proteins. We were able to detect reproducibly a total of 114 RWE proteins in HEK293T cells with the genes encoding m6A eraser proteins (i.e., ALKBH5, FTO) and the catalytic subunit of the major m6A writer complex (i.e., METTL3) being individually ablated. Notably, eight proteins were altered by more than 1.5-fold in the opposite directions in HEK293T cells depleted of METTL3 and ALKBH5. Analysis of published m6A mapping results revealed the presence of m6A in the corresponding mRNAs of four of these proteins. Together, we integrated SIL peptides into our LC-PRM method for quantifying epitranscriptomic RWE proteins, and our work revealed potential crosstalks between m6A and other epitranscriptomic modifications. Our modified LC-PRM method with the use of SIL peptides should be applicable for high-throughput profiling of epitranscriptomic RWE proteins in other cell types and in tissues.