Structure of the human apolipoprotein C-II gene promoter

To localize transcriptional active cis elements and to study the effect of a single base transition at -86 derived from a patient (PS) with an inherited severe form of hypertriglyceridemia a reporter gene transfection assay with apo C-II promoter fragments was performed. Sequences from -170 to -140, -140 to -59 and -59 to -39 were transcriptional active. The A to G transition at -86 reduced promoter activity to 25% (pC2PS-13). A nuclear protein bound sequence specific to a DNA fragment from -102 to -70, but disappeared when the point mutation at -86 was introduced. We found that one of these cis elements enhances promoter activity as a response of cAMP elevation. Apo CII mRNA level increases after incubation of HepG2 cells with 10 microM forskolin within 2 hours as measured by northern blot analyses. Incubation of transfected cells (pC2W) with forskolin [10 microM] or a cAMP analogue resulted in an 6-fold increase of luciferase activity within 6 hours and a subsequent decrease. The results suggest that several positive acting elements are located between -170 and -36 and that one of them may be responsible for promoter activation by cAMP. The reduction of promoter activity by the point mutation may be a consequence of impaired protein-DNA interaction.