Figure 5. Transcriptional activity of CREM isoforms. For functional studies, SKUT-1B cells were transfected with the reporter construct pCRE/-36rPRL/luc3, an expression vector for the catalytic subunit of PKA (Cß; shaded bars) or an inactive mutant thereof (Cßmut; open bars), and the indicated CREM-expression vectors. Controls received the empty expression vector pcDNA/FLAG-His. Luciferase activities were measured as relative light units (RLU) and normalized to the value obtained with empty vector plus Cß (set to 100). Results represent the means ± SEM of 3 independent experiments. Asterisks indicate statistically significant difference from the activity obtained with empty vector plus Cß (*P < .05; **P < .001).