LTRs spanning the TSS of truncated ERBB4 display transactivation activity. I20ΔERBB4 and I12ΔERBB4 5′ untranslated regions (UTRs) are localized in human endogenous retrovirus LTRs. Luciferase assays were performed in HEK-293T cells transfected with LTR sequences upstream of the luciferase gene. Three independent experiments are shown as fold activation compared to pGL3 (pGL3 empty) basic activity (set as 1). Error bars represent normalized standard deviation (***P < .001). Ctrl, control; REN, renilla.