Receptor-mediated in vitro gene transformation by a soluble DNA carrier system

Abstract

We present, here, evidence that foreign DNA can be specifically delivered to cells by a soluble carrier system that takes advantage of receptor-mediated endocytosis. Our experiments were based on the following concepts: hepatocytes possess a unique receptor that binds and internalizes galactose-terminal (asialo-)glycoproteins; DNA can bind to polycations in a strong but noncovalent manner forming soluble complexes; and the gene for chloramphenicol acetyltransferase, a bacterial enzyme that acetylates chloramphenicol, is not present in mammalian cells. We coupled asialoorosomucoid (ASOR) to poly-L-lysine to form an asialoorosomucoid-poly-L-lysine conjugate. The plasmid, pSV2 CAT, was complexed to the conjugate in a molar ratio of 1:2. To test this complex, a model system was used consisting of hepatoma cell lines, Hep G2, asialoglycoprotein receptor (+), and SK-Hep 1, receptor (-). Each cell line was incubated with filtered ASOR X poly-L-lysine X DNA complex, or controls consisting of DNA plus ASOR, DNA plus poly-L-lysine, or DNA alone. Cells were assayed for the presence of chloramphenicol acetyltransferase activity as a measure of gene transformation. SK-Hep 1, receptor (-) cells, produced no detectable acetylated chloramphenicol derivatives under any condition. However, Hep G2, receptor (+) cells, incubated with the ASOR X poly-L-lysine X DNA complex were transformed as indicated by the presence of chloramphenicol acetyltransferase activity (0.028 chloramphenicol acetyltransferase units/10(6) cells). Mixtures of individual components of the complex failed to transform these cells. Competition by a 10-fold excess of ASOR prevented gene transformation by the ASOR X poly-L-lysine X DNA complex.