Environmental factors affecting transcription of the human L1 retrotransposon. II. Stressors.

Retrotransposons have clearly molded the structure of the human genome. The reverse transcriptase coded for by long interspersed nuclear elements (LINEs) accounts for 35% of the human genome, with 8-9 x 10(5) copies of the most common human LINE element, L1Hs. Retrotransposons cycle through an RNA intermediate with transcription as the rate limiting step. Because various retrotransposons have been demonstrated to be induced by environmental stimuli, we investigated the response of the L1Hs promoter to various agents. L1Hs promoter activity was analyzed by transfecting an L1Hs-expressing cell line with plasmids containing one of two L1Hs promoters fused to the LacZ reporter gene. L1Hs promoter activity was then monitored with a beta-galactosidase assay. Treatment with UV light and heat shock resulted in a small increase in beta-galactosidase activity from one promoter, while treatment with tetradecanoylphorbol 13-acetate resulted in small increases in beta-galactosidase activity from both promoters. No increase in beta-galactosidase activity was observed after exposure to X-rays or hydrogen peroxide.