Analysis of DNA transposition by DNA transposases in human cells
This manuscript discusses the recent report "Cognate restriction of transposition by piggyBac-like proteins" in Nucleic Acids Research by Beckermann et al and related recent publications about the inability to detect DNA transposition activity of human domesticated DNA transposase PGBD5. Measuring DNA transposition activity of transposases in human cells, where these enzymes can act on endogenous genomic substrates and induce DNA damage, is complicated by these and other cellular responses. Possible reasons for the discordant findings of Beckermann et al with prior independent reports of PGBD5 DNA transposition by Helou et al and Henssen et al and specific details of experimental methods in human cells are presented. In particular, by using independent experiments that reproduce PGBD5-mediated genomic integration, we demonstrate how supraphysiologic and ectopic overexpression of PGBD5 can cause DNA damage and cell death, and artifactual loss of apparent activity in clonogenic transposition reporter assays. While PGBD5 can support apparent DNA transposition, its cellular activity predominantly involves double-strand DNA breaks, deletions and other DNA rearrangements. We discuss the implications of this phenomenon for the interpretation of experimental assays and activities of domesticated DNA transposases.