The transgene expression of the catalytic subunit APOBEC-1 of the apo B mRNA editing enzyme-complex can cause hepatocellular carcinoma in mice and rabbits. It has been proposed that aberrant editing of mRNA may represent a novel oncogenic principle. This investigation aimed to define whether such aberrant hyperediting mediated by APOBEC-1 occurs in human carcinomas. Editing and hyperediting of apo B, NAT1 or NF1 mRNA was not identified in any of 28 resected tumor specimens, including hepatocellular, bile duct, gastric, colorectal, pancreatic adeno- and neuroendocrine, lung adeno-, medullary thyroid and breast carcinoma, soft tissue sarcoma and neuroblastoma. In most types of carcinoma, significant levels for full-length APOBEC-1 mRNA could not be detected. Low level expression of APOBEC-1 was found in colorectal and gastric carcinoma where most of the APOBEC-1 mRNA is inactivated by alternate splicing. The 'auxiliary' components of the apo B mRNA editing enzyme-complex are missing in many tumors including colorectal and gastric carcinoma, but are highly expressed in hepatocellular, lung adeno- and breast carcinoma all of which lack APOBEC-1. Taken together, either APOBEC-1 or the 'auxiliary' components of the apo B mRNA editing enzyme-complex or both are missing in human carcinomas resulting in the absence of mRNA editing. Currently, there is no evidence that aberrant editing mediated by APOBEC-1 contributes to the tumorigenesis of natural human carcinomas.
