Environmental factors affecting transcription of the human L1 retrotransposon. I. Steroid hormone-like agents.

The L1 retrotransposon has significantly shaped the structure of the human genome. At least 30% of human genome sequence can be attributed to L1 reverse transcriptase activity. There are 10(5) copies of the human L1 retrotransposon, L1Hs, most of which are defective, although approximately 8-9 x 10(3) are full length. L1Hs elements transpose through an RNA intermediate and transcription is thought to be the rate limiting step in retrotransposition. Because transcription of retrotransposons in a variety of organisms has been shown to respond to environmental stimuli, we investigated the influence of various agents on transcription from two different L1Hs promoters. The activity of the L1Hs promoters was analyzed by transfecting L1Hs-expressing cell lines with plasmids containing the L1Hs promoters fused to the LacZ reporter gene and monitoring expression with a beta-galactosidase assay. Small increases in beta-galactosidase activity were observed with both L1Hs promoters after treatment with serum, testosterone, dihydrotestosterone and organochloride pesticides, indicating that these agents can influence L1Hs transcription.