COMPLEMENTATION OF APOLIPOPROTEIN-B MESSENGER-RNA EDITING BY HUMAN LIVER ACCOMPANIED BY SECRETION OF APOLIPOPROTEIN B48

Mammalian small intestine secretes a truncated apolipoprotein B (apoB4 8) species as a result of tissue-specific post-transcriptional RNA edi ting. The human liver, by contrast, contains only unedited apoB mRNA a nd secretes only apoB100. We have recently isolated a cDNA clone from rat small intestine which encodes an apoB mRNA editing protein, REPR ( Teng, B., Burant, C. F., and Davidson, N. O. (1993) Science 260, 1816- 1819). The current study demonstrates that homogenates of Xenopus oocy tes expressing REPR confer editing ability upon S100 extracts prepared from human liver when tested on a synthetic apoB RNA template in vitr o. Transfection of REPR into HepG2 cells resulted in editing of endoge nous apoB mRNA and the appearance of an apoB48-like protein in the med ia. Extracts prepared hom these transfected cells edit mammalian apoB RNA templates when incubated alone and with enhanced efficiency in the presence of chicken intestinal S100 extracts. The results suggest tha t human liver expresses factor(s) which are critical to apoB mRNA edit ing and which allow functional complementation of REPR in vivo.