Frequent increased gene copy number and high protein expression of tRNA (cytosine-5-)-methyltransferase (NSUN2) in human cancers

NSUN2, also known as SAKI or MISU, is a methyltransferase which catalyses (cytosine-5-)-methylation of tRNA. The human NSUN2 gene is located on chromosome 5p15.31-33. We show that NSUN2 gene copy number is increased in oral and colorectal cancers. Protein expression levels of NSUN2 were determined by immunoblot using novel polyclonal antibodies raised against a synthetic peptide corresponding to the C-terminal region of the protein. In most normal tissues, NSUN2 expression levels were extremely low. On the other hand, oral and colorectal cancers typically expressed high levels of NSUN2. The level of NSUN2 was similar in interphase and mitotic cells, and immunohistochemical analysis demonstrated strong staining for NSUN2 in oral and colon cancer tissues when compared with normal tissues, providing a distinct diagnostic significance for NSUN2 in comparison with Ki-67, a widely used marker of actively proliferating cells. In addition, elevated protein expression of NSUN2 was confirmed by immunohistochemical analysis of various cancers including esophageal, stomach, liver, pancreas, uterine cervix, prostate, kidney, bladder, thyroid, and breast cancers. NSUN2 is regulated by Aurora-B, a newly developed molecular target for cancer therapy, leading us to propose that NSUN2 might become a valuable target for cancer therapy and a cancer diagnostic marker.