RBM33 Acts as an m6A Reader Essential for ALKBH5-mediated m6A Demethylation and Head and Neck Squamous Carcinoma Tumorigenesis [m6A-seq]

Head and neck squamous cell carcinoma (HNSC) is one of the most common malignant cancers worldwide. However, it is always detected at an advanced stage because of a lack of biomarkers for early diagnosis. Here, we identify the RNA binding motif protein 33 (RBM33) is commonly up-regulated in HNSC and it is essential for tumorigenesis. Mechanistically, RBM33 is an m6A reader protein and forms a complex with ALKBH5. RBM33 plays crucial roles in ALKBH5-mediated mRNA m6A demethylation not only by recruitment ALKBH5 to substrate but also activation its demethylase activity through inhibition it’s SUMOylation. Moreover, global transcriptomic and epitranscriptomic analyses identify that DDIT4 is a functional downstream target gene for RBM33 in HNSC and RBM33-mediated HNSC tumorigenesis by inhibition the mTOR pathway through the inhibition of m6A-dependent DDIT4 mRNA decay. Taken together, our study uncovers a novel molecular mechanism that RBM33/ALKBH5/m6A/DDIT4/mTOR axis regulates HNSC progression through the inhibition of mTOR pathway and targeting RBM33 may be a promising strategy for HNSC treatment. To identify the functional downstream target genes responsible for the observed phenotype, UM-SCC-1 cells stably expressing scramble, ALKBH5 siRNA#1, ALKBH5 siRNA#2, RBM33 siRNA#1, RBM33 siRNA#2 were used for m6A-Seq analyses.